Zero Net Energy Retrofits at UC Davis

Transcription

1 Zero Net Energy Retrofits at UC Davis Demonstrating ground-source heating and cooling systems to achieve ZNE in a retrofit ET Project Number: Project Manager: Mananya Chansanchai and Peter Turnbull Pacific Gas and Electric Company Prepared By: UC Davis Energy Institute Bryan Jenkins - Principal Investigator; Kurt Kornbluth Co-PI William Glassley, Elise Brown, Magdalena Brum, Steve Wiryadinata-Researchers; Tobias Barr-Project Manager; Lisa Meline of Meline Engineering-Principal Engineer 1605 Tilia Street, Suite 100 Davis, CA Issued: December 30, 2014

2 Copyright, 2014, Pacific Gas and Electric Company. All rights reserved.

3 ACKNOWLEDGEMENTS Pacific Gas and Electric Company s Emerging Technologies Program is responsible for this project. It was developed as part of Pacific Gas and Electric Company s Emerging Technologies - Technology Assessment subprogram under internal project number. The UC Davis Energy Institute conducted this technology evaluation for Pacific Gas and Electric Company with overall guidance and management from Peter Turnbull (PG&E) and Anna LaRue and Dr. Carrie Brown (Resource Refocus LLC). For more information on this project, contact Peter Turnbull at PWT1@pge.com. LEGAL NOTICE This report was prepared for Pacific Gas and Electric Company for use by its employees and agents. Neither Pacific Gas and Electric Company nor any of its employees and agents: (1) makes any written or oral warranty, expressed or implied, including, but not limited to those concerning merchantability or fitness for a particular purpose; (2) assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, process, method, or policy contained herein; or (3) represents that its use would not infringe any privately owned rights, including, but not limited to, patents, trademarks, or copyrights. 1

4 ABBREVIATIONS AND ACRONYMS AEC AHJ CEC CES CUES CZ DEER EUI EUS EWT FCZ GHX GHEW GSHP GTAC HDD HEUS HVAC IGSHPA LCOS PTAC PTHP RFP Architectural Energy Corporation Authority Having Jurisdiction California Energy Commission Carbon Emissions of Service CA Commercial End-use Survey Climate Zone Database for Energy Efficient Resources Energy Use Intensity Energy Use of Service Entering Water Temperature Forecasting Climate Zone Ground Heat Exchanger Ground Heat Exchange Well (same as GHX) Ground Source Heat Pump Ground-Source Thermal Air Conditioner Horizontal Directional Drilling HVAC Only Energy Use Heating Ventilation and Air Conditioning International Ground Source Heat Pump Association Levelized Cost of Service Packaged Terminal Air Conditioner Packaged Terminal Heat Pump Request for Proposal 2

5 SAM SCHA TAM WWAC ZNE Served Available Market Solar Community Housing Association Total Addressable Market Window and Wall Air Conditions Zero Net Energy 3

6 FIGURES Figure 1: Summary of Results for Lodging Over Twenty Years Figure 2: Summary of Results for Multifamily Units Over Twenty Years Figure 3: Idealized Subsurface Temperature Profile. Temperature is Indicated as a Function of Depth, Season and Soil Type (modified From [3]) Figure 4:Schematic Diagram of a Geothermal Heat Pump, Operating in Heating Mode (modified From [3]) Figure 5: Geothermal Loop Configurations Source: EERE [4] Figure 6: California Climate Zones, as Identified by the California Energy Commission [5]. The Representative City for Each Zone, and The Zone Identifying Number, are Shown Figure 7:Domes Construction Circa 1970 (source: [6]) Figure 8: Domes Site Map (Source Solar Community Housing Association) Figure 9: Domes Floor Plan (Source Solar Community Housing Association) Figure 10: Domes Estimated Energy Use Breakdown Figure 11: Typical Central Plant Layout Originally Proposed for the Domes Figure 12: Proposed Shared GHX Diagram for Domes Site (Source: Meline Engineering) Figure 13: Example of Proposed Configuration for Radiant Sails (Source UC Davis Design Charrette) Figure 14: Final Domes GHX Configuration Figure 15: Observed Domes data February 6th through March 31st 2014 (Source AEC) Figure 16: Additional Supply and Return Ground Loop Temperature Sensors Installed May 7 th, Figure 17: Heating Event Captured at Dome 14 with Updated Entering Water Temperature (EWT, F) Sensor Configuration, May Figure 18: Representative Building for Lodging with GHX Layout Figure 19: MASControl Interface Figure 20: Representative Buildings for Multifamily Housing Figure 21: PTAC

7 Figure 22: HDD GHX Bore Figure 23: Daily Average Temperature Profiles Figure 24: Lodging Piping Schematic Figure 25: Multifamily Piping Schematic Figure 26: Summary of Lodging Analysis Figure 27: Summary of Multifamily Analysis Figure 28: California Geologic Map (Source[31]) Figure 29: Map Legend for California Geologic Map (Source:[31]) Figure 30: Total energy use per year per residence, in kwh/yr, for conventional HVAC systems (vertical axis), compared to energy use resulting from use of geothermal heat pump systems (horizontal axis). (Source:[31]) Figure 31:Overhead view of Proposed Horizontal Bore GHX (Source Meline Engineering) Figure 32: Cross Sectional View of the Proposed Horizontally Bored GHX (Source Meline Engineering) Figure 33: Estimated Aggie Village End Use Breakdown TABLES Table 1: Sensitivity Test for Lodging in CZ Table 2: Sensitivity Test for Lodging in CZ Table 3: Sensitivity Test for Multifamily in CZ Table 4: Sensitivity Test for Multifamily in CZ Table 5: Physical Building Characteristics Modeled Table 6: Annual Climatic Summary Table 7: Consumption Tiers (Source PG&E) Table 8: Lodging Heating and Cooling Loads Table 9: 20-Year Energy Consumption and Peak Demand Table 10: Implementation Cost Summary Table 11: CZ13 Cost Summary Table 12: CZ13 Ground Source Heat Pump Design Summary Table 13: Geothermal Heat Exchanger Design Summary Table 14: Distribution Loop GHX Design Flow Summary Table 15: Sensitivity Results for Lodging in CZ Table 16: Sensitivity Results for Lodging in CZ

8 Table 17: Heating and Cooling Loads Table 18: 20-Year Energy Consumption Peak Demand and Emissions Table 19: CZ3 Cost Summary Table 20: CZ13 Cost Summary Table 21: Ground Source Heat Pump Design Summary Table 22: Geothermal Heat Exchanger Design Summary Table 23: Distribution Loop and GHX Design Flow Summary Table 24: Sensitivity Results for Multifamily in CZ Table 25: Sensitivity Results for Multifamily in CZ Table 26: Basis Data for Lodging Building Type Table 27: Basis Data for Multifamily Building Type Table 28: Shares of PTHPs, Furnaces and PTACs for US Lodging buildings (Source: US Energy Information Administration, 2003) Table 29: Shares of HPs, Furnaces and PTACs for US Multifamily Buildings [30] Table 30: Market Size Estimate for 1 ton GTAC Units Table 31: Comparison of Annual Total Energy Consumption of Conventional HVAC Systems and Geothermal Heat Pump Systems, by Climate Zone. (Source [31]) EQUATIONS Equation 1: Soil Thermal Conductivity Equation 2: Thermal Diffusivity Equation 3: 1 Ton Equivalent Equation 4: Total Number of Model Buildings of Each Type and Climate Equation 5: Total Number of Deployable 1-Ton GSHP Units Equation 6:Multifamily TAM Calculation based on Population and Number of Households by Climate Zone Equation 7: Calculation for Total Floor Area of Multifamily Households Equation 8: Fraction of Lodging Floor Area with Space Heating Equation 9: Multifamily Serviceable Heating Market Share Equation 10:Lodging Share of Serviceable Cooling Market

9 Equation 11: Multifamily Share of Serviceable Cooling Market Equation 12: Approximate Market Share for SAM Equation 13: SAM Expressed in Total Number of Deployable 1-Ton GSHP Units Equation 14: Approximation of Target Market for GTAC Technology 103 Equation 15: Multifamily Target Market Equation 16:Target Market for Space Cooling Equation 17: Total Share of Target Market and Number of Units in Target Market for GSHP

10 CONTENTS EXECUTIVE SUMMARY 11 PROJECT OVERVIEW 15 INTRODUCTION 32 GTAC Costs and Energy Savings Modeling 18 Commercial Lodging Category 18 Commercial Lodging Sensitivity Analysis 22 Residential Multifamily 25 Residential Multifamily Sensitivity Analysis 28 BACKGROUND ON DOMESTIC GEOTHERMAL HEAT PUMP SYSTEMS 32 EMERGING TECHNOLOGY 40 THE DOMES SITE 40 Principles of Operation 33 Physics of GHP Systems 37 Soil Thermal Conductivity, Thermal Diffusivity and Saturation 37 Subsurface Temperature 38 Local Climate 38 Temperature Balance 39 Horizontal Directional Drilling Ground Source Heat Pumps 40 Ground-Source Packaged Air-Conditioner 40 Advantages for Research 42 Introduction to Domes Site 43 HVAC Options for the Site 46 GHP Systems Advantages and Challenges (Specific to Site) 49 Local Conditions at the Site 50 Design 50 Site Properties 50 Constraints 50 Selected Design 51 Permitting and System Installation 53 Permitting 53 System Installation 53 MODELING AND DATA ANALYSIS OF INSTALLED SYSTEM 54 Predicted Energy Performance 54 Monitored Energy Performance 54 Update May 19,

11 PERFORMANCE MODELING AND ANALYSIS 56 Modeling Overview 56 Building Characteristic 58 Commercial Lodging 58 Residential Multifamily 60 HVAC Systems 62 Packaged Terminal Air Conditioners with Gas Furnace Heating 62 Horizontal Directional Drilling Ground Source Heat Pumps 63 Climate Zone 64 Energy Usage and Demand Rates 66 Commercial Lodging 66 Residential Multifamily 66 Modeling Methodology 67 Results 74 Commercial Lodging 74 Results (Sensitivity Analysis) 84 Residential Multifamily 86 Results (Sensitivity Analysis) 95 Modeling Conclusions and Recommendations 97 MARKET ASSESSMENT 99 Market Assessment Overview 99 Market Assessment Methodology 99 Results 104 AGGIE VILLAGE SITE 105 Total Addressable Market (TAM) 100 Served Available Market (SAM) 101 Target Market (TM) or Serviceable Obtainable Market 103 Introduction to Aggie Village Site 105 HVAC Options for the Site 105 GHP System Advantages and Challenges (Specific to Site) 105 Permitting 105 Procurement Problems 106 Lack of drillers/new certification 106 Previous studies applicable to local region (CGEC modeling study) 107 Challenges in model validation: data monitoring 111 Local Conditions at Aggie Village Site 112 Design 112 Site Properties 112 Constraints 112 9

12 LESSON LEARNED 116 Analysis 115 Performance Predictions and Observations 115 Predicted Efficiency and Energy Consumption 115 General Considerations and Issues 115 Project Conclusions 116 RECOMMENDATIONS 116 REFERENCES 118 APPENDICES 120 APPENDIX I 121 DETAILED METHODOLOGY FOR GTAC LEVELIZED COST MODELING 121 Detailed Methodology 121 Annual Energy Consumption and Maximum Electrical Demand 121 Baseline HVAC Calculations 122 Proposed HVAC Calculations 123 Levelized Cost of Service and Energy Use of Service Calculations 125 Ground Loop Temperature Calculations 126 Ground Loop Bore Length Calculations: 127 Pump Calculations 130 Cost of Service 132 Implementation Cost 132 Baseline Implementation Costs 132 PTAC Costs 132 Warm Air Furnace Costs 134 Proposed Implementation Costs 135 Water Source Heat Pump Costs 135 Pump Costs 135 Piping Costs 137 GHX Installation Costs 139 Energy Cost 139 Commercial Lodging 139 Residential Multifamily 141 Maintenance Cost 142 Load Profiles

13 EXECUTIVE SUMMARY Geothermal heat pump systems have the potential to reduce electricity consumption while also reducing the costs of heating and cooling homes and commercial building spaces. The reduced energy consumption can also directly reduce emissions associated with fossil fuel based power generation and space conditioning, thus leading to lower greenhouse gas emissions and reduced generation of atmospheric pollutants. Even with these energy, economic and environmental benefits, the number of installed geothermal heat pump systems in California remains limited. In an effort to better quantify potential energy and cost savings and market potential, a project was initiated under PG&E s Emerging Technologies Program to evaluate the efficacy of state-of-the-art groundsource heat pump heating and cooling retrofit systems. The primary objectives of this project were to understand the energy efficiency and cost performance of the technology and to evaluate various retrofit techniques and applications that could potentially lead to reductions in installed cost with influences on market demand. The project initially was organized into three main tasks: 1. retrofit of an innovative residential community (Baggins End, also referred to as the Domes) on the UC Davis campus by which to obtain experimental data on a groundsource heat pump system, 2. retrofit of a single-family home in the Aggie Village community of Davis, California, with a ground-source heat pump to complement other energy efficiency and renewable energy generation measures already installed at the home in an attempt to achieve zero net energy. 3. development of a simulation model to predict energy and cost savings of lodging and multifamily building types when replacing conventional heating and cooling equipment with ground-source heat pump technologies. Although the second of these objectives, the retrofit at the single family Aggie Village home, was suspended after permitting delays and high bid costs for ground loop heat exchanger installation exceeded project schedule and budget, results from all three provide a basis for understanding key implementation issues for ground source heat pump deployment. The ground-source heat pump (GSHP) retrofit at the Domes was successfully implemented and preliminary data were available for this report. Longer term monitoring is ongoing. Simulation modeling was applied to the lodging and multifamily building types and was used with a variety of deployment scenarios to estimate when energy efficiency gains and cost savings might be achieved. Source: EERE,

14 METHODS The first demonstration site at the Domes was located on the campus of the University of California, Davis, and consisted of 15 student housing structures, each with an occupancy of two students. Permitting of the installation was under the jurisdiction of the University of California and proceeded with no undue delays. Although a central GSHP system serving multiple residences or domes was intended, cost considerations shifted the final design to independent geothermal (ground-source) terminal air conditioner (GTAC) units modified from conventional packaged terminal air conditioner (PTAC) units to allow for coupling to the ground loop heat exchanger. A PTAC unit was also installed on one dome to serve as an experimental control. Site limitations also required shifting from a vertical bore ground loop to the use of trenchless horizontal directional drilling (HDD) to reduce impacts on existing landscaping and community infrastructure. Performance monitoring was tasked to Architectural Energy Corporation, San Francisco, CA. Following initial data review, additional temperature sensing was separately installed in order to confirm ground-loop supply and return temperatures to the GTAC units. Monitoring is ongoing. Simulation modeling was undertaken in an effort to assess energy, cost, and environmental (carbon) performance for GSHP retrofits across a larger range of building types within multiple California climate zones. The modeling investigated potential energy savings and the resulting cost effectiveness, if any, of commercial deployment of small (1 cooling ton) ground-source heat pump (GSHP) systems employing a horizontal directional drilling (HDD) technique in medium density commercial lodging and residential multifamily building categories. Energy demand data for both electricity and natural gas from the California End Use Survey (CEUS) and the Database for Energy Efficient Resources (DEER) databases along with PG&E tariff information were used in modeling energy use of service, levelized cost of service, and carbon emissions of service to compare electric GSHP systems against baseline PTAC units with natural gas space heating. Two climate zones as identified by the California Energy Commission were compared: California climate zone 3 (CZ3) representing a more moderate bay area location (Oakland, CA as the reference city) and California climate zone 13 (CZ13) representing a somewhat more extreme inland location with higher cooling load (Fresno, CA as the reference city). The lodging facility was modeled as a 4- story building with a total floor area of approximately 157,000 ft 2. The multifamily facility consisted of two 2-story buildings with a total floor area of approximately 25,000 ft 2. RESULTS Preliminary data from the Domes project were accumulated over two months of operation during February and March Average energy use was 0.64 kwh/ft 2 for the GSHP units against 0.71 kwh/ft 2 for the PTAC unit. A separate electric resistance heated dome resulted in 1.10 kwh/ft 2. The GSHP technology had lower energy use compared with both of the more conventional technologies, however, ongoing monitoring will provide additional data needed to assess the significance of these results for annual energy and cost determination. For the purposes of the model simulations, the technology modeled, a Ground-source Terminal Air Conditioner (GTAC), was intended to replace a Packaged Terminal Air Conditioner (PTAC) that does not use gas. The typical baseline practice in actual mediumdensity lodging and multifamily units is PTAC with electric strip heating or packaged terminal heat pumps. The limitation of available data from CEUS and DEER instead required the selection of PTAC with separate gas furnace heat as the baseline system. Thus the modeling results are of PTAC retrofits of this type, but not necessarily of PTAC units that also include gas or electricity for heating. The characteristics of the model baseline would 12

15 change if gas were eliminated for heating. For example, in heating seasons in both climates, the electricity demand of the baseline case would increase significantly, potentially increasing savings for GTAC units in heating-dominated climates. Additionally, installed costs of the baseline systems could decrease as a result of excluding the separate gas infrastructure in the building. For the lodging building type, model results indicate that HDD GSHP systems offer significant energy and cost savings over the baseline PTAC system with natural gas heating. Despite the increased facility electrical energy consumption due to the fuel switching for space heating from natural gas to electricity, the total proposed energy use of the facility (electricity and gas expressed in common units) is lower than the baseline due to higher GSHP efficiencies both in heating and cooling. Overall cost savings of 7 and 5 percent were estimated for the GSHP in CZ3 and CZ13, respectively. For the building size modeled, the total cost savings were approximately $640,000 and $470,000 over a 20 year-period for CZ3 and CZ13, respectively. Although the energy cost savings in CZ13 was three times larger than in CZ3, the cost of implementing the GSHP system in CZ13 is much greater than in CZ3 due to the larger cooling load in CZ13, thus necessitating the implementation of the proposed GSHP system on a larger scale. In both climates, the maintenance cost was taken to be the same. HVAC energy savings of 48 and 39 percent were estimated in CZ3 and CZ13, respectively, while total facility energy savings were 8 and 10 percent, the difference being in other non-heating and cooling energy uses associated with these types of facilities, which dilute the overall effects of the change in space conditioning appliances. Reductions in facility carbon dioxide (CO 2 ) emissions were of a similar magnitude at 8 and 9 percent for CZ3 and CZ13. While energy savings accrue overall, power demand varies depending on climate with a 45 kw lower demand in CZ13 but a 5 kw higher demand in CZ3 than the baseline alternative due to smaller differences between ground and air temperatures in the more moderate CZ3 climate. Due to space limitations, vertical geothermal heat exchangers are the typical ground loop configuration used to serve buildings of similar type and energy demand. The lengths of horizontal bores needed to meet the heating and cooling loads for the building size modeled approximately 33,000 and 90,000 ft for CZ3 and CZ13, respectively may prove to be challenging to implement. Installation of the bores below the building grade could be considered to minimize the footprint. Similar findings apply to the multifamily building type. Overall cost savings of 10 and 2 percent were estimated for CZ3 and CZ13, respectively, or for the building size modeled, approximately $83,000 and $17,000 savings over 20 years. The electric usage rates at different consumption tiers affect the extent of energy cost savings. PG&E s E1 rate schedule Tier 1 consumption limit in CZ13 is much higher than in CZ3. Thus, most of the consumption in the inland climate is subject to the lowest Tier 1 rate, which for a given energy use reduction - reduces the magnitude of cost savings compared to CZ3. HVAC 13

16 energy savings were 72 and 47 percent in CZ3 and CZ13, with total facility energy savings of 9 and 8 percent and facility CO 2 emissions reductions of 9 and 7 percent. In CZ13, the maximum demand of the GSHP was about 9 kw lower than the baseline. In CZ3, the GSHP power demand was 1 kw higher for the same reasons noted above for the lodging building type. Sensitivity analyses for both building types explored a number of alternative scenarios for technical and economic performance and are detailed in the report. While permitting at the Domes was not an obstacle to completing the installation, cancelation of the Aggie Village installation demonstrated the need for further development of regulatory and permitting guidelines for geothermal or ground-source systems. More specific information was needed pertaining to the impacts of the types of borehole technologies available. Additionally, both sites incurred (or would have incurred) substantial cost for the ground-loop heat exchanger installation due to permitting and licensing uncertainties as well as the limited installation experience within this market to date. The high cost of ground-loop heat exchanger installation was also identified by the modeling as a main challenge for GSHP system implementation. Building Type 20 year Cost Savings (%) Model results for GSHP application 20 year Cost HVAC Energy Savings Savings ($) (%) Total Energy Savings (%) CO 2 Reductions (%) Climate Zone 3 (Bay Area) Lodging 7 640, Multifamily 10 83, Climate Zone 13 (San Joaquin Valley) Lodging 5 470, Multifamily 2 17, CONCLUSIONS AND RECOMMENDATIONS Results from the physical installation of the GSHP system at the Domes and the model estimates from the lodging and multifamily facility simulations suggest the potential for improved energy efficiency associated with the use of ground-source heat pump technology for space heating and cooling applications compared to more conventional technologies. Cost savings can also accrue. Installation costs remain high, however, partially due to uncertainties associated with regulations, permitting, and licensing. The limited experience of installers in this market may also keep installation costs higher, although substantial relevant experience may exist elsewhere, such as in the utility and related sectors. Resolving these issues and identifying innovative solutions will be important for realizing overall cost reductions for these types of systems. Identifying means to reduce installation costs should be an important objective for the industry. Further research into HDD and other innovative techniques should be undertaken and a fuller investigation initiated into site environmental impacts to better inform regulatory and permitting procedures. 14

17 PROJECT OVERVIEW Beginning in November 2012, the UC Davis Energy Institute initiated a project under PG&E s Emerging Technologies Program to evaluate the efficacy of state-of-the-art ground-source heat pump heating and cooling retrofit systems. The primary objectives of this project were to understand the energy efficiency and cost performance of this modern technology and to evaluate various retrofit techniques and applications that could potentially lead to reductions in installed cost with influences on market demand. The project initially was organized into three main tasks including: 1. retrofit of an innovative residential community (Baggins End, also referred to as the Domes) on the UC Davis campus by which to obtain experimental data on a groundsource heat pump system, 2. retrofit of a single-family home in the Aggie Village community of Davis, California, with a ground-source heat pump to complement other energy efficiency and renewable energy generation measures already installed at the home in an attempt to achieve zero net energy. 3. development of a simulation model to predict energy and cost savings of lodging and multifamily building types when replacing conventional heating and cooling equipment with ground-source heat pump technologies. The ground-source heat pump (GSHP) retrofit at the Domes was successfully implemented with preliminary data available for this report and longer term monitoring ongoing. The retrofit at the single family Aggie Village home was suspended after permitting delays and high bid costs for ground loop heat exchanger installation exceeded project schedule and budget. Simulation modeling was successfully applied to the two building types based on published energy use data for California and was used with a variety of deployment scenarios to estimate when energy efficiency gains and cost savings may accrue. PROJECT GOAL The goal of these retrofit projects was to understand the costs and energy savings attributable to retrofit ground-source heat pumps for heating and cooling applications and to assess performance under different climate conditions typically found in California. Additionally, through the experience of implementing a ground heat exchanger (GHX), the project identified a number of permitting and deployment challenges in California. PROJECT DESCRIPTION As noted above, two initial demonstration sites were selected for retrofit applications of the ground-source heat pump technology (GSHP). The first location, Baggins End Student Housing Community, also known as the Domes, is located on the campus of the University of California, Davis, and consists of 15 student housing structures, each with an occupancy of two students. Permitting of the installation was under the jurisdiction of the University of California and proceeded with no undue delays. Although a central GSHP system serving multiple residences or domes was intended, cost considerations shifted the final design to independent geothermal (ground-source) terminal air conditioner (GTAC) units modified from conventional packaged terminal air conditioner (PTAC) units to allow for coupling to the ground loop heat exchanger. A PTAC unit was also installed on one dome to serve as an 15

18 experimental control. Site limitations also required shifting from a vertical bore ground loop to the use of trenchless horizontal directional drilling (HDD) to reduce impacts on existing landscaping and community infrastructure. Performance monitoring was tasked to Architectural Energy Corporation (San Francisco, CA) although following initial data review additional temperature sensing was separately installed in order to confirm ground-loop supply and return temperatures to the GTAC units. The second location was a single family home located in the faculty and staff housing community of Aggie Village that is located in downtown Davis, California. This half-plex unit had previously been retrofitted with integrated PV-thermal and battery storage. Addition of a GSHP was planned to evaluate whether net zero energy from the grid could be achieved on an annual basis. Permitting was under the authority of the City of Davis. The increased housing density generated more concern over potential groundwater contamination and although a variance was eventually issued, setback requirements from sewer laterals made the originally planned vertical ground-loop borehole infeasible. A HDD borehole was investigated but the small footprint of the site and the high cost of the bid received due to uncertainties associated with licensing requirements for installers of these types of bores resulted in a final cancellation of the task. Simulation modeling was undertaken in an effort to assess energy, cost, and environmental (carbon) performance for GSHP retrofits across a larger range of building types within multiple California climate zones. Energy demand data for both electricity and natural gas from the California End Use Survey (CEUS) and the Database for Energy Efficient Resources (DEER) databases along with PG&E tariff information were used in modeling energy use of service, levelized cost of service, and carbon emissions of service to compare electric GSHP systems against baseline PTAC units with natural gas space heating. Two climate zones are characterized by the California Energy Commission were compared for application: California climate zone 3 (CZ3) representing a bay area location (Oakland, CA as the reference city) and California climate zone 13 (CZ13) representing an inland location (Fresno, CA as the reference city). PROJECT FINDINGS/RESULTS Only preliminary data are available from the Domes project by which to compare the GSHP units against the more conventional PTAC unit. Monitoring of total energy use over two months of operation during February and March 2014 yielded an average of 0.64 kwh/ft 2 for the GSHP units against 0.71 kwh/ft 2 for the PTAC. A separate electric resistance heated dome resulted in 1.10 kwh/ft 2 across the same time interval. Insufficient information exists at this time to assess the significance of these results and a fuller analysis awaits additional monitoring. Cancelation of the Aggie Village installation precluded any direct observations of thermal or economic performance although other conclusions pertain to potential siting elsewhere. Principal among these are the need for further development of regulatory and permitting guidelines for geothermal or ground-source systems with more specific information pertaining to the impacts from the types of borehole technologies available. Additionally, studies at both sites have shown that ground-loop heat exchanger installation incurs substantial cost in part due to permitting and licensing uncertainties but additionally due to limited experience within this market to date. The high cost of ground-loop heat exchanger installation was also identified by the modeling effort as a main challenge for GSHP system implementation. Identifying means to reduce installation costs should be an important objective for the industry. Further research into HDD and other innovative techniques should be undertaken and a fuller investigation initiated into site environmental impacts to better inform regulatory and permitting procedures. 16

19 The objective of the modeling effort was to gauge potential energy savings and the resulting cost effectiveness, if any, of commercial deployment of small (1 cooling ton) ground-source heat pump (GSHP) systems employing a horizontal directional drilling (HDD) technique in medium density commercial lodging and residential multifamily building categories. The lodging facility was modeled as a 4-story building with a total floor area of approximately 157,000 ft 2. The multifamily facility consists of two 2-story buildings with a total floor area of approximately 25,000 ft 2. The baseline heating and cooling demand data that were used to model the energy and cost savings are limited in various ways. To develop the baseline used for this analysis, the data used were from the California Energy Commission Commercial End-use Survey (CEUS) and the Database for Energy Efficient Resources (DEER), which include natural gas for heating. The technology modeled, a Ground-source Terminal Air Conditioner (GTAC), was intended to replace a Packaged Terminal Air Conditioner (PTAC), which does not use gas. The typical baseline practice in actual medium-density lodging and multifamily units is PTAC with electric strip heating or packaged terminal heat pumps. The limitation of available data of PTAC alone drove the selection of PTAC with separate gas furnace heat as the baseline system. Thus the modeling results are of PTAC retrofits of this type, but not necessarily of PTAC units that also include gas or electricity for heating. The characteristics of the model baseline would change if gas were eliminated for heating. For example, in heating seasons in both climates, the electricity demand of the baseline case would increase significantly, potentially increasing savings for GTAC units in heating-dominated climates. Additionally, installed costs of the baseline systems could decrease as a result of excluding the separate gas infrastructure in the building. There are currently no additional incentives beyond direct cost savings for fuel switching as is the case with the model. An actual PTAC replacement would most likely be eligible for PG&E s Customized Retrofit Incentive program $0.15/kWh and $100/kW reduction based on first year performance, increasing savings further. 17

20 GTAC COSTS AND ENERGY SAVINGS MODELING The following metrics were used to characterize model performance, with lower values indicating that a system is more cost and energy efficient as well as environmentally friendly in terms of greenhouse gas (expressed as CO 2 equivalents) emissions reduction. A 20 year analysis period was used. Levelized Cost of Service (LCOS): total lifecycle implementation, energy and maintenance costs over cooling and heating energy delivery HVAC energy use of service (HEUS): HVAC-only energy use over cooling and heating energy delivery Energy use of service (EUS): total building energy use over cooling and heating energy delivery Carbon emissions of service (CES): CO 2 emissions over cooling and heating energy delivery, as calculated using total building energy use and the PG&E carbon footprint indices. Potential economic benefits associated with any carbon credits identified were not, however, assessed within the cost analysis here. Other greenhouse gases other than CO 2 were not evaluated. The total savings in LCOS represent savings for the entire building energy use. The specific HVAC energy and costs savings are typically higher. The 20 year analysis period required a replacement of the PTAC unit in year 16 due to the 15 year economic life assumed for this equipment. The economic life of GSHP units is longer and so no replacement was assumed. For both types of equipment, thermal performance was assumed to degrade over time with use. COMMERCIAL LODGING CATEGORY For the commercial lodging building type in the two climate zones, results are shown in Figure 1 for the following outcomes: Space heating and cooling loads Total HVAC and non-hvac: o o o o Electricity consumption Maximum electrical demand Natural gas consumption Combined energy consumption (expressed in common energy units) Operational (implementation, energy, maintenance) costs CO 2 emissions Major conclusions from modeling of the commercial lodging building type include: In both climate zones, the proposed HDD GSHP system offers significant energy and cost savings over the baseline PTAC system with natural gas heating. Despite the increased facility electrical energy consumption due to the fuel switching for space heating from natural gas to electricity, the total proposed energy use of the facility (electricity and gas expressed in common units) is lower than the baseline due to higher GSHP efficiencies both in heating and cooling. 18

21 Overall cost savings of 7 and 5 percent, can be achieved by the GSHP in CZ3 and CZ13, respectively. In terms of absolute values for the building size modeled, the percentage total cost savings translates to approximately $640,000 and $470,000 over the 20 year-period for CZ3 and CZ13, respectively. Although the energy cost savings in CZ13 is three times larger than in CZ3, the cost of implementing the GSHP system in CZ13 is much greater than in CZ3 due to larger magnitude of cooling load in CZ13, thus necessitating the implementation of the proposed GSHP system on a larger scale. In both climates, the maintenance cost is the same, as for the model it was calculated on a per-area basis. HVAC energy savings of 48 and 39 percent can be achieved in CZ3 and CZ13, respectively. Note that the energy savings do not correspond directly to energy cost savings due to fuel switching from the baseline to the proposed systems. Electricity is 3 to 4 times more expensive than natural gas per unit of energy, therefore, the effect of gas savings for heating diminishes the potential savings during the heating season. The value of electricity savings is more evident for the cooling season. Model results show substantially greater energy cost savings in CZ13 with significantly larger cooling loads compared to CZ3. Total facility energy savings of 8 and 10 percent can be achieved in CZ3 and CZ13, respectively. HVAC-only energy savings in the coastal climate are larger than in the inland climate. But the opposite result was found when total building energy is considered because miscellaneous loads in the coastal climate are a larger proportion of the building s energy end-use than in the inland climate, which again diminishes the effect of HVAC savings. Reductions in facility carbon dioxide (CO 2 ) emissions of 8 and 9 percent can be achieved in CZ3 and CZ13, respectively. The emissions reductions are directly related to the reduced energy use for the technologies compared. Higher operating efficiency of the GSHP in cooling mode results in lower electrical energy consumption for cooling. This effect is more dominant in CZ13 as the high condensing (outside air) temperature for an air-source PTAC unit at peak cooling load translates to reduced operating efficiency when compared to the lower condensing temperature of a GSHP, which takes advantage of the much cooler ground temperature. o In CZ13, the proposed maximum power demand is about 45 kw lower than the baseline. o In CZ3, the peak power demand is 5 kw higher. The effect of higher GSHP cooling efficiency is reduced due to two factors: (1) the milder CZ3 climate results in small differences in ground and air temperatures, and (2) the benefit is eclipsed by the degradation in efficiency over time. Since within the model the baseline system benefits from a "restart" of efficiency at the 16th year of operation, while the GSHP system continues to experience 19

22 degradation past the 16th year, the overall maximum demand over the 20 year period is greater for the GSHP. Due to space limitations, vertical geothermal heat exchangers (GHXs) are the typical ground loop configurations used to serve buildings with the magnitude of heating/cooling loads as the modeled building. The lengths of horizontal GHX bores needed to meet the heating and cooling loads for the building size modeled approximately 33,000 ft and 90,000 ft for CZ3 and CZ13, respectively may prove to be challenging to implement. Installation of the bores below the building grade could be considered to minimize the footprint. 20

23 Total Cost (1000 $) CO2 Emissions (1000 lb) Natural Gas Use (1000 Therms) Combined Energy Use (MWh) Total Space Load (MMBtu) Electricity Use (MWh) Maximum Demand (kw) PG&E s Emerging Technologies Program 120, ,000 Cooling Heating 35,000 30,000 Baseline Proposed Baseline Proposed 80,000 60,000 40,000 20,000 25,000 20,000 15,000 10,000 5, CZ3 1,400 1,200 CZ13 - Baseline Proposed CZ3 CZ13 80,000 70,000 - CZ3 Baseline Proposed CZ13 1,000 60, ,000 40,000 30,000 20, ,000 - CZ3 CZ13 - CZ3 CZ13 10,000 9,000 8,000 7,000 Baseline Proposed 35,000 30,000 25,000 Baseline Proposed 6,000 5,000 4,000 20,000 15,000 3,000 2,000 1,000 10,000 5,000 - CZ3 CZ13 - CZ3 CZ13 FIGURE 1: SUMMARY OF RESULTS FOR LODGING OVER TWENTY YEARS 21

24 COMMERCIAL LODGING SENSITIVITY ANALYSIS Sensitivity analyses were conducted around the reference results described above. Many scenarios were considered, but relative to the baseline (which is constant for all scenarios) the following scenarios were tested: 1) Reference case, as shown in Figure 1 and discussed in the preceding section. 2) GSHP installation cost equal to baseline cost. This simulates a market condition where the GSHP market penetration is equivalent to the air source heat pump penetration and reliable GHX installation services are widely available, i.e. technology is mature. 3) Ground conditions in which thermal conductivity is lower than the reference case with poorer overall thermal performance. 4) Ground conditions with higher soil thermal conductivity and hence enhanced overall thermal performance. 5) 10 percent improvement in the GSHP efficiency but 16 percent more expensive than the reference case based on actual equipment cost-performance relationships. 6) Ground-loop fluid pumping power is reduced (equivalent to increased pumping demand of 15 hp/100 ton) compared to the reference case efficiency (6 hp/100 ton).the reference pumping power demand for multifamily facilities is approximately 8 hp/100 attributable to the inherently lower efficiency of the smaller pumps included in the design. 7) Average burial depth of the HDD ground-loop heat exchanger (GHX) is reduced to 12 ft, compared to the reference 15 ft. This increases heat transfer to the surface. Major conclusions of the sensitivity analysis are summarized as follows: The main challenge with implementation of GSHP systems identified here is the high cost of GHX installation. If the installation cost can be reduced, GSHP systems would be much more cost effective. As shown in Scenario 2, cost savings increased to 12.1 and 15.3 percent from the reference in CZ3 and CZ13, respectively. The larger increase in savings for CZ13 is attributed to the larger required GHX. o This analysis does not consider a GSHP system serving space heating and cooling as well as domestic hot water heating. In such a system, heat from high temperature water leaving the heat pump during cooling mode could be recovered to pre-heat water for domestic uses. This has the combined benefit of reducing water heating energy use and reducing the load on the GHX field, which can substantially reduce the field size and its associated costs. 22

25 o Utility incentives might also be offered to stimulate rapid deployment of GSHPs. Incentives were not included in this cost analysis since fuel switching was ineligible for any incentives that might have been considered here. Poor soil performance - as shown by Scenario 3 reduced potential cost savings to 6.1 and 1.7 percent, respectively. Facilities with larger magnitude and duration of loads (either cooling or heating) show greater response to changing ground conditions, as shown by the larger drop in savings in CZ13 where the cooling load is much higher. Soils with higher thermal conductivity improve the cost effectiveness of GHP projects. As shown in Scenario 4, cost savings increased to 8.1 percent and 7.5 percent in CZ3 and CZ13, respectively. Depending on the scale of deployment, more efficient but more expensive GSHPs can in some cases improve the cost effectiveness of geothermal heat pump projects. As shown by Scenario 5, cost savings increased slightly in CZ3 and CZ13. This is not a universal outcome, however, and careful consideration must be given to both cost and efficiency when selecting for more efficient units. As shown by Scenario 6, savings dropped to 6.3 percent and 3.5 percent for CZ3 and CZ13 when an inefficient pumping system was assumed for GSHP projects. Since GSHP systems inherently require fluid pumping to achieve the required heat transfer, proper design of the system becomes very important. The effect of GHX burial depths on project cost effectiveness depends on the annual variation in ground temperature and the temperature coincident to the design heating or cooling load. As shown in Scenario 7, savings for CZ3 remained unaffected, but savings for CZ3 dropped to 4 percent. This is because the annual variation in ground temperature in CZ3 is not as large as in CZ13. At 12 ft and 15 ft depth, ground temperature during the cooling period for CZ3 is similar, but in CZ13 is higher at the time of peak load, which results in the need for a longer GHX. 23

26 Relative Cost Savings Scenario Description Savings from over 20 Years Baseline (%) ($) 1 Reference 7.3% 641,351 2 HDD GSHP technology has reached maturity in terms of implementation cost 12.1% 1,061,513 3 GHX in reduced ground thermal performance (30% less than reference) 6.1% 535,167 GHX in enhanced ground thermal performance (80% higher 4 than reference) 8.1% 712, % higher efficiency, 16% more costly GSHP units 7.6% 668, System pumping efficiency is reduced (150% less efficient than reference) GHX burial depth reduced to 12 ft (20% shallower than nominal) TABLE 1: SENSITIVITY TEST FOR LODGING IN CZ3 6.3% 552, % 639,196 Relative Cost Savings Scenario Description Savings from over 20 Years Baseline (%) ($) 1 Reference 5.0% 466,969 2 HDD GSHP technology has reached maturity in terms of implementation cost 15.3% 1,431,818 3 GHX in reduced ground thermal performance (30% less than reference) 1.7% 155,578 4 GHX in enhanced ground thermal performance (80% higher than reference) 7.6% 704, % higher efficiency, 16% more costly GSHP units 5.3% 491,732 6 System pumping efficiency is reduced (150% less efficient than reference) 3.5% 329,419 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 4.0% 376,776 TABLE 2: SENSITIVITY TEST FOR LODGING IN CZ13 24

27 RESIDENTIAL MULTIFAMILY For the residential multifamily building type in the two climate zones, Figure 2 shows the results of the 20-year lifecycle study for the same parameters as the lodging building type. Major conclusions for the multifamily facility model analysis are as follows: In both climate zones, the proposed HDD GSHP offers significant energy and cost savings over the baseline system. Despite the increased facility electrical energy consumption due to the fuel switch for space heating from natural gas to electricity, the total proposed energy use of the facility (electricity and gas expressed in common units) is lower than the baseline. Overall cost savings of 10 and 2 percent can be achieved in CZ3 and CZ13, respectively. In absolute values for the building size modeled, the percent savings translates to approximately $83,000 and $17,000 over 20 years for CZ3 and CZ13, respectively. The electric usage rates at different consumption tiers affect the magnitude of energy cost savings. PG&E s E1 rate schedule Tier 1 consumption limit in CZ13 is much higher than in CZ3. Thus, most of the consumption in the inland climate is subject to the lowest Tier 1 rate, which for a given energy use reduction - reduces the magnitude of cost savings compared to CZ3. HVAC energy savings of 72 and 47 percent can be achieved in CZ3 and CZ13, respectively. The magnitude of energy savings is attributed primarily to the efficiencies of the baseline and proposed systems. For heating, the baseline system has an efficiency of 80 percent while the proposed system has a coefficient of performance (COP) of approximately 3.9 at design conditions. For cooling, the baseline and proposed systems have design COP of 3.2 and 3.6, respectively. Since CZ3 is heating dominated while CZ13 is cooling dominated, the influence of switching from gas heating to electrical heating drives the higher energy savings in CZ3. Total facility energy savings of 9 and 8 percent can be achieved in CZ3 and CZ13, respectively. Reduced facility CO 2 emissions of 9 and 7 percent can be achieved in CZ3 and CZ13, respectively. Higher operating efficiency of the GSHP in cooling mode results in lower electrical energy consumption for cooling. This effect is more dominant in CZ13 as the high condensing (outside air) temperature for an air-source unit at peak cooling load translates to reduced operating efficiency compared to the lower condensing temperature of a GSHP that takes advantage of the much cooler ground temperature, similar to the lodging building type analysis. 25

28 o In CZ13, the maximum demand of the GSHP is about 9 kw lower than the baseline. o In CZ3, the proposed demand of the GSHP is 1 kw higher for the same reasons noted above for the lodging building type. 26

29 Total Cost (1000 $) CO2 Emissions (1000 lb) Natural Gas Use (1000 Therms) Combined Energy Use (MWh) Total Space Load (MMBtu) Electricity Use (MWh) Maximum Demand (kw) PG&E s Emerging Technologies Program 7,000 6,000 5,000 4,000 3,000 2,000 1,000 - Cooling Heating CZ3 CZ ,000 2,500 2,000 1,500 1, Baseline Proposed Baseline Proposed CZ CZ13 8,000 Baseline Proposed 7,000 6,000-5 Baseline Proposed CZ3 CZ13 1, CZ3 Baseline Proposed CZ3 CZ13 CZ13 5,000 4,000 3,000 2,000 1,000 4,000 3,500 3,000 2,500 2,000 1,500 1, CZ3 Baseline Proposed CZ3 CZ13 CZ13 FIGURE 2: SUMMARY OF RESULTS FOR MULTIFAMILY UNITS OVER TWENTY YEARS 27

30 RESIDENTIAL MULTIFAMILY SENSITIVITY ANALYSIS Table 3 and Table 4 show the results of sensitivity analyses for the multifamily building type in CZ3 and CZ13. The scenarios tested were the same as the commercial lodging category. Conclusions of the sensitivity analysis for the multifamily facility are similar to those for the lodging facility type: The main challenge with implementation of GSHP systems is the high cost of GHX installation. If the cost of GHX installation can be reduced, GSHP systems become very cost effective. As shown in Scenario 2, cost savings increased to 16.0 and 12.8 percent from the reference case in CZ3 and CZ13, respectively. The larger increase in savings for CZ13 is attributed to the larger required GHX. This building type might also benefit from utilizing heat rejection during cooling mode for domestic water preheating. Poor soil performance - as shown by Scenario 3 reduced potential cost savings to 8.5 percent in CZ3 and increased cost by 1.2 percent in CZ13. In this particular case, the added cost (negative savings) for CZ13 is attributed to the electricity consumption rate tiers discussed previously and to the economies of scale. The installation of much larger capacity (such as in Lodging) results in lower installed costs on a per-ton basis than for these smaller multifamily units. Soils with higher thermal conductivity improve the cost effectiveness of GSHP projects. As shown in Scenario 4, cost savings increased to 11.6 percent and 4.5 percent in CZ3 and CZ13, respectively. Unlike Lodging, more efficient GSHPs do not improve the cost effectiveness of GSHP projects for multifamily facilities. As shown in Scenario 5, cost savings remained the same for CZ13 and decreased to 9.9 percent for CZ3. This can be attributed to operating duration of the GSHPs. The cooling and heating loads in CZ3 require the HVAC system to operate only a fraction of the time compared to CZ13. Since energy savings due to increased efficiency are strongly dependent on operating hours, more efficient GSHPs do not pay for the increased capital cost in CZ3. As shown by Scenario 6, savings dropped to 5.6 percent and costs increased by 3.8 percent for CZ3 and CZ13, respectively, when an inefficient pumping system was assumed for GSHP projects. The importance of proper pumping system design applies to all building types in any climate. The effect of reducing GHX burial depths on project cost effectiveness depends on the variation in annual ground temperature and the temperature coincident to the design heating or cooling period. As shown by Scenario 7, savings for CZ3 increased slightly to 10.3 percent since higher ground temperature is coincident to the design 28

31 heating load. However, higher ground temperature is encountered for the design cooling period for CZ13, which results in a longer GHX and reduces cost savings to 1.5 percent. Scenario Description Relative Savings from Baseline (%) 1 Reference 10.2% 83,019 2 HDD GSHP technology has reached maturity in terms of implementation cost 16.0% 129,332 3 GHX in reduced ground thermal performance (30% less than reference) 8.5% 69,048 4 GHX in enhanced ground thermal performance (80% higher than reference) 11.6% 93, % higher efficiency, 16% more costly GSHP units 9.9% 80,265 6 System pumping efficiency is reduced (150% less efficient than reference) 5.6% 45,421 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 10.3% 83,278 TABLE 3: SENSITIVITY TEST FOR MULTIFAMILY IN CZ3 Cost Savings over 20 Years ($) Scenario Description Relative Savings from Baseline (%) 1 Reference 2.0% 17,492 2 HDD GSHP technology has reached maturity in terms of implementation cost 12.8% 111,184 3 GHX in reduced ground thermal performance (30% less than reference) -1.2% (10,409) 4 GHX in enhanced ground thermal performance (80% higher than reference) 4.5% 39, % higher efficiency, 16% more costly GSHP units 2.0% 17,492 6 System pumping efficiency is reduced (150% less efficient than reference) -3.8% (33,063) 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 1.5% 12,751 TABLE 4: SENSITIVITY TEST FOR MULTIFAMILY IN CZ13 Cost Savings over 20 Years ($) 29

32 PROJECT RECOMMENDATIONS Both the broader modeling and the physical installation of the GSHP system at the Domes suggest the potential for improved energy efficiency associated with the use of groundsource heat pump technology for space heating and cooling applications. Cost savings can also accrue. Installation costs remain high, however, at least partly due to uncertainties associated with regulations, permitting, and licensing, but also likely due to limited experience of installers in this market although substantial relevant experience may exist elsewhere, such as in the utility and related sectors. Resolving these issues and identifying innovative solutions will be important for realizing overall cost reductions for these types of systems. Additionally, certain recommendations apply for deployment and technology development. Recommendations for practitioners considering deployment of GTAC units: Engage authorities early to understand the local requirements relating to GHX drilling. Under both building types, modeling results show the technology to be more advantageous in regions, such as CZ3, where cooling loads are smaller, thus requiring less investment in GHX capacity. This reduces installed costs further and increases overall savings. With both building types and climate zones, sensitivity analysis resulted in higher cost savings if local ground properties demonstrate higher than normal thermal conductivity. While direct control over the physical and thermal properties of soils is not always possible, taking advantage of wet soils, such as those where irrigation is used, may be effective. Full lifecycle evaluations should be considered, however, to assess any other impacts associated with these types of modifications to ground conditions or soil properties. Site investigations when considering a geothermal installation should consider determination of soil properties and opportunities to enhance heat transfer for improved system performance. The cost of such evaluations remains to be determined. Recommendations for continued technology development of GSHP/GTAC units: Given the significant potential energy savings resulting from the model analysis, actual building load profile data from facilities actually using PTAC and heat pump equipment should be applied to model validation. Greater confidence in model results would greatly enhance market assessments for the technology. Additional modeling efforts should also consider benefits of GTAC systems that can also provide hot water to the building. GTAC unit efficiency at partial load could be explored. This analysis assumes that small units do not have variable capacity controls (i.e., they are either on or off). A more comprehensive lifecycle analysis to account for carbon credits due to natural gas usage reduction from fuel switching could be performed. Building envelope degradation, which could affect heating and cooling loads across the years of operation, could be accounted for. 30

33 More sophisticated energy cost projection techniques could be employed to estimate future energy cost rates. Vertical boreholes for the ground-loop heat exchanger should also be modeled to evaluate thermal performance and cost impacts. Monitoring of the Domes installation should be continued with sensor validation and calibration to obtain year-round performance data. Such data would be useful both for documenting technical performance and aiding model validation. 31

34 INTRODUCTION Under a PG&E Emerging Technologies Project, the UC Davis Energy Institute investigated the potential for ground source heat pump (GSHP) retrofits for building heating and cooling applications to understand current costs, constraints and energy savings through model analysis and actual demonstrated performance. Additionally, the advantages, if any, of ground source heating and cooling systems over typical high efficiency air-source units were evaluated to assess energy demand in retrofit applications. Feasibility analyses and retrofit design solutions were undertaken for two sites 1) a student housing community known as Baggin s End on the campus of the University of California, Davis (also known as the Domes site due to the architectural design of the structures), and 2) a retrofit project on a single-family home, a half-plex, located in the Aggie Village community in downtown Davis, California. The home was already being used for a number of technology retrofits funded by the California Solar Initiative and the California Energy Commission. Utilizing a combination of PV, solar thermal, and battery storage systems installed at the Aggie Village home, the project was designed to help evaluate how a GSHP and other efficiency retrofits in the home could assist in achieving zero net energy on an annual basis. As detailed below, the project at Aggie Village could not be implemented due to permitting constraints and high construction costs associated with this university-owned home site. The Baggins End project was installed and evaluated with the results described here along with results of the more generalized modeling and market assessment. BACKGROUND ON DOMESTIC GEOTHERMAL HEAT PUMP SYSTEMS Geothermal heat pump systems (geothermal heat pumps; also known as ground source heat pumps, water source heat pumps, ground-coupled heat pumps or geo-exchange systems) are used for space heating and cooling. Such systems are among the most efficient and cost-effective means for heating and cooling buildings. These systems can be easily deployed in commercial and residential buildings, and have flexible designs that can accommodate almost any existing site. According to the Energy Efficiency and Renewable Energy (EERE) Office of the Department of Energy, geothermal heat pump systems use 25 percent to 50 percent less electricity than conventional heating and cooling systems [2]. The U.S. Environmental Protection Agency, as referenced by the EERE, noted that geothermal heat pumps consume 44 percent less energy than air-source heat pump systems and 72 percent less energy than standard electric resistance heating equipment. Geothermal heat pump systems thus have the potential to significantly reduce electricity consumption while also reducing the costs of heating and cooling homes and commercial building spaces. The reduced energy consumption can also directly reduce emissions associated with fossil fuel based power generation because of the decrease in electrical demand, thus leading to lower greenhouse gas emissions and reduced generation of atmospheric pollutants. Despite their energy, economic and environmental benefits, the number of installed geothermal heat pump systems in California remains limited. As cited by the EERE and 32

35 according to the Energy Information Agency (EIA), in 2009 the capacity of geothermal heat pumps shipped to California was 6,998 tons, down from 9,522 tons in The total capacity (in tons) of heat pumps shipped within the U.S. in 2009 was 338,689 tons, indicating that California accounted for less than 2.1 percent of the total capacity shipped and placing it 19th out of the 50 states in geothermal heat pump use. These systems are deployable in most settings, as the successful installations of geothermal heat pump systems have been accomplished in climate zones across the United States (FEMP, 2003). The UC Davis California Geothermal Energy Collaborative (CGEC) recently completed a GHP Deployment Study for the California Energy Commission, evaluating these systems across the 16 California climate zones. This study found that in 15 of the 16 zones, these systems were more efficient than conventional forced-air HVAC systems and that in 15 of the 16 cases, reductions were achieved in both greenhouse gas and criteria air pollutant emissions when taking into account the current energy sources they would be displacing. The minimum energy savings in the 15 zones was 22.3 percent, while the maximum was 77.6 percent, with an average among all zones of 44.3 percent. PRINCIPLES OF OPERATION Heat pumps are devices for transferring heat against an adverse temperature gradient. They do so by generating temperatures that are either above or below those of the space to be conditioned depending on whether heating or cooling is desired while exchanging energy with the environment. Geothermal heat pumps exchange heat with the ground and typically operate at higher temperature differentials and therefore higher efficiencies compared to direct exchange with the outside air. These systems rely on the fact that temperatures in the subsurface remain relatively constant and are usually between ~47 F and ~79 F (~10 C and ~26 C) year round across California. This constant temperature falls between the high temperatures that occur in summer months when interior air cooling is needed (exterior temperatures exceed ~80 F) and cold temperatures during winter months when interior air heating is needed (exterior temperatures are less than ~50 F). These circumstances allow heat to be removed from building interiors during summer months and deposited in the subsurface, while during winter months, subsurface heat can be extracted and transferred to building interiors. The nearly constant temperatures in the subsurface are the result of the interactions between several processes. The ground surface temperature varies significantly by season, weather and time of day. These variations reflect the short-term effect of fluctuating solar energy absorption by the ground as expressed through solar insolation, soil transpiration, precipitation, infiltration and vegetation. At depths of tens of feet this variability is dramatically reduced through physical processes that diffuse and retard transmission and radiation of thermal energy. In addition, there is a constant flux of thermal energy from earth s interior toward the surface, averaging a modest 87 mw/m 2. This flux results in a geothermal gradient in which the subsurface temperature tends to approach a near-constant value with depth. The interaction of these combined processes varies from place to place, but the overall consequence is that at some depth, the temperature in any particular location is nearly constant (Figure 3). 33

36 FIGURE 3: IDEALIZED SUBSURFACE TEMPERATURE PROFILE. TEMPERATURE IS INDICATED AS A FUNCTION OF DEPTH, SEASON AND SOIL TYPE (MODIFIED FROM [3]) Geothermal heat pumps transfer heat between buildings and the subsurface using the same principles that are used in typical home refrigerators. In a refrigerator, a fluid that boils at very low temperatures (between 35 F and 45 F) is circulated in thermal contact with the interior of the refrigerator across a heat exchanger. If the interior temperature is above the boiling temperature of the fluid, the fluid will evaporate, absorbing heat from the interior. This evaporating fluid extracts heat from the interior of the refrigerator as it circulates and the vapor is then passed through a compressor and heat exchanger that allows the heat in the fluid to be transferred to the room. The vapor condenses as it loses heat through this second heat exchanger and is circulated back to the refrigerator interior to repeat the cycle. For a geothermal heat pump system, the basic principles are the same, except that the fluid path through the device can be reversed when heat is to be transferred from the earth to the room when operating in heating mode (Figure 4). Although heat pumps rely on the thermodynamic properties of the circulating fluid to accomplish heat transfer, they are dependent on an external electrical supply or other source to power the compressor and to pump fluid in the ground loop. 34

37 FIGURE 4:SCHEMATIC DIAGRAM OF A GEOTHERMAL HEAT PUMP, OPERATING IN HEATING MODE (MODIFIED FROM [3]). Transferring heat to or from the earth is accomplished by pumping a second fluid (either water or a water/antifreeze solution) through a closed-loop underground piping system (i.e., the ground heat exchanger). There are three main types of closed-loop geothermal heat pump piping systems: horizontal, pond, and vertical (Figure 5). Open-loop systems exist and take fluid from a fluid reservoir, such as an aquifer, river or pond for the heat pump and then discharge it back to the source or another reservoir. As suitable reservoirs are typically unavailable, the most commonly deployed systems for commercial buildings and residences are closed-loop vertical bore and horizontal loop systems (Figure 3) to exchange heat with the ground. 35

38 FIGURE 5: GEOTHERMAL LOOP CONFIGURATIONS SOURCE: EERE [4] The horizontal loop geothermal heat pump system consists of coiled tubing laid at the bottom of a trench. A trench (or set of trenches) is dug deep enough to be below the frost line to avoid freezing in the winter months but tends to be less than 10 feet deep. Once the trench has been dug and the tubing laid, the trench is back-filled with soil and the fluid used for heating and cooling is pumped through the tubing. This method can require a larger amount of land for the tubing to be installed than vertical loop systems. The pond-loop geothermal heat pump system arranges the piping on a platform or scaffolding that is sunk into a nearby body of water. This system requires a sufficiently large pond for the energy storage to accomplish adequate heating/cooling. A vertical loop borehole geothermal heat pump system is composed of vertical tubing inserted into a borehole. The borehole is filled in with an insulating grout to hold the piping in place, to prevent surface contamination and to prevent cross connection of aquifers, and to facilitate heat transfer. New configurations that may bring down the costs of drilling and materials are now being deployed. A helix system is currently being tested at the Honda Smart Home located at UC Davis West Village for efficiency in relation to cost. These systems use coiled tubing that is roughly two feet in diameter with each band of coil separated by 36

39 six inches. If these systems prove to be efficient, they may serve as a preferred alternative for many users as the drilling rig is small and efficient, and materials are inexpensive. The site conditions for these systems are however somewhat constrained, as they require soft soil to a depth of feet. PHYSICS OF GHP SYSTEMS Although simple in concept and design, the efficiency and long-term performance of geothermal heat pump installations are affected by a variety of factors. Some of these factors relate to natural site characteristics (such as soil properties and local climate), some to the building properties (size, insulation, orientation, construction methods, etc.) and some to loop design (pump sizes, borehole construction, etc.). Below is a discussion of some of the key properties that should be considered when selecting a system design. SOIL THERMAL CONDUCTIVITY, THERMAL DIFFUSIVITY AND SATURATION Design of geothermal heat pump subsurface loops requires the ability to predict heat transfer rates. Soils and rocks in which heat transfer rates are slow will experience relatively rapid changes in temperature near boreholes, while fast heat transfer rates will result in relatively small changes in temperature near boreholes. The efficiency of a geothermal heat pump system depends directly on the temperature difference between the heat reservoir surrounding the borehole and the temperature of the circulating fluid in the loop. Designing efficient and sustainable geothermal heat pump installations is critically dependent on the ability to model heat transfer processes in the subsurface. The most critical parameters that affect heat transfer rates are thermal conductivity, thermal diffusivity, and deep earth temperatures. This is particularly important in California because of the state s diverse and complex geology. These properties are specific to a rock/soil type and the local hydrological regime. The thermal conductivity of the underlying rock refers to the ability of the rock to conduct heat. The flow of heat is expressed by the following equation (1): q th = k th T x EQUATION 1: SOIL THERMAL CONDUCTIVITY Where the heat flow is q th, (in units of W/m 2 or Btu/hr-ft 2 ) and the thermal conductivity as k th (in W/m-K or Btu/hr-ft- F). T is the temperature gradient over the distance x. Equation 1 demonstrates that heat flow increases with increasing thermal conductivity, for any given temperature gradient over a given distance. This means that the higher the value of thermal conductivity is of a soil/rock, the faster the heat will transfer. Conversely, if the soil/rock has a lower value of thermal conductivity, the soil/rock will act more like an insulator and retard the rate at which heat is transferred. 37

40 Thermal diffusivity, κ, is a measure of the rate at which heat transfer occurs. Thermal diffusivity has the units of m 2 /s or ft 2 /s. It is defined as the ratio of the thermal conductivity, k th to the heat capacity (by volume) of a material (CV, in J/m 3 - K or Btu/lb- F): κ = k th / C V. EQUATION 2: THERMAL DIFFUSIVITY Heat capacity is the amount of heat required to raise the temperature of a unit volume of a material by 1 Kelvin (or by 1 C). The higher the value of thermal diffusivity for a specific rock, the greater the rate at which heat will spread through the rock. Much like the thermal conductivity, if a material has a low thermal diffusivity value it will act like an insulator. As with thermal conductivity, thermal diffusivity is specific to a particular soil/rock. It is important to take these values into consideration, though available measured values are limited. In the CGEC GHP Deployment Study, an approach was developed for estimating thermal diffusivity from thermal conductivity values that are more commonly available. Water saturation refers to the percentage of the pore space of a material that contains water. Since the thermal conductivity of air is significantly less than that of water, the more water that is contained in a material, the greater the thermal conductivity will be. It is therefore important to take into account the degree of saturation. SUBSURFACE TEMPERATURE The efficiency of a geothermal heat pump system is directly related to the temperature difference between the circulating fluid in the loop and the temperature in the subsurface. This is implicit in the expression for thermal conductivity (Equation 1). Although rule-of-thumb approaches have been applied to estimating subsurface temperatures for the design of geothermal heat pump loops, the factors that influence subsurface temperatures are sufficiently different locally and regionally that significant error can be introduced if temperatures are not measured. The observed temperature range for each region is substantial, varying from 42 F to more than 100 F in California. Because of this variability, it is important that site temperatures be established in order to accurately design an efficient and sustainable geothermal heat pump system. LOCAL CLIMATE The two project sites discussed in this report are located within the City of Davis and reside within California s Climate Zone 12. Interbedded sand and gravel with clay is anticipated to a depth of 300 feet. This is typical of valley floor or river bottom conditions. Since both projects identified for this research project are residential, it was not anticipated that the design depth of a vertical loop system would extend beyond the 300 foot depth. The depth to groundwater in Davis is typically around 20 feet below grade. 38

41 PG&E s Emerging Technologies Program One of the primary factors that determine the size of a geothermal heat pump system are the heating and cooling loads to which the system must respond. The loads are a direct function of local climate since local climate will influence whether a building will require mainly heating, mainly cooling or approximately equal heating and cooling demands. Of course, building attributes (e.g., orientation, construction quality, insulation, window coverage and type, usage patterns, etc.) are also critically important in establishing loads within a given climate zone. In the CGEC GHP Deployment Study the 16 California climate zones (Figure 6) that have been identified [5] were examined. FIGURE 6: CALIFORNIA CLIMATE ZONES, AS IDENTIFIED BY THE CALIFORNIA ENERGY COMMISSION [5]. THE REPRESENTATIVE CITY FOR EACH ZONE, AND THE ZONE IDENTIFYING NUMBER, ARE SHOWN. TEMPERATURE BALANCE Efficient operation of geothermal heat pump systems relies on a predictable subsurface temperature. If the subsurface temperature changes significantly from that which was used for the design of the loop, the efficiency of the system will be affected. Geothermal heat pump systems that operate in both heating and cooling mode must be operated in such a way as to assure that the subsurface thermal reservoir does not change its characteristics significantly from those upon which the design was originally based. This is important in order to assure that performance and efficiency are maintained. In many instances, movement of pore water/groundwater will assure that thermal stability is maintained. In other instances, design parameters can be adjusted, or system load balancing can be done in order to assure consistent lifetime performance. In the modeling described below, loop design was constrained to result in subsurface temperature changes of less than 2 F over twenty years, assuming a static groundwater system. 39

42 EMERGING TECHNOLOGY Originally, the goal of this project was to install fairly traditional ground source heat pump systems. At the Baggins End (Domes) site, a central heat ground loop shared by multiple domes was anticipated. At Aggie Village, a vertical loop ground heat exchanger was planned. Due to cost constraints and other issues the final proposed GHX configuration was a departure from what was originally envisioned. HORIZONTAL DIRECTIONAL DRILLING GROUND SOURCE HEAT PUMPS Due to the constraints at Aggie Village, and concerns at the Domes site that a vertical drill rig would damage trees and landscaping, a horizontally bored ground heat exchanger (GHX) was installed. Horizontal boring is common in utility applications but has not been widely used in ground source heat pump applications. This application is referred to as horizontal directional drilled (HDD) ground-heat exchanger (GHX) and has various advantages and disadvantages. For the types of applications investigated here, the boring machine is relatively small, can access tight spaces and be easily transported with a double-axle trailer. The length of high density polyethylene (HDPE) tubing in the ground varies with the size of the system; thus at Aggie Village the total length was higher than at the Domes. The Domes also had an advantage due to the large area of land available to extend the horizontal bore. HDD GHX systems are installed at depths up to ft. and typically have the lowest installed cost compared to other drilled closed-loop GHX. However, they can suffer from performance penalties due to ground temperature swings experienced at short burial depths; require significantly more land area, which limits their application in densely populated areas; and consume more pumping energy due to the length of ground loop. Lastly, given the shallow depth of HDD GHX systems, setbacks and permitting requirements are typically less than that of vertically drilled GHX. GROUND-SOURCE PACKAGED AIR-CONDITIONER The Ground-Source Thermal Air Conditioner (GTAC) system that was installed at the Domes site was one that had been converted from a conventional Packaged Terminal Air Conditioner (PTAC). The conversion was performed by Enertech Global LLC (Greenville, IL), which manufactures geothermal heat pump units. Given the size of the market for PTACs in the lodging and some multifamily building categories, it was desirable to understand how a ground source packaged air conditioner could potentially provide energy efficiency and cost advantages in California. To our knowledge, this is the first demonstration using a ground source packaged airconditioner. The units were bench tested by Enertech prior to shipping and were found to achieve an EER rating of THE DOMES SITE The Domes, which are officially known as Baggins End Innovative Housing, are located on the western edge of the main campus at UC Davis. The Domes opened in the fall of

43 The project came about in the 1960s when the campus was exploring ways to build less expensive student housing on campus. Designs were solicited from students and faculty and varied greatly. Given the popularity of fiberglass material at the time, it was eventually decided that a fiberglass dome structure would be the icon of the site. One of the perceived advantages, which turned out to be incorrect, was the idea that fiberglass domes could be easily constructed on site with a single mold. As they discovered, removing the fiberglass dome structure from the mold was difficult and in the end the project was not able to achieve their construction costs estimates due to delays and problems perfecting the onsite mold and removal process. While the cost goals were not achieved, the project was considered a success since the students and faculty on campus succeeded in constructing a community entirely from student and faculty designs and achieved all construction with community volunteer labor. Subsequently the Domes have become a mature community with a deep sense of fraternity and volunteerism. The residents contribute significantly to the campus and local Davis community. Over the years the Domes have hosted many community services and events. In return the community continues to visit the site and provide needed services such as free labor for upgrades. As an example, much of the unskilled coordination activities and construction labor with this retrofit project were provided in-kind by Domes residents. In 2011, Baggins End was released by University Housing and was slated for demolition. However, Real Estate Services department at UC Davis worked with the Solar Community Housing Association (SCHA) to lease the property to this non-profit organization dedicated to community housing. The lease was executed with the understanding that SCHA would continue to improve the site and engage with academic programs, faculty and researchers to create research and education opportunities at the Domes. 41

44 FIGURE 7:DOMES CONSTRUCTION CIRCA 1970 (SOURCE: [6]) ADVANTAGES FOR RESEARCH While the building structure at the Domes is not typical of most residential construction, the building and site attributes were carefully considered during project planning and proposal phases. It was ultimately decided that the Domes site had certain distinct advantages that made it a valuable and acceptable research site for the ground source HVAC demonstration. For example: While the Domes construction is unique, the thermal envelope is similar to many residential construction types built in California during the 1960s and 70s. The Domes conveniently demonstrates a heating and cooling load of 1 ton, making scaling up loads in increments of 1 ton reasonable to represent larger building loads. The Domes community is actively engaged and supportive of research within the community. Residents support, accommodate and volunteer to assist research projects. This was particularly important due to the disruptions experienced by residents during construction and the ongoing assessment and commissioning at the site. The location is on campus and can be easily accessed, making the site an excellent venue for showcasing technologies for research and industry. 42

45 While the site is located on campus, the site is fully controlled by an independent entity, which allows for streamlined execution of construction activities and reduced costs. INTRODUCTION TO DOMES SITE The Domes community consists of 15 dome structures spread across 2.78 acres located off of Orchard Park Circle on the UC Davis main campus. Each dome accommodates two students. FIGURE 8: DOMES SITE MAP (SOURCE SOLAR COMMUNITY HOUSING ASSOCIATION) 43

46 These structures are served by electricity only and are currently all connected to one master site meter. The homes have approximately 450 square feet in the floor plan on concrete slabs, with fiberglass and polyurethane wall construction, double-pane aluminum-framed windows, and wooden doors. The overall R-value of the envelope, including walls, doors, and windows, is between ft 2 F hour/btu. The equipment in the homes includes refrigerators, electric ovens & ranges, electric domestic hot water heaters, general lighting, and electric space heaters. There is currently no space cooling installed, aside from the three units retrofitted under this project, which now have cooling, improved envelope upgrades and LED lighting. 44

47 FIGURE 9: DOMES FLOOR PLAN (SOURCE SOLAR COMMUNITY HOUSING ASSOCIATION) 45

48 On average a total of 20 residents live in the Domes community. The current site energy consumption ranges from a total of roughly 2,400 kwh per month in the summer to over 10,000 kwh per month during the winter. This equates to an annual average consumption of approximately 62,000 kwh per year (approximately 4,500 to 6,000 kwh per year per dome), or an equivalent average energy use intensity (EUI, annual energy use per area) of 35 kbtu/ft 2 year. Because the whole community is only served by one meter, the end use load distribution was estimated through pervious modeling and research performed by UC Davis. After modeling, testing and surveys of residents, the following end use breakdown for baseline loads was determined. Domes energy use breakdown 13% 20% Based on an average consumption of 300kWh/month energy usage 4% Heating Cooling Water Heater Misc. 63% FIGURE 10: DOMES ESTIMATED ENERGY USE BREAKDOWN It is important to note that the un-retrofitted domes only have resistance electric heating and no mechanical cooling systems. The four percent in the breakdown is attributed to electric fan energy use in the summer time. HVAC OPTIONS FOR THE SITE Given the space heating and water heating energy use discovered through the previous analysis performed by UC Davis, the project team wanted to address reducing all those loads through the ground source system. Thus, originally the team proposed a central plant using ground source heat pump throughout, which included heating, air-conditioning and hot water production. A plan was fully developed, but the costs of the central plant system turned out to be cost prohibitive as the bids collected by contractors could not be accommodated within the project budget. 46

49 FIGURE 11: TYPICAL CENTRAL PLANT LAYOUT ORIGINALLY PROPOSED FOR THE DOMES The central plant, while estimated to be quite efficient, would have required a larger heat pump, multiple storage tanks and significant trenching to supply each dome with hot and cold water for both domestic use and heating and cooling. 47

50 FIGURE 12: PROPOSED SHARED GHX DIAGRAM FOR DOMES SITE (SOURCE: MELINE ENGINEERING) 48

51 Other options that were considered along with the central plant and shared GHX were radiant panels or sails. Originally the team hoped to demonstrate innovative radiant sail technology by Talbot Solar that can provide both heating and cooling. However after close evaluation it was determined that mounting the radiant sails would be too difficult and time consuming not only due to the shape of the dome but also the limited structural strength of the fiberglass shell for hanging the sails. The team did develop multiple scenarios that would have supported the sails with a spine frame, but these again were considered overly labor intensive and time consuming, increasing cost. FIGURE 13: EXAMPLE OF PROPOSED CONFIGURATION FOR RADIANT SAILS (SOURCE UC DAVIS DESIGN CHARRETTE) GHP SYSTEMS ADVANTAGES AND CHALLENGES (SPECIFIC TO SITE) Retrofitting heating and cooling systems into existing buildings can be challenging. In the case of the Domes, the wall shape provided the biggest challenge for integrating the outdoor GHX piping with the indoor geothermal heat pump equipment. This coupled with the requirement to integrate a flow meter as part of the data collection system resulted in exterior above-ground plumbing to connect the interior system to the ground loop. This then needed to be protected and housed at the building perimeter. The chosen piping arrangement was also driven by the requirement to connect and switch over to a (future) alternate ground heat exchanger at Domes 13 and 14 (see Figure 8), to accommodate future research on innovative helix type ground loop heat exchanger design. 49

52 As mentioned previously, due to the many trees and landscape on the site and given the large amount of land space to work with, it was determined that a horizontally bored GHX would be utilized for the project. LOCAL CONDITIONS AT THE SITE At the Domes there are many existing trees and shrubs that contribute to the landscaping and ambiance of the Domes that were requested to be mostly left undisturbed. This is not an unusual requirement for retrofit projects. The main power to the site comes underground to the transformer and single meter located on the north end of Dome 4. From this location, power is run underground to a sub-panel at each of the 15 domes. There is a dense buried utilities corridor running from the west end of the project site between Domes 14 and 15 to the east end between Domes 7 and 6 that needed to be avoided and required hand digging for new buried pipe. The utilities include underground electrical power, telecom, fire alarm, sanitary sewer and domestic water pipe. DESIGN SITE PROPERTIES During the feasibility phase of the project, several ground heat exchanger options were explored: trenched (slinky and horizontal pipe), horizontal directional drilled (HDD) and vertical closed loop. Keeping in mind that a project might be undertaken in the future to connect additional Domes to the system, the trenched options were not pursued. The vertical loop system was the most expensive solution and most invasive to the existing site landscaping. Access to the open spaces at Baggins End was challenging. In the end, the HDD solution was selected. This was due to cost but also to the anticipated drilling conditions at feet below grade, which were expected to be sand, clay and perhaps smaller gravel. The soil thermal properties estimated for the design were as follows: Deep Earth: 65 F Thermal grout conductivity: 0.88 Btu/hr-ft- F (specified) Soil conductivity: 0.88 Btu/hr-ft- F (specified) Soil thermal diffusivity: 0.56 ft 2 /day The initial design of this system included a HDD ground loop consisting of four 1 diameter HDPE horizontal boreholes to 250 feet in length on 10 ft. centers. The ground loop was sized to support a 5-ton heat pump load associated with a maximum of five (5) connected domes. CONSTRAINTS Total budget was limited for the installation. While it was challenging to work within the specified budget, it did provide a pathway to the final system selection, which may not have been considered otherwise. Even with a 50

53 scaled-down central plant design, preliminary contractor pricing was double the original estimated construction budget. Also, as was mentioned above, the unique shape of the dome structures made it challenging to incorporate the radiant sails into the living space and that aspect of the project was abandoned. SELECTED DESIGN After several discussions between the research and design teams, an alternate heating and cooling solution was proposed by Meline Engineering (Sacramento, CA). Due to the small footprint and heating and cooling requirement of each dome, an extended-range water-cooled (or geothermal) packaged terminal air conditioner (PTAC) unit was considered which is here referred to as a geothermal terminal air conditioner or GTAC. Currently, this product does not exist in mass production; however, a prototype was made available, and two units were purchased by the University for this project. A third traditional PTAC was purchased as a control for the experiment. PG&E supported this change in equipment and agreed that there could be potential for scalability and market penetration by the geothermal heat pump industry for building types traditionally specifying lower-cost terminal equipment such as affordable housing, senior housing as well as hotel/motels and other lodging. 51

54 FIGURE 14: FINAL DOMES GHX CONFIGURATION 52

55 An air-to-water heat pump was selected as the central hot water heater for three of the domes with domestic hot water return pump to ensure hot water delivery to each dome. The existing 30-gallon electric hot water heaters were to be removed at each of the 3 domes (Domes 13, 14 and 15). PERMITTING AND SYSTEM INSTALLATION PERMITTING Because the project site is located on campus, the project was under the jurisdiction of UC Davis, not the City of Davis. Before the University approves construction permits on campus, plans are circulated for review between all the applicable departments and facilities on campus for comments. This is true even for a property they do not control, such as the Domes. Thus, permitting the project took an additional two weeks due to the amount of time needed to circulate the plans for comment. Because the HDD GHX was no deeper than 25 feet and the project had a detailed plan set with specific instructions for drilling, there were no issues with permitting. The permit was obtained and the inspector met the construction team on site to launch the project and to discuss any concerns. SYSTEM INSTALLATION As noted previously, the integration of the outdoor GHX with the indoor geothermal heat pump equipment was a challenge. In new construction, the ground loop header piping is typically buried 3-4 feet below finished grade and terminated inside a mechanical room or closet. Each GTAC was integrated with assistance by SCHA into the dome wall below the operable window in the living area of each of the domes. For the GTAC, it was decided that the small in-line pump that circulates water between the geothermal heat pump and the ground loop would be integrated into the GTAC cabinet. Three Amana PTAC model PTH153G3.5AxxxAA units were purchased. Two were modified as prototypes for this project. Specific modifications to these two Amana units for the GTAC prototypes included: Removal of the outdoor fan motor Removal of the air coil Disconnection of the resistance heater (second stage heat) Addition of a 115V circulation pump (Grundfos UPS 15-58) to operate whenever the compressor operates Addition of a water coil The PTAC and GTAC are controlled by standard 7-day programmable thermostats provided by the PTAC manufacturer. Since the GTACs are single-speed heating or cooling, the programming of the thermostats was modified. The control PTAC continued to operate with a second-stage resistance heater as needed. Since the geothermal heat pump system design changed to a de-centralized system, Domes 13 and 14 were each provided with a single dedicated HDD ground loop of 1 53

56 dia. HDPE drilled to a horizontal depth of 15 feet and borehole length of 175 feet filled with thermally enhanced grout. The final project design provided for a central air-to-water heat pump in an enclosed mechanical room off Dome 14. The domestic water pipe was tapped at this location and partial flow diverted to the new A.O. Smith PHPT-80 air-to-water heat pump. From this location, the three domes were provided with hot water with a recirculation line to the heat pump (Taco 006-BC4-5PNP). Each hot water supply line was retrofitted with a flow meter to monitor consumption. MODELING AND DATA ANALYSIS OF INSTALLED SYSTEM PREDICTED ENERGY PERFORMANCE Beyond the estimated baseline energy use determined previously, it was difficult to gauge the predicted performance for a few reasons. First, the domes were not individually metered, and second the retrofit systems added cooling, which was previously not available other than by manually controlled electric fan if provided by the residents. With an efficient GTAC, the energy consumption was estimated to remain as is shown in Figure 10 but with the added benefit of cooling. MONITORED ENERGY PERFORMANCE Architectural Energy Corporation (now Noresco) was tasked to perform the monitoring and verification of the installed GTAC units and PTAC baseline units. AEC completed the installation of monitoring equipment in December As of April 15 th, 2014 the monitored energy performance suggested the GTACs were operating more efficiently than the PTAC; however due to concerns over the quality of the ground loop temperature data being collected, the calculation has not been able to be completed of the unit coefficient of performance (COP) based off the heat pump efficiencies. Some of the values reported by the temperature sensors that are monitoring the supply and return from the ground loop may be erroneous as one of the surface mounted sensors may be influenced by another heat source, either the pump or the compressor. Uncertainties in the data were suspected early on and verified with splits taken locally with temperature probe sensors inserted into the access point wells on the supply and return with average differences of 4 F and 7 F on Domes 13 and 14 respectively. Additional effort will be needed to resolve these temperature uncertainties within the dataset. The energy consumption data also seem to point to higher efficiencies for the GTAC units over the baseline PTAC, although data are somewhat inconclusive due to short cycle times for the equipment. Energy consumption is shown in Table 14. The programmable thermostats were not initially properly programmed. Adjustments were made to the thermostat programing and it is anticipated run times will be higher in the last 3 quarters of monitoring during

57 FIGURE 15: OBSERVED DOMES DATA FEBRUARY 6TH THROUGH MARCH 31ST 2014 (SOURCE AEC) UPDATE MAY 19, 2014 Following instructions from Meline Engineering, two additional surface mounted temperature sensors were installed to monitor supply and return temperatures of the ground loop on Dome 14. The sensors were placed on the surface of the copper pipe, beneath the insulation and placed on the 90 elbow fittings. Sensors were covered in heat conducting gel, taped, zip-tied, (as seen in Figure 16) and then insulated in attempt to obtain a temperature as close that of the pipe wall as possible (and hence the fluid). FIGURE 16: ADDITIONAL SUPPLY AND RETURN GROUND LOOP TEMPERATURE SENSORS INSTALLED MAY 7 TH,

58 After monitoring for a week, the data were downloaded and analyzed. During this time the weather was mild (May in Davis, CA) but one heating event did occur. The COP of this one heating event is shown below in Figure 17. This 20-minute heating event shows COP of above 4 and up to 7. FIGURE 17: HEATING EVENT CAPTURED AT DOME 14 WITH UPDATED ENTERING WATER TEMPERATURE (EWT, F) SENSOR CONFIGURATION, MAY 2014 PERFORMANCE MODELING AND ANALYSIS MODELING OVERVIEW This section of the report details the 20-year lifecycle modeling effort undertaken to gauge the cost effectiveness of commercial deployment of small (1 cooling ton) groundsource heat pump (GHP) systems employing horizontal directional drilling (HDD). Levelized cost of service (LCOS) total lifetime cost over cooling and heating energy delivery and energy use of service (EUS) total energy use over cooling and heating energy delivery metrics were used to quantify the results, with lower values indicating more energy- and cost-efficient systems, along with other metrics as follows: Levelized cost of service, LCOS (total implementation, energy and maintenance costs over cooling and heating energy delivery) HVAC energy use of service, HEUS (HVAC-only energy use for cooling and heating energy delivery) Energy use of service, EUS (total building energy use for cooling and heating energy delivery) 56

59 Carbon emissions of service, CES (carbon dioxide (CO 2 ) emissions for cooling and heating energy delivery as calculated using total facility energy use and the PG&E carbon footprint indices Modeling was conducted for two building types: 1) commercial lodging and 2) residential multifamily. The analyses in this report consider packaged terminal air conditioning systems with gas furnace heating as the baseline practice, and HDD ground-source heat pumps as the alternative or proposed approach. In California, there are a total of 16 Climate Zones (CZ) (see Figure 6). The climactic effects of two of these zones were analyzed: Coastal: CZ 3 (Reference City: Oakland) Inland: CZ 13 (Reference City: Fresno) The following sections present the modeling and cost estimation procedures, show the results, and give a discussion of major findings, and are organized as follows: Building Characteristic the physical characteristics of the modeled building and methodology for developing the cooling and heating loads are described. HVAC Systems the baseline and proposed HVAC systems, including their expected useful lives are described. Climate Zones the climatic effect on the HVAC systems are explained. Energy Costs the methodology for obtaining rates for calculating energy costs are explained. Analysis Methodologies the methodology for analysis is described. Detailed equations are presented in Appendix I. Results detailed results of the analyses as well as major conclusions are presented. Needs and recommendations needs and recommendations for additional research are described. In addition, sensitivity analyses were performed for LCOS at with six additional scenarios as described in the section on Performance Modeling and Analysis. The typical baseline practice in actual medium-density lodging and multifamily is PTACs with electrical resistance heating or packaged terminal heat pumps (PTHPs). Initially it was hoped to have access to load profiles from an actual lodging and multifamily facility. Ultimately, PG&E and the project team decided to develop baseline energy use profiles using data from the California Commercial End-use Survey (CEUS) and the Database for Energy Efficient Resources (DEER) load profiles, which shows space heating primarily by natural gas. This resulted in the selection of PTACs with gas furnace heat as the baseline system against which the GTAC retrofit was compared for this report. 57

60 BUILDING CHARACTERISTIC COMMERCIAL LODGING The physical characteristics for the evaluated lodging site were not based on a specific existing building; instead a model building was developed with electricity prices based on the PG&E Medium General Service A10S rate schedule. The combination of the California Commercial End Use Survey (CEUS) energy consumption data (reference) and floor area as well as the A10S schedule were used to derive basic characteristics of the building through the following methodology: Maximum electrical demand intensity (max kw/ft 2 ) was calculated from CEUS. Since the highest and lowest monthly maximum demand of 499 kw and 200 kw are required parameters for A10S eligibility, floor area of the representative building was estimated using the electrical demand intensity. o o The maximum demand through the 20-year lifecycle analysis period was checked to ensure that the A10s upper and lower demand limits were met. A 4-story square building was assumed for simplicity, and height and perimeter were calculated accordingly. Table 5 lists the basic physical characteristics of the building. Note that the parameters for lodging were rounded values due to their nature as estimations. Floor areas describe interior areas (excluding wall thicknesses) served by heating and cooling systems as defined by CEUS. Parameters for multifamily were extracted directly from simulation as explained in the Horizontal Directional Drilling Ground Source Heat Pumps section. Physical Building Characteristic Dimension Lodging # Multifamily* Total Floor Area 157,000 12,376 Side length, L b (ft) Width, W b N/A 68 Height, H b Number of floors 4 2 * Per building # Rounded values. Multifamily parameters were extracted directly from simulation data provided. TABLE 5: PHYSICAL BUILDING CHARACTERISTICS MODELED 58

61 (Distribution piping shown in red. Dotted line represents interior lines for only top floor.) FIGURE 18: REPRESENTATIVE BUILDING FOR LODGING WITH GHX LAYOUT The load profiles for this building were estimated as follows: 1) HVAC and miscellaneous (non-hvac) energy consumption data for lodging in the two climate zones were taken from CEUS, which is organized based on California Energy Commission (CEC) Forecasting Climate Zones (FCZ). Reference cities of Oakland and Fresno were used to match FCZ to CZ. FCZ 5 and 3 are analogs to CZ3 and 13. 2) The CEUS hourly HVAC and miscellaneous data were scaled down to obtain load profiles whose monthly maximum demand across the 20-year lifecycle analysis falls between 200 and 400 kw per A10S schedule requirement. This required an iterative procedure to arrive at the needed profiles. 3) The space heating and cooling loads for lodging were developed from the scaled HVAC consumption data by using manufacturer s performance curves for electrical space cooling and the 2001 California Title 24 (T24) minimum equipment efficiency for gas space heating. The 2001 version of T24 was selected, as it was the closest to the CEUS publication year. a. For cooling energy use via electricity, performance curves from present-day air conditioners of various manufacturers were obtained and normalized to 2001 levels using the ratio of 2013 and 2001 Title 24 PTAC cooling efficiencies. b. Approximately 7 percent of cooling energy consumption in the coastal CZ is by gas. It is assumed that direct-fired single-effect absorption chillers with T24 efficiency of 60 percent are the primary equipment utilized. 59

62 c. For heating energy use via gas, the efficiency was taken as a gas-fired, warm-air unit heater with a T24 thermal efficiency of 80 percent. d. Approximately 22 percent and 13 percent of heating energy consumption in the coastal and inland CZ, respectively, is by gas. It is assumed that electric resistance heaters are the primary equipment utilized. Appendix Figure 1 and Appendix Figure 2 in Appendix I show the load profiles for this building type. RESIDENTIAL MULTIFAMILY Relevant data for this building type were developed using Measure Analysis Software (MASControl) [8] and the Quick Energy Simulation Tool (equest) [9]. MASControl was used to create weather-sensitive models for multifamily housing with the following dropdown selections (Figure 19 shows a screen capture of the selection interface). Building type: MFM Climate Zones: 3 and 13 Vintage: 1975 HVAC type: AC Thermostat Option: 2 Case: CAv Tech ID: D08-RE-HV-ResAC-13C 60

63 FIGURE 19: MASCONTROL INTERFACE The.pd2 output files from MASControl were executed in equest, a graphical building energy simulation tool developed by J.J. Hirsch and built on the DOE 2.2 engine [10]. The following hourly data were then extracted from equest: HVAC energy consumption Miscellaneous equipment (non-hvac) energy consumption Heating and cooling loads Physical building characteristics Table 5 lists the basic physical characteristics of the building. 61

64 Figure 20 shows a simplified schematic of the building. FIGURE 20: REPRESENTATIVE BUILDINGS FOR MULTIFAMILY HOUSING. HVAC SYSTEMS PACKAGED TERMINAL AIR CONDITIONERS WITH GAS FURNACE HEATING The baseline HVAC system considered in the modeling is the packaged terminal air conditioner (PTAC) that describes unitary air-source units designed to provide space cooling. Cooling is achieved via a vapor compression refrigeration cycle. Heating can be provided either through electrical resistance heaters, hydronic heating coils or warm-air gas furnaces. Since these systems are installed through the wall and do not need additional ductwork, they are widely used in hotels, motels and apartments to serve a single zone. CEUS data used to establish the heating and cooling loads are an aggregate of energy consumption of various HVAC systems including PTACs, rooftop packaged units, central chiller with air handlers, and others. The contribution of only PTAC units cannot be extracted from the aggregate to use in this modeling effort so the comparison is more general. PTACs have a typical service life of years, given regular maintenance [11]. 62

65 FIGURE 21: PTAC HORIZONTAL DIRECTIONAL DRILLING GROUND SOURCE HEAT PUMPS Given regular maintenance, GSHPs have a typical service life of years [11], while the GHX can last up to 50 years [12]. The extended life of GSHPs is attributed to lower mechanical stresses due to a shorter range of operating temperatures compared to air-source equivalents. There are multiple types of GSHP, as shown in Figure 5. HDD, U-tube GSHPs were analyzed in this modeling effort (Figure 22). HDD GHXs are installed up to 12to 15 ft. depth and typically have the lowest installed cost compared to other closed loop GHX. However, as noted earlier they can suffer from performance penalties due to ground temperature swings experienced at short burial depths and require significantly more land area, which limits their application in densely populated areas. 63

66 CLIMATE ZONE Modeling was focused on two California Climate Zones: o o Coastal: CZ 3 (Reference City: Oakland) Inland: CZ 13 (Reference City: Fresno) Table 6 shows a summary of climatic data for the two zones. Outside air temperature (T oa ) data for each climate zone were obtained from equest, which utilizes historical California weather files for energy simulation. Undisturbed ground temperature (T g ) was calculated based on methodology outlined in, and utilized input values from Table 5.11 in the International Ground Source Heat Pump Association s (ISGPHA) Residential and Light Commercial Design and Installation Manual [13]. Design heating and cooling months describe the month of peak heating and cooling loads, respectively. Annual Climatic Summary Item CZ3 CZ13 Toa Tg* Toa Tg* Daily Average Temperature (F) Daily Maximum Temperature (F) Daily Minimum Temperature (F) Warmest Month September October July July Coolest Month December April December February *Based on mean burial depth of 6 ft (total depth of 12 ft) and soil thermal diffusivity of 0.6 sq ft/day TABLE 6: ANNUAL CLIMATIC SUMMARY Figure 22 shows a simplified schematic of this technique. Based on discussion with Meline Engineering, the burial depth of 15 ft was utilized in this modeling effort, and this depth is reached within the first 26 ft of horizontal bore travel. Bore lengths are highly sensitive to various parameters as shall be discussed in the following sections. However, typical bores are at least 250 ft long [14] and thus a much larger portion of the bore is subject to the ground temperature at 15 ft. Figure 23 shows plots the daily average outside air and ground temperatures over the year, based on climate files from equest and undisturbed ground temperature calculated based on the methodology described above. Significant variations in ground temperatures may be experienced based on soil properties, climate zone and depth. 64

67 F PG&E s Emerging Technologies Program FIGURE 22: HDD GHX BORE Figure 3 shows the idealized annual ground temperature according to depth. HDD ground loops, which are buried to depths of ft, may be subject to T g variations over the year. As an example, during the cooling period, T g is higher than it would be during the heating period. This effectively reduces the efficiency and capacity of the GSHP as it would have to operate at a higher condensing temperature during cooling mode and lower evaporating temperature during heating mode. Inland Tg Inland Toa Coastal Tg Coastal Toa Days FIGURE 23: DAILY AVERAGE TEMPERATURE PROFILES 65

68 ENERGY USAGE AND DEMAND RATES COMMERCIAL LODGING The lifecycle cost of energy consumption for lodging was evaluated based on the A10S (Medium General Demand-Metered Service) non-time-of-use (TOU) rate schedule for electricity and the GNR-1 (Gas Service to Small Commercial Customers) rate schedule for gas. To qualify for the A10S schedule, a commercial customer s monthly maximum demand must fall between 200 and 499 kw. To qualify for the GNR-1 schedule, a commercial customer s monthly natural gas consumption must fall below 20,800 therms. Historical rates were extracted from PG&E s website [15] and the general trends of rates over time were developed, as shown in Appendix Figure 19 through Appendix Figure 22 in Appendix I. The best-fit curves were then applied to energy cost analysis. It should be noted that these figures were intended to show the yearly averages and general trend (increasing or decreasing) of energy rates over time. Specific variations in rates are a function of economic drivers whose analysis is beyond the scope of this work. RESIDENTIAL MULTIFAMILY The lifecycle cost of energy consumption for multifamily units was evaluated based on the E-1 (Residential) rate schedule for electricity and the G-1 (Residential) rate schedule for gas. Historical rates were extracted from PG&E s website[15] and the general trends of rates over time were developed, as shown in Appendix Figure 22 and Appendix Figure 24 in Appendix I. The residential rates vary based on consumption tiers, which are summarized in Table 7 for a 24-unit multifamily facility. As an example, if the 6-month summertime coastal electrical energy consumption is 35,000 kwh, then the first 32,580 kwh would be subject to the Tier 1 rate while the remainder is subject to the Tier 2 rate. The gas consumption tier is separated into two tiers only: baseline and excess. Excess consumption above the baseline falls under the excess rates. E-1 All Electric schedule applies to sites with space heating via electricity, or the proposed GSHP case in this analysis. 66

69 Consumption kwh Tiers Region Coastal Inland Season Summer Winter Summer Winter E-1 Schedule Basic (kwhs) Tier 1 32,580 51,667 74,282 51,667 Tier 2 42,354 67,167 96,567 67,167 Tier 3 65, , , ,334 E-1 Schedule All Electric (kwhs) Tier 1 39,530 85,229 90, ,363 Tier 2 51, , , ,372 Tier 3 79, , , ,726 G-1 Schedule Baseline 2,824 8,920 1,868 8,037 TABLE 7: CONSUMPTION TIERS (SOURCE PG&E) MODELING METHODOLOGY The methodology for analysis was as follows: 1. Heating and cooling loads were developed as outlined in building size and climate zone sections above for lodging and multifamily. 2. The PTAC full load cooling efficiencies as a function of outside air temperature were developed based on manufacturer s data and shown in Appendix Figure 1. This represents the baseline performance curve at the 16th year of operation when the baseline PTAC is due for a replacement at the end of its useful life of 15 years. The ratio of 2013 and 2001 Title 24 PTAC cooling efficiencies was used to scale the 16th year performance curve to obtain the baseline performance curve at the first year of operation. Similarly, GSHP full load heating and cooling efficiencies as a function of entering water temperature were developed and shown in Appendix Figure 2 and Appendix Figure The baseline cooling and heating consumption were taken to be electrical and gas, respectively. The annual HVAC electrical energy consumption at the first year of operation was calculated on an hourly basis using the performance curve developed in (2) above and the outside air (condensing) temperature. The annual HVAC natural gas consumption at the first year of operation was calculated on an hourly basis using the 2001 T24 warm-air gas unit heater efficiency. 4. The proposed (GSHP) cooling and heating consumption were taken to be entirely electrical. The proposed annual HVAC energy consumption at the first year of operation was calculated on an hourly basis using the performance curves developed in (2) above and the entering water temperature. The latter parameter was derived from the ground temperature, and soil and borehole thermal properties assumptions, which are documented in Appendix I. 5. The total site energy consumption was obtained by summing the HVAC energy use and the usage of other loads such as lighting, kitchen equipment, etc., which were included in the baseline data provide to UC Davis. These non-hvac loads are referred to as miscellaneous loads. 67

70 6. Lifecycle energy consumption over the course of 20 years - based on GSHP service life - was calculated by incorporating an annual HVAC efficiency degradation factor of 1.1 percent to the HVAC consumption[16]. a. As the service life of the baseline system is assumed to be 15 years, the baseline energy consumption beginning at the 16th year was recalculated using the PTAC performance curve from (2), and the 2013 T24 warm-air gasfired unit heater efficiency of 80 percent. 7. Ground loop bore length was calculated according to the methodology outlined by Bernier [17] with one modification. In his paper, Bernier presented sample design calculations for a vertical GHX system that experiences long term temperature penalties at deep burial depths due to thermal imbalance. In other words, due to the distance between the ground surface and the burial depth, heat stored by a deep GHX is not dissipated to the surface as effectively as it would be for horizontal GHX at much shallower depths, thus gradually increasing the undisturbed ground temperature. The bore length correction factor from the International Ground Source Heat Pump Association s (IGSHPA) Manual was used in place of the temperature penalty since the latter is more appropriate for deep earth, vertical GHXs. Thus, the bore length - as calculated in this analysis - is a function of the following: a. Ground and borehole (pipe and grout) thermal resistances. Mid-range soil (wet shale) and thermally enhanced grout resistance values were assumed in this analysis. Details on these values can be found in Appendix I. b. Three thermal pulses: yearly average ground load, highest monthly ground load and peak hourly ground load. c. Mean fluid temperature across the heat pump, which is a function of entering, water temperature (EWT), leaving water temperature (LWT), heat pump efficiency and GHX flow rate. d. Ground temperatures at the average burial depth of 15 ft. e. Bore length multiplier obtained IGSHPA Manual which is a function of the net annual ground load, the design heating and cooling loads and soil conductivity [13]. The results from the modified Bernier approach were compared to the results using International Grounds Source Heat Pump Association s methodology for a horizontally-bored, closed-loop GHX design (Section 5.4 of the Manual) [13] and accounting for the bore multiplier. The calculated design bore lengths from the two methodologies somewhat agree with each other for Multifamily analysis, with the modified Bernier approach showing more conservative results (longer bore lengths). Additionally, Table 11 in 2007 ASHRAE Applications [14] provides recommended lengths of bore per ton for horizontal 2-pipe GHX based on design ground temperatures. ASHRAE s lengths were found to validate the modified Bernier approach as the recommended lengths were much closer to the results of the modified Bernier approach than the IGSHPA s methodology. The conservative results using the modified Bernier approach are presented in this analysis. A potential added benefit of longer GHX is higher heat pump efficiencies as water temperatures will 68

71 approach the ground temperature closer than water temperatures using smaller GHX will. 8. The facility pump power requirement was calculated based on the following: a. Total flow rate based on design 3 gallons per minute (gpm)/ton b. Pump efficiency c. Frictional pressure drop based on pipe diameter, lengths and number of parallel arrangement i. Determination of pipe diameters, lengths, interior distribution loop parallel arrangement and the GHX parallel arrangement were based on building geometries and the pump power design benchmarks from Table 5.1 of Kavanaugh 1997 [1]. B-grade pump power benchmark of 5 to 7.5 hp /100 ton was used for lodging. ii. C-grade pump power benchmark of hp/100 ton was used for multifamily units. iii. The discrepancy between the design grades is due to larger pumps (lodging) having larger pump efficiencies than very small pumps (Multifamily) and the use of Variable Frequency Drive (VFD) control scheme for the lodging pump compared to on/off scheme for the multifamily pump. iv. Pressure drops were estimated based on design flow, pipe diameter, length, typical water properties and minor loss coefficients using an online calculator [18]. Figure 24 and Figure 25 show the simplified schematics of the GSHP water loop for lodging and Multifamily, respectively. The schematics were developed for energy use and pump sizing calculations and are not to be used as actual design schematic. The total facility pump size includes pressure drops through the GHX, heat pump water coil and distribution loop (header and interior loops). Under the ISO Standard , manufacturers are required to rate COPs while accounting for the heat pump water coil pressure drop. Therefore, the pump energy consumption calculations consider only flows through the GHX and distribution loop. 9. Total cost of service was calculated as the sum of implementation cost, energy cost and maintenance cost. a. For lodging, the electrical energy and demand costs were calculated based on the A10S non-tou schedule, and natural gas consumption were calculated based on the GNR-1 schedule. For Multifamily use, the electrical energy costs were calculated based on the E-1 schedule, and natural gas consumption was calculated based on the G-1 schedule. Energy costs utilized trends shown in Energy Cost in Appendix I. b. Material and labor costs for the baseline PTAC with gas furnace heat, proposed GSHP, HDPE piping and insulation, pumps, VFD controllers, HDD drilling and piping were obtained from RS Means Mechanical Cost Data 2014 [18] and conversations with Geonomic Developments, a geothermal system contractor responsible for the Domes GHP project. 69

72 c. Annual maintenance costs for the baseline and proposed systems were calculated based on the building physical characteristics and $/ft 2 publically available values [19, 20]. d. All costs were normalized to the same time frame using the Consumer Price Index (CPI). 10. The levelized cost of service, LCOS, was calculated as the ratio of the total cost of service to the total 20-year heating and cooling energy delivery. Higher ratios represent more expensive situations. 11. The HVAC energy use of service, HEUS, was calculated as the ratio of the HVAConly energy consumption to the total 20-year heating and cooling energy delivery. Higher ratios represent more energy intensive situations. 12. The energy use of service, EUS, was calculated as the ratio of total energy consumption of the facility to the total 20-year heating and cooling energy delivery. Higher ratios represent more energy intensive situations. 13. The energy-based carbon dioxide (CO2) emission of service, CES, was calculated as the ratio of the CO2 emission to the total 20-year heating and cooling energy delivery. Emission was calculated from the total facility energy consumption and the PG&E carbon footprint indices of lb CO 2 /kwh electricity and lb CO 2 /therm natural gas [21]. 14. Sensitivity tests were performed for the proposed LCOS for the following independent (non-cumulative) scenarios: a. Nominal case, as shown in the figures and tables in the Results section. b. The total implementation cost of GSHP consisting of mechanical equipment material and labor as well as GHX labor - is comparable to an equivalent air source heat pump. This simulates a market condition where the GSHP market penetration is equivalent to the air source heat pump penetration and reliable GHX installation services are widely available, i.e. technology is mature. c. Ground conditions with reduced thermal performance, k = 0.7 Btu/h-ft- F. The nominal (scenario 1) soil conductivity is, k = 1 Btu/h-ft- F. The associated effective ground thermal resistances were obtained from Bernier d. Ground conditions with enhanced thermal performance, k = 1.8 Btu/h-ft- F, such as might be obtained under wet conditions. e. GSHP is 10 percent more efficient and 16 percent more expensive than the nominal case. The relation between efficiency and cost increase were assumed based on data from Geonomics Developments for 16 seasonal energy efficiency ratio (SEER) and 19 SEER air source heat pumps. f. System pumping efficiency is significantly reduced to 15 hp/100 ton according to the low end of D-grade benchmark from Kavanaugh 1997 [1]. Note: this is a conservative assumption. g. Average burial depth of HDD GHX is reduced to 12 ft. The above list is intended to showcase some critical parameters that influence the cost effectiveness and the design of HDD GHX system. It is not intended to be 70

73 exhaustive. Other scenarios may be tested using the supplied spreadsheet model developed as part of this effort. A detailed description of the calculation methodology can be found in Appendix I. 71

74 FIGURE 24: LODGING PIPING SCHEMATIC 72

75 FIGURE 25: MULTIFAMILY PIPING SCHEMATIC 73

76 RESULTS The results of the analyses have been organized according to the building type (lodging and multifamily). Under each type, the following are presented: Presentation and discussion of results of the nominal scenario whose methodology was described in the section above. Presentation and discussion of results of the sensitivity analysis whose methodology was also described above. COMMERCIAL LODGING Results (Nominal Scenario) The following is a summary of the results for the modeled lodging building. All heating and cooling load profiles for this building are located in Appendix I. For this building type in the two climate zones, Figure 26 shows the following results of the 20-year lifecycle study: o o Space heating and cooling loads Total HVAC and non-hvac: Electricity consumption Maximum electrical demand Natural gas consumption Combined energy consumption (expressed in common kwh unit) o o Operational (implementation, energy, maintenance) costs CO 2 emissions Table 8 and Table 16 detail the results of the analysis. 74

77 Total Cost (1000 $) CO2 Emissions (1000 lb) Natural Gas Use (1000 Therms) Combined Energy Use (MWh) Total Space Load (MMBtu) Electricity Use (MWh) Maximum Demand (kw) PG&E s Emerging Technologies Program 120, ,000 Cooling Heating 35,000 30,000 Baseline Proposed Baseline Proposed 80,000 60,000 40,000 20,000 25,000 20,000 15,000 10,000 5, CZ3 1,400 1,200 CZ13 - Baseline Proposed CZ3 CZ13 80,000 70,000 - CZ3 Baseline Proposed CZ13 1,000 60, ,000 40,000 30,000 20, ,000 - CZ3 CZ13 - CZ3 CZ13 10,000 9,000 8,000 7,000 Baseline Proposed 35,000 30,000 25,000 Baseline Proposed 6,000 5,000 4,000 20,000 15,000 3,000 2,000 1,000 10,000 5,000 - CZ3 CZ13 - CZ3 CZ13 FIGURE 26: SUMMARY OF LODGING ANALYSIS 75

78 Table 8 shows the design (peak) and the 20-yr total heating and cooling loads of the facility in CZ 3 and 13 based on the profiles developed from CEUS. The peak and total loads correspond to the ambient air temperature conditions in each climate zone. In both climate zones, the facility is dominated by cooling. Heating and Cooling Loads CZ3 CZ13 Item Heating Cooling Heating Cooling Design Load (kbtu/hr) 492 1, , year Total Load (kbtu) 18,747,451 60,077,413 17,002, ,899,274 TABLE 8: LODGING HEATING AND COOLING LOADS Table 9 shows the summary of electrical energy, demand and natural gas consumption as well as CO 2 emissions of the building in the two climate zones, separated by HVAC-only results and total-facility results. 20-year Energy Consumption, Peak Demand and Emissions CZ3 Item Baseline (PTAC with Gas Heating) Proposed (GSHP) CZ13 Baseline (PTAC with Gas Heating) Proposed (GSHP) HVAC Only Space Cooling Electrical Energy Consumption (kwh) 4,474,816 4,342,830 8,407,916 7,444,698 Space Heating Electrical Energy Consumption (kwh) - 1,575,652-1,294,319 Total Electrical Energy Consumption (kwh) 4,474,816 6,082,728* 8,407,916 9,136,386* Maximum Demand (kw) Space Heating Natural Gas Consumption (therms) 250, ,749 - HEUS (kwh/kbtu) Total Facility (HVAC and Non-HVAC) Electrical Energy Consumption (kwh) 30,233,006 31,840,918 31,163,366 31,891,835 Maximum Demand (kw) Natural Gas Consumption (therms) 1,291,704 1,041, , ,692 CO2 emissions (lb CO2) 33,210,347 30,691,031 28,383,146 25,715,998 EUS (kwh/kbtu) CES (lbco2/kbtu) *Includes energy consumption of GSHP distribution loop pump TABLE 9: 20-YEAR ENERGY CONSUMPTION AND PEAK DEMAND 76

79 Major conclusions are as follows: In both climate zones, the proposed HDD GSHP offers significant energy and cost savings over the baseline system. Despite the increased facility electrical energy consumption due to the fuel switch for space heating from natural gas to electricity, the total proposed energy use of the facility (electricity and gas expressed in common units) is lower than the baseline due to higher GSHP efficiencies both in heating and cooling. Overall cost savings of 7.3 percent and 5 percent, as evaluated by the difference between baseline and proposed LCOS over the baseline LCOS, can be achieved in CZ3 and CZ13, respectively. Note that LCOS is evaluated on a per-kbtu basis. In terms of absolute values, the percentage savings translates to approximately $640,000 and $470,000 over the 20 years period for the model systems analyzed in CZ3 and CZ13, respectively. Although the energy cost savings in CZ13 is 3 times larger than in CZ3, the implementation cost increase over the baseline in CZ13 is much greater than in CZ3 due to larger magnitude of cooling load in CZ13, thus necessitating the implementation of the proposed system on a larger scale. In both climates, the maintenance cost is the same, as it was calculated on a per-area basis. HVAC energy savings of 48.4 percent and 39.3 percent, as evaluated by the difference in the baseline and proposed HEUS over the baseline HEUS, can be achieved in CZ3 and CZ13, respectively. Note that the energy savings does not correspond directly to energy cost savings due to fuel switching from the baseline to the proposed systems. Per unit of energy, electricity is 3 to 4 times more expensive than natural gas. Therefore, the effect of gas savings for heating dilutes the potential savings during the heating season. The value of electricity savings is more evident for the cooling season. The results for energy cost savings in CZ13 which has significantly larger cooling loads - is 3 times the savings in CZ3. Total facility energy savings of 8.4 percent and 10.3 percent, as evaluated by the difference between the baseline and proposed EUS over the baseline EUS, can be achieved in CZ3 and CZ13, respectively. HVAC-only energy savings in the coastal climate is larger than in the inland climate, but the opposite result was found when total building energy is considered because miscellaneous loads in the coastal climate is a larger proportion of the building s energy end-use than in the inland climate, thereby diluting the effect of HVAC savings. Facility greenhouse gas (CO2) emissions can be reduced by 7.6 percent and 9.4 percent, as evaluated by the difference between the baseline and proposed CES over the baseline CES in CZ3 and CZ13, respectively. The emissions reduction is directly related to EUS. Higher operating efficiency of the GSHP in cooling mode results in lower proposed electrical energy consumption for cooling. This effect is more dominant in CZ13 as 77

80 the high condensing temperature (outside air) for an air-source unit at peak cooling load translates to reduced operating efficiency compared with the lower condensing temperature of a GSHP, which takes advantage of the much cooler ground temperature. o In CZ13, the proposed maximum demand over the 20-year study is about 45 kw lower than the baseline. o In CZ3, the proposed demand is 5 kw higher. The effect of higher GSHP cooling efficiency is reduced due to two factors: (1) the milder CZ3 climate results in smaller differences in ground and air temperatures, and (2) benefit is eclipsed by the efficiency degradation over time. Since the baseline system benefits from a "restart" of efficiency at the 16th year of operation, while the proposed system continues to experience degradation past the 16th year, the overall maximum demand over the 20 year period is greater for the proposed case. Due to space limitations, vertical geothermal heat exchangers (GHXs) are the typical ground loop configurations used to serve buildings with the magnitude of heating/cooling loads as the modeled building. The lengths of horizontal GHX bores needed to meet the heating and cooling loads for this building type approximately 33,000 ft. and 90,000 ft. for CZ3 and CZ13, respectively (as shown in Table 13: Geothermal Heat Exchanger Design Summary) may prove to be challenging to implement. Installation of the bores below the building grade must be considered to minimize the footprint. Table 10 and Table 11 show the 20-year total implementation and operational costs of the modeled building in CZ3 and CZ13, respectively. Determination of the size of the GHX, and the number of GTAC units are detailed as follows: The number of 1-ton baseline and proposed systems were based on the number needed to meet the greater of the heating and cooling loads of each building. Since the baseline system is replaced at year 16 of this analysis (useful life of 15 years), the future baseline implementation cost in 2029 (15 years from 2014) was accounted for from assumed interest rates. The length of the GHX bore was calculated from design parameters presented in Table 8. The length of the GHX piping is simply twice the bore length to represent U- tube HDD GHX. The interior distribution piping was calculated based on modeled building dimensions and pump power benchmarks from Kavanaugh 1997 [1]. The header piping length was conservatively assumed to be the same as the length of one side of the modeled building. An appropriate header diameter, detailed in Appendix I, was selected to satisfy the pump power benchmark. Central pumping with a VFD control scheme was specified for Lodging. Costs per unit of activity accounts for city cost multipliers from 2014 RS Means, except for the GHX bore that was obtained from a horizontal drilling contractor (Geonomic Developments) quote. 78

81 The geothermal piping network, including the geothermal heat exchanger and distribution piping, constitutes the majority of the proposed implementation costs. The size of the network has the largest influence on implementation cost, which is reflected by the numbers for CZ13. The proposed energy and maintenance costs are typically lower than the baseline. CZ13 shows higher energy cost savings than CZ3 due to larger magnitude of cooling load and the benefit of higher operating efficiencies of the GSHP during cooling periods compared to the baseline system. In considering these findings, note the following: Even though buildings with the same exterior properties (number of floors, area, etc.) were modeled in the two climate zones, they do not necessarily represent completely identical buildings. Based on the data sets utilized, the miscellaneous (non-hvac) loads vary greatly in the two zones, which suggest different interior configurations. Thus, specifications of the HVAC system (number of heat pumps, size of system pump, etc.) were based on the greater of space heating and cooling loads rather than the building interior configuration. Due to space limitations, vertical GHX are typically utilized for facilities with similar magnitudes of cooling and heating loads as the building modeled in this project. HDD GHX was analyzed in this effort to explore the cost viability of this type of GHX. The specified lengths of bore may be challenging to implement and installation below the building grade should be considered to optimize the use of space. 79

82 Item CZ 3 Cost Summary Units Unit Cost ($/unit) Baseline Total Cost ($) Unit Cost ($/unit) Proposed Total Cost ($) Implementation Packaged air conditioner with gas heat (1 ton), 2014$ 137 2, ,641 Engineering, management, profit markup (25%) 76,410 Packaged air conditioner with gas heat (1 ton), 2029$ 137 2, ,661 Engineering, management, overhead, markup (25%) 392,661 Water-to-air heat pump (1 ton) 137 2, ,862 GHX bore (drilling, grouting, testing) 33,247 ft ,908 GHX piping (1" diameter HDPE) 66,494 ft ,544 Interior distribution piping (4" diameter HDPE + 1" fiberglass insulation) 6,636 ft ,728 Header piping (6" diameter HDPE + 1" fiberglass insulation) 198 ft ,612 Distribution & GHX pump (10 hp + VFD & 1 backup) 2 9,327 18,654 Engineering, management, overhead, markup (25%) 208,077 Total Implementation Cost 872,878 1,040,385 Energy Total Energy Cost 6,552,290 6,502,338 Maintenance Total Maintenance Cost 1,331, ,833 LCOS ($/kbtu) TABLE 10: IMPLEMENTATION COST SUMMARY 80

83 Item CZ13 Cost Summary Units Unit Cost ($/unit) Baseline Total Cost ($) Unit Cost ($/unit) Proposed Total Cost ($) Implementation Packaged air conditioner with gas heat (1 ton), 2014$ 242 2, ,477 Engineering, management, profit markup (25%) 127,869 Packaged air conditioner with gas heat (1 ton), 2029$ 242 2, ,101 Engineering, management, overhead, markup (25%) 164,275 Water-to-air heat pumps (1 ton) 242 2, ,275 GHX bore (Drilling, grouting, testing) 89,837 ft ,081 GHX piping (1" diameter HDPE pipe) 179,675 ft ,464 Interior distribution piping (4" diameter HDPE + 1" fiberglass insulation) 6,636 ft ,158 Header piping (6" diameter HDPE + 1" fiberglass insulation) 198 ft ,306 Distribution & GHX pump (20 hp + VFD & 1 backup) 2 13,020 26,039 Engineering, management, overhead, markup (25%) 393,081 Total Implementation Cost 1,460,722 1,965,404 Energy Total Energy Cost 6,541,769 6,327,997 Maintenance Total Maintenance Cost 1,329, ,057 LCOS ($/kbtu) TABLE 11: CZ13 COST SUMMARY Table 12 lists the performance parameters of the GSHP at design conditions (peak load) in the two climate zones. Higher cooling EWT and lower heating EWT generally reduce the required length of GHX bores but significant GSHP performance penalties may result. Conversely, lower cooling EWT and higher heating EWT will ensure optimal GSHP performance but unfeasibly large GHX will be needed. Based on the 2007 ASHRAE Applications Handbook [14] recommendations, the best balance between cost and efficiency is achieved when EWT is F higher than Tg for cooling and F lower than Tg for heating. Meline Engineering suggested EWTs of 90 F for cooling and 45 F for heating. However, due to the coincident ground temperature at design load, EWT of 90 F for cooling and 50 F for heating was utilized in order to stay within ASHRAE s recommended ranges. The effect of using a higher heating EWT is increased bore lengths for heating-dominated facilities and higher heat pump efficiency, which produces a more conservative result in terms of overall cost savings. Additionally, a design flow of 3 gpm/ton was utilized. 81

84 CZ 13 Ground Source Heat Pump Design Summary CZ3 CZ13 Item Heating Cooling Heating Cooling Required Capacity (Btu/hr) 504,000 1,644, ,000 2,904,000 COP at Design EWT Entering Water Temperature ( F) TABLE 12: CZ13 GROUND SOURCE HEAT PUMP DESIGN SUMMARY Table 13 lists the design parameters of GHX in the two climate zones. The difference between the bore lengths in the two climate zones is dictated primarily by the larger cooling loads in CZ13. One GHX header on one side of the building was specified as shown in Figure 24. Effective borehole resistance represents soil with k = 1 Btu/hr-ft- F as specified by Bernier referenced earlier [17]. The differences in effective ground thermal resistance in the three thermal pulses is associated with increasing cycle run time fraction (in heating and in cooling) due to reduced GSHP performance (efficiency and capacity) as it ages and the unbalanced ground load. According to IGSHPA, ambient weather conditions near the ground have a diminishing effect on the energy balance in the ground surrounding the GHX at greater than 8 ft. Though not as drastic as the unbalanced ground loads for deep earth vertical GHX, the heat rejected to or absorbed from the ground by HDD GHX at 15 ft. is not dissipated to the ground surface as effectively as GHXs at shallower depths. The calculated bore length accounts for the contribution of a bore length multiplier from the IGSHPA Manual. The specified number of parallel GHX loops was based on the pump power benchmark from Kavanaugh [1]. Bore depth was based on discussion with Meline Engineering. Ground temperature at depth represents the coincident temperature at the design load. Heat pump EWT is the same as the GHX leaving water temperature (LWT). 82

85 Item Geothermal Heat Exchanger Design Summary CZ3 CZ13 Heating Cooling Heating Cooling Number of Bore Headers 1 1 Total Bore Length (ft) 33,247 89,837 Peak Ground Load (Btu/hr)* 303,364 (1,986,490) 683,288 (3,558,221) Max Monthly Ground Load (Btu/hr)* 8,631 (673,959) 84,788 (1,462,007) Yearly Net Ground Load (Btu/hr)* (339,487) (637,522) Effective Borehole Thermal Resistance (hr-ft- F/Btu) hour Effective Ground Thermal Resistance (hr-ft- F/Btu) month Effective Ground Thermal Resistance (hr-ft- F/Btu) year Effective Ground Thermal Resistance (hr-ft- F/Btu) Ground Temperature at Bore Depth ( F) HDD Borehole Depth (ft) Borehole Separation (ft) Normalized Net Annual Ground Load (Btu/ft- F) 2,439 (cooling) 2,438 (cooling) Bore Length Multiplier ( F) Number of Parallel Loops Heat Pump LWT ( F) Heat Pump EWT ( F) TABLE 13: GEOTHERMAL HEAT EXCHANGER DESIGN SUMMARY Table 14 shows the pump design parameters for the interior distribution, header, GHX and GSHP coil in the two climate zones. Flows and pressure drop through each line and their associated pump power requirement were specified. Flows through each line were calculated as the ratio of design flow and the number of parallel lines. Pressure drops were calculated through each line. Under the ISO Standard [22], manufacturers are required to rate COPs while accounting for the heat pump water coil pressure drop. Therefore, the pump energy consumption considers only flows through the GHX, header and distribution loop. The variable frequency drive (VFD) control load factor was based on the ratio of the hourly net ground load to the maximum net ground load and the VFD power curve for pumps [20]. For cost analysis purposes, the next larger standard pump size was specified based on the facility s total required pump power. 83

86 Distribution Loop and GHX Design Flow Summary CZ3 CZ13 Interior Interior GSHP GSHP Distribution Header GHX Distribution Header GHX Coil Coil Item Loop Loop Pipe Diameter (in) Number of Parallel Lines or Number of GSHPs Flow Rate Through Each Line or GSHP (gpm) Total Length (ft) 6, ,494 6, ,675 Pressure Drop through Line or GSHP (ft H 2 O) Pump Efficiency Required Pump Power (bhp) Distribution, Header & GHX Power (bhp) Motor Efficiency Average Control Load Factor (VFD) Annual Energy Consumption (kwh/yr) 8,212 19,868 Total Facility Pump Requirement (bhp) Specified Facility Pump Size (hp) TABLE 14: DISTRIBUTION LOOP GHX DESIGN FLOW SUMMARY RESULTS (SENSITIVITY ANALYSIS) Table 15 and Table 16 show the results of sensitivity tests in terms of relative cost savings as evaluated according to LCOS from the baseline cases for CZ3 and CZ13, respectively. Each scenario is independent of others and cost savings were evaluated from the baseline. For these scenarios the GSHP project always pays back within the 20-year lifecycle analysis. 84

87 Sensitivity Results for Lodging in CZ3 Scenario Description Relative Savings from Baseline (%) Cost Savings over 20 Years ($) 1 Nominal 7.3% 641,351 HDD GSHP technology has reached maturity in terms of 2 implementation cost 12.1% 1,061,513 3 GHX in reduced ground thermal performance, k = 0.7 Btu/hft- F (30% less than nominal) 6.1% 535,167 4 GHX in enhanced ground thermal performance, k = 1.8 Btu/h-ft- F (80% higher than nominal) 8.1% 712, % higher efficiency, 16% more costly GSHP units 7.6% 668, System pumping efficiency is reduced to 15 hp/100 ton (150% less efficient than nominal) GHX burial depth reduced to 12 ft (20% shallower than nominal) TABLE 15: SENSITIVITY RESULTS FOR LODGING IN CZ3 6.3% 552, % 639,196 Scenario Sensitivity Results for Lodging in CZ13 Description Relative Savings from Baseline (%) Cost Savings over 20 Years ($) 1 Nominal 5.00% 466,969 2 HDD GSHP technology has reached maturity 15.34% 1,431,818 3 GHX in reduced ground thermal performance, k = 0.7 Btu/hft- F (30% less than nominal) 1.67% 155,578 4 GHX in enhanced ground thermal performance, k = 1.8 Btu/h-ft- F (80% higher than nominal) 7.55% 704, % higher efficiency, 16% more costly GSHP units 5.27% 491,732 6 System pumping efficiency is reduced to 15 hp/100 ton (150% less efficient than nominal) 3.53% 329,419 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 4.04% 376,776 TABLE 16: SENSITIVITY RESULTS FOR LODGING IN CZ13 85

88 RESIDENTIAL MULTIFAMILY The following is a summary of the results for the modeled multifamily facility. A detailed description of the calculation methodology can be found in Appendix I. All heating and cooling load profiles for this building are located in Appendix I Load Profiles section. For this building type in the two climate zones, Figure 27 shows the 20-year totals of the following: o o Space heating and cooling loads Total HVAC and non-hvac: Electricity consumption Maximum electrical demand Natural gas consumption Combined energy consumption (expressed in common kwh unit) o o Operational (implementation, energy, maintenance) costs CO 2 emissions Table 17 through Table 23 detail the results of the analysis. 86

89 Total Cost (1000 $) CO2 Emissions (1000 lb) Natural Gas Use (1000 Therms) Combined Energy Use (MWh) Total Space Load (MMBtu) Electricity Use (MWh) Maximum Demand (kw) PG&E s Emerging Technologies Program 7,000 6,000 5,000 4,000 3,000 2,000 1,000 - Cooling Heating CZ3 CZ ,000 2,500 2,000 1,500 1, Baseline Proposed Baseline Proposed CZ CZ13 8,000 Baseline Proposed 7,000 6,000-5 Baseline Proposed CZ3 CZ13 1, CZ3 Baseline Proposed CZ3 CZ13 CZ13 5,000 4,000 3,000 2,000 1,000 4,000 3,500 3,000 2,500 2,000 1,500 1, CZ3 Baseline Proposed CZ3 CZ13 CZ13 FIGURE 27: SUMMARY OF MULTIFAMILY ANALYSIS 87

90 Table 17 shows the design (peak) and the 20-yr total heating and cooling loads of the facility in CZ3 and CZ13 based on the profiles developed from CEUS. The peak and total loads correspond to the ambient conditions in each climate zone. Heating and Cooling Loads CZ3 CZ13 Item Heating Cooling Heating Cooling Design Load (kbtu/hr) year Total Load (kbtu) 2,210, ,788 1,707,406 6,188,956 TABLE 17: HEATING AND COOLING LOADS Table 18 shows the summary of electrical and natural gas demand as well as CO 2 emissions of the building in the two climate zones, separated by HVAC-only results and total-facility results. Major conclusions are summarized below, many similar to those for the lodging analysis described above but with several differences. 20-year Energy Consumption, Peak Demand and Emissions Item Baseline PTAC with Gas Heat CZ3 Proposed (GSHP) Baseline PTAC with Gas Heat CZ13 Proposed (GSHP) HVAC Only Space Cooling Electrical Energy Consumption (kwh) 45,296 38, , ,335 Space Heating Electrical Energy Consumption (kwh) - 180, ,501 HVAC Electrical Energy Consumption (kwh) 45, ,089* 548, ,021* HVAC Maximum Demand (kw) Space Heating Natural Gas Consumption (therms) 29,482-22,771 - HEUS (kwh/kbtu) Total Facility (HVAC and Non-HVAC) Facility Electrical Energy Consumption (kwh) 2,111,117 2,317,910 2,699,689 2,801,191 Facility Maximum Demand (kw) Facility Natural Gas Consumption (therms) 170, , , ,121 Facility CO2 emissions (lb CO2) 3,398,885 3,110,827 3,510,757 3,257,766 EUS (kwh/kbtu) CES (lbco2/kbtu) TABLE 18: 20-YEAR ENERGY CONSUMPTION PEAK DEMAND AND EMISSIONS 88

91 Major conclusions are as follows: In both climate zones, the proposed HDD GSHP offers significant energy and cost savings over the baseline system. Despite increased electrical energy consumption, due to the fuel switch for space heating from natural gas to electricity, the total proposed energy use of the facility (electricity and gas expressed in common units) is lower than the baseline. Overall cost savings of 10 percent and 2 percent, as evaluated by the difference between baseline and proposed LCOS over the baseline LCOS, can be achieved in CZ3 and CZ13, respectively. In absolute values, the percent savings translates to approximately $83,000 and $17,000 over 20 years for CZ3 and CZ13, respectively. The electric usage rates at different consumption tiers affect the magnitude of energy cost savings. PG&E s E1 rate schedule Tier 1 consumption limit in CZ13 is much higher than in CZ3. Thus, most of the consumption in the inland climate is subject to the lowest Tier 1 rate, which for a given energy use reduction reduces the magnitude of cost savings compared to CZ3. HVAC energy savings of 72 percent and 46 percent, as evaluated by the difference between the baseline and proposed HEUS over the baseline HEUS, can be achieved in CZ3 and CZ13, respectively. The magnitude of energy savings is attributed primarily to the differences in the efficiencies of the baseline and proposed systems. For heating, the baseline system has an efficiency of 80 percent while the proposed system has a coefficient of performance (COP) of approximately 3.9 at design conditions (Refer to Section 2.6 for details). For cooling, the baseline and proposed systems have design COP of 3.2 and 3.6, respectively. Thus, since CZ3 is heating dominated while CZ13 is cooling dominated, the influence of switching from gas heating to electrical heating drives the higher energy savings in CZ3. Total facility energy savings of 9.2 percent and 7.8 percent, as evaluated by the difference between the baseline and proposed EUS over the baseline EUS, can be achieved in CZ3 and CZ13, respectively. The facility CO 2 emissions reduction of 8.5 percent and 7.2 percent, as evaluated by the difference between the baseline and proposed CES over the baseline CES, can be achieved in CZ3 and CZ13, respectively. Higher operating efficiency of the GSHP in cooling mode results in lower proposed electrical energy consumption for cooling. This effect is more dominant in CZ13 as the high condensing temperature (outside air) for an air-source unit at peak cooling load translates to reduced operating efficiency compared to the lower condensing temperature of a GSHP, which takes advantage of the much cooler ground temperature. o In CZ13, the proposed maximum demand over the 20-year study is about 9 kw lower than the baseline. 89

92 o In CZ3, the proposed demand is 1 kw higher. The effect of higher GSHP cooling efficiency is reduced due to two factors: (1) the milder CZ3 climate results in smaller differences in ground and air temperatures, and (2) benefit is eclipsed by the efficiency degradation over time. Since the baseline system benefits from a "restart" of efficiency at the 16th year of operation, while the proposed system continues to experience degradation past the 16th year, the overall maximum demand over the 20-year period is greater for the proposed case. 90

93 Table 19 and Table 20 list the 20-year total implementation and operational costs of the modeled building in CZ3 and CZ13, respectively. Design selection is detailed as follows: The number of 1-ton baseline and proposed systems was based on the number needed to meet the greater of the heating and cooling loads of each building. Since the baseline system is replaced at year 16 of this analysis (useful life of 15 years), baseline implementation cost in 2029 (15 years from 2014) was accounted for from assumed interest rates. The length of GHX bore was calculated from design parameters presented in the subsequent tables. The length of the GHX piping is simply twice the bore length to represent U-tube HDD GHX. Header piping includes both the header length and vertical length shown in Figure 25. The header piping was conservatively assumed to be the same as the length of one side of the modeled building. An appropriate header diameter was selected to satisfy the pump power benchmark. Each GSHP was specified with a dedicated pump. Costs per unit of activity accounts for city cost multipliers from 2014 RS Means, except for GHX bore which was obtained from the contractor quote. The geothermal piping network including the geothermal heat exchanger and distribution piping constitute the majority of the proposed implementation costs. The size of the network has the largest influence on implementation cost, which is reflected by the numbers for CZ13. The proposed energy and maintenance costs are typically lower than the baseline. CZ3 shows higher energy cost savings than CZ13 due to the heating-dominated climate of CZ3 and the benefit of higher operating efficiencies of the GSHP in heating compared to the baseline system. 91

94 Item CZ 3 Cost Summary Units Unit Cost ($/unit) Baseline Total Cost ($) Unit Cost ($/unit) Proposed Total Cost ($) Implementation Packaged air conditioner with gas heat (1 ton), 2014$ 12 2,231 26,771 Engineering, management, profit markup (25%) 6,693 Packaged air conditioner with gas heat (1 ton), 2029$ 12 2,866 34,394 Engineering, management, overhead, markup (25%) 8,598 Water-to-air heat pumps (1 ton) 12 2,868 34,411 GHX bore length (Drilling, grouting, mobilization, supply lines) 3,032 ft 10 29,411 GHX piping (1 diameter HDPE) 6,063 ft 1 5,612 Header piping (2" diameter HDPE + 1" fiberglass insulation) 440 ft 10 4,394 GHX pump (1/12 hp per heat pump) 12 1,058 12,699 Engineering, management, overhead, markup (25%) 21,632 Total Cost 76, ,159 Energy Electricity and Natural Gas Usage 628, ,678 Maintenance Maintenance 105,371 45,324 LCOS ($/kbtu) TABLE 19: CZ3 COST SUMMARY 92

95 Item CZ13 Cost Summary Units Unit Cost ($/unit) Baseline Total Cost ($) Unit Cost ($/unit) Proposed Total Cost ($) Implementation Packaged air conditioner with gas heat (1 ton), 2014$ 24 2,114 50,725 Engineering, management, profit markup (25%) 12,681 Packaged air conditioner with gas heat (1 ton), 2029$ 24 2,715 65,167 Engineering, management, overhead, markup (25%) 16,292 Water-to-air heat humps (1 ton) 24 2,716 65,184 GHX bore length (Drilling, grouting, mobilization, supply lines) 6,669 ft ,494 GHX piping (1" diameter HDPE) 13,338 ft ,912 Header & Distribution Piping (2" diameter HDPE + 1" fiberglass insulation) 592 ft ,449 GHX pump (1/12 hp per heat pump) ,974 Engineering, management, overhead, markup (25%) 41,753 Total Implementation Cost 144, ,765 Energy Total Electricity and Natural Gas Usage Cost 621, ,193 Maintenance Total Maintenance Cost 105,371 45,324 LCOS ($/kbtu) TABLE 20: CZ13 COST SUMMARY Table 21 lists the performance parameters of the GSHP at design conditions (peak load) in the two climate zones. As for the lodging design, a flow of 3 gpm/ton and EWT of 90 F for cooling and 50 F for heating were used in the design calculations. Ground Source Heat Pump Design Summary CZ3 CZ13 Item Heating Cooling Heating Cooling Required Capacity (Btu/hr) 144, , , ,000 COP at Design EWT Entering Water Temperature ( F) TABLE 21: GROUND SOURCE HEAT PUMP DESIGN SUMMARY Table 22 lists the design parameters of GHX in the two climate zones. CZ3 is dominated by heating and CZ13 by cooling. The difference between the bore lengths in the two climate zones is dictated primarily by the larger cooling loads in CZ13. One GHX header on each of the long side of the building was specified as shown in Figure 25. Effective borehole resistance represents ground with k = 1 Btu/hr-ft- F. The calculated bore length accounts for the bore length multiplier from the IGSHPA Manual. The specified number of parallel GHX loops was based on the same pump 93

96 power benchmark used before. Bore depth was based on discussion with Meline Engineering. Ground temperature at depth represents the coincident temperature at the design load. Geothermal Heat Exchanger Design Summary CZ3 CZ13 Item Heating Cooling Heating Cooling Number of Bore Headers 4 4 Total Bore Length per Header (ft) 758 1,667 Peak Ground Load (Btu/hr) 18,787 (38,036) 32,764 (82,059) Max Monthly Ground Load (Btu/hr) 5,076 (2,532) 6,628 (31,482) Yearly Net Ground Load (Btu/hr) 1,350 1,350 (9,051) Effective Borehole Thermal Resistance (hr-ft- F/Btu) hour Effective Ground Thermal Resistance (hr-ft- F/Btu) month Effective Ground Thermal Resistance (hr-ft- F/Btu) year Effective Ground Thermal Resistance (hr-ft- F/Btu) Ground Temperature at Bore Depth ( F) HDD Borehole Depth (ft) Borehole Separation (ft) Normalized Net Annual Ground Load (Btu/ft- F) 1,253 (heating) 1,684 (cooling) Bore Length Multiplier ( F) Number of Parallel Loops 3 6 Geothermal Heat Exchanger Entering Fluid Temperature ( F) Geothermal Heat Exchanger Leaving Fluid Temperature ( F) TABLE 22: GEOTHERMAL HEAT EXCHANGER DESIGN SUMMARY Table 23 lists the pump design parameters for the interior distribution, header, GHX and GSHP coil in the two climate zones. For this building type, distribution piping describes the vertical piping sections shown in Figure 25. Flows and pressure drops through each line and their associated pump power requirements were specified. Flows through each line were calculated as the ratio of design flow and the number of parallel lines. For CZ3 with 3 GSHP per header, one GSHP is assumed to be on the 2nd floor, with only one vertical section per header. Pressure drops were calculated through each line. Pumps operate in an on/off control scheme according to the individual unit operation. Under the ISO Standard , manufacturers are required to rate COP while accounting for the heat pump water coil pressure drop. Therefore, the pump energy consumption considers only flows through the GHX, header and distribution loop. For cost analysis purposes, the next larger standard pump size was specified based on the required pump power for each GSHP. 94

97 Distribution Loop and GHX Design Flow Summary CZ3 CZ13 Item Distribution Header GHX GSHP Coil Distribution Header GHX GSHP Coil Number of Bore Headers 4 4 Pipe Diameter (in) Number of Parallel Lines or GSHPs per Header Flow Rate Through Each Line or GSHP (gpm) Total Length per Header (ft) , Pressure Drop through Line or GSHP (ft H2O) Pump Efficiency Required Pump Power per Header (bhp) Negligible Negligible Distribution, Header & GHX Power per Header (bhp) Motor Efficiency Average Utility Load Factor (on-off) Annual Energy Consumption (kwh/yr) 1,622 2,759 GSHP Pump Requirement (bhp/ton) Specified GSHP Pump Size (hp) 1/12 1/12 TABLE 23: DISTRIBUTION LOOP AND GHX DESIGN FLOW SUMMARY RESULTS (SENSITIVITY ANALYSIS) Table 24 and Table 25 show the results of sensitivity tests in terms of relative cost savings from the baseline case as evaluated from LCOS for CZ3 and CZ13, respectively. Conclusions from the sensitivity analysis are as follows: The main challenge with implementation of GSHP systems is the high cost of GHX installation. If the cost of GHX installation can be reduced, GSHP systems become very cost effective. As shown in Scenario 2, cost savings increased by 16 percent and 13 percent from the nominal in CZ3 and CZ13, respectively. The larger increase in savings for CZ3 is attributed to the larger required GHX. This building type will also benefit from utilizing heat rejection during cooling mode for domestic water preheating. Poor soil thermal conductivity under Scenario 3 drives potential savings down to 8.5 percent and -1.2 percent (the negative sing indicating a cost increase for the GSHP case), respectively. In this particular case, the negative savings for CZ13 can be attributed to the electricity consumption rate tiers discussed previously and to the economies of scale. Larger installations with hundreds of tons of GHX such as in the case of the lodging facilities is less expensive on a per-ton basis than the smaller installations with the multifamily units. 95

98 Soils with higher thermal conductivity improve the cost effectiveness of GSHP projects. As shown in Scenario 4, cost savings increased to 11.6 percent and 4.5 percent in CZ3 and CZ13, respectively. Unlike lodging, more efficient GSHP do not improve the cost effectiveness of GSHP projects for multifamily. As shown in Scenario 5, cost savings remained the same as in Figure 27 for CZ13 and decreased to 9.9 percent for CZ3. This can be attributed to operating duration of the GSHPs. The cooling and heating loads in CZ3 require the HVAC system to operate only a fraction of the time compared to CZ13. Since energy savings due to increased efficiency is strongly dependent on operating hours, more efficient GSHP does not pay for the increased cost premium in CZ3. As shown in Scenario 6, savings dropped to 5.6 percent and -3.8 percent (cost increase) for CZ3 and CZ13, respectively when an inefficient pumping system is specified for GSHP projects. The importance of proper pumping system design applies to all building types in any climate. The effect of GHX burial depth reduction on project cost effectiveness depends on the swing in annual ground temperature (Tg) and the temperature coincident to the design heating or cooling period. As shown in Scenario 7, savings for CZ3 increased slightly to 10.3 percent since higher Tg is coincident to the design heating load. However, higher Tg is encountered with the design cooling period for CZ13, which results in longer GHX and reduces cost savings to 1.5 percent. Scenario Sensitivity Results for Multifamily in CZ3 Description Relative Savings from Baseline (%) Cost Savings over 20 Years ($) 1 Nominal 10.2% 83,019 2 HDD GSHP technology has reached maturity in terms of implementation cost 16.0% 129,332 3 GHX in reduced ground thermal performance, k = 0.7 Btu/hft- F (30% less than nominal) 8.5% 69,048 4 GHX in enhanced ground thermal performance, k = 1.8 Btu/h-ft- F (80% higher than nominal) 11.6% 93, % higher efficiency, 16% more costly GSHP units 9.9% 80,265 6 System pumping efficiency is reduced to 15 hp/100 ton (87% less efficient than nominal) 5.6% 45,421 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 10.3% 83,278 TABLE 24: SENSITIVITY RESULTS FOR MULTIFAMILY IN CZ3 96

99 Scenario Sensitivity Results for Multifamily in CZ13 Description Relative Savings from Baseline (%) Cost Savings over 20 Years ($) 1 Nominal 2.01% 17,492 2 HDD GSHP technology has reached maturity in terms of implementation cost 12.75% 111,184 3 GHX in reduced ground thermal performance, k = 0.7 Btu/hft- F (30% less than nominal) -1.19% (10,409) 4 GHX in enhanced ground thermal performance, k = 1.8 Btu/h-ft- F (80% higher than nominal) 4.51% 39, % higher efficiency, 16% more costly GSHP units 2.01% 17,492 6 System pumping efficiency is reduced to 15 hp/100 ton (87% less efficient than nominal) -3.79% (33,063) 7 GHX burial depth reduced to 12 ft (20% shallower than nominal) 1.46% 12,751 TABLE 25: SENSITIVITY RESULTS FOR MULTIFAMILY IN CZ13 MODELING CONCLUSIONS AND RECOMMENDATIONS Some additional conclusions and recommendations for future expansion of the modeling work include: Under both building types, modeling results showed GSHP technology to be advantageous in CZ3, where cooling loads are smaller, thus requiring less investment in GHX capacity. This reduces installed costs further and increases overall savings. With both building types and climate zones, sensitivity analysis resulted in higher cost savings if local ground properties demonstrate higher than normal thermal conductivity. In high conductivity cases (80 percent higher than normal possibly under wet conditions) savings increased significantly. The HVAC unit efficiency at partial load should be explored. This analysis assumes that small units do not have capacity controls (i.e. are either on or off ). An integrated space heating/cooling and domestic water heating GSHP system could be considered. More sophisticated energy cost projection techniques (e.g. using longer term utility rate forecasting) could be employed to estimate the projected energy costs. Air-source heat pumps could be considered as the baseline system in order to make direct comparison of energy consumption (electricity to electricity) between the proposed and baseline scenarios. Additionally, this would enable consideration of utility incentives to help reduce implementation costs [23]. A more comprehensive lifecycle analysis to account for carbon credits (due to natural gas usage reduction from fuel switching) could be performed. 97

100 Building envelope degradation could be modeled to better account for longer term changes in heating and cooling loads. Resale value of equipment or parts at the end of their service lives could be accounted for. 98

101 MARKET ASSESSMENT MARKET ASSESSMENT OVERVIEW A first assessment of the market size for small (1 ton of cooling) ground-source heat pumps (GSHP) is presented below. The assessment was conducted for the geographical areas corresponding to the Coastal (CZ3) and Inland (CZ13) climate zones in California as indicated in the lifecycle model in the section above. Within these regions, two building types were considered as potential markets for the installation of GSHP units: commercial lodging and residential multifamily. The estimates presented in this section follow the approach proposed by ORC International [24], in which basis data are used to estimate the total addressable market, and relational data are used to narrow the total market of potential users to increasingly more likely consumer segments: the served available market and the target market [25]. Basis data used to estimate the total addressable market include total lodging floor area and average multifamily household floor area in CZ3 and CZ13, as well as space conditioning loads and simulated building floor area from the results presented in the performance modeling section. Relational data incorporate national shares of space conditioning equipment by type, taken from the Commercial Building Energy Consumption Survey [26] and the Residential Energy Consumption Survey [27]. MARKET ASSESSMENT METHODOLOGY The following tables present a description of basis data used for the assessment. Symbol Description CZ3 Value CZ13 AL,TOT Total floor area for lodging building stock (ft 2 ) 21,096,342 54,494,472 AL,1 bldg Model building floor area for lodging type 157,000 Q H,Max,L Q C,Max,L Peak heating load for model lodging building (kbtu/h) Peak cooling load for model lodging building (kbtu/h) ,644 2,897 Source CEUS Database [28] Modeling Section TABLE 26: BASIS DATA FOR LODGING BUILDING TYPE 99

102 Symbol Description Value CZ3 CZ 13 Source Population Total population 3,183,561 3,193,991 CPUC [29] A MF,1 house, W Average floor area per multifamily housing unit in West census region 1 (ft 2 ) A MF,1 bldg Model multifamily building floor area (ft 2 ) 12,376 Q H,Max,MF Q C,Max,MF Peak heating load for model multifamily building (kbtu/h) Peak cooling load for model multifamily building (kbtu/h) TABLE 27: BASIS DATA FOR MULTIFAMILY BUILDING TYPE 123 kbtu/h kbtu/h RECS [27] Modeling Section TOTAL ADDRESSABLE MARKET (TAM) To calculate the number of 1-ton GSHP units that could be deployed for the total stock of each building type and each climate zone, first the number of 1-ton GSHP units for one model building was estimated. For that, the peak cooling load of the model building is divided by 12 kbtu/h, equivalent to 1 refrigeration ton: EQUATION 3: 1 TON EQUIVALENT N GSHP,1 bldg = Q C,Max 12 1 West census regions states: California, Alaska, Hawaii, Oregon, Washington, Colorado, Idaho, Montana, Utah, Wyoming, Arizona, New Mexico and Nevada. 100

103 Then, the total number of model buildings of each type and each climate zone is calculated as: NB = A TOT A 1 bldg EQUATION 4: TOTAL NUMBER OF MODEL BUILDINGS OF EACH TYPE AND CLIMATE Finally, the TAM, i.e., the total number of deployable 1-ton GSHP units is given by TAM = (NB)(N GSHP,1 bldg ) EQUATION 5: TOTAL NUMBER OF DEPLOYABLE 1-TON GSHP UNITS The multifamily sector requires additional calculations to estimate the TAM, as there are no available data on total building floor area per climate zone. This value was assessed based on total population and number of households in each climate zone. First, the total number of multifamily households was estimated from the total population, assuming that in California there is an average of three people per household and that approximately 33 percent of the households correspond to multifamily homes [29]. N Houses,MF = 0.33 X ( Population ) 3 EQUATION 6:MULTIFAMILY TAM CALCULATION BASED ON POPULATION AND NUMBER OF HOUSEHOLDS BY CLIMATE ZONE The total floor area of the multifamily building stock on each climate zone was then estimated by multiplying the number of multifamily households by the average floor area per multifamily housing unit in the Western census region (Table 27). A MF,TOT = (N Houses,MF )(A MF,1 house,w ) EQUATION 7: CALCULATION FOR TOTAL FLOOR AREA OF MULTIFAMILY HOUSEHOLDS SERVED AVAILABLE MARKET (SAM) In order to estimate the portion of this total addressable market for which 1-ton GSHP units can realistically compete, a served available market was assessed, based on market shares of packaged terminal heat pumps (PTHP), packaged terminal air conditioners (PTAC) and gas furnaces in lodging buildings. For multifamily buildings, market shares of furnaces, heat pumps (HP) and window/wall air conditioners (WWAC) were used. National shares for the sector (Table 28 and Table 29) were used to narrow the market due to lack of data on a climate zone basis. 101

104 Symbol Description Area (ft 2 ) A TOT, L,US Total lodging floor area in the US 5,096 x10 6 A PTHP,L,US Total lodging floor area in the US with PTHPs for space heating 662 x10 6 A Furnace,L,US Total lodging floor area in the US with furnaces for space heating 1,065 x10 6 A PTAC,L,US Total lodging floor area in the US with PTAC for space cooling 651 x10 6 TABLE 28: SHARES OF PTHPS, FURNACES AND PTACS FOR US LODGING BUILDINGS (SOURCE: US ENERGY INFORMATION ADMINISTRATION, 2003). Symbol Description Area (ft 2 ) A TOT, MF,US Total multifamily floor area in the US 26,100 x10 6 A HP,L,US Total multifamily floor area in the US with heat pumps for space heating x10 6 A Furnace,MF,US Total multifamily floor area in the US with furnaces for space heating 10,692 x10 6 A WWAC,L,US Total multifamily floor area in the US with window/wall AC for space cooling TABLE 29: SHARES OF HPS, FURNACES AND PTACS FOR US MULTIFAMILY BUILDINGS [30] 5752 x10 6 These following assumptions were made to calculate market shares for the SAM: 1. PTHPs and furnaces do not coexist in the same lodging floor area 2. Heat pumps and furnaces do not coexist in the same multifamily floor area 3. PTACs share floor area either with PTHPs or furnaces in lodging buildings 4. WWAC share floor area either with heat pumps or furnaces in multifamily buildings The fraction of lodging floor area with space heating through PTHPs or Furnaces (the serviceable heating market share) is calculated as: %SAM H,L = 100 A PTHP,L,US + A Furnace,L,US A TOT,L,US EQUATION 8: FRACTION OF LODGING FLOOR AREA WITH SPACE HEATING For the multifamily sector, the serviceable heating market share is estimated as: %SAM H,MF = 100 A HP,MF,US + A Furnace,MF,US A TOT,MF,US EQUATION 9: MULTIFAMILY SERVICEABLE HEATING MARKET SHARE Similarly, the share of serviceable cooling market, i.e. the fraction of lodging floor area with space cooling through PTACs, is: %SAM C,L = 100 A PTAC,L,US A TOT,L,US 102

105 EQUATION 10:LODGING SHARE OF SERVICEABLE COOLING MARKET While the share of cooling SAM for multifamily buildings is: %SAM C,MF = 100 A WWAC,MF,US A TOT,MF,US EQUATION 11: MULTIFAMILY SHARE OF SERVICEABLE COOLING MARKET The market share for the SAM is then approximated as the maximum between the heating and the cooling shares: EQUATION 12: APPROXIMATE MARKET SHARE FOR SAM %SAM = max (%SAM H, %SAM C ) Finally, the SAM, expressed in total number of deployable 1-ton GSHP units is: SAM = (%SAM/100) (TAM) EQUATION 13: SAM EXPRESSED IN TOTAL NUMBER OF DEPLOYABLE 1-TON GSHP UNITS TARGET MARKET (TM) OR SERVICEABLE OBTAINABLE MARKET Since GSHPs can easily replace packaged-type units such as PTHPs, PTACs, and WWAC units, the most likely users of GSHP within the SAM are the ones that are already using this type of unit (PTHP, PTAC and WWAC). The target market for GSHP is then assessed using national data for packaged-type and window/wall unit shares for each building type (Table 28 and Table 29). The logic for the calculations is the same as the one used for the SAM. The share of target market for space heating is approximated as the share of PTHP within the lodging sector: %TM H,L = 100 A PTHP,L,US A TOT,L,US EQUATION 14: APPROXIMATION OF TARGET MARKET FOR GTAC TECHNOLOGY 103

106 The TM share for the multifamily sector: %TM H,MF = 100 A HP,MF,US A TOT,MF,US EQUATION 15: MULTIFAMILY TARGET MARKET The share of target market for space cooling is equivalent to that of the SAM: %TM C,L = 100 A PTAC,L,US A TOT,L,US %TM C,MF = 100 A WWAC,MF,US A TOT,MF,US EQUATION 16:TARGET MARKET FOR SPACE COOLING Finally, the total share of the target market and the number of units in the target market for GSHP are estimated as: %TM = max (%TM H, %TM C ) TM = (%TM/100) (TAM) EQUATION 17: TOTAL SHARE OF TARGET MARKET AND NUMBER OF UNITS IN TARGET MARKET FOR GSHP RESULTS Estimated market sizes for climate zones CZ3 and CZ13, expressed in total number of 1-ton GSHP units are shown in the table below. Markets Total addressable market (TAM) Served available market (SAM) Total Market for 1-ton GTAC Units Lodging (number of units) Multifamily (number of units) CZ3 CZ13 Total CZ3 CZ13 Total 18,495 84, , , , ,898 6,473 29,476 35, , , ,115 Target market 2,404 10,948 13,352 57, , ,558 TABLE 30: MARKET SIZE ESTIMATE FOR 1 TON GTAC UNITS 104

107 AGGIE VILLAGE SITE INTRODUCTION TO AGGIE VILLAGE SITE Aggie Village is a faculty and staff single-family home community located in downtown Davis, CA. During 2013 and 2014, a number of technology demonstration activities were being implemented at an Aggie Village home, including solar PV and battery storage. This led to a recommendation to include a ground source heating and cooling system, a retrofit that was believed could lead to the home achieving zero net energy. In addition to striving to achieve zero net energy under the retrofit, evaluation was to be made of state-of-the-art options for installing ground source heat pumps and heat exchanger systems for the site. HVAC OPTIONS FOR THE SITE Meline Engineering was hired to evaluate the ground source heating and cooling options for this site and offered a number of options for this home, taking into account the heating and cooling loads. All options included 2 vertical loops to a depth of 250 to 300 feet. The final depth of the GHX would depend on the equipment, pipe diameter and grout selected. An option to include a desuperheater to contribute to the domestic hot water supply was considered but rejected for a number of reasons. First, we wanted to be able to measure the efficiency of the system for space heating and cooling, as that is normally how these systems are deployed. While it is interesting to include domestic hot water, it would have been difficult to separate the energy demand for the domestic hot water and understand exactly how the additional heating load would affect the ground heat exchanger and annual ground conditions. Also, this home already had solar thermal panels for domestic hot water that were being evaluated in another study for the California Solar Initiative RD&D Program. A repetitive hot water heating system was therefore not included. Other items that were taken into consideration were whether or not the system should be placed outside where the current air conditioning condenser was located, or if a packaged GHP system should be moved into the attic space above the second floor, or in the garage. By installing the system in the attic or garage, it would free up space outside while reducing noise on the resident s patio. Additional indoor piping and wiring would have potentially increased costs and installation time. All options included a GHP system and an air handler in place of an air coil/furnace unit. GHP SYSTEM ADVANTAGES AND CHALLENGES (SPECIFIC TO SITE) Based on the GHP deployment, the proposed GSHP system was expected to save about 50 percent of energy needed to heat and cool the home. Greenhouse gas emissions were expected to be diminished by about the same degree. However, because of a number of challenges, this system was not installed. PERMITTING Showcasing modern GSHP technologies and drilling techniques at the Aggie Village had to address the space constraints present at the site. One of the drivers for the 105

108 project was validating the use of this retrofit technology under space constraints. In this case applicable regulation by the authority having jurisdiction (AHJ), the City of Davis, as well as the State of California on ground heat exchange wells did not substantially exist. Most jurisdictions default to their water well drilling standards which have restrictions related to set-backs from contamination sources, such as sewer mains. In the case of the project s AHJ, sewer laterals from the homes are also considered contamination sources. While the AHJ was willing to work with the project team and eventually provided a variance, the variance only allowed for a horizontally drilled ground heat exchanger, since this was the only configuration that could accommodate a 10-foot clearance from the sewer lateral of the home. Additionally, the AHJ required a soil test be performed at the site to be certain that no preexisting soil contamination was present. While the AHJ was accommodating, they were extremely concerned with contamination and sensitive to the potential risks of this GHX. Additionally, little familiarity with modern seal ground loop heat exchangers had been acquired and the California Department of Water Resources had not established GHX code standards. A number of factors may have contributed to the sensitivity to contamination risk, including the following: A recent successful water rate referendum in the City of Davis will significantly increase water rates with the possibility to increase water well drilling requests. Vertical GHX on a small property could set a precedent for water well drilling. The City was or had been involved in litigation related to ground water contamination from other sources. Until more specific regulations are in place to accommodate vertical GHX installation, permitting may remain uncertain for many locations throughout the state. PROCUREMENT PROBLEMS Because the home is currently owned and controlled by UC Davis, procurement was through the university s Design and Construction Management office for issues related to system installation. This office is responsible for all design and construction activities on campus. The home was treated like any small project (less than $150k) and was required to go out to bid for purchasing, first for the vertical GHX installation and then for the HDD installation based on the variance allowed by the city. This added additional delays that ultimately could not be accommodated under the project schedule. Once the project did solicit bids, only one bid was received and proved higher than allowed under the project budget. With a second solicitation constituting additional delay and cost, the project team and PG&E project managers jointly decided not to proceed with the installation of this system. Subsequent informal conversations with installers put the range of installation costs between $30,000 and $40,000 for full turnkey installations utilizing prevailing wage labor, but no formal accounting of these estimates is available. LACK OF DRILLERS/NEW CERTIFICATION It was generally understood that the project only received one bid due to the requirement that the drillers hold a so-called C57 license. This license is required for water well drillers but horizontal boring contractors are largely unfamiliar with the certification because horizontal boring contractors do not typically install water wells. 106

109 This requirement resulted in many contractors not meeting the prerequisite for submitting a bid. PREVIOUS STUDIES APPLICABLE TO LOCAL REGION (CGEC MODELING STUDY) The California Geothermal Collaborative was previously commissioned by the California Energy Commission [31] to evaluate the potential for ground source heating and cooling systems across California climate zones. The Geothermal Collaborative estimated this by examining the HVAC energy demand according to geothermal (Figure 29) and climate zones, and estimated the energy reduction that would result from switching to ground source heat pumps (Figure 30). This was made possible by overlaying a map of the California Climate Zones with the known geological ground conditions. The work resulted in a better understanding of the unique soil conditions in each region that directly affect the efficiency of a ground source heating and cooling system. 107

110 PG&E s Emerging Technologies Program FIGURE 28: CALIFORNIA GEOLOGIC MAP (SOURCE[31]) 108

111 FIGURE 29: MAP LEGEND FOR CALIFORNIA GEOLOGIC MAP (SOURCE:[31]) 109

112 Total Energy Used, Conventional HVAC (kwh/ yr) PG&E s Emerging Technologies Program 80% 50% 20% 11 16, , , , ,000 8,000 12,000 16,000 Total Energy Used, GHPs (kwh/ yr) FIGURE 30: TOTAL ENERGY USE PER YEAR PER RESIDENCE, IN KWH/YR, FOR CONVENTIONAL HVAC SYSTEMS (VERTICAL AXIS), COMPARED TO ENERGY USE RESULTING FROM USE OF GEOTHERMAL HEAT PUMP SYSTEMS (HORIZONTAL AXIS). (SOURCE:[31]) 110

113 The results from this analysis indicate that for all but climate zone 15, which has the greatest cooling load demand, geothermal heat pump systems would reduce overall HVAC energy consumption by between 22 percent and 77 percent per average residence. The results indicate that the greatest reduction in energy consumption occurs in those climate zones most dominated by heating loads. This reflects the relatively higher efficiency of geothermal heat pump systems operating in heating mode as opposed to cooling mode. Nevertheless, even for the most strongly coolingdominated climate zone, total energy use with a geothermal heat pump system overlaps that of a conventional HVAC system at the 10 percent uncertainty level (Figure 30). Conventional Energy (kwh) GHP Energy (kwh) Energy Reduction (kwh) Energy Reduction (%) Climate Zone 1 17,539 3,926 13, ,675 5,432 9, ,828 3,462 6, ,214 4,220 5, ,216 3,980 7, ,288 3,128 1, ,051 2,943 1, ,659 3,620 1, ,599 5,308 2, ,693 5,510 3, ,967 7,845 8, ,707 6,805 7, ,771 7,775 5, ,161 9,319 6, ,147 10,651 (504) (5) 16 15,510 7,667 7, Average = 44 TABLE 31: COMPARISON OF ANNUAL TOTAL ENERGY CONSUMPTION OF CONVENTIONAL HVAC SYSTEMS AND GEOTHERMAL HEAT PUMP SYSTEMS, BY CLIMATE ZONE. (SOURCE [31]) CHALLENGES IN MODEL VALIDATION: DATA MONITORING One of the objectives of the Aggie Village project was to validate the model previously created by the Geothermal Collaborative. This is important to continue to develop ground source heating and cooling system adoption, especially as modeling allows for long-term predictions of the performance of these systems. 111

114 LOCAL CONDITIONS AT AGGIE VILLAGE SITE DESIGN As mentioned above, originally a vertical heat exchange well was proposed but could not be installed due to set back restrictions in the jurisdiction having authority. The site was then assessed for a horizontally bored system, and it was determined that a horizontal system could be configured on the property. The heating loads for the home were calculated as follows: o o o 19,408 Btu/h heating 19,19 Btu/h sensible cooling 1,464 Btu/h latent cooling. The horizontal loop configuration is shown below in Figure 31 and Figure 32. SITE PROPERTIES The half-plex (a duplex in which each domicile is privately owned) selected for the geothermal heat pump system retrofit was of typical home size and configuration; however the parcel upon which the townhome is sited is very small. Equipment access was therefore limited. Inspection of the site for buried utilities resulted in two specific locations for vertical boreholes: one clearing the gas, electricity, and water laterals into the home and the other in the driveway. For the design of the ground loop, the same thermal properties were used: Deep Earth: 65 F Thermal grout specified conductivity: 0.88 Btu/hr-ft- F (specified) Soil conductivity: 0.88 Btu/hr-ft- F (specified) Soil thermal diffusivity: 0.56 ft 2 -day CONSTRAINTS During the permitting phase of the project, the vertical loop system design was rejected. HDD was then evaluated since insufficient land was available to install a horizontal trenched system. 112

115 FIGURE 31:OVERHEAD VIEW OF PROPOSED HORIZONTAL BORE GHX (SOURCE MELINE ENGINEERING) 113

116 FIGURE 32: CROSS SECTIONAL VIEW OF THE PROPOSED HORIZONTALLY BORED GHX (SOURCE MELINE ENGINEERING) 114

117 ANALYSIS PERFORMANCE PREDICTIONS AND OBSERVATIONS The project was striving to achieve ZNE as a retrofit and thus also had other retrofits not associated with but related to this effort. As discussed above, these systems consisted of a solar system (PV and thermal) and a battery storage system. The annual energy breakdown prior to retrofits was estimated (Figure 33) and is based on a total average monthly use of 550 kwh/month. Based on a 500 kwh per month average FIGURE 33: ESTIMATED AGGIE VILLAGE END USE BREAKDOWN PREDICTED EFFICIENCY AND ENERGY CONSUMPTION As mentioned above, ZNE was intended for the retrofit. The appliances were replaced and a 2.2 kw solar PV and Thermal hybrid system had been installed in order to increase overall efficiency and on-site generation. GENERAL CONSIDERATIONS AND ISSUES As discussed above, the combination of a constrained area as a site condition and the lack of local code language identifying rules and regulations specific to GHX installation caused additional delays and costs for the project. 115