Combined Cooling, Heating, Power, and Ventilation (CCHP/V) Systems Integration

Transcription

1 Combined Cooling, Heating, Power, and Ventilation (CCHP/V) Systems Integration Fred Betz PhD. Dissertation Center for Building Performance and Diagnostics School of Architecture College of Fine Arts Carnegie Mellon University Pittsburgh, Pennsylvania May 11, 2009 Copyright Frederik Betz, All rights reserved.

2 Copyright Declaration I hereby declare that I am the sole author of this thesis. I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to lend this thesis to other institutions or individuals for the purpose of scholarly research. I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. Copyright Frederik Betz, All rights reserved. 2

3 Acknowledgements I would like to thank Dr. Volker Hartkopf for chairing my thesis committee and for bringing me to the Center for Building Performance and Diagnostics four years ago. He helped me gain a new perspective and appreciation for the built environment. His never ending supply of energy and optimism is truly inspiring. Dr. David Archer has guided my day to day tasks since my arrival in the Intelligent Workplace four years ago. Through his tireless efforts he inspired me to persevere through my entire project from preliminary design ideas all the way through construction and evaluation of a complex system. Prof. John Wiss provided me with invaluable insight into engine technology and always helped me stay grounded with his years of practical experience. I would especially like to thank Sharilynn and Jim Jarrett who provide support services in the Intelligent Workplace, which allowed all of the faculty and staff to function as a team. Flore Marion generously spent months of her time assisting me with her fantastic TRNSYS programming skills without which an entire chapter of my thesis would never have existed. I am truly thankful to have had her assistance on this thesis. I would like to thank all of the students working in the IW for their support and encouragement over the years. In particular I would like to thank Philip Kwok, Bing 3

4 Dong, Joonho Choi, and Viraj Srivastava. Their advice and attitude made working long hours enjoyable. I would like to thank my parents Karin and Al Betz for helping me develop and maintain a work ethic that has made all of my success to date possible. Finally, I would like to thank my brother Ingo, whose sense of humor helped me keep a smile on my face for the last four years in the face of some tough challenges. 4

5 Dedication I would like to dedicate this dissertation to my wife Victoria. Without her love and support everyday for the last four years this dissertation would not have been possible. 5

6 Abstract Combined heat and power (CHP) systems are frequently used to reduce energy consumption in a facility due to the increased energy efficiency. System efficiencies range between 65% and 85%, whereas the average utility efficiency for electric power supply is 31% and for heating from a natural gas supply is around 80%, which yields a combined efficiency of approximately 50% for all energy supplied in the United States of America. Buildings use 70% of all electricity generated in the U.S., 40% of all U.S. primary energy to heat, light, ventilate and cool facilities. Therefore, it makes sense to site power plants near both the electrical and thermal loads to make use of the nearly 70% of energy that is annually wasted by large central power plants. CHP systems are frequently reserved for larger facilities due to high first costs and complex operations, however 75% of all buildings in the U.S. have an area of less than 10,000 ft 2 (929 m 2 ). There have been several attempts made by various corporations to break into the micro CHP market with limited success. Studies commissioned by the Department of Energy show that two of the key barriers to the adoption of CHP systems in smaller facilities is the high first cost and the lack of packaged plug-and-play systems. To address this challenge, the Center for Building Performance and Diagnostics (CBPD) has designed, installed, operated and evaluated a 25 kwe biodiesel fueled CHP system that is integrated with an absorption chiller system and an enthalpy recovery ventilation system with solid desiccant dehumidification in a single system that provides all of the electric, cooling, heating, and ventilation needs of the Intelligent Workplace, IW. The 6

7 chiller and ventilation systems are well understood with three published dissertations in the last four years. This dissertation integrates elements of each subsystem through the use of calibrated simulations to determine the effectiveness of operating such a system in a commercial office building as well as potentially in a data center. Key contributions of this work include: A complete accounting of how the CHP system is setup and how it operates with both Diesel and biodiesel fuel. A generic preliminary design procedure for the CHP system of a building as well as the specific design procedures for the biodiesel fueled CHP system. A simplified TRNSYS CHP system performance model that can be easily adjusted to be used for different buildings and/or for different prime movers. A conceptual systems integration model, which identifies how components and sub-systems may fit together. Key results in this dissertation include: The results show that for efficient and effective performance of a CHP system in a high performance building it is essential to have electrical and thermal grids available to export and/or import CHP energy. The grids allow the CHP system to operate continuously at the design load. The grids also provide back up in case of system outage. 7

8 The results of operating the biodiesel fueled CHP system in the IW yields an average annual efficiency of about 66% and a peak of 78%. A scaled up system for the Building As Power Plant (BAPP) will achieve similar efficiencies unless a larger load for the coolant energy can be found. Data centers offer an ideal location for CHP systems as they do not have such highly variable loads such as office buildings. Furthermore, data centers do not have latent cooling or heating loads, which simplifies systems integration, as the only components required for the system are an engine or turbine, heat recovery equipment, and absorption chillers. A CHP system with absorption chillers has been calculated in this dissertation to achieve an average efficiency of 78% in data centers. There are many possible next steps; however the three most important steps in the development of the CCHP/V technology are to complete the automation and integration of the CHP system with the rest of the IW. Second, to refine the BAPP data for the TRNSYS simulation and to create a modular CHP system in TRNSYS so the development of BAPP mechanical system can proceed and provide a future testing ground for packaged CCHP/V systems. Third, to conceive and develop the means for reducing equipment and installation costs by a factor of 10 to 20 must be developed. 8

9 Table of Contents Copyright Declaration... 2 Acknowledgements... 3 Dedication... 5 Abstract... 6 Table of Contents... 9 List of Figures List of Tables Nomenclature Introduction Rationale Market Size Why not CHP? Background DG & CHP Principles Fuels Energy Grids Prime Movers Central Power Plants Boilers and Steam Turbines Gas Turbine Internal Combustion Engines Fuel Cells Prime Mover Summary Heat Loads Space Heating Absorption Cooling Desiccant Regeneration Other Heat Loads Storage Heat Loads Summary Existing Packaged Systems Case Studies IWESS Components and Subsystems Biodiesel Fueled Engine Generator with Heat Recovery System Components Input / Output Operating Description and Results Engine: Measured Data versus Manufacturer s Specifications Pressure Time Crank Angle Measurements Turbocharger Analysis Combustion Gas and Emissions Analysis Heat Recovery Analysis Systems Integration Potential

10 3.2 Steam Driven Double Effect Absorption Chiller System Components Input / Output Operating Description and Results Systems Integration Potential Ventilation System with Enthalpy Recovery and Solid Desiccant Dehumidification System Components Input / Output Operating Description and Results Systems Integration Potential Preliminary Design Guide Generic Design Steps Loads Fuel Selection Energy Grids Prime Movers Auxiliary and Heat Recovery Equipment Operating Strategy CHP System Evaluation Design of Biodiesel Fueled CHP System Load Profiles Fuel Selection Energy Grids Prime Movers Auxiliary and Heat Recovery Equipment Operations Evaluation Submittals TRNSYS Modeling IWESS Model Biodiesel Fueled Engine Generator with Heat Recovery Modeling Double Effect Steam Driven Absorption Chiller Ventilation Unit with enthalpy recovery and solid desiccant wheel Computational Model Issues Combined IWESS Model IWESS Simulations Mode Zero: Design Operation Mode One: Thermal Load Follow Mode Two: Regeneration Load Follow IWESS Simulation Discussion BAPP Model Engine Modification BAPP Simulations Mode Zero: Design Operation Mode One: Thermal Load Follow

11 Mode Two: Regeneration Load Follow BAPP Simulation Discussion Data Center CHP Operation Systems Integration Individual Systems Integration Packaged Systems Integration Contributions, Conclusions, and Future Work Contributions Conclusions Future Work References Appendix

12 List of Figures Figure 1: U.S. Electrical Energy Flow for Large Central Plants (Quadrillion BTUs) [2] 21 Figure 2: Energy Flow for Distributed Generation with Heat Recovery (Quadrillion BTUs) (Adapted from Reference 2) Figure 3: Basic CHP Flow Diagram Figure 4: CHP System Components Figure 5: Baldor Engine Generator Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kwe Figure 7: Assembled Components: Engine Generator (Left), Steam Generator (Right).. 41 Figure 8: Steam - Hot Water Converter Figure 9: Coolant Heat Exchanger with Piping before Insulation Figure 10: Remote Mounted Radiator Figure 11: Engine Generator Onboard Interface Figure 12: Engine Generator Onboard Interface Figure 13: Automated Logic CHP User Interface for the Heat Recovery/Rejection System Figure 14: Pressure vs. Time for One Cylinder at 12 kwe using Low Sulfur Diesel Fuel Figure 15: Pressure vs. Time for One Cylinder at 12 kwe using Low Sulfur Diesel Fuel Figure 16: Turbocharger Compressor Map [] Figure 17: Summer Operation of the Steam Generator T-Q Diagram Figure 18: T-Q Diagram for Coolant Heat Exchanger at 25 kwe Figure 19: Steam Driven Absorption Chiller Flow Diagram [] Figure 20: Absorption Chiller Process and Instrumentation Diagram [31] Figure 21: Automated Logic Absorption Chiller User Interface Figure 22: Absorption Chiller Component Heat Transfers vs. Cooling Load [31] Figure 23: Plan View of Ventilation Unit [] Figure 24: Interior View of the Ventilation Unit [33] Figure 25: Ventilation Unit Flow Diagram [33] Figure 26: Psychrometric Chart for Ventilation System Operation [33] Figure 27: Enthalpy Removal Breakdown by Component [33] Figure 28: Moisture Removal Breakdown by Component [33] Figure 29: Operating Cost Breakdown by Component [33] Figure 30: IW Heating and Cooling System Flow Diagram\ Figure 31: CHP system input / output module Figure 32: Double effect absorption chiller input / output module Figure 33: Ventilation system input / output module Figure 34: Combined TRNSYS Model Figure 35: Combined/Simplified IWESS TRNSYS Model Figure 36: BAPP TRNSYS Simulation Figure 37: CHP Major Component Diagram

13 Figure 38: Absorption Chiller Major Component Diagram Figure 39: Ventilation System Major Component Diagram Figure 40: CCHP/V Energy Cascade Figure 41: Major Component Piece-wise Systems Integration Figure 42: Packaged CCHP/V System Figure 43: CCHP/V Summer Operation Flow Diagram Figure 44: CCHP/V Winter Operation Flow Diagram Figure 45: Cost Breakdown of CHP System

14 List of Tables Table 1: Prime Mover Performance Summary Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results Table 4: Averaged Winter Biodiesel Experimental Results Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel Table 9: Absorption Chiller Test Program and Results [31] Table 10: Typical U.S. Commercial Building Loads Table 11: Prime Mover Performance Summary Table 12: IWESS Design Operation Simulation Results Table 13: IWESS Thermal Load Follow Simulation Results Table 14: IWESS Regeneration Load Follow Simulation Results Table 15: IWESS 25 kwe CHP Coolant Heat Exchanger Results vs. Power Level Table 16: Estimated BAPP 200 kwe CHP Coolant Heat Exchanger Results vs. Power Level Table 17: IWESS 25kWe CHP Air Flow Rate vs. Power Level Table 18: Estimated BAPP 200 kwe CHP Air Flow Rate vs. Power Level Table 19: BAPP Design Operation Simulation Results Table 20: BAPP Thermal Load Follow Simulation Results Table 21: BAPP Regeneration Load Follow Simulation Results Table 22: IWESS Input / Output Table Table 23: IWESS Component List Table 24: Packaged System Component List

15 Nomenclature BAPP: Building As Power Plant CHP: Combined Heat and Power, also known as cogeneration CCHP: Combined Cooling Heat and Power, also known as trigeneration CMU: Carnegie Mellon University CBPD: Center for Building Performance and Diagnostics DG: Distributed Generation IC: Internal Combustion IW: Intelligent Workplace IWESS: Intelligent Workplace Energy Supply System kw: kilowatt kwc: kilowatt chemical (fuel energy) kwe: kilowatt electric kwt: kilowatt thermal 15

16 1.0 Introduction The work described in this dissertation covers the preliminary design, procurement, detailed design, installation, operation, and evaluation of a 25 kwe combined heat and power subsystem as well as the future integration with installed absorption chillers and an enthalpy recovery ventilation system with solid desiccant dehumidification as a combined energy supply system. The goals of the integration is to show how the three subsystems operate together as a system by combining three validated simulation models and to show how the first and operating costs can be reduced through systems integration. 1.1 Rationale While the cost of energy has dropped substantially in the last year, experts agree that the price will rebound to historic highs as the world economy recovers [1]. Due to the double threat of high energy cost and global climate change there is increased interest in the use of combined heat and power systems, which can reduce the primary energy consumption of power and heat by up to 50% for building and plant operations. Currently the U.S. average efficiency for producing electricity is 32% including transmission and distribution losses [2]. If heating efficiencies are considered, then standard practice efficiency is around 50% for heating and electricity. Typical CHP system efficiencies range from 65% to 90% efficiency, including the Intelligent 16

17 Workplace Energy Supply System (IWESS) CHP system which has achieved 76% efficiency. Studies commissioned by the Department of Energy [3, 4, 5] show that one of the key barriers to the use of CHP systems is the high first cost and the availability of packaged systems. This PhD. dissertation attempts to address these two issues by providing a first step in the creation of a packaged plug-and-play system that can be delivered to a facility and be connected rapidly. Furthermore, the packaged system will have reduced overall costs of design, engineering, and field assembly as compared to a system purchased piecewise. One of the key problems when using a CHP system is to find a sufficient heat load that matches the heat output of the CHP system. CMU s Intelligent Workplace (IW) offers two thermal loads during the summer; the regeneration of a desiccant wheel in the ventilation system and the operation of absorption chillers. During the winter, the IW has a space heating load. These loads allows the CHP system to operate year round, with the possible exception of the intermediate seasons, spring and fall, where a properly designed building should have little need for air conditioning (heating, cooling, or dehumidification). However, because there are Carnegie Mellon campus electrical, steam, and chilled water grids, year round export of energy is possible from the IW s CHP system. 17

18 1.2 Market Size Several studies commissioned by the Department of Energy in 2002 have looked into the market size of CHP systems using current technology [3, 4, 5]. Between 2003 and 2017: 7% of hospitals plan to install CHP systems within 2 years, starting in 2003, 3% of supermarkets plan to install CHP systems within 2 years, starting in 2003, 4% of hotels plan to install CHP systems within 2 years, starting in 2003, 2% of big-box retailers plan to install CHP systems within 2 years, starting in 2003 [4]. Institutions construct new buildings every year, which require power for lighting and ventilation as well as thermal energy for heating and cooling. Approximately 42,000 new commercial buildings are built every year; 75% of the buildings have peak loads below 200 kwe [6]. Several markets would be impacted by improvements in CHP systems most notably hospitals, supermarkets, and hotels [5]. A total of 3,075 sites were identified for kwe CCHP retrofits. For new construction through 2020, 2,464 CHP sites were identified [5]. It should be noted that this study was conducted in 2002 and 2003, and the market will have shifted somewhat as fuel and electricity prices have increased several fold since the publication of this report. Also, the study did not include large institutional complexes such as universities, in the market sizing. 1.3 Why not CHP? The advantage of standard electrical and natural gas utilities, boilers and chillers that provide energy to buildings inefficiently over CHP systems is that it is simple for the 18

19 building owner and/or occupant. The job of keeping the power on falls to the utility company and chillers and boilers may include warranties and service contracts in addition to being mature technologies. Furthermore, the first cost is low for the builder. In essence, the risk for the consumer is low, while the energy and associated environmental and economic impacts are large even though CHP systems have existed as long as utilities have existed. Currently, CCHP/V systems have a greater perceived risk to the owner or occupant versus a conventional energy supply system. A buyer would choose a CCHP technology based on first cost, operating cost, and maintenance cost and reliability. A major objective of this project is to reduce the first cost by working on systems integration strategies that reduce the number and complexity of components in the CCHP system. Reduced first cost would make an owner/occupant more likely to purchase a CCHP system, which would help refine the technology to the level of relatively simple boilers and chillers and make it more robust. An additional objective is the reduction of operating costs by making maximum use of the fuel energy going into the prime mover (engine, microturbine, etc.). This would include the electrical energy for office equipment and lighting, high temperature heat for absorption chillers to make cooling, and low temperature heat for space heating, dehumidification, and domestic hot water. 19

20 2.0 Background Buildings account for approximately 40% of all primary energy consumption in the United States, and consume about 70% of the electricity [6]. Furthermore, approximately 57% of that electricity is generated using coal [7]. These coal power plants use what is called a Rankine cycle process which entails burning coal in a boiler, to generate steam. That steam passes through a turbine, which turns a generator. The first steam power plants in the 1880s had an efficiency of approximately 8%, or in other words 8% of the heat of combustion of the coal was converted to electrical energy, the rest was rejected as heat to the surroundings [7]. Steady increases in conversion efficiency occured through the 1960s, but have peaked at about 35%; the other 65% of the energy is still lost as heat [8]. In the early 1880s, Thomas Edison realized this large inefficiency and sold the heat to neighboring buildings in a successful effort to increase his bottom line [8]. In a sense, the first Edison steam plants were combined heat and power (CHP) plants. The same is true today of CHP plants. Heat that is normally rejected can be recovered from exhaust gases and coolant and applied in a useful way. This can improve the efficiency of power generation facilities from 35% to over 80% [9,10,11,12,13]. This improvement in efficiency reduces the overall demand for fuel and green house gas emissions. 2.1 DG & CHP Principles Distributed generation (DG) is simply defined as any electrical generating source with a capacity of less than five megawatts. Combined heat and power (CHP) is defined as the 20

21 simultaneous production and use of electricity and heat from a single fuel source. This concept can be applied to large and small generating facilities. Another term used for CHP is cogeneration. Also, sometimes cooling is added to the acronym resulting in combined cooling heating and power (CCHP), or trigeneration. Figures 1 and 2 show how electrical power is typically generated in the U.S. As shown in Figure 1, the largest energy flow is the conversion losses seen at the top. Figure 1: U.S. Electrical Energy Flow for Large Central Plants (Quadrillion BTUs) [2] In Figure 2, the recoverable conversion losses are highlighted along with the transmission and distribution losses which are avoided by producing electricity locally. 21

22 Figure 2: Energy Flow for Distributed Generation with Heat Recovery (Quadrillion BTUs) (Adapted from Reference 2) The amount of heat recoverable heat varies depending on the building loads; however the goal of CHP systems is well described. 2.2 Fuels There are many fuels available for the operation of CHP systems including: natural gas, petroleum products (gasoline, Diesel, etc.), biomass (biogas, biodiesel, ethanol, solids), coal, and waste fuels (waste coal, garbage, etc.). Many of these fuels are associated with a particular type of prime mover and vary in energy content, cost, availability, and emissions. Natural gas is by far the most common fuel type accounting for about 75% of all CHP systems in operation in the U.S. [14]. The reason for this is that the fuel is readily available with a nationwide distribution network, the cost per unit of energy is relatively 22

23 low, and the emissions are relatively clean. However, it should be noted that while the cost of natural gas is relatively low as compared to many other common fuels, the price is very volatile making operating costs projections problematic. Diesel fuel is the most common petroleum product used for CHP systems as Diesel engines provide a high electrical efficiency. Furthermore, Diesel fuels can be stored relatively easily adding a margin of security in case of a power outage, which may also affect the flow of natural gas. The cost is relatively high as Diesel fuel for CHP applications must still compete with Diesel fuel used for transportation, which is on average three times as expensive as natural gas per unit energy. Renewable fuels such as biomass are gaining market share due to their emissions characteristics and public appeal. Biomass can come in a gaseous, liquid or solid form. Biogas often comes from landfills and waste water treatment facilities. The first cost of treatment systems for the fuel is high; however operational costs are very low. Biogas is typically difficult to distribute, therefore it is often used on site or in nearby locations. Biodiesel on the other hand has a growing distribution network yet is being primarily used for transportation rather than power and heat generation. Biodiesel is typically made from soybean oil in the U.S., but can be made from many different plant oils and animal fats. The cost is relatively high as biodiesel is primarily used as a transportation fuel and does divert feed stocks from the food supply. 23

24 Ethanol, which is typically made from corn is the most common liquid biofuel in the U.S. and is typically used for transportation, but would work in gasoline fueled engine generators that have been modified to operate with E85, or a gasoline-ethanol mixture that is 85% ethanol. Corn based ethanol is a controversial fuel, which may or may not provide energy independence or a net energy gain, as well as diverting a food source to fuel production. Ethanol from cellulose (corn husks, grass clippings, etc.) may solve the issue of diverting food production to fuel production and would be relatively inexpensive, however cellulosic ethanol is not commercially available yet. Finally, ethanol is a problematic fuel from an engineering point of view. Ethanol is hygroscopic, meaning it absorbs water, it has a relatively low energy density, and requires the modification of engines to run on E85. Cellulosic butanol may be the best of both worlds providing a fuel that is very similar to gasoline in energy density and performance, while not requiring engines to be significantly altered [15]. Cellulosic butanol is still in the laboratory scale development and will not be commercially available for several years. Solid fuels, referred to as biomass include wood chips, saw dust, grass clippings and any other solid biological material can be burned in an incinerator to generate steam and drive a turbine to generate electricity. Biomass is considered a relatively crude fuel and is somewhat difficult to distribute, however it is usually inexpensive. The emissions vary, and care must be taken when using biomass to fuel a CHP system, but it can be clean. Coal is typically used in larger CHP systems and carries with it negative emissions characteristics including high CO 2, particulates, SO 2, NO X, heavy metals, etc.. However, 24

25 the distribution system is relatively good and the cost is relatively low and steady. The emissions characteristics of coal systems are highly regulated by the EPA and getting permits may be difficult, especially in urban environments. Finally, waste fuels such as waste coal, garbage and heavy oils can be used in CHP systems; however such systems typically require significant emissions controls. Garbage presents an interesting challenge as the actual fuel composition on site is unknown; however it can be successfully implemented in a CHP system. For example, the Hennepin Energy Recovery Center in downtown Minneapolis, MN burns garbage providing electricity and heat to the downtown area [16]. 2.3 Energy Grids There are several types of energy grids, most commonly the electric utility grid. This grid is nationwide and offers some flexibility to operators of CHP systems. Each utility grid operator has different sets of rules and regulations; therefore it is important to contact the utility when considering the installation of a CHP system. Thermal grids are sometimes available for CHP operators such as steam, hot water and chilled water. These grids can provide sources and sinks for thermal energy. Energy grids enable CHP operators to manage both excess and shortages of energy. Buildings typically have varying loads over the course of a day as occupants come and go and as the weather changes. Furthermore, various energy loads may not be coincident. There may be a large electrical load and a low heating load during the day as the sun is 25

26 shining and people are present on a fall day. However at night, the temperature drops and additional heating is required but there is little demand for electricity. CHP systems tend to operate better with steady conditions simultaneously generating electricity and heating that should be used. Some energy grids allow CHP systems to operate flexibly giving and taking a variety of forms of energy as they are needed or not needed depending on the regulations set by the primary grid operator. Furthermore, energy grids provide a great backup source of energy in case the CHP system fails. Energy grids found on college campuses are particularly effective, providing electricity, heating, and cooling to a mix of institutional and residential applications. As students are preparing for the day they are using energy in their dormitories, then they move to laboratories, classrooms, and offices and continue to use energy. In the evening they return to their dormitories to study, eat dinner, and enjoy recreation, all of which can use the same CHP system. 2.4 Prime Movers Prime movers are defined as the device that consumes the fuel, delivers power, and rejects heat; such as a boiler with a steam turbine, a Diesel engine, or a gas turbine Central Power Plants Many central power plants are of the boiler steam turbine type and burn coal to generate steam in a boiler, and then send that high pressure steam through a turbine to generate electricity. Furthermore, these central power plants typically have very large 26

27 generating capacity, in excess of 500 MW and sometimes greater than 1,000 MW. The efficiency of these plants appears to have reached a maximum at about 35%, although 38% efficiency is possible with very sophisticated and expensive equipment [8]. Nuclear power plants operate in a similar way with the exception of using enriched uranium as a fuel to provide heat rather than coal. Note, a combination of boiler and steam turbine can be used on a smaller scale, and are often used with low grade fuels making them cheap to operate Boilers and Steam Turbines The combination of a boilers and steam turbines is an effective way of using low quality, inexpensive fuels such as biomass and waste fuels to generate electricity and heat. The electrical efficiency of these systems is relatively low, 10% to 15%; however a lot of low quality steam is available for a variety of applications. The emissions generated from this type of system vary, and will require detailed study for permitting. These systems come in a variety of sizes, typically 100 kwe and up Gas Turbine Gas turbines for power generation typically use natural gas, however examples of turbines using kerosene, jet fuel, biogas, and biodiesel among others can be found. Gas turbines come in a variety of sizes from 30 kw up to 50 MW. The efficiencies of gas turbines can vary based on the technology used. A simple gas turbine can have an electrical efficiency as low as 15%, but as high as 45% [8]. This difference is primarily based on the use of a regenerator to preheat incoming air or the use of a combined cycle 27

28 process that captures waste heat to generate steam and drive an additional turbine. Distributed Generation systems typical operate around 15-25% electrical efficiency Internal Combustion Engines Internal combustion (IC) engines can use multiple types of fuel but typically use natural gas, Diesel, or gasoline for operation. Biodiesel and biogas have also been frequently used, but are much less common. Efficiencies also vary for reciprocating engines based on the technology but a natural gas fired IC engine would have a high efficiency of 25%, whereas a very efficient Diesel engine can reach an efficiency of 40% Fuel Cells Fuel cells have taken on a variety of forms, fuel types, and efficiencies. While fuel cells are arguably the most efficient form of generating electricity, the high cost both in raw materials and manufacturing has not allowed them to become a mainstream prime mover in the last century. Therefore, fuel cells will not be considered in this paper as possible DG source, although the future potential of this technology is considerable Prime Mover Summary In a CHP system it should be noted that none of these prime movers is inherently better than another on an energy basis. If each CHP system achieves an efficiency of 80%, then the factors that vary are the proportion of electricity to heat, and the ability to use the various fuels effectively. As the goal is to use as much reject heat as possible, a CHP operator will have to be aware of many issues, including how much heat and electricity are demanded by the building and its surrounding facilities and how much is available and in what forms. First costs, cost of fuel, cost of heat and electricity, and maintenance 28

29 costs will all vary and need to be accounted for. Also, while there isn t necessarily a cost associated with emissions, this too may be regulated in the future. Furthermore, the EPA has designated some locations as non-attainment zones for sulfur oxides, nitrogen oxides, and particulates, etc. that may have a mitigation cost associated with it. A summary of prime movers, fuels, and performance is shown in Table 1. Prime Mover Boiler + Steam Turbine Fuels Electrical Efficiency Nat. gas, coal, waste fuels, biomass % Recoverable Heat CHP Efficiency Heat to Power Ratio % low quality steam % 4.3 Gas Turbine Natural gas, biogas % % 600 o F exhaust % 2.8 IC Engine -Diesel Diesel, biodiesel % % 190 o F coolant, % 900 o F exhaust % 1.6 -Spark Gasoline, E85, natural gas % % 190 o F coolant, % 900 o F exhaust % 2.0 Fuel Cell -SOFC Natural gas % % 500 o F exhaust % 0.8 -PEM Hydrogen % % 300 o F exhaust % 0.8 Table 1: Prime Mover Performance Summary 2.5 Heat Loads The earliest use for reject heat from power generation facilities was in the 1880s with Thomas Edison s Pearl street power plant in New York [8]. The plant was only about 8% efficient and Edison recognized that he could improve his bottom line by selling the excess heat to neighboring buildings in the winter for space heating [8]. Over the last century additional uses for reject have been found and implemented to varying degrees around the world, many of which are found in the Intelligent Workplace. Reject heat temperatures vary greatly depending on the type of prime mover; however ball park temperatures are available. A Diesel engine would supply exhaust at 29

30 temperatures in excess of 900 o F (482 o C) and coolant at 195 o F (91 o C). A microturbine might provide exhaust around 600 o F (316 o C). All of these heat sources provide a high enough temperature for many applications, which will be discussed below Space Heating Space heating is probably the most common application for reject heat utilization. This heat can be utilized using radiant and convective systems typically found in many buildings. Space heat is particularly effective as the temperature is relatively low with a wide range of useful temperature possible. Operating temperatures range between 90 o F (32 o C) for the radiant surfaces in the Intelligent Workplace to 120 o F (49 o C) common for air handling units Absorption Cooling A heat pump is a technology that enables the transfer of heat from a low temperature to a high temperature [17]. Heat pumps can be mechanical driven using electricity and a motor or by heat. Absorption chillers are heat driven heat pumps [17]. Absorption chillers come in three common types based on the type of refrigerant that they use; ammonia and water, lithium-bromide and water, and lithium-bromide, water, and hydrogen [17]. The types of chillers used as part of IWESS are both lithium-bromide and water. Furthermore, different configurations of absorption chillers are available; single effect, double effect and triple effect [17]. The higher the number of chiller stages, the higher the overall efficiency [17]. However, the control system becomes more expensive and there is an increased cost per unit of cooling. A typical single effect chiller will have 30

31 a coefficient of performance (COP) of around 0.5 to 0.7, whereas a double effect chiller can reach a COP of 1.2. It should be noted that normal chillers have a COP of 3.2 on average or greater [18]. However, the electricity used to drive the chiller must be paid for, whereas the heat used to drive the absorption chiller is nearly free in the form of solar energy or engine exhaust as demonstrated in the IWESS project Desiccant Regeneration A common method of humidity control in buildings is to cool incoming outside air to a temperature at which the water vapor in the air condenses and is removed from the air stream, and then to reheat the air to the desired set point temperature. Needless to say this is an energy intensive process that can be accomplished more efficiently using a desiccant to absorb moisture [19]. As the desiccant absorbs water from the incoming air it becomes saturated overtime. Therefore, the desiccant needs to be regenerated using a hot air stream, which could come from a natural gas burner as is presently the case in IWESS or from a hot water heating coil in the future [19] Other Heat Loads There are many other places to utilize waste heat such as domestic hot water, which is found in almost every building. Additional heat demands include, but are not limited to; heating pools, drying laundry, process energy, and thawing sidewalks and streets as is done at Sierra Nevada College in Incline Village, Nevada. Research is being conducted 31

32 into additional usages of reject heat; however the ones stated above are currently employed Storage As discussed in section 2.3 CHP systems tend to operate best in steady modes while buildings operate in dynamic modes. When an energy grid is not available to import and export energy, storage is an option to be considered by the engineer. While the electric grid is almost always available, banks of batteries have been used for electrical storage as well as using electrical resistance heaters to generate hot water or vapor compression chillers to generate chilled water. Thermal storage is most commonly used for domestic hot water in most businesses and homes. The same concept can be used for chilled and hot water, which can provide a buffer between the CHP system s outputs and the buildings demands. Based on the loads an engineer must decide if storage should last for an hour or a day or longer. Ice storage is a common way of storing large amounts of cooling energy. An absorption chiller can be used to generate ice, however it must be an ammonia water chiller as lithium-bromide absorption chillers can only achieve a minimum of 3 o C, which is insufficient to create ice Heat Loads Summary As stated in the previous section that there are a number of possible heat sinks that can provide a use for reject heat from a CHP system. The overall goal is to have a steady demand for heat year round, which improves the economics of the CHP system. Some technologies are applied year round, some in a heating season and some in the cooling 32

33 season; it is up to the CHP system designer to use the given building and site loads to find the proper balance. 2.6 Existing Packaged Systems There are a number of packaged units with varying degrees of integration. Some manufacturers only provide a packaged generator set (prime mover plus generator with controls). Additional equipment such as automatic transfer switches and soft load controllers allow the engine generator to provide backup power and/or operate in parallel with the utility electric supply. Soft load controllers are rarely included in the packaged engine generator sets. Integrated heat recovery is found in some 60 and 65 kwe Capstone microturbines as well as many Schmitt Enertec units [20, 21]. Capstone has the majority of the microturbine market in the U.S. as they offer a compact, low maintenance system with a small enough electrical output to open a large market. The Capstone units have a sophisticated onboard diagnostic system that enables remote diagnosis of faults and speeds repairs. United Technologies Carrier has put together a CCHP system with grid paralleling capabilities. This system can combine four to six 60 kw Capstone microturbines with a direct fired absorption chiller. The system can be shipped loose or as a skid mounted package. Furthermore, parallel grid connection control capabilities exist [22]. A search of Ingersoll Rand s website yielded little in the way of packaged systems. It does mention that Ingersoll Rand microturbines have been used in CHP systems. 33

34 Furthermore, Trane, recently acquired by Ingersoll Rand, makes mention of possible CHP applications for their packaged absorption chiller units yet there is no combination available at this time [23]. The Baldor unit installed at CMU uses a John Deere Diesel engine, a Stamford generator and an Intelligen controller. All of these pieces were purchased by Baldor, assembled on a skid and shipped to CMU. Typically the unit also includes a radiator from ITT for rejection of heat from the engine coolant; however, a special request was made to separate the unit from the engine [13]. Units similar to the Baldor package are available from several integrators, including Kohler Power Systems, Cummins, Caterpillar, Kato, and Generac to name a few. Some of these companies develop and use their own engines in their generator sets, while others select engines from the dozens of Diesel, gasoline, and natural gas engine available on the open market. 2.7 Case Studies There are literally thousands of DG, CHP and CCHP systems installed throughout the U.S. varying in size from a few kilowatts to multi-megawatt systems. Many of these systems are registered in the U.S. CHP database, which outlines location, owner/operator, installation year, prime mover, capacity, and fuel type [24]. The database was searched for units with a capacity of less than one megawatt and fueled with biomass (biogas, biodiesel, ethanol, etc.). Sixty-six systems have been identified. 34

35 Most of these systems use waste from food processing, waste water treatment, or other agriculture processes that is generated and used on site in reciprocating engines. This is logical as the fuel for the prime mover would be free other than the fuel treatment costs. There are only three examples of biomass fueled units being operated on non-locally sourced fuel, two of which are on the campuses of the University of Montana in Missoula and California Polytechnic State University in San Luis Obispo and one at a local utility in Perry, New York. Two biogas units, one a 30 kw microturbine and one a 30 kw reciprocating unit, both with a custom heat recovery system are installed and are being operated in Sun Prairie, Wisconsin at a waste water treatment facility [25]. These units have operated for several years and have different operating characteristics. The reciprocating unit needs more maintenance in the form of oil changes, general inspections, and requires a complete rebuild after 8,000 operating hours. The microturbine has an onboard diagnostic system, which detects faults and has a lifetime of 40,000 hours before needing replacement. Furthermore, the first cost of the microturbine is about 20-50% higher than the reciprocating unit. Both operate with a plant efficiency of about 80%, yet the proportion of electricity generated by the reciprocating engine is higher than for the microturbine. The majority of DG, CHP, and CCHP units are natural gas fired as there is little that has to be done to provide fuel for the prime mover other than piping, which simplifies the work for the operator of the system. A 60 kw microturbine was installed by the City of Milwaukee, Department of Public Works to examine the potential economic benefits of 35

36 CHP systems. At the time of the installation an integrated heat recovery system was not available, which led to difficulties in the controls of the system. The heat recovery unit suggested by the manufacturer of the microturbine did not communicate using the same protocol, making analysis and more importantly control of the heat recovery unit difficult. A custom solution had to be developed by the engineering staff to rectify this issue, which the manufacturer has now solved by offering a unit with integrated heat recovery. In 2007, a 240 kwe CCHP system was installed at the University of Toronto at Mississauga, Canada and has been operated for nearly two years [26]. The system studied was a four microturbine system with a double effect absorption chiller system designed by United Technologies Carrier as mentioned in section 2.6. The system was a turn-key contract in which the manufacturer provided all the parts, services, and installation required to operate the system. It is not explicitly stated in the case study how the components of the system were delivered or assembled, however, based on the provided images; the major components (microturbines and chiller) are mounted on a concrete pad and not on a single skid. This implies that each piece was shipped loose and mounted on site. Furthermore, the case study does not state whether or not a grid interconnection system was included or if that had to be purchased separately. 36

37 3.0 IWESS Components and Subsystems Three components of the IWESS will be integrated in this dissertation including the biodiesel fueled engine generator with heat recovery, the steam driven double effect absorption chiller, and the ventilation system with enthalpy recovery and solid desiccant dehumidification. Each piece of the system will be assessed in the following sections with the goals of: describing the components of the system, noting the inputs and outputs, describing the operation of the system, and describing how these three systems could be integrated. 3.1 Biodiesel Fueled Engine Generator with Heat Recovery The biodiesel fueled engine generator with heat recovery system has been operating for over a year achieving a maximum efficiency of 76%, and efficiency comparable to other CHP systems System Components There are four major components in the biodiesel CHP system: engine generator, steam generator, coolant heat exchanger, and automatic transfer switch (ATS) / soft load controller (SLC) shown in Figure 3. 37

38 Figure 3: Basic CHP Flow Diagram Expanding upon Figure 3, Figure 4 shows the complexity of the CHP system with parts from no less than twenty-three direct suppliers, manufacturers, and integrators. Furthermore, this list does not include the installers for the piping, placing the equipment, masonry work, electrical connections, instrumentation, and programming. 38

39 Biodiesel Fill Station 2 Fuel Tank 2 Diesel Fill Station 1 Fuel Tank 1 Motor Valve 5 Valve 6 Motor VFD Coolant Heat Exchanger Radiator Fan Motor Fuel Pump 1 Day Tank 1 Fuel Pump 2 Day Tank 2 Air Muffler Blowdown Separator Motor Pump Valve 4 Motor Motor Valve 3 Engine-Generator Engine Turbocharger Steam Generator Starter Generator Controler Steam Generator Bypass Tee Control Column Back Pressure Valve Automatic Transfer Switch Motor Valve 2 Motor Valve 1 Steam Converter Campus Steam Grid Absorption Chiller Electric Grid Intelligent Workplace Mullion Fan Coil Radiant Panel Supplier/Manf/Integrator Baldor John Deere Stamford Intelligen ASCO Vaporphase Kickham Broad ITT Pryco Magnetek BorgWarner Belimo Bell & Gossett Highland Tank Marathon Penn Separator Corp. Thermoflo General Electric Siemens Nelson Pomeco OPW Marathon Electric Feed Water Valve Cool Wave Figure 4: CHP System Components Condensate Pumps (2) Motor (2) Condensate Receiver w/ Controller The engine generator is a standard engine generator assembled by Baldor Electric Company shown in Figure 5. It uses a 43 hp (33kW) four cylinder, 2.4 L John Deere Diesel Engine and a Stamford, Inc. generator. It includes a standard engine generator controller made by Intelligen, Inc. Figure 5: Baldor Engine Generator 39

40 The engine generator is connected to the grid via an ASCO 7000 automatic transfer switch (ATS) and soft load controller (SLC) shown in Figure 6. The ATS/SLC allows the engine generator system delivers excess power to the grid during operation, while allowing the grid to power the mechanical room when the system is offline. The operation of the ATS/SLC is fully automated, and once a power level is set and the start command given, the engine generator is started and paralleled to the utility in less than five seconds. Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kwe. 40

41 The steam generator made by Vaporphase, Inc. shown in Figure 7 is essentially a double pass fire tube boiler without a burner. In lieu of a burner, the high temperature exhaust is routed from the engine to the steam generator. The steam generator also acts as an exhaust silencer, however the silencing effects are lost if the exhaust is bypassed; therefore an extra muffler has been installed. Steam is generated at 87 psig (6 bar) in the summer at 68 pounds per hour (31 kg/hr) for the absorption chiller and at 30 psig (2 bar) and 65 pounds per hour (29 kg/hr) in the winter, spring, and fall for space heating the IW and exporting the campus steam grid. Figure 7: Assembled Components: Engine Generator (Left), Steam Generator (Right) It should be noted that while there is about 18 kwt of heat recovered from the exhaust, the system is greatly oversized and can handle up to 250 kwt of heat transfer. This unit was selected because it is the smallest commercially available exhaust heat recovery 41

42 steam generator. A steam generator was required for this project as the absorption chiller used in this project is steam driven. For new systems, direct firing of an absorption chiller and high pressure hot water heat recovery can be considered to achieve space and cost savings. To deliver hot water to the IW, a steam hot water converter is used that can use steam from the steam generator or the campus grid. The converter is shown in Figure 8. Figure 8: Steam - Hot Water Converter The coolant heat exchanger shown in Figure 9 is a standard plate and frame heat exchanger made by ITT, Inc. The heat exchanger operates in parallel with a standard 42

43 engine generator radiator, which has been removed and sits outside of the mechanical room shown in Figure 10. Figure 9: Coolant Heat Exchanger with Piping before Insulation 43

44 Figure 10: Remote Mounted Radiator There are several control loops within this CHP system that allow for robust control of the system while also assuring safe operations. The engine controller monitors status, power level, oil pressure, coolant temperature and level, battery conditions, etc. on an engine mounted interface shown Figures 10 and 11. Figure 11: Engine Generator Onboard Interface 44

45 Figure 12: Engine Generator Onboard Interface The Soft Load Controller (SLC) and the Automatic Transfer Switch (ATS) takes over control of the governor in the engine, which was initially controlled by the Intelligen controller to vary the speed to aid in paralleling the engine to the grid. The SLC/ATS monitors the grid s voltage and phase so that the generator output frequency, phase, and voltage match the grid. The SLC/ATS monitors any disruptions in the grid or the engine and protect either the grid or the generator from severe damage. If there is a failure the ATS/SLC will separate the engine generator from the grid and will send a shutdown order to the engine. The engine will continue to operate for five minutes powering lights, ventilation, etc. so that occupants have enough time to vacate the lab. Then the engine will go into its standard shutdown procedure, which includes a five minute cool down. The steam generator has its own stand alone pneumatic control system that has three principal tasks. First, it makes sure that the steam generator does not run dry as hot exhaust gases can warp the coils if the heat is not dissipated. It can call for makeup water 45

46 based on the output of a low level alarm and if makeup water is not available, it will bypass the exhaust around the steam generator. The second task for the pneumatic controller is to maintain the set point pressure inside the steam generator using a back pressure control valve. The steam pressure is measured inside the steam generator and downstream from the back pressure valve. If the pressure inside the steam generator drops below the set point, the back pressure control valve will restrict the flow of steam until the pressure rises again. The purpose of this controller is to prevent a sudden drop in steam pressure, which can cause the steam generator to implode. The third task is to match heat input to the output steam flow. The exhaust gas flow to the steam generator is modulated by the bypass control valve to maintain a set point pressure of the output steam flow. This arrangement allows the steam generator to operate at partial loads, while the engine operates at full power. The control of the steam is accomplished through a series of two position valves and pressure reduction valves. During the summer, two two-position valves block flow to the grid/hot water converter and route the steam flow to the absorption chiller. During the rest of the year the flow to the chiller is blocked and directed towards the grid and hot water converter. A pressure reduction valve reduces the steam supply pressure to the hot water converter to 9 psig (0.6 bar) and the steam from the grid is reduced to 7 psig (0.5 bar) with another pressure reduction valve. The steam from the CHP system is prioritized over the steam from the grid because the 9 psig steam will prevent the 7 psig pressure 46

47 reduction valve from opening as the pressure on the outlet side is too high. If there is a short fall of pressure from the CHP system, the steam grid will start to makeup the difference once the pressure falls below 7 psig (0.5 bar). Schematics from the steam system are shown in Appendix A. The coolant system controller is designed to prevent the engine from over-heating. This is accomplished by removing heat either through a plate and frame heat recovery exchanger or a remotely mounted radiator with a fan. The coolant controller has two modulating valves which allow the controller to proportion flows to control the amount of heat removed. This arrangement allows the engine to operate at full power, while only recovering a portion of the coolant energy. This controller is a part of the overall Webbased building automation system (BAS). The BAS operates the overall dispatch of the CHP system and logs all of the sensor data. The previously mentioned controllers all function together to allow the system to address varying thermal and electrical energy demands Input / Output The Inputs for this system include: fuel (Diesel or biodiesel) air (fresh air for combustion) condensate hot water return 47

48 The outputs for this system include: electricity (208 V, 3 phase) exhaust steam hot water data (Modbus, 4-20mA, 0-5 V converted to BACNET and available on the web) Data inputs and outputs from sensors and actuators in the heat recovery system are compiled in the Automated Logic web based user interface shown in Figure 13. Figure 13: Automated Logic CHP User Interface for the Heat Recovery/Rejection System Operating Description and Results The core of the biodiesel fueled engine generator with heat recovery is the engine generator, which burns fuel in order to generate electricity which is sent to the grid, and 48

49 generates heat in the forms of high temperature exhaust at 160 o C (360 o F) and lower temperature engine coolant at 90 o C (190 o F). The high temperature exhaust can be rejected to atmosphere or recovered using a steam generator, which can generate steam at varying pressure levels. The steam can be used to heat the IW in the winter or drive an absorption chiller in the summer. Furthermore, the steam system is connected to a campus grid system, which allows for excess steam to be exported to the grid. The coolant energy is recovered through another heat exchanger to heat water or rejected through a radiator. The hot water is used in the winter for space heating in the IW. Tables 2 through 4 show the compiled commissioning and experimental results, from the operation of the engine generator, the heat recovery systems (exhaust and coolant), and the integration with the Intelligent Workplace and campus systems. The engine was operated at various loads and conditions for over 400 hours as shown in Appendix B. Summer CHP Diesel Results Power Output (kwe) Fuel Input (kwc) Plant Power (kwe) Coolant Heat Recovered (kwt) Exhaust Heat Recovered (kwt) CHP Efficiency % % % % Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results Winter CHP Diesel Results Power Output (kwe) Fuel Input (kwc) Plant Power (kwe) Coolant Heat Recovered (kwt) Exhaust Heat Recovered (kwt) CHP Efficiency % % % % Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results 49

50 Winter CHP Biodiesel Results Power Output (kwe) Fuel Input (kwc) Plant Power (kwe) Coolant Heat Recovered (kwt) Exhaust Heat Recovered (kwt) CHP Efficiency % % % % Table 4: Averaged Winter Biodiesel Experimental Results The results shown in Tables 2 through 4 show average plant efficiency between 47% and 76%, consistent with typical CHP efficiencies. There is a substantial fall off in efficiency as the power level drops, which indicates that the system operates more efficiently at full load than part load. This is not surprising as engine efficiency usually peaks at about 80% of the maximum engine rating, or 25 kwe of 33kWe. Furthermore, the power required to operate pumps and fans, plant power, remains constant, and becomes a larger percentage of the total power at the lower loads. 50

51 Engine: Measured Data versus Manufacturer s Specifications It has been difficult to precisely compare all of the engine s specifications with the measured data as the manufacturer s specifications are written for operation at 32 kwe, whereas the engine has been operated at part loads from 6 kwe to 25 kwe electrical. Note, the specification column is written for the maximum engine rating of 32kWe using No.2 low sulfur Diesel fuel. System Specification Data Notes Air System Max. temp. rise, amb. to inlet 15 F (8C) ~15 F Varies due to room air temperature Engine Air Flow 99 CFM (2.8 m3/min) 83 CFM at 25 kwe Steady increase in flow rate with power (6 kw = 64 CFM, 12kW = 68 CFM, 18kW = 74 CFM) Intake Manifold Pressure 9 psig (64 kpa) 0.4psi (6kWe), 0.9psi (12kWe), 1.6psi (18kWe), 2.3psi (25kWe) Fuel System Total Fuel Flow 185 lb/hr (84 kg/hr) NA The individual fuel flow meters do not provide independent outputs. Fuel Consumption (6 kwe) 4.7 lb/hr (2.1 kg/hr) 4.6 lb/hr (2.1 kg/hr) Verified with weigh tank measurement Fuel Consumption (12 kwe) 7.0 lb/hr (3.2 kg/hr) 7.9 lb/hr (3.6 kg/hr) Verified with weigh tank measurement Fuel Consumption (18 kwe) 9.8 lb/hr (4.4 kg/hr) 10.6 lb/hr (4.8 Verified with weigh tank kg/hr) measurement Fuel Consumption (25 kwe) 13.3 lb/hr (6.1 kg/hr) 14.1 lb/hr (6.4 Verified with weigh tank kg/hr) measurement Fuel Consumption (32 kwb) 17.9 lb/hr (8.1 kg/hr) NA Cooling System Engine Heat Rejection 1303 BTU/min (23 kw) 18 kw at 25 kwe Coolant Flow 24 GPM (91 L/min) 10.2 GPM Thermostatic Valve start to open 185 F (82 C) Thermostatic Valve fully open 201 F (94 C) Exhaust Exhaust Temperature 963 F (517 C) Max allowable back pressure 30 in-h2o (7.5 kpa) 930 F (499 C) at 25 kwe 14 in-h2o at 25 kwe Soft load controller will allow a maximum power of 25 kw Spec assumes radiator attached to engine Verified by comparing start of coolant flow and coolant temperature Verified by comparing by observing steady flow above 201 F Used a pressure gauge mounted between the engine exhaust and steam generator Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications 51

52 Table 5 shows that the measured data corresponds well to the manufacturer s specifications; however, there is a small margin of error. This margin of error probably comes from minor differences between engines during manufacturing and the sensors used by the manufacturer and the IWESS team during testing. Table 6 shows similar results to Table 5 for biodiesel fuel. System Specification Data Notes Air System Max. temp. rise, amb. to inlet 15 F (8C) Engine Air Flow Intake Manifold Pressure Fuel System 99 CFM (2.8 m3/min) 79 CFM at 25 kwe Steady increase in flow rate with power (6 kw = 64 CFM, 12kW = 68 CFM, 18kW = 74 CFM) 9 psig (64 kpa) 1.7psi (6kWe), 2.15psi (12kWe), 2.84psi (18kWe), 3.67psi (25kWe) Total Fuel Flow 185 lb/hr (84 kg/hr) No Measurement Available Fuel Consumption (6 kw) 4.7 lb/hr (2.1 kg/hr) Verified with weigh tank measurement Fuel Consumption 8.8 lb/hr ( lb/hr (3.2 kg/hr) (12 kw) kg/hr) Verified with weigh tank measurement Fuel Consumption 12.6 lb/hr ( lb/hr (4.4 kg/hr) (18 kw) kg/hr) Verified with weigh tank measurement Fuel Consumption 13.3 lb/hr ( lb/hr (7.3 (25 kw) kg/hr) kg/hr) Verified with weigh tank measurement Fuel Consumption 17.9 lb/hr (8.1 Soft load controller will allow a maximum power of NA (32 kw) kg/hr) 25 kw Cooling System Engine Heat 1303 BTU/min (23 Rejection kw) 16 kw at 25 kwe Coolant Flow 24 GPM (91 L/min) 10.2 GPM Spec assumes radiator attached to engine Thermostatic Valve start to open Thermostatic Valve fully open Exhaust Exhaust Temperature Max allowable back pressure 185 F (82 C) 201 F (94 C) 963 F (517 C) 30 in-h2o (7.5 kpa) 890 F (477 C) at 25 kwe 14 in-h2o at 25 kwe Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications Verified by comparing start of coolant flow and coolant temperature Verified by comparing by observing steady flow above 201 F Biodiesel experiments only conducted during winter at this time, may cause low temp. Used a pressure gauge mounted between the engine exhaust and steam generator As shown in Tables 5 and 6, the primary difference between Diesel fuel and biodiesel fuel is that the fuel flow rate is greater for biodiesel fuel. The reason for this is that the energy density of biodiesel is lower than Diesel fuel, thus the engine controller naturally 52

53 increases the fuel demand to meet power demand. As the engine operates below its maximum, prime power operation, the fuel pump has no problem meeting this challenge Pressure Time Crank Angle Measurements Pressure sensors have been installed in each engine cylinder to obtain information on how the combustion process changes when using different fuels. In combination with a crank angle encoder, the pressure measurements are collected using a high speed data acquisition system, and plotted as shown in Figure 14. Figure 14: Pressure vs. Time for One Cylinder at 12 kwe using Low Sulfur Diesel Fuel 53

54 Figure 14 shows the pressure vs. crank angle curve, and shows injection combustion taking place around top dead center (TDC). Figure 15: Pressure vs. Time for One Cylinder at 12 kwe using Low Sulfur Diesel Fuel As can be observed in Figure 15, the wave forms shifts from injection and combustion at TDC to a delayed combustion of about 15 degrees after TDC. The effect of a delayed combustion is that the peak combustion temperature is reduced. The purpose of reducing the peak temperature is to reduce NO X formation to meet U.S. Environmental Protection Agency regulations. An additional effect of this control strategy is the reduction of engine capacity and efficiency. Further analysis on these wave forms is under way to compare the performance of the various fuels. 54

55 Turbocharger Analysis The engine s turbocharger was completely instrumented with temperature, pressure and flow sensors. The data collected from the turbocharger indicates a mass flow rate of kg/sec and a maximum compression ratio of 1.25 at 25kWe. These data are plotted in Figure 16, the compressor map provided in by the turbocharger manufacturer. They show that this turbocharger is not suited for this engine operating under the specified conditions. Figure 16: Turbocharger Compressor Map [27] It should be noted, that while the turbocharger is not effective for the duty cycle of this engine, it may operate more efficiently at 33 kwe, the power level for which the 55

56 turbocharger was designed. CHP system designers should be aware of this fact and request a turbocharger that will operate more efficiently in the appropriate range Combustion Gas and Emissions Analysis Emissions of gas-phase pollutants [carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen dioxide (NO2), nitrogen oxide (NO), unburned hydrocarbons (UHC), and oxygen (O2)] have been measured over four loads using both low sulfur Diesel fuel and soy based biodiesel fuel. Load (kwe) % O2 % CO % CO2 UHC (PPM) NO (PPM) NO2 (PPM) Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel Load (kwe) % O2 % CO % CO2 UHC (PPM) NO (PPM) NO2 (PPM) Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel The data in Tables 7 and 8 agree with published results [28, 29, 30] with significant reductions in CO, and UHC. However, typically soy based biodiesel generates more NO X, and the averaged data does not reflect that. The NO X emissions for this engine are reduced due to the engine timing adjustments to meet emissions requirements, which may account for the similar levels of NO X. Further research into the emissions is warranted if 56

57 large scale use of biodiesel in CHP systems is to be achieved as emissions must be understood to meet EPA regulations. A combustion analysis has been conducted for the engine generator operating at 25 kwe using Diesel fuel. The stoichiometric material balance for Diesel fuel. C O2 3. N2 bco2 ch 2O dn2 12H 23 a 76 C: 12 = b(1) b = 12 H: 23 = c(2) c = 11.5 O: a(2) = b(2) + c(1) 2a = 2x = 35.5 a = N: a(3.76)(2) = d(2) d = 66.7 C O2 3.76N2 12CO2 11.5H 2O H N Determine the molar air to fuel ratio. AFR moles O moles _ N mole _ Fuel _ Determine quantity of excess air. 57

58 mair 165kg / hr AFRMeasured m 6.4kg / hr fuel MW AFRMeasured AFR Measured MW moles _ O2 moles _ N2 AFR mole _ Fuel EA AFR AFR Measured The material balance C Fuel Air O2 3. N2 aco2 bh 2O cn2 2 12H do C: 12 = a(1) a = 12 H: 23 = b(2) b = 11.5 O: 1.76 x x 2 = a(2) + b(1) + d(2) 62.5 = 2a + b + 2d 62.5 = d 27 = 2d d = 13.5 N: 1.76 x x 3.76 x 2 = c(2) C 235 = 2c c = O2 3.76N2 12CO2 11.5H 2O 117.5N H O The percentage of the emissions on a molar basis of O2 and CO2 and compare to the results in Table 7 on a dry basis. Calculated Percentage of CO 2 = 8.4% Calculated Percentage of O 2 = 9.4% 58

59 Both the CO 2 and O2 emissions are consistent with the measured data in Table 7. The heat release from the engine has been calculated. n h h Q f P R n W f n n CO f h P h R o o o o 2 h f h CO 2 n H 2O h f h H 2O n N 2 h f h N 2 no 2 h f h o o o h f N 2 N 2 O 2 f h n h f h n h f h O 2 O 2 The number of moles shown below and the necessary enthalpy values with the units of kj/kg-mol C O2 3.76N2 12CO2 11.5H 2O 117.5N H O h h h h h h P P P P R R ,520 31,1549,364CO ,820 27,1259, ,0858,669N ,8508,682O ,730CO ,599H 2O ,416N ,168 4,460,760 2,582, ,693, ,768 5,145,000.5kJ / kg mol 1 7,014,000 0f N O 2 7,014,000kJ / kg mol H 2O O2 59

60 f n m f MW f kg 6.4 hr kg 167 kg mol kg mol hr 5 kg mol sec W W Electric Generator 25 kwe 28.4 kj 0.88 sec Q W n f n f Q W n h f P h h h kj Q sec kj Q sec kj kj Q sec sec kj Q kWt sec P R R 5 5 kg mol kj 5,145, ,014,000 sec kg mol kg mol kj 1,868,999.5 sec kg mol The amount of heat captured by the heat recovery system is approximately 36 kwt from Tables 2, 3, and 4, which leaves about 12 kwt for radiant and convective losses to the space from the engine and losses in the pipes and heat exchangers, which is realistic Heat Recovery Analysis The steam generator and the coolant heat exchanger have been analyzed using temperature heat transfer or T-Q diagrams. T-Q diagrams are an effective way of describing the operation of heat exchangers by showing the stream temperatures versus 60

61 heat transfer between them. The required area for heat transfer between the streams, A, can be calculated from the following function: dq A, UT where U = heat transfer coefficient, dq = heat transfer, T = temperature difference between the two streams 1000 Steam Generate T-Q Diagram Temperature ( o F) Exhaust at 6 kwe Exhaust at 25 kwe Saturated Steam (87psig) Condensate Domestic Hot Water Heat Transfer (kwt) Figure 17: Summer Operation of the Steam Generator T-Q Diagram Figure 17 shows the T-Q diagram for the steam generator during summer operation with exhaust entering on the left at a high temperature. The heat in the exhaust is transferred to the water inside the steam generator, which evaporates at a rate of 65 lbs/hr (28 kg/hr) at 61

62 87 psig (6 bar) or 18 kwt. This steam generator uses a pool of water, which is directly replenished rather than preheating make up condensate, however condensate entering at 212 o F (100 o C) could be preheated. As shown on the right side of the T-Q diagram, additional energy is available from the exhaust which leaves the steam generator at approximately 360 o F (160 o C). Domestic Hot water is typically delivered at 140 o F (60 o C), and is supplied from city water at 50 o F (10 o C). Recovering additional heat from the exhaust (8 kwt) to heat domestic hot water represents approximately a 40% increase in the heat recovery potential, and would increase the CHP efficiency from 78% to 87%. However, the downside of reducing the exhaust temperature down to below 100 o C is that the moisture in the exhaust will condense, which can form rust in the exhaust pipes. Therefore, it is necessary to build these sections out of stainless steel. Additionally, Figure 17 shows the operation of the steam generator when the engine generator is operating at 6 kwe. The effect of operating at lower loads is that the exhaust temperature and flow rate are lower, thus reducing steam production. Figure 18 shows the T-Q diagram for the coolant heat exchanger during both summer and winter operation. Using engine coolant heat to heat the water used for space heating in the winter is somewhat problematic as the required temperatures are relatively low, which forces the temperature of the engine coolant to the relatively low temperature of 185 o F, where as an ideal temperature would be about 195 o F as shown in Figure 18. During winter operation the water side of the exchanger typical has a flow rate of four gallons per minute with an inlet temperature of 95 o F and an outlet temperature of 110 o F. 62

63 During the summer, a higher temperature is desired for the regeneration of a solid desiccant, and therefore a higher over all temperature is maintained. Coolant Heat Exchanger T-Q Diagram at 25kWe Temperature ( o F) Coolant (12 GPM) Summer Operation Water (12 GPM) Coolant (2 GPM) 110 Water (4 GPM) Winter Operation Heat Transfer (kwt) Figure 18: T-Q Diagram for Coolant Heat Exchanger at 25 kwe To remedy the relatively low coolant operating temperatures during the winter, two options exist. First, the water flow rate could be further reduced with an improved control system, which would shift the winter operation water line up to a higher temperature. The second, option is to bypass some of the water around the coolant heat exchanger essentially reducing the flow. The two flows would then be mixed and the desired temperature achieved Systems Integration Potential The CHP system is made up of dozens of components, which include four primary control systems: 63

64 engine generator automatic transfer switch / soft load controller coolant heat recovery steam generator As this system was assembled from disparate components resolving communications compatibility issues cost a lot of time and money. Integrating these controllers would reduce installation time and cost. Furthermore, it would simplify the operation of the CHP system as each controller has its own user interface. The heat recovery system captures reject heat from the engine and converts it to steam and hot water via to heat exchangers. The steam could be used in a double effect absorption chiller to provide cooling during the summer to a building. The steam generator in this CHP system provides saturated steam at 87 psig (6 bar) and 360 o F (160 o C), therefore the exhaust temperature is approximately 370 o F (165 o C). The remaining exhaust heat could be used to make domestic hot water at 140 o F (60 o C) or drive a single effect absorption chiller. The coolant energy could be used to drive the desiccant regeneration process of the ventilation system, which is necessary to provide dehumidified air to the IW. Alternatively, the coolant energy could be used to drive a single effect absorption chiller to provide additional cooling. 64

65 3.2 Steam Driven Double Effect Absorption Chiller Drs. Hongxi Yin and Ming Qu have both completed dissertations on the steam driven double effect absorption chiller and the solar thermal high pressure hot water driven double effect absorption chiller respectively. Each dissertation includes extensive descriptions of both their components and operation. These chillers were selected as models for this dissertation as they have both been previously tested and analyzed, both are on site to allow visual inspection, and both are very compact designs as compared to other manufacturer s models. The chillers are nearly identical except for the high temperature generator as one is designed for steam and the other is designed for high pressure hot water. Furthermore, the high pressure hot water unit includes an auxiliary natural gas burner System Components Figure 19 shows a complete cross section of the absorption chiller including the inputs and outputs of the system. The auxiliary equipment originally installed with this system will not be included as it was replaced by the CHP system. 65

66 Figure 19: Steam Driven Absorption Chiller Flow Diagram [31] This packaged system includes; the absorption chiller, cooling tower, control system, pumps, valves, and sensors. The same concept of creating a packaged system out of the chiller components is applied in packaging the biodiesel CHP system, absorption chiller, and ventilation unit Input / Output The Inputs for this system include: High pressure steam Chilled water return Electricity to operate pumps, fan, control system, etc. Treated water (for the cooling tower) The outputs for this system include: Chilled water supply 66

67 Water vapor (from cooling tower) Condensate Data 1 (Internal control system with separate display) Data 2 (4-20mA and 0-5 V converted to BACNET and available on the web) Finally, extensive information exists on the instrumentation used to operate and monitor the absorption chiller as shown in Figure 20. This information will be helpful in determining which points are necessary for operation. ALC control panel ME-LGR 25 Cable Cable T10 Controller T15 T16 Hot Humid Air L3 T14 SS T17 L1 T18 F6 P7 T25 P4 T22 F2 T7 SV P1 F6 2 1 WS F7 T29 P11 CTW T28 P10 3 Steam Supply P5 T23 Condensate BFT BFP T21 P3 T9 T2 CHWS T8 T11 ESB CR T13 T5 T19 Absorption Chiller CWBPV HWR TLHX Chiller control panel CHWS 5 Building CHWR CHWS Campus 6 CHWR HWS HWR 4 T0 H0 T6 RBPV L2 HWS L4 DV L5 DD RP RPH T30 P2 T20 F1 B1 T1 B2 SP T3 T CTV 7 City water F8 CHWR Timing water Empty City water CHWP CWV T12 CWP Air Chiller Chiller ALC inputs ALC Figure 20: Absorption Chiller Process and Instrumentation Diagram [31] Figure 21 shows one of the user interface screens for the absorption chiller system. 67

68 Figure 21: Automated Logic Absorption Chiller User Interface The chiller is a very compact unit with a width of 1,143 mm (45 inches) a depth of 660 mm (26 inches) and a height of 1,829 mm (76 inches). The unit does include onboard controls; however a separate panel is required for running auxiliary equipment. Much of this auxiliary equipment is not necessary when the unit operates in a CHP mode, and was only necessary during the stand alone testing phase of the project Operating Description and Results As shown in Table 9, the test program used by Dr. Yin varies five operational parameters and measures and calculates the effect on the chillers performance and capacity. 68

69 Table 9: Absorption Chiller Test Program and Results [31] The data in Table 9 provides the necessary information for creating an empirical operating model of the chiller, which can be integrated with the output of the steam generator from the CHP system. Figure 22 provides insight into the operation of the absorption chiller and shows how each component within the packaged absorption chiller operates versus cooling load. 32 Heat transfer on chiller component (kw) BPHX Cooling tower Absorber Evaporator HTRG LTRG Condenser HTHX LTHX HRHX BPHX Cooling tower Absorber Evaporator HTRG LTRG HTHX Condenser LTHX HRHX Actual cooling load (kw) Figure 22: Absorption Chiller Component Heat Transfers vs. Cooling Load [31] 69

70 The evaporator is where the cooling takes place and the primary heat input is into the high temperature regenerator (HTRG). The cooling tower shows how much heat is rejected to atmosphere and how much can be captured. These pieces of data further refine the simulation model and provide insight into what quantity of energy is required to operate the chiller, and how much energy is produced and rejected Systems Integration Potential Opportunities for improving the chiller system include integration of controls and recovering cooling tower heat. The control system requires several operational inputs that are also required for the heat recovery system which could be shared. Furthermore, a common control system would simplify writing control algorithms for automatic startup, operation and shutdown. As can be seen in Figure 22 about 28 kwt of low quality thermal energy is available at around 35 o C (96 o F) from the cooling tower, which would be sufficient for preheating domestic hot water during the summer as city water typically arrives at 13 o C (55 o F). Using a heat exchanger rather than a cooling tower would most likely save on first cost as well as operating costs as removing heat using a pump versus a fan is more efficient [32]. Finally, removing the cooling tower would also save on operating costs for cooling tower water and chemicals to treat the cooling tower water that is evaporated. 70

71 3.3 Ventilation System with Enthalpy Recovery and Solid Desiccant Dehumidification The ventilation system in the IW has operated for several years and employs both a passive enthalpy recovery wheel and an active desiccant dehumidification wheel to condition the air, as well as a heat pump for providing the required heating or cooling loads of the ventilation air. In her dissertation work at CMU, Dr. Chaoqin Zhai operated this piece of equipment and focused her work on the performance modeling of the desiccant wheel and its operation System Components The ventilation unit itself is an example of systems integration. The unit includes a fan for air handling, two energy wheels (one active, one passive), and a heat pump for primary heating and cooling. These subsystems are all operated by a single controller and are packaged by one company. The acceptance of these systems would be greatly reduced if building operators had to assemble them on site. Instead, the unit arrives on a single skid and only requires power, gas, and duct connections to operate. Figure 23: Plan View of Ventilation Unit [33] 71

72 The ventilation unit is also very compact. All of the components are placed inside with an overall width of 1,753 mm (69 inches) a depth of 737 mm (29 inches) and a height of 991 mm (39 inches). The integrated and packaged enthalpy recovery wheel, desiccant wheel, heat pump, and necessary controls needed to make this system work serve as an example for a systematic integration of the three IWESS components Input / Output The Inputs for this system include: electricity to operate fans, wheels and control system (208 V, 3 phase) outside air for ventilation, desiccant regeneration, and heat pump operation return air (from conditioned space) natural gas (for desiccant regeneration) The outputs for this system include: dehumidified ventilation air exhaust (from desiccant regeneration) exhaust air (from the heat pump) exhaust air (from the space) data (4-20mA and 0-5 V converted to BACNET and available on the web) While the same user interface capability exists for the ventilation system, there is no graphical interface like the CHP and chiller systems have in Figures 13 and

73 3.3.3 Operating Description and Results Figures 24 through 26 describe how the components of the ventilation system operate and how they affect each other. Figure 24: Interior View of the Ventilation Unit [33] Figure 24 shows the operation of the ventilation unit. 1. Outside air enters the unit (and mixes optional return air). 2. The outside air passes through the passive energy recovery wheel. 3. The air goes through a DX coil for cooling and moisture removal. 4. Part of the air passes through an active desiccant and is warmed and dehumidified by the desiccant wheel. 5. The warmer, drier air is mixed with the cool bypassed air and sent to the space at the set point humidity and temperature. 73

74 6. A separate outside air stream (regeneration air) is heated by a gas burner to regenerate the desiccant in the desiccant wheel, and is then rejected to atmosphere. The flow diagram shown in Figure 25 provides additional insight into how the ventilation system operates. Figure 25: Ventilation Unit Flow Diagram [33] Figure 26: Psychrometric Chart for Ventilation System Operation [33] Figures 27 through 29 were developed to show the cost and benefit of operating the ventilation system. 74

75 Figure 27: Enthalpy Removal Breakdown by Component [33] Figure 27 shows that the majority of the sensible heat removal is handled by the heat pump and then followed by the enthalpy recovery module. Nearly zero enthalpy is removed by the desiccant wheel, which makes sense as the moisture is removed by an adiabatic process and the temperature increases as shown in Figure 26. Figure 28 shows that the moisture removal by the active desiccant does account for 52% of the total moisture removal. Some moisture is removed at the heat pump by the DX coil due to condensation, and the remainder is transferred to the exhaust air as it picks up moisture from the enthalpy recovery module. Figure 28: Moisture Removal Breakdown by Component [33] 75

76 Finally, Figure 29 shows that the active desiccant module has the highest operating cost mainly due to the high cost of natural gas. Therefore, if reject heat were used to regenerate the desiccant rather than burning natural gas, the operating cost of ventilation system would decrease by approximately half. This represents a major opportunity for using reject heat from the CHP system. Figure 29: Operating Cost Breakdown by Component [33] The following has been quoted directly from Dr. Zhai s thesis justifying the feasibility of integrating the ventilation system with the CHP system. A procedure has been outlined to develop operating strategies for the active desiccant wheel integrated CHP system. The validated performance model has been applied in predicting the supply air conditions from the integrated system under different settings of the control variables. Performance maps that relate the supply air conditions and different settings of the control variables have been constructed for the proposed system in the IWESS project. These performance maps show that the desired supply air condition can be achieved with certain settings of the control variables, namely the regeneration air temperature, the regeneration air flow rate, the leaving DX air condition, the wheel rotation speed, and the bypass ratio. The settings of the control variables to achieve the desired supply air condition are not unique. It is an optimization problem to determine the control settings to achieve the lowest system operating energy consumption or cost, in which the system operating energy consumption or cost is the objective function, and different control factors are the variables. [33] 76

77 The detailed controls of this process are outside the scope of this dissertation; however, the plumbing, sensor inputs and outputs, and heat transfer calculations will be conducted to facilitate the integration Systems Integration Potential The desiccant wheel requires a large thermal input, currently in the form of natural gas combustion, to regenerate the desiccant wheel, which has become saturated from incoming air. The operation of the desiccant wheel contributes about 62% of the total operating cost of the ventilation system including the heat pump and the enthalpy recovery wheel [19]. In lieu of burning natural gas, it has been proposed to use coolant energy from the engine generator to regenerate the desiccant. This would reduce the operating costs by about 62%, as the reject coolant heat from the engine would be free minus the pumping power required to move the thermal energy from the coolant heat exchanger to the air to water heat exchanger mounted in the ventilation unit. The setup in the IW would not be ideal as there would be several hundred feet of piping required to move the heat from the engine to ventilation unit. This would be another reason for creating a compact packaged unit that would cut down on the overall piping length. The control systems could also be integrated to reduce cost and simplify operation. It so happens that the manufacturer for the ventilation controls is the same as the manufacturer for the supervisory controls and the ATS/SLC controls. A few sensors (two temperatures 77

78 and water flow) could be shared between the control system on the engine coolant side and the regeneration heat exchanger to reduce some first cost as well. Perhaps the largest first cost saving in creating an integrated CCHP/V package would be the replacement of the heat pump by a heated and chilled water coil as is also suggested by Dr. Zhai [33]. Detailed costs are not available at this time, but it is reasonable to assume that the first cost of a heating and a cooling coil, a control valve and a pump are much cheaper than an entire heat pump. Furthermore, there would also be operating cost reductions, as running a pump for the heating and cooling coils would be cheaper than operating the compressor in the heat pump. 78

79 4.0 Preliminary Design Guide This section has two parts: a generic guide for the preliminary design of a cogeneration system that provides power, cooling, heating, and ventilation to a building and a specific example based on the biodiesel fueled CHP system designed, installed, operated and evaluated at Carnegie Mellon University. The design process is iterative; however seven steps in sequence are recommended. Throughout the design process engineers should be aware of local code requirements as they affect decisions. 4.1 Generic Design Steps The general procedure for designing a CHP system is to: 1. determine the electrical and thermal loads, load profiles and the required flow rates and temperatures of cooling and heating streams. 2. determine which fuel types are locally available, how they are distributed, and their cost. 3. determine what energy grids are available, what their operating conditions and costs are, and if it is possible to interface with them. 4. select a prime mover that best fits the load profile and load proportions. 5. select auxiliary and heat recovery equipment to match the prime mover and the fluids used to transfer energy. 6. choose an operating strategy (thermal or electrical load follow, base load operation, etc.) 7. evaluate the options on a capital, operating, and environmental cost basis. 79

80 As these seven steps are carried out the following documents should be created: 1. flow diagram, 2. material and energy balances, 3. equipment descriptions, 4. operating descriptions, 5. process and instrumentation diagram, 6. preliminary layout, and 7. cost estimates for equipment These documents provide the basis for equipment procurement, detailed design, installation, and operation Loads The first task is to identify the energy loads for the CHP system. These include, but are not limited to: electrical (lighting, pumps, fans, computers, etc.), space cooling and heating, ventilation, dehumidification, and process energy. Lawrence Berkley National Labs (LBNL) publishes generic annual load values for U.S. buildings on a square foot basis shown in Table 10 [6]. Space Heating Water Heating U.S. Commercial Office Building Energy Intensity (kbtu/ft2-year) Cooling Cooking Ventilation Lighting Refrigeration Office Equipment * *Electrical energy for operation of a vapor compression chiller. Table 10: Typical U.S. Commercial Building Loads Other 80

81 Table 10 shows thermal and electrical loads assuming average furnace and chiller efficiencies of 80% and COP = 3.2 respectively. The cooking load is not specified as an electrical or thermal load in the LBNL report. Ventilation energy is assumed to be for a forced air system that delivers the heating, cooling, and fresh air. The information in Table 10 gives annual energy demands; however, to properly size and evaluate a CHP system, peak and base loads and annual hourly load profiles are required. The full table with IWESS systems applied is shown in Appendix C, which shows the steps necessary for transforming the average load data for electricity, heating, cooling, and ventilation into a form for the IWESS systems. These values along with a conditioned square footage of a building will provide annual total loads for many building types. Hourly load data can come from metered data or from building energy simulations. Simulation data should be used carefully and it is reasonable to add a safety factor of 1.1 when sizing the system, however metered data is best. Over sizing systems will lead to inefficiency, but reality dictates that metered data are not always readily available. When analyzing hourly data it important to find the peak (maximum) and base (minimum) electrical and thermal loads. Details about these loads such as voltage, temperatures, flow rates, and pressures should be determined as appropriate Fuel Selection There are many fuels available for the operation of CHP systems including: natural gas, petroleum products (gasoline, Diesel, etc.), biomass (biogas, biodiesel, ethanol, solids), 81

82 coal, and waste fuels (waste coal, garbage, etc.). Many of these fuels are associated with a particular type of prime mover. They vary in energy content, cost, availability, and emissions. The CHP system designer must determine what options are available based on this list of criteria and tabulate them to assist in the selection of a prime mover, and in the estimation of the operating costs of the system Energy Grids The availability of energy is an important consideration in the design of a CHP system for a building. Energy grids can come in many forms; electrical, natural gas, chilled water, steam, heated water, compressed air, etc. The most common energy grid is the electric utility grid. The interface with the electric utility grid must be coordinated with the local electric utility, which will have individual requirements governing the operation of CHP systems, which will detail voltages, power quality requirements, and cost structures for providing and accepting power. Larger systems may be required to generate a certain amount of power. Thermal grids (steam, chilled water, etc.) are operated by some large utilities or by smaller private entities. Similar to the electric utility grid, CHP system designers must contact the grid operators to determine if it is possible to interface with the grids. Typical performance requirements for interfacing with thermal grids include; temperatures, pressures, and flows. Furthermore, these temperatures, pressures, and flows may change throughout the year as thermal demands change throughout the year. 82

83 The ultimate goal of interfacing with energy grids is to have a source and sink for all the forms of energy generated by the CHP system and needed by the facility. Many types of commercial buildings have varying loads throughout the year, whereas CHP systems operate most efficiently at steady state. Energy grids provide level load profiles for buildings so that the CHP system can operate independently of the local building loads. Also, importantly the energy grid can act as a back up in case of a plant failure Prime Movers The fourth step is to select a prime mover that will provide sufficient thermal and/or electrical energy at the proper conditions. Table 11 lists the prime movers most frequently considered for CHP systems in buildings along with some of their performance characteristics. Based on the building load profiles and the fuel data one or more prime movers will emerge as the best fit for a particular application. As previously stated, the design process is iterative. Therefore, some prime mover options may be eliminated in subsequent steps. Prime Mover Boiler + Steam Turbine Fuels Electrical Efficiency Nat. gas, coal, waste fuels, biomass % Recoverable Heat CHP Efficiency Heat to Power Ratio % low quality steam % 4.3 Gas Turbine Natural gas, biogas % % 600 o F exhaust % 2.8 IC Engine -Diesel Diesel, biodiesel % % 190 o F coolant, % 900 o F exhaust % 1.6 -Spark Gasoline, E85, natural gas % % 190 o F coolant, % 900 o F exhaust % 2.0 Fuel Cell -SOFC Natural gas % % 500 o F exhaust % 0.8 -PEM Hydrogen % % 300 o F exhaust % 0.8 Table 11: Prime Mover Performance Summary 83

84 4.1.5 Auxiliary and Heat Recovery Equipment The fifth step in the design process is to select auxiliary heat recovery equipment that uses exhaust, coolant or steam to meet the desired loads. This equipment may include: heat exchangers absorption chillers (single and double effect) dehumidifiers thermal storage arrangements Section 2.5 discusses the temperature and medium of these thermal outputs with respect to engine type. There are several ways of transferring heat and there are several types of heat exchangers that are tailored to particular mediums and applications. An important tool in selecting and designing equipment for recovery and utilization of thermal energy, heat, in CHP systems is the T-Q diagram as shown in Figures 16 and 17. T-Q diagrams should be constructed for each exchange of thermal energy in the system. It may be necessary to contact several manufacturers to determine the best match for the selected prime mover and fuel. An effective method for determining if a heat exchanger will meet the design requirements is using a T-Q diagram, and plotting the inlet and outlet temperatures versus the heat transfer. At this point, it is possible to start to develop a preliminary flow diagram so that the CHP system designer can get an over view of the options thus far. There may be multiple flow diagrams at this point as a single prime mover and fuel may not have been selected yet, but there is sufficient information to get started. The preliminary flow diagrams allow the 84

85 designer to visualize what forms of energy are available and what the loads are. As information becomes available and decisions are made in subsequent steps, the flow diagram is revised. Furthermore, it is prudent to develop multiple designs in parallel using different components and eliminating options as details become available Operating Strategy The sixth step in designing a CHP system is determining an operating strategy. There are many options available to engineers but they primarily include: steady state operation at either the peak or base, minimum, loads of the system thermal or electrical load following operation Load following may be based on a thermal or electrical load and partially depends on the available auxiliary equipment and grid types. Electrical load follow is a mandatory operating method unless battery storage or a grid interconnection exists as more electricity can not be generated than is consumed, stored or dissipated. Both battery storage and grid interconnection may be expensive, yet they allow the CHP system to operate much more efficiently allowing electricity to flow to and from the utility grid so the CHP operator only has to focus on effectively recovering and utilizing heat. Design operation typically takes on two forms: base loading and peak loading. Design operation is defined as operating the prime mover at a constant load and importing or exporting thermal and electrical energy as appropriate. Base loading has the prime mover generating the minimum amount of thermal and/or electrical energy that will always be used by the building. The caveat to this mode of operation is that back up sources of 85

86 heating, cooling, and electricity must be available to cover the load variability. These backups can come from standard boilers and chillers and/or the utility grids (electrical and thermal). Peak design operation on the other hand has the prime mover operating at a setting that will always generate sufficient electrical and thermal energy to meet any building load. The downside to this mode of operation is that there will be instances when there are excess amounts of thermal and electrical energy, which will have to be exported to an energy grid or rejected. Rejecting energy decreases over all efficiency, but extra equipment will not be required to meet peaks (boilers and chillers). The decisions regarding operating strategies including startup and shut down will establish the requirements for the sensor, actuator and control system components and will provide the basis for the piping and instrumentation diagram CHP System Evaluation Evaluation in this step has a dual meaning. First, if multiple CHP system options exist the designer must weigh these options on an engineering, economic, and environmental basis. The second meaning of evaluation is that the CHP system designer should determine a way of evaluating the efficiency, economic, and environmental performance as required by the conditions set by regulatory bodies, the system owner and the system operator. Regulatory bodies may want information on the quantity of emissions generated. Owners may be interested in how much money has been saved by operating the CHP system. 86

87 CHP system operators may need information to diagnose problem and determine if the system is operating properly. The result of this step is to determine the best CHP system configuration and operating conditions to meet the demands of the building, which are economic. 4.2 Design of Biodiesel Fueled CHP System A biodiesel fueled CHP system was designed, installed, operated and evaluated according the design guide described above Load Profiles The thermal and electrical load profiles from the Intelligent Workplace (IW) were developed from a combination of metered and name plate data. A decision was made early on that the CHP system would be designed to meet the peak loads of the IW to demonstrate a facility that could be powered entirely by renewable fuels. Using data on existing HVAC, lighting, and plug loads a peak electrical demand of approximately 20 kwe was determined. Metered data for the double effect steam absorption chiller was available, which showed the peak demand as 16 kwt in the form of saturated steam at 87 psig (6 bar) with a flow rate of 65 lb/hr (29 kg/hr). Furthermore, metered data for the heating system showed a peak heating demand of approximately 40 kwt at 40 o C (104 o F), which can change rapidly as he IW does not have 87

88 a lot of thermal mass, therefore outdoor temperature changes are felt in the building relatively quickly. The heating season typically lasts from early October to late March. The heating system was fed by the steam grid which operated at about 7 psig (0.5 bar) during the winter. Note, the main steam supply pressure is 150 psig (10 bar) during the winter, but this is stepped down inside the buildings on campus as appropriate. An additional load that was identified is regenerating the desiccant dehumidification wheel in the ventilation system. Desiccant regeneration, like the chiller is also a seasonal load, however it is steadier than the chiller load. The metered data of the ventilation system showed a required temperature for regenerating the desiccant of approximately 195 o F (95 o C) with a peak demand of about 20 kwt Fuel Selection Local fuels that were available included natural gas and biodiesel fuel. As this was a demonstration facility, it was decided that using a renewable fuel was the most important design consideration when selecting a fuel. Another group on the Carnegie Mellon University campus had just commercialized a biodiesel refining process. This new commercial entity agreed to donate the fuel for this system, which also made it the most economic fuel choice by default. Distribution of the biodiesel was not as simple as natural gas, which has a pipe line infrastructure in Pittsburgh, PA. Provision for filling fuel storage tanks had to be made, which were addressed during the detailed design and layout phase. 88

89 4.2.3 Energy Grids Carnegie Mellon s campus has many energy grids including; electric, steam, and chilled water. These grids are connected to every building on campus; the steam and chilled water are generated at a central plant. The local utility, Duquesne Light, was contacted to determine what their requirements were for installing a utility paralleled engine generator with a capacity of between 20 and 30 kwe. Due to the configuration of the Carnegie Mellon campus, electricity enters the campus at two points. Therefore, it is unlikely that the 20 to 30 kwe system would be noticed in a campus system that draws between two and five megawatts of electricity from Duquesne Light. Based on this information, Duquesne Light set no requirements for grid protection on this system. It was assumed that if there was a grid outage and the generator was operating it would immediately be over loaded by the huge electrical demand from the campus, which would cause the engine generator to shut down. Additional protections were put in place as this is a demonstration facility, which will be discussed further during auxiliary equipment. The campus chilled water and steam grids are operated year round by Carnegie Mellon s facilities management service. The university agreed to allow the CHP system to interface with the campus thermal grids to allow for importing and exporting of steam and chilled water. The chilled water operates year round at approximately 45 o F (7 o C). The steam grid also operates year round to prevent thermal expansion and contraction; 89

90 however the pressures vary from about 15 psig (1 bar) in the summer to 150 psig (10 bar) during the winter. The fall and spring pressures are approximately 40 psig (3 bar). Another smaller grid was available in the building: a hot water grid. This grid is not campus wide, but was considered as a possible outlet for thermal energy. The building hot water grid has an operating range of 26 o C to 40 o C (78 o F to 105 o F) Prime Movers Three options were available, microturbines, Diesel engines, and fuel cells. Fuel cells were eliminated quickly as the cost was too high, approximately 100 times the cost of the microturbine and Diesel engines per kwe. The smallest microturbine available at the time was a 30 kwe unit, which corresponds to approximately 90 kwt at 530 o F (270 o C), much too large for this system. Diesel generator sets are available from many manufacturers that would provide about 20 kwt of high temperature exhaust. A 32 kwe Diesel engine generator was selected from John Deere. John Deere was ultimately selected for two reasons, it was locally supported and John Deere showed interest in the work. Next, as this is a prime power setup, as opposed to a backup power setup, the engine would not be operated at full power (32 kwe) for an extended period of time. An 80% power rating is reasonable for prime power applications or 25 kwe. Assuming that Diesel engines are about 33% electrically efficient, it was assumed that a Diesel engine operating at 25 kwe would produce approximately 25 kwt exhaust and coolant heat each. Based on this reasoning, a Diesel engine generator set was selected. Because of the high steam pressure and temperature 90

91 required by the two stage absorption chiller the amount of available exhaust energy was closer to 18 kwt, and therefore diminished the operation of the heat recovery system. Specification sheets from engine manufacturers typically don t include part load values or exact values for CHP systems. Conservative estimates are recommended Auxiliary and Heat Recovery Equipment Sizing the heat recovery is where the first major difficulty arose for this system configuration, as there are no commercially available steam generators in the kwt size range. The smallest steam generator available for exhaust heat recovery was a 200 kwt unit from Vaporphase, Inc. The consequence of using a steam generator of this size is that the heat up time is very long, approximately nine hours from cold start to steady state, not including heating up the pipes. However, as a proof of concept, this was deemed an acceptable configuration. A high pressure hot water system would be recommended for a new system that would also include the purchase of an absorption chiller. Next, the remaining thermal energy stream from the engine coolant needs to be handled. A plate and frame heat exchanger was selected to recover this energy and transfer it to water that is utilized in the IW s heating system. The configuration of the IW s existing heating system allowed for the dual use of the hot water pipes for space heating in the winter and regenerating desiccant in the summer as the loads are not simultaneously active. It should be noted that this is not a common system configuration. Many buildings use what is called a four pipe heating system in which hot and cold water is available to the heating and cooling system as many buildings have to heat and cool at the same time, 91

92 especially during the spring and fall. The passive design of the IW allows for the use of what is incorrectly assumed to be an inferior two pipe system. The IW does not require heating and cooling at the same time, and therefore an entire set of pipes can be eliminated as shown in Figure 30 below. Figure 30: IW Heating and Cooling System Flow Diagram\ The coolant energy has a use during the summer for regenerating the desiccant and in the winter for space heating, however there are no reliable loads in the spring and fall. Therefore, a remotely mounted radiator is used to dump excess coolant energy to the atmosphere as there must always be an outlet for the coolant energy to prevent the engine from over heating. An alternative to this would have been to purchase a single effect absorption chiller to generate additional chilled water that could be exported to the 92

93 chilled water grid, or to make a connection with the domestic hot water system of the building. Finally, the electrical energy needs to be sent to the power grid. The advantage of connecting power to the utility grid is that it allows operational freedom to produce the reject heat in the quantity required. If a CHP system does not have the flexibility to export electricity, the prime mover must always match the electrical demand other wise the electrical circuits will overload. As electrical and thermal demands don t necessarily coincide, too much waste heat could be generated, or not enough. The requirements of the utility paralleling gear (Automatic Transfer Switch / Soft Load Controller ATS/SLC) are up to the local utility. Typically for very small systems, less than 100 kwe, the utility s requirements are minimal. However, as this is a demonstration facility, a much more complex ATS/SLC was selected, which could provide additional operational flexibility and realism for larger systems. Based on all of this information several flow diagrams were generated and frequently revised as details emerged on equipment, pipe sizes, and sensor and actuator requirements. Due to the scattered nature of this CHP installation, the heat recovery equipment had to be placed in a relatively distant location from the absorption chiller. Therefore, piping losses (thermal and pressure) had to be considered as the piping distance is about 220 feet (67 meters) including a 70 foot (21 meter) vertical rise. A pressure drop of 5 psi (0.3 bar) 93

94 and a thermal loss of 2.5 kwt were calculated based on these estimates as shown in Appendix D. Therefore, a minimum of 18.5 kwt was needed to drive the absorption chiller. It was decided to add a little padding to this number and set the requirements to 20 kwt Operations A specific operational strategy was not selected for this project as one of the research goals of this project is to compare operational strategies. The control system and infrastructure in place for this system allow the system to thermal load follow, electrical load follow, base load, and peak load. There is an extra cost associated with this decision, but as a demonstration facility cost was not a driving factor Evaluation The fuel type, prime mover, and auxiliary equipment were selected relatively quickly for this application as there were a lot of constraints on equipment selection between the existing chiller and ventilation systems, the energy grids, and the demands of the building. The long term evaluation of all facets of this system was the primary focus of this project, and is outlined in section 3. The evaluation of this system was meant to satisfy CHP system designers, builders, operators, owners, and regulators as well as educational entities. Therefore, there is a great emphasis on data acquisition and dissemination. Over 200 data points are continuously measured and available on the web. 94

95 4.2.8 Submittals Flow diagrams, material and energy balances, equipment descriptions, operating descriptions, process and instrumentation diagrams, preliminary layout, and cost estimates for equipment were all created and submitted to an engineering firm for detailed evaluation and the creation of construction drawings. The engineering firm created a detailed flow diagram, and a layout which had to balance educational/scientific goals. The detailed flow diagram and the layout went through several iterations as the educational and scientific goals weren t always understood by the engineering firm. Code requirements often clashed with scientific requirements, however eventually a compromise was met. Upon completion of the construction drawings, bids were sought and awarded for placing and connecting the equipment, installing instrumentation and controls, and commissioning the system. Details on the construction process can be viewed on the project website: 95

96 5.0 TRNSYS Modeling An overall TRNSYS model has been programmed by Flore Marion to simulate the performance of individual and combined systems in various operational modes. Many of the IWESS components have been modeled using TRNSYS in order to develop generic models for future building HVAC design. These models include the absorption chiller, the engine generator with heat recovery, and the ventilation system. The purpose of the model is to estimate what fraction of the thermal requirements of the IW can be met by the biodiesel CHP system in various operational modes and what portion of the thermal output must rejected to the surroundings. 5.1 IWESS Model The IWESS model is built out of three main components, the biodiesel fueled CHP system, the double effect absorption chiller, and the enthalpy recovery ventilation system. Each of these systems has had a previously developed empirical model, which was implemented in TRNSYS. Empirical models had to be used as computational models were to calculation intensive. The model uses three measured data files which include the heating, cooling, and regeneration loads of the IW. The outputs include the electrical generation, fuel demand, and the necessary flows and temperatures of the thermal streams Biodiesel Fueled Engine Generator with Heat Recovery Modeling The design of the engine generator with heat recovery model has been completed and tested at 6, 12, 18 and 25 kwe. The first model used manufacturer s specifications as 96

97 inputs [34]. The model has been validated using measured data, which as shown in section very closely matches the specifications of the manufacturer. The look up tables developed for this engine generator are shown in Appendix E. Using the look up table a simple TRNSYS module for the CHP system was developed that equates fuel flow to electricity generation, hot water generation via the coolant heat exchanger, and steam production via the steam generator. Figure 31: CHP system input / output module Double Effect Steam Driven Absorption Chiller A complex Engineering Equation Solver (EES) model was developed for the absorption chiller sub-system. However, this model was to computationally intensive for TRNSYS to run so a table look up model was developed and implemented in TRNSYS. The TRNSYS absorption chiller model is based on empirical data collected during the operation of the chiller over various loads [35]. The operating data has been distilled to a simple relationship, which equates cooling capacity with heat input. Figure 32 shows the input and output of the chiller model. 97

98 High Pressure Steam Flow and Pressure Absorption Chiller Module Cooling Demand Figure 32: Double effect absorption chiller input / output module Ventilation Unit with enthalpy recovery and solid desiccant wheel. The ventilation system has also been modeled in TRNSYS, and is also quite complex. For the purposes of the integrated system model, empirical data for the regeneration demand from the ventilation system were used to create a table look up model that relates regeneration demand to a demand of hot water from the CHP system [36]. Figure 33 shows the simple input / output module for the ventilation system. Hot Water Flow and Temperature Ventilation Module Regeneration Demand Figure 33: Ventilation system input / output module Computational Model Issues While it is possible to use computational models rather than empirical models there are several drawbacks. First and foremost, the performance of the systems and how they interact with each other in every time step must be calculated. Building a computational model was carried out; however the system was so complex that it had to be run in small simulation time increments (about two weeks) with a time step of five minutes to get 98

99 accurate results. While, this is sufficient for scientific purposes it is ineffective as a design tool. To illustrate some of the computations necessary the following is the process by which cooling is delivered. 1. A cooling demand is set by the building load file. 2. The chiller then calls for steam by calculating how much steam is required to meet the new cooling demand. 3. Steam is drawn from the steam generator, which calls on the engine to adjust its output to provide the correct amount of heat to the steam generator based on its heat transfer characteristics. 4. Next the engine calculates the amount of fuel necessary to meet the new demand. Simultaneously the coolant loop is operating which also has various thermal demands, and calculates how much heat should be recovered and rejected. On top of that an over all control strategy is running that decides which form of heat is more important, coolant or exhaust. Figure 34 shows the combined computational model for the CHP system with all of the components needed to operate the system including the pipes and valves themselves. 99

100 Figure 34: Combined TRNSYS Model Combined IWESS Model To resolve the performance issues of the computational model it was decided to use the look up tables and simplify the entire program so that a full year simulation could be run in a relatively short amount of time. To simplify the entire program the following steps were taken: 1. The engine generator with coolant heat recovery were merged into a single component based on a look up table. 100