EP1938021A1 - Heat pump water heating system using variable speed compressor - Google Patents

Heat pump water heating system using variable speed compressor

Info

Publication number
EP1938021A1
EP1938021A1 EP05793392A EP05793392A EP1938021A1 EP 1938021 A1 EP1938021 A1 EP 1938021A1 EP 05793392 A EP05793392 A EP 05793392A EP 05793392 A EP05793392 A EP 05793392A EP 1938021 A1 EP1938021 A1 EP 1938021A1
Authority
EP
European Patent Office
Prior art keywords
refrigerant
performance
coefficient
heat
variable speed
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05793392A
Other languages
German (de)
French (fr)
Other versions
EP1938021A4 (en
Inventor
Yu Chen
Lili Zhang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Carrier Corp
Original Assignee
Carrier Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Carrier Corp filed Critical Carrier Corp
Publication of EP1938021A1 publication Critical patent/EP1938021A1/en
Publication of EP1938021A4 publication Critical patent/EP1938021A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
    • F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/025—Motor control arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2309/00—Gas cycle refrigeration machines
    • F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
    • F25B2309/061—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide with cycle highest pressure above the supercritical pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2339/00—Details of evaporators; Details of condensers
    • F25B2339/04—Details of condensers
    • F25B2339/047—Water-cooled condensers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2500/00—Problems to be solved
    • F25B2500/19—Calculation of parameters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/02—Compressor control
    • F25B2600/025—Compressor control by controlling speed
    • F25B2600/0253—Compressor control by controlling speed with variable speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/17—Control issues by controlling the pressure of the condenser
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Definitions

  • the present invention relates generally to a heat pump or refrigeration system including a variable speed compressor that changes the speed of refrigerant flowing through the compressor to optimize the Coefficient of Performance (COP) of the system, which is usually defined as a ratio of the heating capacity to the electric power consumption of the compressor and the fan.
  • COP Coefficient of Performance
  • Carbon dioxide is an environmentally friendly refrigerant that is commonly used in a refrigeration system. Carbon dioxide has a low critical point, and most refrigeration systems utilizing carbon dioxide as the refrigerant run transcritically or partially above the critical point.
  • the pressure of a subcritical fluid is a function of temperature under saturated conditions (when both liquid and vapor are present). However, when the temperature of the fluid is higher than the critical temperature or supercritical, the pressure becomes a function of the density of the fluid.
  • a heat pump system can operate under a wide range of conditions.
  • the outdoor air temperature can vary from approximately -10 0 F in the winter to approximately 120°F in the summer. Therefore, the refrigerant evaporating temperature can vary from approximately -20 0 F in the winter to approximately 100 0 F in the summer.
  • the carbon dioxide density at the compressor suction is eight to ten times greater in the summer than the carbon dioxide density at the compressor suction in the winter.
  • the heating load of the refrigeration system does not change much as the outdoor air temperature changes.
  • the heating capacity and the mass flow rate of the refrigerant should be maintained approximately constant.
  • the mass flow rate is a product of the refrigerant density at the compressor suction and the volumetric flow rate. Because the refrigerant suction density is increased in the summer, the volumetric flow rate in the summer should be significantly lower than the volumetric flow rate in the winter.
  • Variable speed compressors have been used to regulate the volumetric flow rate to maintain the mass flow rate of the refrigerant under different working conditions.
  • the compressor speed is related to the outdoor air temperature. The compressor operates at a minimum speed when the outdoor air temperature is close to the highest design temperature, and the compressor operates at a maximum speed when the outdoor air temperature is close to the lowest design temperature. This requires a preset correlation between the compressor speed and the outdoor air temperature to regulate the volumetric flow rate of the refrigerant.
  • the compressor speed is based on the cooling load of the evaporator. The compressor operates at a minimum speed when the cooling load of the evaporator is the highest, and the compressor operates at the maximum speed when the cooling load is the lowest.
  • the compressor speed is lower in the summer to maintain a nearly constant heating capacity.
  • the preset compressor speed for a certain outdoor air temperature may not be the optimal compressor speed to achieve the optimal coefficient of performance.
  • the preset compressor speed cannot accommodate any changes in the COP caused by degradation of the system components over time. That is, the preset compressor speed is not adaptive. Therefore, there is a need for a heat pump or refrigeration system including a variable speed compressor that is adaptive and able to vary the compression speed to achieve the optimal coefficient of performance under all operating conditions.
  • a heat pump or refrigeration system includes a compressor, a gas cooler, an expansion device, and an evaporator.
  • Refrigerant is circulated though the closed circuit system.
  • carbon dioxide is used as the refrigerant.
  • Carbon dioxide has a low critical point, and systems utilizing carbon dioxide as the refrigerant usually run transcritically.
  • the refrigerant is compressed in the compressor and then cooled in a gas cooler.
  • the refrigerant in the gas cooler rejects heat to a fluid medium, such as water, heating the water.
  • the refrigerant then passes through the expansion device and is expanded to a low pressure. After expansion, the refrigerant flows through the evaporator and is heated by ambient outdoor air.
  • the refrigerant is then compressed, completing the cycle.
  • a variable speed drive controls the speed of the refrigerant flowing through the compressor. Varying the speed of the refrigerant flowing through the compressor changes the mass flow rate of the refrigerant in the system and affects the performance of the gas cooler and the evaporator.
  • Figure 1 schematically illustrates a diagram of a refrigeration system employing a variable speed compressor.
  • FIG. 1 illustrates a transcritical refrigeration system 20 including a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28.
  • Refrigerant circulates through the closed circuit system 20.
  • carbon dioxide is used as the refrigerant.
  • carbon dioxide has a low critical point, and systems utilizing carbon dioxide as the refrigerant usually run transcritically.
  • the refrigerant exits the compressor 22 at a high pressure and a high enthalpy.
  • the refrigerant flows through the gas cooler 24 and loses heat, exiting the gas cooler 24 at a low enthalpy and a high pressure.
  • a fluid medium such as water flows through a heat sink 30 of the gas cooler 24 and exchanges heat with the refrigerant.
  • a water pump 32 flows the fluid medium through the heat sink 30.
  • the cold fluid 34 enters the heat sink 30 at the heat sink inlet or return 36 and flows in a direction opposite to the direction of flow of the refrigerant. After accepting heat from the refrigerant, the heated water 38 exits at the heat sink outlet or supply 40.
  • the refrigerant enters the gas cooler 24 at a refrigerant inlet 62 and exits at a refrigerant outlet 64.
  • the refrigerant is expanded to a low pressure in the expansion device 26.
  • the expansion device 26 can be an electronic expansion valve (EXV) or other type of expansion device.
  • EXV electronic expansion valve
  • the refrigerant exits the expansion device at a low pressure and a low enthalpy.
  • the refrigerant flows through the evaporator 28 and accepts heat from the outdoor air.
  • Outdoor air 44 flows through a heat sink 46 and rejects heat to the refrigerant passing through the evaporator 28.
  • the outdoor air enters the heat sink 46 through the heat sink inlet or return 48 and flows in a direction opposite to the direction of flow of the refrigerant.
  • a fan 54 moves the ambient air across the evaporator 28 and controls the speed of the air that moves across the evaporator 28.
  • the cooled outdoor air 50 exits the heat sink 46 through the heat sink outlet or supply 52.
  • the refrigerant enters the evaporator 28 at a refrigerant inlet 68 and exits at a refrigerant outlet 66.
  • the refrigerant exits the evaporator 28 at a high enthalpy and a low pressure.
  • the speed of the compressor 22 is adjusted to achieve the optimal coefficient of performance for any outdoor air 44 temperature. Coefficient of performance is defined as the heating capacity of the system 20 divided by the power input of the system 20.
  • the heating capacity of the system 20 is the amount of heat transfer in the gas cooler 24, and the power input of the system 20 is the work of the compressor 22 plus the work of the fan 54 that blows air over the evaporator 28.
  • a variable speed drive 70 controls the speed of the refrigerant flowing through the compressor 22. Varying the speed of the refrigerant flowing through the compressor 22 changes the mass flow rate of the refrigerant in the system 20 and affects the heat transfer performance of the gas cooler 24 and the evaporator 28. Decreasing the mass flow rate causes the refrigerant to flow through the gas cooler 24 and the evaporator 28 more slowly, increasing the energy exchanger per unit flow rate of the refrigerant and improving the performance of the gas cooler 24 and the evaporator 28. However, as the mass flow rate is reduced, the power of the fan 54 per unit flow rate increases. Therefore, as the power of the fan 54 per unit flow rate increases, the coefficient of performance decreases.
  • a sensor 74 detects the coefficient of performance of the system 20 and sends this value to a control 72.
  • the control 72 is programmed to determine if the detected coefficient of performance is the optimal coefficient of performance.
  • the control 74 varies the speed of the compressor 22 accordingly to provide the optimal coefficient of performance.
  • the system 20 can be dynamically adapted to different environmental conditions and system degradations to achieve the optimal coefficient of performance at all times. There is an optimal operating speed for the compressor 22 for every environmental condition that achieves the optimal coefficient of performance.
  • This system 20 can be used in a stand alone way or jointly with other system operating methods.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Air Conditioning Control Device (AREA)

Abstract

A transcritical refrigeration system includes a compressor, a gas cooler, an expansion device, and an evaporator. Refrigerant is circulated though the closed circuit system. Preferably, carbon dioxide is used as the refrigerant. A variable speed drive controls the speed of the refrigerant flowing through the compressor. Varying the speed of the refrigerant flowing through the compressor changes the mass flow rate of the refrigerant in the system to optimize the coefficient of performance.

Description

HEAT PUMP WATER HEATING SYSTEM USING VARIABLE SPEED
COMPRESSOR
BACKGROUND OF THE INVENTION
The present invention relates generally to a heat pump or refrigeration system including a variable speed compressor that changes the speed of refrigerant flowing through the compressor to optimize the Coefficient of Performance (COP) of the system, which is usually defined as a ratio of the heating capacity to the electric power consumption of the compressor and the fan.
Carbon dioxide is an environmentally friendly refrigerant that is commonly used in a refrigeration system. Carbon dioxide has a low critical point, and most refrigeration systems utilizing carbon dioxide as the refrigerant run transcritically or partially above the critical point. The pressure of a subcritical fluid is a function of temperature under saturated conditions (when both liquid and vapor are present). However, when the temperature of the fluid is higher than the critical temperature or supercritical, the pressure becomes a function of the density of the fluid. A heat pump system can operate under a wide range of conditions. The outdoor air temperature can vary from approximately -100F in the winter to approximately 120°F in the summer. Therefore, the refrigerant evaporating temperature can vary from approximately -200F in the winter to approximately 1000F in the summer. As a result, the carbon dioxide density at the compressor suction is eight to ten times greater in the summer than the carbon dioxide density at the compressor suction in the winter. However, the heating load of the refrigeration system does not change much as the outdoor air temperature changes.
To avoid oversizing the system or the heat exchangers, the heating capacity and the mass flow rate of the refrigerant should be maintained approximately constant. The mass flow rate is a product of the refrigerant density at the compressor suction and the volumetric flow rate. Because the refrigerant suction density is increased in the summer, the volumetric flow rate in the summer should be significantly lower than the volumetric flow rate in the winter.
Variable speed compressors have been used to regulate the volumetric flow rate to maintain the mass flow rate of the refrigerant under different working conditions. In one system, the compressor speed is related to the outdoor air temperature. The compressor operates at a minimum speed when the outdoor air temperature is close to the highest design temperature, and the compressor operates at a maximum speed when the outdoor air temperature is close to the lowest design temperature. This requires a preset correlation between the compressor speed and the outdoor air temperature to regulate the volumetric flow rate of the refrigerant. In another system, the compressor speed is based on the cooling load of the evaporator. The compressor operates at a minimum speed when the cooling load of the evaporator is the highest, and the compressor operates at the maximum speed when the cooling load is the lowest.
In both of these systems, the compressor speed is lower in the summer to maintain a nearly constant heating capacity. However, the preset compressor speed for a certain outdoor air temperature may not be the optimal compressor speed to achieve the optimal coefficient of performance. Additionally, the preset compressor speed cannot accommodate any changes in the COP caused by degradation of the system components over time. That is, the preset compressor speed is not adaptive. Therefore, there is a need for a heat pump or refrigeration system including a variable speed compressor that is adaptive and able to vary the compression speed to achieve the optimal coefficient of performance under all operating conditions.
SUMMARY OF THE INVENTION
A heat pump or refrigeration system includes a compressor, a gas cooler, an expansion device, and an evaporator. Refrigerant is circulated though the closed circuit system. Preferably, carbon dioxide is used as the refrigerant. Carbon dioxide has a low critical point, and systems utilizing carbon dioxide as the refrigerant usually run transcritically.
The refrigerant is compressed in the compressor and then cooled in a gas cooler. The refrigerant in the gas cooler rejects heat to a fluid medium, such as water, heating the water. The refrigerant then passes through the expansion device and is expanded to a low pressure. After expansion, the refrigerant flows through the evaporator and is heated by ambient outdoor air. The refrigerant is then compressed, completing the cycle. A variable speed drive controls the speed of the refrigerant flowing through the compressor. Varying the speed of the refrigerant flowing through the compressor changes the mass flow rate of the refrigerant in the system and affects the performance of the gas cooler and the evaporator. Decreasing the refrigerant mass flow rate causes the refrigerant to flow through the heat exchangers more slowly, increasing the energy exchanger per unit flow rate of the refrigerant and improving the performance of the heat exchangers. However, as the mass flow rate is reduced, the fan power per unit flow rate increases in the evaporator coil. As the power of the fan per unit flow rate increases, the coefficient of performance decreases. For any environmental condition, there is an optimal operating speed for the compressor that achieves the optimal coefficient of performance. In general, the higher the outdoor temperature, the lower the optimal speed of the compressor to obtain the optimal coefficient of performance. These and other features of the present invention will be best understood from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
Figure 1 schematically illustrates a diagram of a refrigeration system employing a variable speed compressor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 illustrates a transcritical refrigeration system 20 including a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28. Refrigerant circulates through the closed circuit system 20. Preferably, carbon dioxide is used as the refrigerant. Although carbon dioxide is described, other refrigerants may be used. Carbon dioxide has a low critical point, and systems utilizing carbon dioxide as the refrigerant usually run transcritically. When operating in a water heating mode, the refrigerant exits the compressor 22 at a high pressure and a high enthalpy. The refrigerant flows through the gas cooler 24 and loses heat, exiting the gas cooler 24 at a low enthalpy and a high pressure. A fluid medium, such as water, flows through a heat sink 30 of the gas cooler 24 and exchanges heat with the refrigerant. A water pump 32 flows the fluid medium through the heat sink 30. The cold fluid 34 enters the heat sink 30 at the heat sink inlet or return 36 and flows in a direction opposite to the direction of flow of the refrigerant. After accepting heat from the refrigerant, the heated water 38 exits at the heat sink outlet or supply 40. The refrigerant enters the gas cooler 24 at a refrigerant inlet 62 and exits at a refrigerant outlet 64.
The refrigerant is expanded to a low pressure in the expansion device 26. The expansion device 26 can be an electronic expansion valve (EXV) or other type of expansion device. The refrigerant exits the expansion device at a low pressure and a low enthalpy. After expansion, the refrigerant flows through the evaporator 28 and accepts heat from the outdoor air. Outdoor air 44 flows through a heat sink 46 and rejects heat to the refrigerant passing through the evaporator 28. The outdoor air enters the heat sink 46 through the heat sink inlet or return 48 and flows in a direction opposite to the direction of flow of the refrigerant. A fan 54 moves the ambient air across the evaporator 28 and controls the speed of the air that moves across the evaporator 28. After exchanging heat with the refrigerant, the cooled outdoor air 50 exits the heat sink 46 through the heat sink outlet or supply 52. The refrigerant enters the evaporator 28 at a refrigerant inlet 68 and exits at a refrigerant outlet 66. The refrigerant exits the evaporator 28 at a high enthalpy and a low pressure. The speed of the compressor 22 is adjusted to achieve the optimal coefficient of performance for any outdoor air 44 temperature. Coefficient of performance is defined as the heating capacity of the system 20 divided by the power input of the system 20. The heating capacity of the system 20 is the amount of heat transfer in the gas cooler 24, and the power input of the system 20 is the work of the compressor 22 plus the work of the fan 54 that blows air over the evaporator 28.
A variable speed drive 70 controls the speed of the refrigerant flowing through the compressor 22. Varying the speed of the refrigerant flowing through the compressor 22 changes the mass flow rate of the refrigerant in the system 20 and affects the heat transfer performance of the gas cooler 24 and the evaporator 28. Decreasing the mass flow rate causes the refrigerant to flow through the gas cooler 24 and the evaporator 28 more slowly, increasing the energy exchanger per unit flow rate of the refrigerant and improving the performance of the gas cooler 24 and the evaporator 28. However, as the mass flow rate is reduced, the power of the fan 54 per unit flow rate increases. Therefore, as the power of the fan 54 per unit flow rate increases, the coefficient of performance decreases. In general, the higher the outdoor temperature 44, the lower the optimal speed of the compressor 22. A sensor 74 detects the coefficient of performance of the system 20 and sends this value to a control 72. The control 72 is programmed to determine if the detected coefficient of performance is the optimal coefficient of performance. The control 74 varies the speed of the compressor 22 accordingly to provide the optimal coefficient of performance. By varying the speed of the refrigerant flowing through the compressor 22, the system 20 can be dynamically adapted to different environmental conditions and system degradations to achieve the optimal coefficient of performance at all times. There is an optimal operating speed for the compressor 22 for every environmental condition that achieves the optimal coefficient of performance. This system 20 can be used in a stand alone way or jointly with other system operating methods.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims

1. A transcritical refrigeration system comprising: a compression device to compress a refrigerant to a high pressure; a heat rejecting heat exchanger for cooling said refrigerant; an expansion device for reducing said refrigerant to a low pressure; a heat accepting heat exchanger for evaporating said refrigerant, and an airflow exchanges heat with said refrigerant in said heat accepting heat exchanger; and a variable speed device that moves said refrigerant through said compressor at a variable speed to optimize a coefficient of performance of the system.
2. The system as recited in claim 1 wherein the refrigerant is carbon dioxide.
3. The system as recited in claim 1 further including a fan that blows a fluid over said heat accepting heat exchanger.
4. The system as recited in claim 3 wherein the coefficient of performance is relating to a heating capacity of the system and an amount of work of the compression device plus an amount of work of the fan, wherein the heating capacity of the system is an amount of heat transfer in the heat rejecting heat exchanger.
5. The system as recited in claim 1 wherein the variable speed device adjusts a mass flow rate of the refrigerant through the compression device.
6. The system as recited in claim 1 wherein decreasing the mass flow rate of the refrigerant increases a power of a fan per unit mass flow of the refrigerant.
7. The system as recited in claim 1 further including a sensor that monitors the coefficient of performance of the system.
8. The system as recited in claim 7 further including a control that controls the variable speed device, and the control adjusts the mass flow rate of the refrigerant with the variable speed device when the sensor determines that the coefficient of performance is not an optimal coefficient of performance.
9. A transcritical refrigeration system comprising: a compression device to compress a refrigerant to a high pressure; a heat rejecting heat exchanger for cooling said refrigerant; an expansion device for reducing said refrigerant to a low pressure; a heat accepting heat exchanger for evaporating said refrigerant, and an airflow exchanges heat with said refrigerant in said heat accepting heat exchanger; a fan that blows a fluid over said heat accepting heat exchanger; a variable speed device that moves said refrigerant through said compressor at a variable speed to optimize a coefficient of performance of the system; a sensor that monitors the coefficient of performance of the system; and a control that controls the variable speed device, and the control adjusts the mass flow rate of the refrigerant with the variable speed device when the sensor determines that the coefficient of performance is not an optimal coefficient of performance.
10. The system as recited in claim 9 wherein the coefficient of performance is relating to a heating capacity of the system and an amount of work of the compression device plus an amount of work of the fan, wherein the heating capacity of the system is an amount of heat transfer in the heat rejecting heat exchanger.
11. A method of optimizing a coefficient of performance of a transcritical refrigeration system comprising the steps of: compressing a refrigerant to a high pressure; cooling the refrigerant; expanding the refrigerant to a low pressure; evaporating the refrigerant; sensing a coefficient of performance of the system; and adjusting a speed of the refrigerant flowing the said compressor based on the coefficient of performance of the system.
EP05793392A 2005-08-31 2005-08-31 Heat pump water heating system using variable speed compressor Withdrawn EP1938021A4 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2005/030881 WO2007027173A1 (en) 2005-08-31 2005-08-31 Heat pump water heating system using variable speed compressor

Publications (2)

Publication Number Publication Date
EP1938021A1 true EP1938021A1 (en) 2008-07-02
EP1938021A4 EP1938021A4 (en) 2010-09-01

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EP05793392A Withdrawn EP1938021A4 (en) 2005-08-31 2005-08-31 Heat pump water heating system using variable speed compressor

Country Status (4)

Country Link
US (1) US20080302118A1 (en)
EP (1) EP1938021A4 (en)
CA (1) CA2616286A1 (en)
WO (1) WO2007027173A1 (en)

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