The Integration of Ammonia-Water Absorption Chillers with Residential Cogeneration Units: A Feasibility Study Kevin Key A thesis submitted in partial fulfillment of the requirements for the degree of BACHELOR OF APPLIED SCIENCE Supervisor: J. S. Wallace Department of Mechanical and Industrial Engineering University of Toronto April, 2008
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The Integration of Ammonia-Water Absorption Chillers with Residential Cogeneration Units:
A Feasibility Study
Kevin Key
A thesis submitted in partial fulfillment of the requirements for the degree of
BACHELOR OF APPLIED SCIENCE
Supervisor: J. S. Wallace
Department of Mechanical and Industrial Engineering University of Toronto
April, 2008
i
Abstract
The goal of this paper was to determine the feasibility of incorporating an absorption chiller with an existing residential cogeneration unit. The reasoning behind this is two-fold. First, absorption chilling reduces the load on the electricity grid when compared with a traditional vapour compression air conditioner. Second, it makes use of the waste heat of the cogeneration unit in the summer which would otherwise be discarded into the atmosphere.
This study found that it is possible to integrate an absorption chiller with an
existing cogeneration unit, but the chiller designed for this study did not achieve the performance of similarly-sized chillers discussed in the literature. As a result, the already costly cogeneration unit had to be scaled in order to provide sufficient heat to the absorption chiller. This means that the initial costs associated with absorption chilling and cogeneration are far too high to make this trigeneration system economically feasible for residential use.
ii
Acknowledgements I would like to thank Professor Wallace of the Mechanical Engineering
Department at the University of Toronto for his assistance throughout the period of
writing this paper. His wealth of knowledge and willingness to help were welcomed and
appreciated and made this process a very enjoyable learning experience.
I would also like to thank my family and friends for their never-ending support
throughout my entire educational career. Without their constant encouragement I would
not have been able to achieve the excellence I have, nor would I be as happy and
confident as I am today.
Whether you think you can or whether you think you cannot, you are right.
Believe in the power of positive thought.
iii
Table of Contents
Abstract i
Acknowledgements ii
Table of Contents iii
List of Symbols v
List of Figures vii
List of Tables ix
1. Background 1
1.1 Reducing our Electricity Demand 1
1.2 The Growing Popularity of Cogeneration 5
1.3 Absorption Chilling 6
2. Purpose of Study 8
3. System Design and Components 9
3.1 Residential Heating and Cooling Loads 9
3.2 Absorption Chiller Design 10
3.3 Cogeneration Unit 15
4. Economic Analysis 17
4.1 Base System and Comparison Systems 17
4.2 Cost of Utilities 20
4.3 Feasibility 22
4.4 Study Limitations 24
4.5 Energy Consumption Figures 25
5. Conclusion 28
iv
5.1 Study Summary 28
5.2 Closing Remarks 29
5.3 Further Studies 29
6. References 31
Appendix A – eQuest Inputs 33
Appendix B – Monthly Heating and Cooling Loads 34
Appendix C – Ammonia-Water Enthalpy-Concentration Diagram 35
Appendix D – Ammonia-Water Specific Volume 36
Appendix E – Ammonia and Water Specific Heats 37
Appendix F - Solutions to System Equations 38
Appendix G – Climate Energy Cogeneration Specification Sheet 40
Appendix H – Climate Energy Demonstration 45
Appendix I – Chiller COP vs. Capacity 57
Appendix J – HTS Fan Coil Selection 59
Appendix K – Armstrong Pump Curve 63
Appendix L – System Run Times 64
Appendix M – Utility Costs 65
Appendix N – Electrical Energy Requirements 66
Appendix O – Natural Gas Requirements 68
Appendix P – Distributed System Costs 70
v
List of Symbols
COP coefficient of performance [dimensionless]
CP specific heat Ckg
kJo
h specific enthalpy kg
kJ
HC heat of combustion kg
kJ
m mass flow rate s
gor
skg
MW molecular weight mol
kg
η thermodynamic efficiency [dimensionless]
P pressure [kPa]
Q heat flow [kW]
R ideal gas constant Kkg
mkPa 3
SEER seasonal energy efficiency ratio
T temperature [oC]
specific volume kg
m3
Vol volume of a gas [m3]
W work [kW]
x liquid mass fraction of ammonia kgLiquid
kgNH3
y vapour mass fraction of ammonia kgVapour
kgNH3
vi
Subscripts
Abs absorber
Cond condenser
Elec electricity
Evap evaporator
Fuel methane fuel
Gen generator
Heat space heating
P pump
Rec rectifier
vii
List of Figures Figure 1.1.1 - Satellite image taken August 13, 2003 before the blackout 1
Figure 1.1.2 - Satellite image taken after the blackout on August 14, 2003 1
Figure 1.1.3 – Canada’s energy consumption since 1990 2
Figure 1.1.4 – Canada’s greenhouse gas emissions since 1990 3
Figure 1.1.5 – Average Earth temperature 4
Figure 1.1.6 – Canadian residential space cooling electrical energy demand 4
Figure 1.3.2 – Velazquez and Best Absorption Chiller 7
Figure 3.2.1 – Cengel and Boles absorption chiller 10
Figure 3.2.2 – Schematic of the absorption chiller designed in this study 11
Figure 3.2.3 – COP of a 2.5 Ton chiller as a function of generator temperature 14
Figure 4.1.1 – Velazquez and Best Absorption Chiller 18
Figure 4.2.1 – Yearly Utility Costs for each Case 22
Figure 4.3.1 – Complete system costs distributed over a selected number 23 of years
Figure 4.5.1 – Case 1 Natural Gas and Electricity Consumption 25
Figure 4.5.2 – Case 2 Natural Gas and Electricity Consumption 25
Figure 4.5.3 – Case 3 Natural Gas and Electricity Consumption 26
Figure 4.5.4 – Case 4 Natural Gas and Electricity Consumption 26
Figure 4.5.5 – Case 5 Natural Gas and Electricity Consumption 27
Figure 4.5.6 – Case 6 Natural Gas and Electricity Consumption 27 Figure B.1 – Monthly Heating and Cooling Loads 34
viii
Figure C.1 – Ammonia-Water Enthalpy-Concentration Diagram from ASHRAE 35 Fundamentals 1993 Figure D.1 – Ammonia-Water Saturated Specific Volume from ASHRAE 36
Fundamentals 1993 Figure E.1 – Specific Heats for various liquids, solids, and foods from Cengel 37
and Boles Figure K.1 – Armstrong Pump Curve for chilled water loop 63
ix
List of Tables Table 3.2.1 – Properties at each state of the designed absorption chiller 15 Table 3.2.2 – Energy transfer of each component 15
Table 4.1.1 – Equipment summary for each case 20
Table 4.1.2 – Cogeneration Unit Costs 20 Table 4.1.3 – Absorption Chiller Costs 20 Table 4.1.4 – Carrier Air Conditioner Costs 20 Table 4.1.5 – HTS Fan Coil Costs 20
Table 4.3.1 – Overall costs associated with each case 23
Table I.1 – 3 Ton chiller state properties and energy exchanges 57 Table I.2 – 2.5 Ton chiller state properties and energy exchanges 57 Table I.3 – 2 Ton chiller state properties and energy exchanges 58 Table L.1 – Run times during the heating season for each case 64 Table L.2 – Run times during the cooling season for each case 64 Table N.1 – Electricity requirements of components used in each case 66 Table N.2 – Monthly energy loads and electricity costs for each case 66 Table O.1 – Natural gas power requirements for each case 68 Table O.2 – Monthly natural gas loads and costs for each case 68 Table P.1 – Distributed System Costs over a selected number of years 70
1
1. Background
Chapter one provides the reader with information pertaining to key topics that will
be useful throughout the paper. The first section highlights the increase in Canadian
energy consumption in general and residential space cooling in particular. The Blackout
of 2003 is also recalled. The next section introduces the growing popularity of
residential cogeneration and one area where improvements can be made. This chapter
concludes with a section on absorption chilling where the basics of absorption chilling
will be explained.
1.1 Reducing our Electricity Demand
“At 4:11 p.m. ET on Aug. 14, 2003, Ontario and much of the northeastern U.S.
were hit by the largest blackout in North America's history. Electricity was cut to 50
million people, bringing darkness to customers from New York to Toronto to North Bay”
[1]. While the cause was determined to be the unexpected shut down of FirstEnergy’s
East Lake power plant, personal electricity consumption may have played a factor as
well. If we all had been consuming less energy, the loss of the East Lake plant may
have had little effect.
Figure 1.1.1 - Satellite image taken August Figure 1.1.2 - Satellite image taken after the
13, 2003 before the blackout [2] blackout on August 14, 2003 [2]
2
Energy consumption has been an increasingly popular subject of discussion this
past decade and will likely remain that way for decades to come. Figure 1.1.3
demonstrates Canada’s energy consumption over the last fifteen years. It can bee seen
that both the total energy demand and the electrical demand have been steadily
increasing. Ontario in particular relies a great deal on coal-fired power plants for
electricity; so if this trend continues there are serious negative implications for Ontario’s
environment. Greenhouse gas emissions are a major result of coal-fired power plants’
processes and it has been shown that greenhouse gas emissions have increased in
Canada over the same fifteen year period (Figure 1.1.4).
Figure D.1 – Ammonia-Water Saturated Specific Volume from ASHRAE Fundamentals 1993 [12]
37
Appendix E – Ammonia and Water Specific Heats
Figure E.1 – Specific Heats for various liquids, solids, and foods from Cengel and Boles [8]
38
Appendix F - Solutions to System Equations Pump Enthalpy
kgkJkPa
kgmPh Pumppump 311.1)1501300(00114.0
3
kgkJ
kgkJhhh Pump 689.38)311.140(78
Refrigerant Mass Flow Rate
sg
skg
kgkJ
kW
hh
Qmmmm
Evap71.700771.0
)1551295(
8792
56
6542
Rectifier Mass Balances
332211 mxmymy
sg
m
sg
kgkgNH
mkg
kgNH
02.11
071.7000.1700.0
1
31
3
321 mmm
sg
m
ms
gs
g
31.3
71.702.11
3
3
Absorber Mass Balances
996677
967
mxmymx
mmm
Combining these two equations gives:
1012
3
3
97
766
9 99.39
)165.0300.0(
)300.000.1(71.7)(
mms
g
kgkgNH
kgkgNH
sg
xx
xymm
1187 70.47)99.3971.7( mms
gs
gm
Heat Exchanger Energy Balance
1212 TCh P
kgkJh
kgCkJ
OkgHCkJ
kgOkgH
kgNHCkJ
kgkgNH
COHCxCNHCxC
o
oo
o
PC
o
PP
185.193
293.4
18.4835.0208.5165.0
)45@()1()45@(
12
2
2
3
3
2939
39
0)()( 9121281111 hhmhhm
kgkJh
kgkJ
sg
kgkJh
sg
3.235
0)520185.193(99.39))689.38((70.47
11
11
Component Energy Balances
1111339911 hmhmhmhmQGen
kW
kgkJ
skg
kgkJ
skg
kgkJ
skg
kgkJ
skg
69.27
3.2351000
7.47800
1000
31.3520
1000
99.391885
1000
02.11
kgkJ
skg
kgkJ
skg
kgkJ
skg
hmhmhmQ c 8001000
31.31320
1000
71.71885
1000
02.11332211Re
kW94.7
kWkg
kJs
kghhmQ
kWkg
kJs
kghhmQ
Evap
Cond
79.8)1551295(1000
71.7)(
98.8)1551320(1000
71.7)(
566
426
kgkJ
skg
kgkJ
skg
kgkJ
skg
hmhmhmQAbs )40(1000
7.472.193
1000
99.391295
1000
71.777101066
kW62.19
kWkg
kJs
kghhmWP 063.0))40(689.38(
1000
7.47)( 787
40
Appendix G – Climate Energy Cogeneration Specification Sheet
TECHNICAL SPECIFICATION
Warm Air freewatt System Model WA-A
COMBINED HEAT AND POWER FOR THE HOME Climate Energy’s freewatt System combines two technologies, an advanced warm air furnace and a natural gas-fired engine-generator. This hybrid heat and power generation package provides unrivaled total energy efficiency in combined heat and power delivery to the home. The freewatt system is designed to be installed in the place of a typical furnace and uses the same ductwork system to deliver the heat to the home
freewatt SYSTEM FEATURES • Honda MCHP Power Generation
Technology o Honda Reliable o Quiet (47 dBA) o Efficient (85%+ = Heat And Power) o 1.2 kW of Electric Power Production o UL 1741 Certified for Grid
Interconnection o Proven Technology
freewatt SYSTEM BENEFITS • Reliable Power Generation, Powered by Honda™ • Significantly Reduces:
o Home’s Carbon Footprint Using Energy Conservation o Monthly Electric Bill by Net-Metering Power Generation &
Use • Enhanced Comfort
o Low Level of Continuous Heat Delivery • Indoor Air Quality – MERV 8 Air Filtration
• Advanced Warm Air Furnace
o Energy-Star Qualified o High Efficiency (93% AFUE) o ECM Blower Motor: Low Power
Consumption • Hybrid Integration Module
o Permanent Magnet Pump o Custom Air Coil Heat Exchanger
High Efficiency Air Filter (MERV 8)
• Supervisory Control System
o freewatt System Controller o Advanced Heat And Power Algorithm o Communicating Thermostat o Internet Connection
• Simple Installation • Compatible with Conventional Air
Conditioning Systems
• Increases house value by $5,000 to $20,000 (National Appraiser’s Institute)
• Return on Investment (ROI) of up to 20% annually • System Monitoring through the Internet Connection • Breakthrough Home Energy Technology • Simplified Grid Interconnection
As an Energy Star partner, Climate Energy has determined that the furnace included as part of the freewatt system meets Energy Star guidelines for energy efficiency.
The Furnace and HI Module assembly is design certified in the US and Canada by the Canadian Standards Association.
The Honda MCHP is an Underwriter’s Laboratory (UL) Listed, “Utility Interactive, Cogeneration, Stationary Engine-Generator Assembly, File Number FTSR.AU2004 (U.S.) and FTSR7.AU2004 (Canada).”
Quiet Operation & Comfort Honda MCHP
• Generates heat & power at a noise level of only 47 dBA
Advanced Warm Air Furnace • Low Heat mode drastically reduces temperature swings,
increases overall comfort and lowers the unit’s noise
freewatt System • Low Heat mode – MCHP operates • High Heat mode – MCHP and furnace operate
Engineered for High Efficiency 1. Honda MCHP
• Delivers a steady-state efficiency of 85%+ while producing power and heat, thereby reducing the amount of energy consumed to generate your power
• Delivers exhaust through PVC Venting 2. Advanced Warm Air Furnace
• Delivers 93% AFUE with a corrosion resistant heavy gauge aluminized-steel tubular triple-pass heat exchanger coupled with a stainless steel heat recovery coil
• Reduces electric power consumption by 20% over conventional blower motors using an electronically commutated motor (ECM) in High Heat mode and over 80% in Low Heat Mode
3. Hybrid Integration Module • Consumes under 30 watts to deliver heat from Honda
MCHP unit to air coil heat exchanger 4. Supervisory Control System
• Advanced heat and power algorithm optimizes power production of Honda MCHP unit
Advanced Technology 5. Onboard Inverter
• Integrated inverter delivers high quality power to the home’s main circuit panel
• UL 1741 Certified for Grid Interconnection 6. Exhaust Heat Exchanger
• High efficiency heat exchanger reduces exhaust products to 140° F, allowing use of PVC venting
7. Combustion Control System • Oxygen sensor feedback allows for excellent emissions
control • Stepping gas valve offers almost unlimited control of
gas:air mixutre
Reliability Honda’s commitment to bringing products to market that improve the quality of people’s life goes well beyond cars and motorcycles. Since 1953, Honda has manufactured over 40 million power products worldwide and continues as a leader in the development of low-emission, fuel efficient, environmentally friendly 4-stroke engines for use in numerous power equipment applications. Now Honda’s unwavering reliability, quality, durability and environmentally conscious efficiency combines with Climate Energy’s freewatt System to bring micro-combined heat and power to the home.
Warm Air freewatt System
123
4
Warm Air freewatt System
Model WA-A
Honda MCHP Unit
5
6
7
™
Warm Air freewatt System
Model WA-A
Model WA-A Hybrid Integration Module Details
Model WA-A Connections
Furnace/HI Module
Electrical: 120 Volts AC, 60 Hz, 1 phase, Less than 12 amps Air Intake/Vent: 2”/3” Sch 40 PVC Natural Gas: ½” NPT Condensate Drain: ½” PVC Internet Connection: RJ45 Honda MCHP
AIRFLOW AND COOLING Cooling Capacity (tons) 3 4 4 Heating - Max cfm @ 0.20” WC 1,200 1,700 1,800 Cooling - Max cfm @ 0.50” WC 1,200 1,600 1,700 Motor – ECM Direct Drive ½ hp ½ hp ¾ hp
DUCTWORK CONNECTION DIMENSIONS Supply Air (F x G) 16 x 20 17.5 x 20 19.5 x 20 Return Air (D x E) 14 x 22 14 x 22 14 x 22
MAXIMUM VENTING LENGTHS (EACH ELBOW EQUALS FIVE FEET) Venting Length (ft.) – Furnace (3”)
100 ft. 100 ft. 100 ft.
Venting Length (ft.) – Honda MCHP (2”)
90 ft. 90 ft. 90 ft.
Model WA-A freewatt Air Filter Details
MERV Rating: 8 Air Flow Rating:
Medium: 1,400 cfm High: 1,750 cfm
Resistance: Medium: 0.19 W.G High: 0.29 W.G.
Face Area: 18.6 sq. ft. Media Area/Face Area: 1.0 sq. ft.
The filter is Class 2 Approved and Listed.
Model WA-A Typical Sidewall Vent/Intake Terminations
Consult Installation Manuals for more details.
Model WA-A Typical Roof Vent/Intake Terminations
Consult Installation Manuals for more details.
Model WA-A Grid Interconnection
The Honda MCHP unit must be grid interconnected in order to operate properly. Depending on the state’s regulations and the electric utility, different grid interconnection application processes are required. Climate Energy is actively educating state governments and electric utilities about the benefits of Micro-CHP and how the freewatt system can be a critical component in their energy conservation portfolio. If any questions surface during the grid interconnection process, please contact your Climate Energy product technician or Climate Energy at 508-359-4500.
45
Appendix H – Climate Energy Demonstration
Summary: Climate Energy partnered with several industry and government organizations to demonstrate the energy conservation benefits of Micro-Combined Heat & Power (Micro-CHP) through the Freewatt™ Demonstration Program. Climate Energy’s Freewatt Demonstration Program began in late 2005 with the identification and confirmation of a number of candidate residential homes. Installations subsequently occurred at 19 sites, mostly in Eastern Massachusetts, and the Freewatt Systems were operated for the 2006 to 2007 heating season. Overall, results were consistent with energy performance expectations and the Freewatt Micro-CHP System was well received by both the system installers and the homeowners. Climate Energy’s unique Freewatt micro-CHP system was shown to have important residential energy conservation and environmental benefits at levels comparable to those of some renewable energy alternatives.
System Description: The Climate Energy Warm Air Freewatt System is designed to replace an existing warm air furnace or install in the place of a conventional warm air furnace in a new home. Each Freewatt Micro-CHP system has four primary parts: a furnace module with a high-efficiency auxiliary burner and ECM blower motor, a Honda MCHP module, a hybrid integration module (HI Module), and a microprocessor based system controller.
Whenever heat is demanded by the room thermostat the Honda MCHP unit turns on and begins to generate 12,000 BTU/hr of heat and 1.0 kW of electricity. (Note - the current production model generates 1.2 kW.) The MCHP unit is a natural gas driven, liquid-cooled, internal combustion engine-generator set (see sidebar) specifically developed by Honda for the home cogeneration application. A similar MCHP product is in widespread use in Japan. The heat that is produced by the Honda MCHP is captured and delivered
2006 – 2007 HOME HEATING SEASON
PROGRAM REPORT Demonstration of Freewatt™
Micro-Combined Heat and Power System
Table of Contents
Summary 1 System Description 1 Internet Connection 3 Certifications 3 Installation 3 Grid Interconnection 4 Net Metering 4 Operations 4 Program Results 7 Conclusion 11 Current Status of Freewatt 11
Participating Groups
American Public Power Association
Braintree Electric Light Department (BELD)
KeySpan Energy Delivery
City of Quincy
HI Module Furnace
Honda MCHP
FreewattController
HI Module Furnace
Honda MCHP
FreewattController
Noel Kelly
Highlight
Rev. 2 2
to a heat exchanger in the HI -Module. The heat is transferred into the return air stream from the building and then delivered into the home by the furnace module blower operating in low air flow mode. The Freewatt System runs in this mode for many thousands of hours per year, maximizing the benefits of combined heat and power as well as improving the comfort of the home by maintaining a more constant temperature.
If more heat is required than can be provided by the MCHP unit alone, the auxiliary burners in the furnace module are automatically operated. This can occur on very cold days or when the thermostat calls for a quick re-warming of the building after a period of night-time temperature setback. The sizing of the auxiliary burners is depends on the maximum heat demand of the home. The specific sizes employed are 60, 80, and 100 MBtu/hr.
The above illustration shows the heat flow in the system during the normal combined heat and power mode of operation. Heat from the Honda MCHP is transferred to the HI Module via a liquid coolant circulating loop. Return air from the home is heated by engine coolant in the heat exchanger in the HI Module and the heated air is supplied to the home by means of the furnace blower.
The furnace module is manufactured for Climate Energy by ECR International and is based on well-established condensing warm air furnace design practices. The HI Module is manufactured by Climate Energy and incorporates mechanical
Honda MCHP Specifications:
Thermal Output: 12,000 BTU/hr
Electrical Output: 1.0 kW as tested (current production units 1.2 kW)
Cogeneration Efficiency: 85%+
Engine Type: Single cylinder, 4-stroke
Generator: Multi-pole, permanent magnet
Grid Tie: Inverter based 240v AC
Exhaust Treatment: 3-way catalytic converter
Noise output: 47 dB
Weight: 179 lbs.
Dimensions: 35”H x 23”W x 15”D
Freewatt System Specifications: Thermal Output: 12,000 – 105,000 BTU/hr Overall Fuel Efficiency: > 90 % Electric Connection: 120v AC and 240 v AC. Venting : PVC pipe Fuel: Natural Gas or Propane Heating Stages: Two 1) Cogeneration 2) Cogeneration + Auxiliary Burners Controller: Rabbit BL2600 Main Blower: 1/2 – ¾ HP ECM
Rev. 2 3
components widely used in the HVAC industry. The demonstration program Honda MCHP 1.0 kW modules were manufactured by Honda to Climate Energy specification for the United States market and are largely based on an existing production model now widely used in Japan. Since the installation of these demonstration systems, Honda now supplies Climate Energy with improved, second generation MCHP units (1.2 kW), similar to the current standard in Japan. The system controller is structured around a high capability, highly reliable micro-processor controller and it communicates digitally with the Honda MCHP and the thermostat, while also controlling the main air blower, the auxiliary burners, and coolant pump and receiving inputs from various sensors.
Internet Connection: Each Freewatt system controller connects to the home’s internal computer network or directly to the internet. Periodically the system sends a report of over 150 operational parameters to a database located at Climate Energy. This allows remote monitoring of the system by the Climate Energy development team. This setup also allows Climate personnel to remotely access the Freewatt system and modify certain operational parameters as necessary. Some of the parameters that are continuously monitored at each test site include: operating mode status, electrical output, coolant temperatures, room temperature, set point temperature, outdoor temperature, engine temperature, engine RPM, operating time for the engine and auxiliary burners, thermostat program, and error/fault status.
Certifications: The furnace module and HI Module were tested by the Canadian Standards Association (CSA) to the ANSI Z21.47/CSA-2.3 Gas Fired Central Furnaces standard. The Honda MCHP was tested to the UL 2200 and UL 1741 standards for stationary generators and grid tied inverters. The Massachusetts State Plumbing Board received the independent test results and granted “Test Site” status to the proposed Freewatt Demonstration sites. Since completion of the test program the Freewatt System has achieved certification to these standards and listing in Massachusetts.
Freewatt Systems improved the indoor air quality in
demonstration homes due to continuous air flow through
a high efficiency filter
Noel Kelly
Highlight
Rev. 2 4
Installation: The Climate Energy Micro-CHP System was designed with the heating and air conditioning trades in mind. The system requires no additional skills to install beyond those already represented in a typical heating system installation crew of electrician, plumber, and duct fitter. Installation of each Freewatt was completed in less than 2 days, including removal of the old heating system.
Grid Interconnection: The Freewatt System connects to the electrical grid automatically using the Honda MCHP’s on-board electronic inverter. Permission to connect to the grid for this class of system is obtained using a one-page Simplified Grid Interconnect permit application in Massachusetts. Most systems were installed by wiring a 240v AC receptacle to a location near the Honda MCHP unit and simply plugging the Honda MCHP unit power cord into it. In most areas, no outside disconnect switch was required.
Net Metering: The Freewatt System produces electrical power as it operates to meet the space heating demand. Electric power is not produced in response to specific, instantaneous on-site electrical power demands. In the net metering mode of operation, when more power is being produced by the Freewatt System than can be used in the home, excess power flows back out to the electric grid. A customer receives an instantaneous “credit” during such occurrences as his electric meter spins backwards. Later, when the customer has a greater power demand than can be supplied by the Freewatt System, the extra power needed is drawn from the power grid and that “credit” is redeemed as the meter spins forward again. At the end of the month, the net excess power produced, if any, is typically credited to the homeowner’s monthly bill. If the homeowner uses more power during the billing month than is generated by the Freewatt, he simply pays for that net amount of power drawn from the grid. The Freewatt electric generation capacity is sized such that the amount of power generation during the winter months would be about equal to the level of consumption of a typical home. Typical home power consumption is, on a 24-hour average, about 1 kW. With the Freewatt system operating nearly continuously in the cogen heating mode during the winter months, the ability to meet much of the power needs of a typical home during the heating season is demonstrated. A number of
Data Collection Example: System #0044: Operation Parameter Totals for the heating season Honda MCHP Run Time: 3,968 hours Furnace Auxiliary Burner Run Time: 450 hours Honda MCHP Gas Usage: 732 Therms Furnace Auxiliary Gas Usage: 360 Therms Combined Gas Usage: 1092 Therms Electrical Generation: 3,968 kilowatt-hours Total Combined Heat Generated: 884 Therms Fraction of Total Annual Heat Delivered by Honda MCHP: 62% Total Combined Annual Efficiency: 93% Energy Cost: $1,747 Combined heat and Electric Energy Cost Savings: $756 Reduction in CO2 Produced: 5,111 lbs. (2.5 tons)
Rev. 2 5
homeowners received net zero electric bills during the coldest months of the heating season. One site experienced no electrical use charges for six months.
Operations:
For the most part, the Freewatt Demonstration Systems operated as designed and expected. The advanced heating algorithm allowed the Honda MCHP to accumulate substantial runtime while using the auxiliary burners in the furnace only sparingly. This result alleviates a common concern about the potential of micro-CHP in residences, which is whether it can actually deliver the significant electrical generation that is needed while operating only in response to the space heating thermostat demand.
After the first two to three installations, it was quickly determined that the initial operating logic programmed into the system was preventing the system from bringing the home’s indoor temperature to the proper setpoint. Instead, the indoor temperature would stabilize at 1 degree F below the setpoint. A minor modification was required to the heating algorithm to remedy the issue.
A few months into the test program, the telemetry data from the units indicated occasional lockouts of several Honda MCHP units after a long period of off time. Testing in Climate Energy’s laboratories showed that the coolant pumps were sticking after being allowed to cool down. Discussions with the manufacturer of the pump led to an investigation at the factory that concluded that a production method had changed between our initial shipment of laboratory test pumps and the receipt of pumps for the demonstration units. All demonstration unit pumps were replaced with new pumps made after a correction was made to the manufacturing process to eliminate the sticking defect. No further occurrence of this issue was encountered. Heating capacity was not lost in any of these MCHP lockouts as the Freewatt automatically operates with the auxiliary burners in such circumstances.
It was observed that the coolant level in the HI Module reservoir was falling faster than expected during the demonstration program, presumably due to evaporation as no leakages were detected. A new gasket was procured for the coolant reservoir covers and installed in a few homes. The homes with the new gaskets experienced a much slower and acceptable rate of coolant loss compared to the other sites. The new gaskets are now installed in all sites and are part of the production system design.
Very minor problems were encountered with the Honda MCHP modules. Occasionally, a spurious error would occur due to an internal sensor reading,
Many Demonstration System homeowners
noticed that the Freewatt System was much quieter overall than their previous
equipment.
Rev. 2 6
such as improper voltage to the oxygen sensor. These errors were cleared with a reset of the unit. In one case, an inverter self diagnosed a problem and was subsequently replaced. The Honda MCHP modules that are part of the current production Freewatt systems are now a second generation production design and all such minor operational problems have been eliminated.
A number of interesting findings came out of the day to day observation of the demonstration systems. Contrary to conventional thinking it was found that the Freewatt Micro-CHP system can cost less to operate when keeping the house at a constant temperature, rather than using a setback program in a programmable thermostat. If large setback of temperature is used, it causes the Honda MCHP to turn off for some lengthy period of time as the building temperature gradually coasts down to the new low setpoint temperature. Later, when the setpoint changes back to the normal indoor temperature, the operation of the auxiliary burners is needed to provide much of the heat needed for the room temperature to recover. This essentially trades steady cogeneration runtime of the Honda MCHP unit for auxiliary burner runtime which reduces the overall number of kilowatt-hours produced – sometimes substantially. The small gas energy cost savings with large setback can be more than offset by the loss of more valuable electricity production.
Another interesting finding is that, by providing a small amount of space heating continuously with this warm air system, heat can actually be delivered with a higher electrical efficiency than with conventional warm furnaces. The Electrically Commutated Motor (ECM) in the furnace module operates at about 10% of full electrical power in the cogeneration mode to deliver up to 20% of full heat capability. This further contributes to the electrical savings of the system.
While difficult to quantify, a number of homeowners reported a more comfortable home with the Freewatt Micro-CHP system. This is directly attributable to the near-continuous heating mode of the Freewatt system as compared to the on – off cycling of participants’ old warm air systems. It is also consistent with general industry finding that modulating and multi-stage warm air heating is generally more comfortable for the building occupants.
Also, a number of homeowners remarked on how quiet the system was in comparison to their old warm air heating systems.
Freewatt Systems saved between $461 and $1,077 in energy costs per site.
These savings will increase by about 20% with
replacement of the field test systems with production
Freewatt systems having a 1.2kW electric output.
Rev. 2 7
Program Results: Over the course of the Demonstration Program, Climate Energy collected nearly 100 million data points for use in quantifying, optimizing, and demonstrating the effects of the Freewatt System. Figure 1 shows the combined total of kilowatt-hours generated by all the Freewatt Demonstration Systems on a monthly basis. This generation profile closely follows the typical seasonal heat output characteristics of a conventional heating system. What is significant about this result is that a small number of Freewatt Systems can, in aggregate, produce a large amount of electric power.
Freewatt Demonstration Systems Total Kilowatt-Hour Production by Month for all homes combined
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Figure 1
Figure 2 is an example of the relative contributions to overall required heat production by the Honda MCHP and the Furnace. Early in the heating season, the Honda MCHP is able to provide the majority of heat required by the home by steadily producing about 12,000 BTU/hr. As the heating season proceeds, the auxiliary burners begin to play a larger role in heating to the point where they may surpass that of the Honda MCHP. After the coldest part of the season, the Honda MCHP is again able to handle the bulk of the heating load. In this example, there were only two months of the year where the Honda MCHP was not able to provide the majority of the heat required for the home.
Freewatt Systems saved an average of 4,500 pounds of
CO2 production per site
Rev. 2 8
Heat Contribution of Honda MCHP and Furnace Auxiliary Burners (Site 0044)
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Figure 2
Freewatt Demonstration Systems Minimum, Average, and Maximum Kilowatt-Hour Production
by Month for Individual Homes
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Figure 3
Freewatt Demonstration homes produced between 2,226 and 5,067 kilowatt-
hours; the average site produced 3,338 kWh
Rev. 2 9
The homes chosen for the Demonstration Program varied in size from 1200 square feet up to 3000 square feet. The homes represented a large variety of shapes, sizes, and vintages. All of these parameters affect the overall heat loss of the home and consequently the number of run hours possible for the Honda MCHP. Figure 3 illustrates the variation in electrical production across all of the Demonstration Systems on a monthly basis. The figure shows the minimum, maximum, and average monthly power generation by the Freewatt systems. As the electrical output of the demonstration systems was 1.0 kW, it is clear from the chart that in the coldest parts of the winter the Honda MCHP module can run for nearly every hour in the month (720 hours in 30 day month). Analysis of some of the lesser performing systems indicates that some additional optimization of operating parameters is possible to increase the number of run hours. Climate Energy is continuously working to improve the performance of the Freewatt System and expects performance to improve nearly across the board in its production systems due to further improvements in the operating algorithm and the higher electrical output of the current model Honda MCHP unit. Additional power generation will result from the integration of domestic hot water heating in future Freewatt models. It is estimated that this will increase total annual power production by 20%
Comparison of Average Freewatt Gas Usage to Average of Replaced Systems at
Demonstration Sites
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Old Heating
Figure 4
As part of the preparation to install the Freewatt Demonstration Systems, Climate Energy collected the specifications for all of the heating systems being
Freewatt Systems have produced a total of over 52,000 kilowatt-hours of
electricity
Rev. 2 10
replaced by the Freewatt System. The operational characteristics of each old system was estimated and compared to the actual operation of the Freewatt System by assuming that each would ultimately need to provide the same amount of heat to the home. As a result of this analysis, Figure 4 shows that gas usage of the Freewatt Systems is very close to that of replaced systems. Thus, as expected for this Freewatt system, the owner will not expect to observe a change in seasonal gas consumption, but will still see a substantial reduction in his electric demand from the grid. The fact that no additional gas consumption is indicated, in spite of the production of significant electric power, stems from the overall improvement in the gas use efficiency in all modes of operation compared to the old heating systems that were replaced.
Figure 5
Comparison of Carbon Footprints for Heating Season Electricity Use
A number of homeowners reported that their Freewatt
Systems increased the thermal comfort of their
homes
Rev. 2 11
Climate Energy’s analysis indicates that the average Freewatt System owner will be able to reduce his carbon footprint significantly compared with his old system. Figure 5 shows the change associated directly with just the electrical generation. Based on the results of the Freewatt demonstration program, a homeowner could expect an overall average of 4,500 lb. reduction in the amount of CO2 produced during the winter in meeting heating and power needs. These projected reductions are based on the actual fuel and generation efficiency of the Freewatt system compared to the average reported for the New England electric grid. A reduction of this magnitude is similar to driving 6,000 fewer miles per year in a typical mid-size automobile or switching to a hybrid automobile. For a typical home, this reduction in carbon dioxide emissions would alone represent the achievement of the curtailment recommendations of the Kyoto Protocol.
Conclusions: The Freewatt Demonstration Systems have delivered a substantial amount of electric power relative to the typical home’s annual usage and have done so without an observable increase in heating fuel consumption. The program has shown that a well-designed Micro-Combined Heat and Power system can operate reliably in typical homes without any inconvenience to the homeowners. Indeed the more steady heat supply of the Freewatt system has shown to be an advantage in providing good thermal comfort. The system can be installed in about the same time as a conventional high-efficiency heating appliance by the same tradesmen. The grid interconnection process is simple and mature. Climate Energy’s Freewatt Micro-Combined Heat and Power product has been shown to save homeowners substantial amounts of energy and operating costs while also significantly lowering their carbon footprint.
The Freewatt Demonstration Systems were based on an early version of the Honda MCHP which produced 1.0 kW of electricity during operation. The current production model produces 1.2 kW – increasing most of the benefits by 20%.
Current Status of Freewatt
Following the successful completion of the demonstration program, the Freewatt Warm Air Micro-CHP System, powered by Honda, was released for general sale to the public in April of 2007. Hydronic heating versions of the system should be available in early 2008. Please see the Climate Energy website at http://www.climate-energy.com for more information on the Freewatt Micro-CHP System.
Freewatt Systems saved the energy equivalent of 313
gallons of gasoline on average per site
Noel Kelly
Highlight
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Appendix I – Chiller COP vs. Capacity
58
59
Appendix J – HTS Fan Coil Selection
60
61
62
63
Appendix K – Armstrong Pump Curve
Figure K.1 – Armstrong Pump Curve for chilled water loop
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Appendix L – System Run Times
65
Appendix M – Utility Costs From the Enbridge website, the following cost data can be obtained for homeowners who purchase their natural gas directly from Enbridge [18]:
14.7859 ¢/m³ for the first 30m3 14.1208 ¢/m³ for the next 55m3 13.5998 ¢/m³ for the next 85m3 13.2118 ¢/m³ for over 170m3
The cost of electricity purchased from Toronto Hydro Electric System is found using the following [19]: Electricity Charges 5.0 ¢/kWh for the first 1000kWh per 30 days
5.9 ¢/kWh for the rest consumed per 30 days Delivery Charges 1.02 ¢/kWh for transmission charge 1.87 ¢/kWh for delivery charges 0.08 ¢/kWh for lost revenue adjustment charges 0.09 ¢/kWh for shared savings charges Regulatory Charges 0.62 ¢/kWh for wholesale market service charges Debt Retirement Charges 0.70 ¢/kWh for retiring the debt of the former Ontario Hydro For the purpose of this study, the $12.97 per 30 days customer charge has been
excluded because it is assumed that the homeowner already pays this fee. Toronto Hydro supports net metering. Monthly production into the grid is
permitted and Toronto Hydro will carry the cost of electricity produced to the next month, up to 10 months. After that time, they will not pay the customer but will set their balance to zero. For the purpose of this study, even if there is net electricity production, the customer will still face delivery, regulatory and debt retirement charges.
66
Appendix N – Electrical Energy Requirements
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Appendix O – Natural Gas Requirements
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Appendix P – Distributed System Costs
Distributed Costs (per year)
2 5 10 15 20 40
Case 1 $65,548.64 $26,629.64 $13,656.64 $9,332.31 $7,170.14 $3,926.89
Case 2 $28,661.11 $11,859.61 $6,259.11 $4,392.28 $3,458.86 $2,058.74
Case 3 $29,499.08 $12,157.58 $6,377.08 $4,450.25 $3,486.83 $2,041.71
Case 4 $10,829.93 $4,537.43 $2,439.93 $1,740.76 $1,391.18 $866.80
Case 5 $11,666.29 $4,833.79 $2,556.29 $1,797.13 $1,417.54 $848.17
Case 6 $28,170.55 $11,579.05 $6,048.55 $4,205.05 $3,283.30 $1,900.68
Table P.1 – Distributed System Costs over a selected number of years