SSL1 Ground Source Heat Pump real world study
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SSL1 Ground Source Heat Pump real world study

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For 6 years a live study has been carried out on the benefits of a GSHP serving the energy requirements of a dwelling. The results of this study are presented in this lecture as well as the theory ...

For 6 years a live study has been carried out on the benefits of a GSHP serving the energy requirements of a dwelling. The results of this study are presented in this lecture as well as the theory governing this technology
Ground Source Heat Pump’s
Key barriers to GSHP’s
Addressing these barriers
The principle of GSHP’s
GSHP configurations
Conventional brine system
Direct evaporation principle
Initial results
Electrical energy requirements
CO2 emissions
Annual financial saving’s
GSHP Theory
Worked Example

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SSL1 Ground Source Heat Pump real world study Presentation Transcript

  • 1. GROUND SOURCE HEAT PUMP - Study Lecture 11 Keith Vaugh BEng (AERO) MEng
  • 2. OBJECTIVES }© Athlone Institute of Technology
  • 3. OBJECTIVES Introduction to domestic ground source heat pumps }© Athlone Institute of Technology
  • 4. OBJECTIVES Introduction to domestic ground source heat pumps The benefits of adapting such for a domestic user }© Athlone Institute of Technology
  • 5. OBJECTIVES Introduction to domestic ground source heat pumps The benefits of adapting such for a domestic user } Discuss why these are not more common given the benefits© Athlone Institute of Technology
  • 6. OBJECTIVES Introduction to domestic ground source heat pumps The benefits of adapting such for a domestic user } Discuss why these are not more common given the benefits Provide an overview of a live space heating study currently being conducted© Athlone Institute of Technology
  • 7. OBJECTIVES Introduction to domestic ground source heat pumps The benefits of adapting such for a domestic user } Discuss why these are not more common given the benefits Provide an overview of a live space heating study currently being conducted Introduce the theory of GHP© Athlone Institute of Technology
  • 8. OBJECTIVES Introduction to domestic ground source heat pumps The benefits of adapting such for a domestic user } Discuss why these are not more common given the benefits Provide an overview of a live space heating study currently being conducted Introduce the theory of GHP Determine the expressions for the thermal efficiencies and coefficients of performance of heat pumps.© Athlone Institute of Technology
  • 9. WHY GROUND SOURCE } HEAT PUMP’s?© Athlone Institute of Technology
  • 10. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water }© Athlone Institute of Technology
  • 11. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water } They have the potential to lower a building’s energy usage i.e COP 1:4 (for every 1 unit of energy input, 4 units of energy are obtained) therefore are Energy Efficient© Athlone Institute of Technology
  • 12. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water } They have the potential to lower a building’s energy usage i.e COP 1:4 (for every 1 unit of energy input, 4 units of energy are obtained) therefore are Energy Efficient Cost effective over a live time when compared with fossil fuels© Athlone Institute of Technology
  • 13. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water } They have the potential to lower a building’s energy usage i.e COP 1:4 (for every 1 unit of energy input, 4 units of energy are obtained) therefore are Energy Efficient Cost effective over a live time when compared with fossil fuels They have a low environmental impact i.e. reduce CO2 emissions© Athlone Institute of Technology
  • 14. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water } They have the potential to lower a building’s energy usage i.e COP 1:4 (for every 1 unit of energy input, 4 units of energy are obtained) therefore are Energy Efficient Cost effective over a live time when compared with fossil fuels They have a low environmental impact i.e. reduce CO2 emissions© Athlone Institute of Technology
  • 15. WHY GROUND SOURCE HEAT PUMP’s? GSHP’s derive energy from natural energy reserves/reservoirs such as soil of bodies of water } They have the potential to lower a building’s energy usage i.e COP 1:4 (for every 1 unit of energy input, 4 units of energy are obtained) therefore are Energy Efficient Cost effective over a live time when compared with fossil fuels They have a low environmental impact i.e. reduce CO2 emissions Why are they not common place?© Athlone Institute of Technology
  • 16. KEY BARRIERS TO GSHP’S }© Athlone Institute of Technology
  • 17. KEY BARRIERS TO GSHP’S High initial cost of GSHP to consumers }© Athlone Institute of Technology
  • 18. KEY BARRIERS TO GSHP’S High initial cost of GSHP to consumers Lack of consumer knowledge and/or trust in the } reported GSHP benefits promoted by suppliers© Athlone Institute of Technology
  • 19. KEY BARRIERS TO GSHP’S High initial cost of GSHP to consumers Lack of consumer knowledge and/or trust in the } reported GSHP benefits promoted by suppliers Lack of regulator knowledge and policy© Athlone Institute of Technology
  • 20. KEY BARRIERS TO GSHP’S High initial cost of GSHP to consumers Lack of consumer knowledge and/or trust in the } reported GSHP benefits promoted by suppliers Lack of regulator knowledge and policy Requires expertise in designing a bespoke system capable of meeting requirements of consumer.© Athlone Institute of Technology
  • 21. KEY BARRIERS TO GSHP’S High initial cost of GSHP to consumers Lack of consumer knowledge and/or trust in the } reported GSHP benefits promoted by suppliers Lack of regulator knowledge and policy Requires expertise in designing a bespoke system capable of meeting requirements of consumer. Lack of faith in installers ability to install and maintain correctly© Athlone Institute of Technology
  • 22. ADDRESSING THESE BARRIERS }© Athlone Institute of Technology
  • 23. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems }© Athlone Institute of Technology
  • 24. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are:© Athlone Institute of Technology
  • 25. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are: ✓ Evaluate the effectiveness of a Horizontal GSHP when compared with a conventional boiler© Athlone Institute of Technology
  • 26. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are: ✓ Evaluate the effectiveness of a Horizontal GSHP when compared with a conventional boiler ✓ Establish the achievable benefits of increasing insulation to current Part L building regulations© Athlone Institute of Technology
  • 27. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are: ✓ Evaluate the effectiveness of a Horizontal GSHP when compared with a conventional boiler ✓ Establish the achievable benefits of increasing insulation to current Part L building regulations ✓ Evaluate multi-thermostat vs. single thermostat control© Athlone Institute of Technology
  • 28. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are: ✓ Evaluate the effectiveness of a Horizontal GSHP when compared with a conventional boiler ✓ Establish the achievable benefits of increasing insulation to current Part L building regulations ✓ Evaluate multi-thermostat vs. single thermostat control ✓ Establish the payback period and confirm the promoted annual savings of 75% on energy bills© Athlone Institute of Technology
  • 29. ADDRESSING THESE BARRIERS To address these barriers it is necessary to assemble independent, statistically valid data on the costs and benefits of adapting GSHP systems } This is the focus of a long term space heating study currently being conducted the objectives of which are: ✓ Evaluate the effectiveness of a Horizontal GSHP when compared with a conventional boiler ✓ Establish the achievable benefits of increasing insulation to current Part L building regulations ✓ Evaluate multi-thermostat vs. single thermostat control ✓ Establish the payback period and confirm the promoted annual savings of 75% on energy bills ✓ Establish if issues exist which are attributed to the collector coil© Athlone Institute of Technology
  • 30. STUDY OVERVIEW }© Athlone Institute of Technology
  • 31. STUDY OVERVIEW The study commenced in 2005 and focuses on a domestic dwelling, approximately 200m2 constructed in compliance with 1997 Part L building regulations }© Athlone Institute of Technology
  • 32. STUDY OVERVIEW The study commenced in 2005 and focuses on a domestic dwelling, approximately 200m2 constructed in compliance with 1997 Part L building regulations } Variables are changed on average every 24-36 months to extend the focus.© Athlone Institute of Technology
  • 33. STUDY OVERVIEW The study commenced in 2005 and focuses on a domestic dwelling, approximately 200m2 constructed in compliance with 1997 Part L building regulations } Variables are changed on average every 24-36 months to extend the focus. Variables will be modified in 2012 to examine cavity wall insulation.© Athlone Institute of Technology
  • 34. STUDY OVERVIEW The study commenced in 2005 and focuses on a domestic dwelling, approximately 200m2 constructed in compliance with 1997 Part L building regulations } Variables are changed on average every 24-36 months to extend the focus. Variables will be modified in 2012 to examine cavity wall insulation. Further work beyond that maybe considered i.e. High Condensing Boiler and Heat Pump combined configuration.© Athlone Institute of Technology
  • 35. THE PRINCIPLE OF GSHP GSHP’s operate on the principle that a constant soil temperature is maintained beneath the earth’s surface. During the summer months the soil acts as heat sink i.e. radiant energy and rainwater replenishes it. During the winter it acts as a heat source, which can } be harnessed for space heating. A collector coil located 1-1.5 m below the earth’s surface collects the heat provided by this source.© Athlone Institute of Technology
  • 36. The heat, which is harnessed, needs to be increased through the assistance of an electrical driven mechanical system commonly referred to as a heat pump. For every one unit of energy used to drive the heat pump (electrical energy), four units of heat energy can be obtained which can be equated to the 70-75% annual energy cost saving. } 1 unit (part) of electricity input Natural resources- 4 units sunlight, rain, etc... (part) equates to 3 parts Heat input output© Athlone Institute of Technology
  • 37. GSHP CONFIGURATIONS Conventional Brine System }© Athlone Institute of Technology
  • 38. GSHP CONFIGURATIONS Conventional Brine System Salt water is pumped through the surface collector coil raising its temperature }© Athlone Institute of Technology
  • 39. GSHP CONFIGURATIONS Conventional Brine System Salt water is pumped through the surface collector coil raising its temperature The salt water returning passes through a } heat exchanger and transfers the heat gained to a coolant© Athlone Institute of Technology
  • 40. GSHP CONFIGURATIONS Conventional Brine System Salt water is pumped through the surface collector coil raising its temperature The salt water returning passes through a } heat exchanger and transfers the heat gained to a coolant The temperature and pressure of the coolant is increased as it passes through the compressor© Athlone Institute of Technology
  • 41. GSHP CONFIGURATIONS Conventional Brine System Salt water is pumped through the surface collector coil raising its temperature The salt water returning passes through a } heat exchanger and transfers the heat gained to a coolant The temperature and pressure of the coolant is increased as it passes through the compressor The coolant transfers the heat energy gained to water in the delivery coil as it passes through a second heat exchanger and in turn is delivered via a pump to the space being heated© Athlone Institute of Technology
  • 42. }© Athlone Institute of Technology
  • 43. Therefore the brine systems consists of }© Athlone Institute of Technology
  • 44. Therefore the brine systems consists of ✓ Surface collector coil containing salt water (brine) }© Athlone Institute of Technology
  • 45. Therefore the brine systems consists of ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water }© Athlone Institute of Technology
  • 46. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant }© Athlone Institute of Technology
  • 47. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant } ✓ Two circulation pumps© Athlone Institute of Technology
  • 48. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant } ✓ Two circulation pumps ✓ One compressor© Athlone Institute of Technology
  • 49. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant } ✓ Two circulation pumps ✓ One compressor ✓ One expansion valve© Athlone Institute of Technology
  • 50. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant } ✓ Two circulation pumps ✓ One compressor ✓ One expansion valve Losses are introduced during the heat transfer process and the pumping stages© Athlone Institute of Technology
  • 51. Therefore the brine systems consists of ✓ ✓ ✓ Surface collector coil containing salt water (brine) One delivery coil containing water One exchange coil containing coolant } ✓ Two circulation pumps ✓ One compressor ✓ One expansion valve Losses are introduced during the heat transfer process and the pumping stages Additional electricity is required also for the additional pump© Athlone Institute of Technology
  • 52. GSHP CONFIGURATIONS Direct Evaporation Principle }© Athlone Institute of Technology
  • 53. GSHP CONFIGURATIONS Direct Evaporation Principle Coolant is circulated through the surface collector coil as result of the pressure differentials thereby raising its temperature as it passes through the heat sink (the soil) }© Athlone Institute of Technology
  • 54. GSHP CONFIGURATIONS Direct Evaporation Principle Coolant is circulated through the surface collector coil as result of the pressure differentials thereby raising its temperature as it passes through the heat sink (the soil) } The temperature of the coolant is increased as it passes through the compressor© Athlone Institute of Technology
  • 55. GSHP CONFIGURATIONS Direct Evaporation Principle Coolant is circulated through the surface collector coil as result of the pressure differentials thereby raising its temperature as it passes through the heat sink (the soil) } The temperature of the coolant is increased as it passes through the compressor The coolant transfers the heat energy gained to water in the delivery coil as it passes through a heat exchanger and in turn is delivered via a pump to the space being heated© Athlone Institute of Technology
  • 56. }© Athlone Institute of Technology
  • 57. Direct expansion GSHP’s achieve higher performance, as the coolant circulates directly in the surface collectors and absorbs the energy (direct evaporation) }© Athlone Institute of Technology
  • 58. Direct expansion GSHP’s achieve higher performance, as the coolant circulates directly in the surface collectors and absorbs the energy (direct evaporation) } Additional mechanical components such as heat exchanger and brine circulation pump are not necessary and as a result increased reliability through fewer parts and improvements in efficiency are obtained.© Athlone Institute of Technology
  • 59. Direct expansion GSHP’s achieve higher performance, as the coolant circulates directly in the surface collectors and absorbs the energy (direct evaporation) } Additional mechanical components such as heat exchanger and brine circulation pump are not necessary and as a result increased reliability through fewer parts and improvements in efficiency are obtained. A Direct Evaporation system was selected for the study being undertaken© Athlone Institute of Technology
  • 60. Heat Pump Surface Collector coils© Athlone Institute of Technology
  • 61. Thermally Heat optimized pipe Pump Surface collector coils Approximately 524 m3 of soil was excavated The collectors were then laid out as shown These were then buried to form the collector© Athlone Institute of Technology
  • 62. The surface collector coils are buried 1.3 m below the surface© Athlone Institute of Technology
  • 63. Manifold Compressor Supply feed not indicated Pressure release valves Pressure gauges Solenoids Expansion Cylinder Heat Return feed (hidden) Exchanger© Athlone Institute of Technology
  • 64. INITIAL RESULTS© Athlone Institute of Technology
  • 65. Cyclic usage of electricity Working harder at night time* * refer to next slide© Athlone Institute of Technology
  • 66. GSHP working more at night, i.e. requires less electricity during the day Trend lines indicate that day time usage is falling while night time is increasing (cheaper electrical rates). This is desired.© Athlone Institute of Technology
  • 67. © Athlone Institute of Technology
  • 68. ELECTRICAL ENERGY REQUIRED TO DRIVE GSHP Period Units Used DifferenceSept 05 - Aug 06 29305 -Sept 06 - Aug 07 32847 3542Sept 07 - Aug 08 33992 1145Sept 08 - Aug 09 31382 -2610Sept 09 - Aug 10 31884 502 Averages 31882 644.75 Unit usage 34000 32750 31500 30250 29000 Sept 05 - Jul 06 Sept 07 - Jul 08 Sept 09 - Jul 10
  • 69. CO2 EMISSIONS Period CO2 GSHP CO2 Oil Boiler* CO2 Reduced Sept 05 - Aug 06 4161.31 13545 -9383.69 Sept 06 - Aug 07 4664.274 13545 -8880.726 GSHP ≈ 65.4% reduction of CO2 over Sept 07 - Aug 08 4826.864 13545 -8718.136 conventional oil boiler Sept 08 - Aug 09 4456.244 12434.31 -7978.066 Sept 09 - Aug 010 4527.528 12434.31 -7906.782 Average 4527.244 13100.724 -8573.48 CO2 Emissions 10000 * Conventional Oil Boiler was monitored between 2002 and 2005 for space heating the same space. It was observed that approximately 5375 liters per year of kerosene was consumed. 9000 Given that 2.52 kg of CO2 is released when one liter of oil is burned. The amount of CO2 emitted per year was - 13,545 kg of CO2 NOTE: CO2 emissions for oil from 2008 8000 onwards have been adjusted to take account of the energy savings made as the variables of the study were changed during this period. 7000 Sept 05 - Jul 06 Sept 07 - Jul 08 Sept 09 - Jul 10© Athlone Institute of Technology
  • 70. ANNUAL FINANCIAL SAVING’s ? GSHP ≈ 35.3% saving over conventional oil boiler© Athlone Institute of Technology
  • 71. ANNUAL FINANCIAL SAVING’s ? Initial results of the study indicate that GSHP’s do not represent a financial saving as promoted by the installers GSHP ≈ 35.3% saving over conventional oil boiler© Athlone Institute of Technology
  • 72. ANNUAL FINANCIAL SAVING’s ? Initial results of the study indicate that GSHP’s do not represent a financial saving as promoted by the installers Monitoring over the period thus far has indicated approximately 35% saving vs the promoted 70-75% GSHP ≈ 35.3% saving over conventional oil boiler© Athlone Institute of Technology
  • 73. ANNUAL FINANCIAL SAVING’s ? Initial results of the study indicate that GSHP’s do not represent a financial saving as promoted by the installers Monitoring over the period thus far has indicated approximately 35% saving vs the promoted 70-75% This saving does not include initial capital expenditure GSHP ≈ 35.3% saving over conventional oil boiler© Athlone Institute of Technology
  • 74. ANNUAL FINANCIAL SAVING’s ? Initial results of the study indicate that GSHP’s do not represent a financial saving as promoted by the installers Monitoring over the period thus far has indicated approximately 35% saving vs the promoted 70-75% This saving does not include initial capital expenditure The financial benefits of study requires further investigation through the usage of sensitive temperature probes attached to the GHSP GSHP ≈ 35.3% saving over conventional oil boiler© Athlone Institute of Technology
  • 75. FURTHER WORK© Athlone Institute of Technology
  • 76. FURTHER WORK Monitor the efficiency of GSHP in situ through the usage of sensitive thermal monitoring equipment© Athlone Institute of Technology
  • 77. FURTHER WORK Monitor the efficiency of GSHP in situ through the usage of sensitive thermal monitoring equipment Establish if losses exist at the GSHP unit itself, or if these losses arise in the transfer from the unit to the control space© Athlone Institute of Technology
  • 78. FURTHER WORK Monitor the efficiency of GSHP in situ through the usage of sensitive thermal monitoring equipment Establish if losses exist at the GSHP unit itself, or if these losses arise in the transfer from the unit to the control space Examine the control space for thermal losses© Athlone Institute of Technology
  • 79. FURTHER WORK Monitor the efficiency of GSHP in situ through the usage of sensitive thermal monitoring equipment Establish if losses exist at the GSHP unit itself, or if these losses arise in the transfer from the unit to the control space Examine the control space for thermal losses Increase the thermal barrier i.e. increase the insulation to current part L standards and monitor© Athlone Institute of Technology
  • 80. FURTHER WORK Monitor the efficiency of GSHP in situ through the usage of sensitive thermal monitoring equipment Establish if losses exist at the GSHP unit itself, or if these losses arise in the transfer from the unit to the control space Examine the control space for thermal losses Increase the thermal barrier i.e. increase the insulation to current part L standards and monitor Conduct a comprehensive pay back analysis and compare with an alternative© Athlone Institute of Technology
  • 81. GSHP STUDY SUMMARY© Athlone Institute of Technology
  • 82. GSHP STUDY SUMMARY GSHP’s represent significant Environmental Benefits i.e. reducing the CO2 emission’s per house hold by approximately 65.4%© Athlone Institute of Technology
  • 83. GSHP STUDY SUMMARY GSHP’s represent significant Environmental Benefits i.e. reducing the CO2 emission’s per house hold by approximately 65.4% Financial benefits achieved in this real world study thus far does not equate to those promoted by the installers© Athlone Institute of Technology
  • 84. GSHP STUDY SUMMARY GSHP’s represent significant Environmental Benefits i.e. reducing the CO2 emission’s per house hold by approximately 65.4% Financial benefits achieved in this real world study thus far does not equate to those promoted by the installers Increased insulation in the control space resulted in savings of approximately 8% - further savings can be achieved here© Athlone Institute of Technology
  • 85. GSHP STUDY SUMMARY GSHP’s represent significant Environmental Benefits i.e. reducing the CO2 emission’s per house hold by approximately 65.4% Financial benefits achieved in this real world study thus far does not equate to those promoted by the installers Increased insulation in the control space resulted in savings of approximately 8% - further savings can be achieved here Multi thermostat control can be utilized however the heat pump does overheat if an adequate sink for the extra thermal energy is not available© Athlone Institute of Technology
  • 86. GSHP STUDY SUMMARY Uneven surfaces above the collector coil are evident at different times during the year therefore these cannot be located under drive ways Significant cracks are also evident© Athlone Institute of Technology
  • 87. GSHP THEORY }© Athlone Institute of Technology
  • 88. GSHP THEORY GSHP theory is a combination of theory presented during previous lectures and comprises of: ✓ Heat Transfer Mechanisms (lecture 1) ✓ Conduction } ✓ Convection ✓ Radiation ✓ Gas laws (lecture 3 & 4) ✓ Compressor theory (lecture 4) ✓ Heat exchangers (lecture 6) ✓ Second Law of Thermodynamics (lecture 9) Refer to these lectures for specific examples on these individual components© Athlone Institute of Technology
  • 89. A heat pump is used to maintain a house at 22ºC by extracting heat from the outside air on a day when the outside air } temperature is 2ºC. The house is estimated to lose heat at a rate of 110,000 kJ/h and the heat pump consumes 5 kW of electric power when running. Is this heat pump powerful enough to satisfy the demand? © Athlone Institute of Technology
  • 90. WORKED EXAMPLE Geothermal heat pump A heat pump is used to maintain a house at 22ºC by extracting heat from the outside air on a day when the outside air } temperature is 2ºC. The house is estimated to lose heat at a rate of 110,000 kJ/h and the heat pump consumes 5 kW of electric power when running. Is this heat pump powerful enough to satisfy the demand? © Athlone Institute of Technology
  • 91. SOLUTION A heat pump maintains a house at a specified temperature. The rate of heat loss 22 deg C of the house and the power consumption of 110,000 kJ/h/ the heat pump are given. It is to be determined if this heat pump can do the 5 kW job HP 2 deg C© Athlone Institute of Technology
  • 92. SOLUTION A heat pump maintains a house at a specified temperature. The rate of heat loss 22 deg C of the house and the power consumption of 110,000 kJ/h/ the heat pump are given. It is to be determined if this heat pump can do the 5 kW job HP 2 deg C© Athlone Institute of Technology
  • 93. SOLUTION A heat pump maintains a house at a specified temperature. The rate of heat loss 22 deg C of the house and the power consumption of 110,000 kJ/h/ the heat pump are given. It is to be determined if this heat pump can do the 5 kW job HP ASSUMPTIONS 2 deg C 1. The heat pump operates steadily© Athlone Institute of Technology
  • 94. ANALYSIS The power input to a heat pump will be a minimum when the heat pump operates in a reversible manner. The coefficient of performance of a reversible heat pump depends on the temperature limits in the cycle only, and is determined from© Athlone Institute of Technology
  • 95. ANALYSIS The power input to a heat pump will be a minimum when the heat pump operates in a reversible manner. The coefficient of performance of a reversible heat pump depends on the temperature limits in the cycle only, and is determined from 1 1 COPHP, rev = = = 14.75  TL   2 + 273K  1−   1−   22 + 273K    TH © Athlone Institute of Technology
  • 96. ANALYSIS The power input to a heat pump will be a minimum when the heat pump operates in a reversible manner. The coefficient of performance of a reversible heat pump depends on the temperature limits in the cycle only, and is determined from 1 1 COPHP, rev = = = 14.75  TL   2 + 273K  1−   1−   22 + 273K    TH  The required power input to this reversible heat pump is determined from the definition of the coefficient of performance to be© Athlone Institute of Technology
  • 97. ANALYSIS The power input to a heat pump will be a minimum when the heat pump operates in a reversible manner. The coefficient of performance of a reversible heat pump depends on the temperature limits in the cycle only, and is determined from 1 1 COPHP, rev = = = 14.75  TL   2 + 273K  1−   1−   22 + 273K    TH  The required power input to this reversible heat pump is determined from the definition of the coefficient of performance to be & QH 110,000 kJ h  1h  & Wnet , in, min = =   = 2.07kW COPHP 14.75  3600s © Athlone Institute of Technology
  • 98. ANALYSIS The power input to a heat pump will be a minimum when the heat pump operates in a reversible manner. The coefficient of performance of a reversible heat pump depends on the temperature limits in the cycle only, and is determined from 1 1 COPHP, rev = = = 14.75  TL   2 + 273K  1−   1−   22 + 273K    TH  The required power input to this reversible heat pump is determined from the definition of the coefficient of performance to be & QH 110,000 kJ h  1h  & Wnet , in, min = =   = 2.07kW COPHP 14.75  3600s  This HP is powerful enough since 5kW > 2.07kW© Athlone Institute of Technology
  • 99. WORKED EXAMPLE Geothermal power plant A geothermal power plant uses geothermal water extracted at } 160°C at a rate of 440 kg/s as the heat source and produces 22 MW of net power. If the environment temperature is 25°C, determine (a) the actual thermal efficiency (b) the maximum possible thermal efficiency (c) the actual rate of heat rejected from this power plant.© Athlone Institute of Technology
  • 100. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined.© Athlone Institute of Technology
  • 101. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily© Athlone Institute of Technology
  • 102. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily 2. The kinetic and potential energy changes are zero© Athlone Institute of Technology
  • 103. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily 2. The kinetic and potential energy changes are zero 3. Steam properties are used for geothermal water© Athlone Institute of Technology
  • 104. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily 2. The kinetic and potential energy changes are zero 3. Steam properties are used for geothermal water PROPERTIES Using appropriate tables, the source and the sink state enthalpies of geothermal water can be found© Athlone Institute of Technology
  • 105. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily 2. The kinetic and potential energy changes are zero 3. Steam properties are used for geothermal water PROPERTIES Using appropriate tables, the source and the sink state enthalpies of geothermal water can be found Tsource = 160°C   hsource = 675.47 kJ kg xsource = 0 © Athlone Institute of Technology
  • 106. SOLUTION A geothermal power plant uses geothermal liquid water at 160ºC at a specified rate as the heat source. The actual and maximum possible thermal efficiencies and the rate of heat rejected from this power plant are to be determined. ASSUMPTIONS 1. The power plant operates steadily 2. The kinetic and potential energy changes are zero 3. Steam properties are used for geothermal water PROPERTIES Using appropriate tables, the source and the sink state enthalpies of geothermal water can be found Tsource = 160°C  Tsink = 25°C   hsource = 675.47 kJ kg  hsink = 104.83 kJ kg xsource = 0  xsink = 0 © Athlone Institute of Technology
  • 107. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant© Athlone Institute of Technology
  • 108. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW© Athlone Institute of Technology
  • 109. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is© Athlone Institute of Technology
  • 110. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is & Wnet , out 22MW ηth = = = 0.0876 & Qin 251.083MW© Athlone Institute of Technology
  • 111. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is & Wnet , out 22MW ηth = = = 0.0876 & Qin 251.083MW (b) The maximum thermal efficiency is the thermal efficiency of a reversible heat engine operating between the source and sink temperatures© Athlone Institute of Technology
  • 112. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is & Wnet , out 22MW ηth = = = 0.0876 & Qin 251.083MW (b) The maximum thermal efficiency is the thermal efficiency of a reversible heat engine operating between the source and sink temperatures TL ηth, max = 1− TH© Athlone Institute of Technology
  • 113. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is & Wnet , out 22MW ηth = = = 0.0876 & Qin 251.083MW (b) The maximum thermal efficiency is the thermal efficiency of a reversible heat engine operating between the source and sink temperatures TL ηth, max = 1− TH (c) The rate of heat rejected is© Athlone Institute of Technology
  • 114. ANALYSIS (a) The rate heat input to the plant may be taken as the enthalpy difference between the source and the sink for the power plant & & Qin = mgeo ( hsource − hsink ) = 440 kg s ( 675.47 − 104.83) kJ kg = 251,083kW The actual thermal efficiency is & Wnet , out 22MW ηth = = = 0.0876 & Qin 251.083MW (b) The maximum thermal efficiency is the thermal efficiency of a reversible heat engine operating between the source and sink temperatures TL ηth, max = 1− TH (c) The rate of heat rejected is & & & Qout = Qin − Wnet , out© Athlone Institute of Technology