Ground Source Heat Pump System Design and Case Studies

Transcription

1 Paul Stull, PE James B. Feild, RG, LHg AMEC Earth & Environmental, Inc. Portland, Oregon Ground Source Heat Pump System Design and Case Studies 2010 ESOH Training Symposium Nashville, Tennessee

2 Outline Ground Source Heat Pump Technical Overview Open vs. Closed Loop Technical Summary Implementation Drivers Recent Testing Results Case Study Cannon AFB Conventional Closed Loop GSHP System Step Function System Case Study Cavalier AFS Conventional Closed Loop GSHP System Hybrid / Step Function Closed Loop System Case Study The Columbian Open Loop GSHP System Summary

3 What is a Ground Source Heat Pump? A ground source heat pump (GSHP) uses the ground and/or groundwater as a source of heat in the winter to heat and a heat sink in the summer to cool a building or structure.

4 Types of GSHPs Open Loop GSHP Extraction and injection wells (reversible) Extracts relatively constant temperature groundwater from the subsurface Transports the groundwater to the structure Returns the groundwater to the subsurface Hydrogeologic assessment Design Options Step Function pump options, injection controls, etc. Closed Loop GSHP Borehole array(s) Uses water or water/compound (antifreeze) mixture to carry heat to and from the structure Water or water/compound mixture never directly contacts the ground or groundwater Geological feasibility testing required for design Design Options Step Function sub-arrays, Hybrid Systems, etc. THERE IS NO UNIVERSAL TONNAGE RATE / BORING EACH SITE IS DIFFERENT Site usage and loads and spatial constraints Site geologic conditions

5 Open Loop GSHP winter

6 Closed Loop GSHP Polyethylene winter

7 Typical borehole schematic GROUND SURFACE POLYETHYLENE PIPE HIGH SOLIDS BENTONITE GROUT

8 GSHP System Comparison Design Considerations Open Loop GSHP Systems Closed Loop GSHP Systems Best Case Use Spatial Requirements Location with shallow and productive water, site spatial constraints Adequate room for thermal separation typically 100+-ft New site construction with adequate space Good lithology and drilling conditions Highly dependent upon having adequate room for boring array can be very large (10,000+-ft^2) Hydrogeologic/Geologic Highly dependent upon groundwater production ability Hydrogeologic conditions do not severe impact Water chemistry and contamination considerations operation Geology drives aquifer characteristics Geologic conditions significantly determine Capital Costs Operational Costs Maintenance Moderate to High Large Well installation, vaults/pitless units, telemetry/controls, trenching Low to Moderate Extraction well pump operation and telemetry systems Moderate to High Pump maintenance, water softening, water level monitoring, etc. effectiveness Typically High Lots of drilling and trenching work, potential site disruption Very little minor costs of transfer pump operation Very little to None repair of lines if breached Permitting Testing / Modeling Options Summary Water Rights This can be critical path Underground Injection Control (UIC) Waste Discharge Permit Well Construction / Construction Permits Sewer Discharge Permit (testing) Aquifer Pump Test High costs / issues Hydrogeolic Thermal Modeling flow/load dep. Step Function Pumping Systems Injection Well Controls Open loop systems are dependent upon more site conditions and have more maintenance and operational costs/issues. Borehole Installation Permit Underground Injection Control (UIC) Construction Permits Thermal Conductivity Test Low costs / issues Thermal Modeling of boring array several models Step Function sub-arrays Hybrid GSHP Systems Closed loop systems are dependent upon spatial constraints and lithology, have high capital costs, but very low operational and maintenance costs/issues.

9 GSHP Implementation Drivers Environmental Green or Sustainable Minimizes consumption of natural resources Lowers carbon footprint Accumulates points toward LEED certification Good business/operational practice Federal Drivers Executive Order passed in 2007 Executive Order % energy reduction by % annual reduction

10 Recent Conductivity Testing Results Results Average subsurface temperatures range from 38F to 70F depending upon location Thermal conductivity is typically near or slightly above 1.00 At sites where multiple tests were conducted results were fairly consistent with rare exceptions

11 Case Study Cannon AFB (Building 1820) Conventional Step Function GSHP System Site was selected during initial site reconnaissance/design charrette meeting Thermal Conductivity Test 400-ft Test Boring determined site is viable for GSHP application Test Boring was sited in a location that allowed for incorporation into the full scale system. Site Building (Club House) has highly variable thermal loading due to spaces and large kitchen operations Large vacant adjacent property with minimal utility conflicts allowed good location for boring array

12 Case Study Cannon AFB Conventional Step Function GSHP Design Conventional GSHP System 240 borings to 400-ft bgs Double Leg Loop Significantly reduces the length of piping 25% Step Function System Highly variable thermal demands due to site operations Four equal sub-arrays allow for % operational increments Allows for more efficient and accurate HVAC system Operation Double Leg Loops Significantly reduces the length of piping

13 Case Study Cannon AFB Summary Boring Array Configuration Despite the large space, placing a single efficient large array was difficult. More inefficient arrays would fit but required more borings (smaller spacing and more square shaped) AMEC split the array into two and modeled two smaller more efficient designs that would easily fit, require less borings, and accommodate the loads 25% Step Function Design In order to accommodate the high load variability, AMEC mechanical and civil engineers developed a Step Function system at split the boring array into four equal sub-arrays that could be independently operated. The Step Function option allows the system to be run and % step increments, which is more energy efficient for HVAC equipment and accommodates the GSHP design condition of constant flow rates. Segregated systems offer greater redundancy and allow partial system operation if a sub-array fails. Double Leg Loop Layout The boring array configuration was selected to allow for using a Double Leg Loop configuration, which significantly reduces the amount of piping and simplifies installation. Cost Analysis Initial low SIR number below 1.0 and payback period > 20 years Low utility rates and unit drilling costs greatly impact SIR and payback period Energy efficiency estimates were between 20 and 35%

14 Case Study Cavalier AFS (Buildings 820/830) Conventional / Hybrid GSHP Systems Initial site reconnaissance/design charrette meeting identified the following atypical requirements: HVAC systems were cooling the building all year Main Building (830) had large - 3,200 tons of cooling Generator Building (820) required approximately 900 tons of cooling Existing Cooling Towers were using large quantities of water and chemical softening agents and routinely had severe freezing issues during the winter. A large vacant and utility free space was available for the boring array Thermal Conductivity Test 400-ft Test Boring determined site is viable for GSHP application and ground temperature was low approximately 38F. Test Boring was sited in a location that allowed for incorporation into the full scale system. Design Options A single conventional GSHP system for entire site Separate conventional GSHP systems for building 820/830 systems Hybrid GSHP system for building 830 system Direct replacement of existing cooling tower system

15 Case Study Cavalier AFS Conventional GSHP Design Conventional GSHP System for Building 830 Modeling determined that over 3,800 borings would be needed to accommodate constant heat load All available space would have been required with difficult modeling and extensive drilling/trenching NOT VIABLE ALTERNATIVE

16 Case Study Cavalier AFS Hybrid Step Function GSHP Design Hybrid GSHP System for Building 830 Modeling determined that about 1,008 borings would be needed to accommodate constant heat load (less than 27% of conventional requirement) Easily accessible space was available with minimal utility conflicts Drilling and trenching time and costs were significantly reduced / Double Leg Loops reduced length of piping by about 1/3 Eight (8) sub-arrays allowed high flexibility into HVAC (Fluid Coolers) operation and greatly increased efficiencies COST and IMPLEMENTATION VIABLE

17 Case Study Cavalier AFS Summary Preliminary Modeling One large system for both buildings (over 4,200 borings) or just 830 (over 3,700 borings) was NOT VIABLE. Drilling alone was estimated to be over $15 million Accurate modeling and spatial constraint made it nearly impossible to implement accurately Hybrid 12.5% Step Function System Design for Main Generator Building (830) Fluid Coolers - By using fluid coolers in series to eliminate 50% of the peak cooling load, boring array was reduce to less than 27% of conventional size. Step Function - To accommodate the high variability in the seasonal performance of the fluid coolers, eight (8) equal sub-arrays that could be independently operated were design to allow 12.5% incremental steps. Higher Efficiency - The Step Function option allows the system to be run at 12.5% step increments, which is more energy efficient and accommodates the GSHP design condition of constant flow rates. Segregated systems separate sub-systems offer greater redundancy and allow partial system operation if a sub-array fails. Double Leg Loop design by using this configuration the piping lengths were reduced by approximately 30% Conventional Segregated GSHP System for Generator Building (820) Separate Sub-Systems Three conventional borings were designed to accommodate the three operational generators Control System controls were developed to allow any of the five generators to run on any of the three boring arrays Cost Analysis Initial low SIR number below 1.0 and payback period > 45 years FINAL SIR number above 1.0 with payback period < 10 years Reduced HVAC water consumption and associated electrical costs by over 90% Chemical use and costs nearly eliminated Direct electrical usage reduced by at approximately 12-15% Total system costs reduced to less than $10 million

18 Case Study - The Columbian - Vancouver, WA GSHP System (Open Loop) 120,000 square foot building System requirement of 1,250 gpm (maximum output) Two extraction wells 12-inch diameter Stainless steel screen 130 feet total depth, screened from 80 to 130 feet in a cobble-size, wellrounded gravel One pitless unit per well (sanitary seal) One injection well 12-inch diameter Stainless steel screen 130 feet total depth, screened from 80 to 130 feet in a cobble-size, wellrounded gravel One pitless unit (sanitary seal)

19 Case Study The Columbian Water Right Permit - Department of Ecology) Time frame to process a water right is approximately 6-8 years without expedited permitting Expedited permitting process is approximately 1 year Use Washington Department of Ecology s Cost Reimbursement Authority Statutes RCW Energy Conservation in Design of Public Facilities EO Sustainable Practices by State Agencies EO Establishing Sustainability and Efficiency Goals for State Operations Persistent Toxic Chemicals (including mercury) West Coast Governor s Global Warming Initiative

20 Case Study The Columbian Additional Permitting Underground Injection Control Permit The Columbian GSHP is Class V use The injection well and GSHP system met the non-endangerment requirement of the UIC program Chemicals and additives will not be used or added to injected water Only change to injected water will be temperature A UIC permit was not required, but Ecology did require registration Injection well was rule authorized A waste discharge permit was not required Well Construction Permit Well driller obtained permits Sewer Discharge Permit Pumping Test was conducted at 1,250 gpm (design rate of GSHP system) Sewer discharge permit obtained from City of Vancouver City limited pumping test to 8 hours duration and off peak hours

21 The Columbian Publishing Company- Vancouver, WA

22 Case Study - The Columbian Pitless Unit Installation

23 Case Study - The Columbian Final Installation

24 Case Study - The Columbian Summary Standard Open Loop system with reversible wells to accommodate future reduced production of extraction wells Significant consulting time to acquire water rights permit and manage construction installation issues Energy Savings Projected 36% annual energy savings over the same building built to non- ASHRAE standards 460,000 kwh/year (approximate) of electricity 4,600 therms/year (approximate) of natural gas Reduce CO 2 emissions by over 150,000 lbs per year Reduce other pollutant by-products of fossil fuel based electricity production Equivalent to planting 225 trees per year 227,000 gallons of water saved per year Use of green energy Actual energy savings 51% (post installation) $80,000 per year energy savings

25 GSHP Summary Open Loop Systems: Water Rights can be a major time and cost issue Groundwater thermal modeling and production testing is critical Moderate to High capital costs and moderate operation costs Moderate maintenance issues GSHP coupled with new efficient building construction can result in high efficiency Closed Loop Systems: Low permitting and regulatory issues Spatial Constraints and Site HVAC Usage are critical design parameters Many Design Options Step Function Systems increase efficiency and redundancy Hybrid Systems Can improve economics and operational efficiency New building construction allows great spatial options and control Cost Analysis Moderate to High Capital Costs Very Low Operational Costs and Maintenance Requirements Initial SIR/Payback numbers are usually conservative Drilling and utility rates are major factors in cost analysis Efficiency goals can be attained

26 Recent Representative AMEC GSHP Projects Open Loop Systems: State of Washington School for the Deaf - Vancouver, Washington Pringle Creek Development - Salem, Oregon The Columbian Vancouver, Washington Closed Loop Systems: Air Force Sites Total of 34 Systems Whiteman AFB Nob Noster, AR (3 Systems) Creech AFB Indian Springs, NV (3 Systems) Cannon AFB Clovis, NM (13 Systems) FE Warren AFB Cheyenne, WY (2 Systems) Cavalier AFS Cavalier, ND (2 Systems) Altus AFB Altus, OK (3 Systems) Vance AFB Enid, OK (3 Systems) Sheppard AFB Wichita Falls, TX (5 Systems) State of Iowa Juvenile Girls Home Toledo, IO (11 Systems)

27 Other Information Sources International Ground Source Heat Pump Association (IGSHPA) American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) National Ground Water Association (NGWA)

28 Ground Source Heat Pump System Design and Permitting Paul Stull III, PE James B. Feild, RG, LHg AMEC Earth & Environmental, Inc. Portland, Oregon Cavalier AFS