US20010048031A1 - Heat-pump water heater - Google Patents
Heat-pump water heater Download PDFInfo
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- US20010048031A1 US20010048031A1 US09/837,107 US83710701A US2001048031A1 US 20010048031 A1 US20010048031 A1 US 20010048031A1 US 83710701 A US83710701 A US 83710701A US 2001048031 A1 US2001048031 A1 US 2001048031A1
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- Prior art keywords
- compressor
- refrigerant
- heat
- control unit
- temperature
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 112
- 239000003507 refrigerant Substances 0.000 claims abstract description 133
- 238000010438 heat treatment Methods 0.000 claims abstract description 46
- 239000012530 fluid Substances 0.000 claims description 49
- 238000001514 detection method Methods 0.000 claims description 16
- 230000003247 decreasing effect Effects 0.000 abstract description 13
- 230000008020 evaporation Effects 0.000 description 13
- 238000001704 evaporation Methods 0.000 description 13
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 8
- 238000010586 diagram Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 6
- 229910002092 carbon dioxide Inorganic materials 0.000 description 4
- 239000001569 carbon dioxide Substances 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 238000007664 blowing Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000008236 heating water Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
- F24H4/00—Fluid heaters characterised by the use of heat pumps
- F24H4/02—Water heaters
- F24H4/04—Storage heaters
-
- 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
- F25B30/00—Heat pumps
- F25B30/02—Heat pumps of the compression type
-
- 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
- F25B41/00—Fluid-circulation arrangements
- F25B41/30—Expansion means; Dispositions thereof
- F25B41/31—Expansion valves
- F25B41/34—Expansion valves with the valve member being actuated by electric means, e.g. by piezoelectric actuators
-
- 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
- F25B2341/00—Details of ejectors not being used as compression device; Details of flow restrictors or expansion valves
- F25B2341/06—Details of flow restrictors or expansion valves
- F25B2341/063—Feed forward expansion valves
-
- 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
- F25B2600/021—Inverters therefor
-
- 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
-
- 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
- F25B2700/00—Sensing or detecting of parameters; Sensors therefor
- F25B2700/21—Temperatures
- F25B2700/2115—Temperatures of a compressor or the drive means therefor
- F25B2700/21152—Temperatures of a compressor or the drive means therefor at the discharge side of the compressor
-
- 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
- F25B2700/00—Sensing or detecting of parameters; Sensors therefor
- F25B2700/21—Temperatures
- F25B2700/2116—Temperatures of a condenser
-
- 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
- F25B2700/00—Sensing or detecting of parameters; Sensors therefor
- F25B2700/21—Temperatures
- F25B2700/2116—Temperatures of a condenser
- F25B2700/21161—Temperatures of a condenser of the fluid heated by the condenser
-
- 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
-
- 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
-
- 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 to a heat-pump water heater that heats water using a super-critical (transcritical) heat pump cycle as a heating source.
- a conventional heat-pump water heater low-temperature water is heat-exchanged with high-temperature refrigerant in a water heat exchanger, and high-temperature water heated in the water heat exchanger is stored in a water tank to be supplied to a user after being temperature-adjusted.
- a target temperature difference ⁇ T between water flowing into the water heat exchanger and refrigerant discharged from the water heat exchanger is set, and high-pressure side refrigerant pressure of the heat pump cycle is controlled based on the target temperature difference ⁇ T for increasing a cycle efficiency of the heat pump cycle.
- the high-pressure side refrigerant pressure is controlled by adjusting a valve opening degree of the expansion valve.
- a low-pressure side refrigerant pressure e.g., evaporation pressure
- temperature of refrigerant discharged from a compressor may exceed a normal operation temperature area of the compressor.
- a heat-pump fluid heater for heating a fluid (e.g., water) using a heat pump cycle as a heating source, in which a refrigerant temperature discharged from a compressor can be controlled in an operation temperature area even when the heat pump cycle is used under a low temperature.
- a fluid e.g., water
- a control unit for controlling operation of the heat pump cycle controls a high-pressure side refrigerant pressure from the compressor and before being decompressed in the heat pump cycle, so that a temperature difference between the fluid flowing into a heat exchanger and refrigerant discharged from the heat exchanger becomes a set target temperature difference.
- the control unit has a detection member for detecting one of a refrigerant temperature and a physical amount relative to the refrigerant temperature discharged from the compressor, and the control unit changes the target temperature difference to be increased when a detection value of the detection member is more than a predetermined value.
- the control unit sets the target temperature difference larger as a low-pressure side refrigerant pressure after being decompressed in the heat pump cycle becomes lower, when the low-pressure side refrigerant pressure in the heat pump cycle is lower than a predetermined pressure.
- the low-pressure side refrigerant pressure e.g., evaporation pressure
- the target temperature difference larger as the low-pressure side refrigerant pressure becomes lower, it can effectively restrict the refrigerant temperature discharged from the compressor from being increased.
- the control unit determines whether or not a load of the compressor is excessive, and the control unit changes the target temperature difference to be increased to a value when it is determined that the load of the compressor is excessive.
- the target temperature difference is made larger, the compressor continuously operates with a relatively lower high-pressure. Accordingly, is can prevent a problem of a heat pump cycle due to an increased load of the compressor. Further, when the fluid is water in a hot water supply system, a desired water-heating capacity can be obtained.
- the control unit has a temperature detection sensor for detecting a refrigerant temperature discharged from the compressor, and the control unit controls a high-pressure side refrigerant pressure from the compressor and before being decompressed in the heat pump cycle, so that a temperature difference between the fluid flowing into the heat exchanger and refrigerant discharged from the heat exchanger becomes a target temperature difference when the refrigerant temperature detected by the temperature sensor is lower than a predetermined temperature.
- the control unit controls the high-pressure side refrigerant pressure of the heat pump cycle so that the refrigerant temperature detected by the temperature sensor becomes lower than the predetermined temperature. Accordingly, the refrigerant temperature discharged from the compressor can be directly controlled without changing the target temperature difference.
- FIG. 1 is a schematic diagram of a heat-pump water heater according to a first preferred embodiment of the present invention
- FIG. 2 is a graph (T-H diagram) showing a relationship between temperature and enthalpy in a heat pump cycle using carbon dioxide as refrigerant, according to the first embodiment
- FIG. 3 is a flow diagram showing a control process of an electronic control unit (ECU) according to the first embodiment
- FIG. 4 is a flow diagram showing a control process of the ECU according to a second preferred embodiment of the present invention.
- FIG. 5 is a characteristic view showing a relationship between an evaporation temperature Ts of refrigerant and a target temperature difference ⁇ T, according to the second embodiment
- FIG. 6 is a flow diagram showing a control process of the ECU according to a third preferred embodiment of the present invention.
- FIGS. 7A and 7B are graphs (T-H diagrams), respectively, each showing a relationship between temperature and enthalpy in a heat pump cycle using carbon dioxide as refrigerant, according to the third embodiment;
- FIG. 8 is a graph showing a relationship between a driving current and a load of a compressor according to a modification of the present invention.
- FIG. 9 is a graph showing a stepwise change of the target temperature difference ⁇ T according to an another modification of the present invention.
- a heat-pump water heater 1 is a hot water supply system, in which heated hot water is stored in a tank 2 and is supplied to a user after being temperature-adjusted.
- the heat-pump water heater 1 includes the tank 2 , an electrical pump 3 forcibly circulating water in a water cycle, and a super-critical (trans-critical) heat pump cycle 4 .
- the tank 2 is made of a metal having a corrosion resistance, such as a stainless steel, and has a heat insulating structure so that high-temperature hot water can be stored for a long time. Hot water stored in the tank 2 can be supplied to a kitchen, a bath or the like, and can be used as a heating source for a floor heater or a room heater or the like.
- the electrical pump 3 , the tank 2 and a water heat exchanger 7 of the heater pump cycle 4 are connected by a water pipe 5 to form the water cycle. Therefore, water circulates between the tank 2 and the water heat exchanger 7 , and water circulating amount in the water cycle can be adjusted in accordance with a rotation speed of a motor disposed in the electrical pump 3 .
- the super-critical heat pump cycle 4 uses carbon dioxide having a low-critical pressure as refrigerant, for example, so that a high-pressure side refrigerant pressure becomes equal to or greater than the critical pressure of carbon dioxide.
- the heater pump cycle 4 includes a compressor 6 , the water heat exchanger 7 , an expansion valve 8 , an air heat exchanger 9 and an accumulator 10 .
- the compressor 6 includes an electrical motor 6 a which is driven by an inverter circuit 16 .
- the compressor 6 compresses sucked gas refrigerant by the rotation of the electrical motor 6 a , so that refrigerant discharged from the compressor 6 has the pressure equal to or greater than the critical pressure of refrigerant.
- the water heat exchanger 7 is disposed to perform a heat exchange between high-pressure gas refrigerant discharged from the compressor 6 and water pumped from the electrical pump 3 . In the water heat exchanger 7 , a flow direction of refrigerant is set opposite to a flow direction of water.
- the expansion valve 8 is constructed so that a valve opening degree can be electrically adjusted.
- the expansion valve 8 is disposed at a downstream side of the water heat exchanger 7 in a refrigerant flow direction, and decompresses refrigerant cooled in the water heat exchanger 7 in accordance with a valve opening degree.
- a fan 11 for blowing air (i.e., outside air) toward the air heat exchanger 9 is disposed so that refrigerant decompressed in the expansion valve 8 is heat-exchanged with air in the air heat exchanger 9 . Therefore, refrigerant is evaporated in the air heat exchanger 9 by absorbing heat from air.
- Refrigerant from the air heat exchanger 9 flows into the accumulator 10 and is separated into gas refrigerant and liquid refrigerant in the accumulator 10 . Only separated gas refrigerant in the accumulator 10 is sucked into the compressor 6 , and surplus refrigerant in the heat pump cycle 4 is stored in the accumulator 10 .
- the heat-pump water heater 1 has an electrical control unit (hereinafter, referred to as ECU) 15 , and plural sensors 12 - 14 .
- the plural sensors 12 - 14 are a first refrigerant temperature sensor 12 for detecting a temperature Td of refrigerant discharged from the compressor 6 , a water temperature sensor 13 for detecting temperature Tw of water flowing into the water heat exchanger 7 , and the second refrigerant temperature sensor 14 for detecting temperature Tr of refrigerant flowing out from the water heat exchanger 7 .
- Detection signals from the sensors 12 - 14 are input into the ECU 15 , and the ECU 15 controls operation of the heat pump cycle 4 .
- the ECU 15 controls a high-pressure side refrigerant pressure in the heat pump cycle 4 based on a temperature difference between water flowing into the water heat exchanger 7 and refrigerant flowing out from the water heat exchanger 7 , so that the heat pump cycle 4 can be operated with a high efficiency. That is, a target temperature difference ⁇ T between water flowing into the water heat exchanger 7 and refrigerant flowing out from the water heat exchanger 7 is set as an index of the cycle efficiency, and the valve opening degree of the expansion valve 8 is electrically controlled so that the target temperature difference ⁇ T is obtained.
- step S 10 the high-pressure side refrigerant pressure of the heat pump cycle 4 is controlled by controlling the valve opening degree of the expansion valve 8 , so that a set target temperature difference ⁇ T (e.g., 10° C.) is obtained.
- step S 20 the refrigerant temperature Td discharged from the compressor 6 is detected by the first refrigerant temperature sensor 12 .
- step S 30 it is determined whether or not the refrigerant temperature Td discharged from the compressor 6 is equal to or higher than a predetermined value Tdp.
- the predetermined value Tdp is set based on a permissible upper limit temperature of the compressor 6 .
- the target temperature difference ⁇ T is increased at step S 40 .
- the control routine returns to step S 10 . Accordingly, the target temperature difference ⁇ T is gradually increased until the refrigerant temperature Td discharged from the compressor 6 becomes smaller than the predetermined value Tdp.
- the water heating capacity can be determined based on a heat quantity of hot water that is heated by refrigerant in the water heat exchanger 7 and is stored in the tank 2 .
- the heat quantity of hot water is calculated in accordance with a hot water temperature and a hot water flow amount. Specifically, when the heat quantity transmitted into water for a predetermined time is equal to or larger than a predetermined value, it is determined that the target water heating capacity is obtained.
- step S 50 When it is determined that the water heating capacity reaches the target water heating capacity at step S 50 , the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity at step S 50 , the rotation speed of the motor 6 a of the compressor 6 is increased for obtaining the target water heating capacity. Thereafter, the control routine moves to step S 10 .
- FIG. 2 shows both states of the heat pump cycle 4 , before and after the valve opening degree of the expansion valve 8 becomes larger.
- Q′ indicates a heat radiating capacity of the water heat exchanger 7 before the valve opening degree of the expansion valve 8 becomes larger
- Q indicates the heat radiating capacity of the water heat exchanger 7 after the valve opening degree of the expansion valve 8 becomes larger
- L′ indicates a compression operation amount (i.e., consumed power) before the valve opening degree of the expansion valve 8 becomes larger
- L indicates the compression operation amount after the valve opening degree of the expansion valve 8 becomes larger.
- a physical amount relative to the refrigerant temperature Td such as an evaporation pressure, an evaporation temperature and a refrigerant pressure discharged from the compressor 6 , may be used.
- the valve opening degree of the expansion valve 8 can be directly controlled so that the refrigerant temperature Td becomes lower than the target temperature Tdp, without changing the target temperature difference ⁇ T or without firstly setting the target temperature difference ⁇ T.
- the target temperature difference ⁇ T is set based on a low-pressure side refrigerant temperature (e.g., evaporation temperature TS of refrigerant).
- a low-pressure side refrigerant temperature e.g., evaporation temperature TS of refrigerant.
- the other parts are similar to those of the above-described first embodiment.
- FIG. 4 is a flow diagram showing a control process of the ECU 15 according to the second embodiment.
- the valve opening degree of the expansion valve 8 is controlled so that a set target temperature difference ⁇ T can be obtained.
- an evaporation temperature Ts of refrigerant is detected at step S 120 , and it is determined whether or not the evaporation temperature Ts is equal to or lower than a predetermined temperature Ts 1 (i.e., protection control start temperature) at step S 130 .
- a predetermined temperature Ts 1 i.e., protection control start temperature
- the target temperature difference ⁇ T is determined based on the evaporation temperature Ts of refrigerant in accordance with the graph of FIG. 5.
- Tp indicates a protection control start point.
- the control routine moves to step S 170 .
- step S 140 After the target temperature difference ⁇ T is determined at step S 140 , an actual temperature difference ⁇ T 0 is detected at step S 150 , and the set target temperature difference ⁇ T is compared with the actual temperature difference ⁇ T 0 at step S 160 . That is, at step S 160 , it is determined whether or not the set target temperature difference ⁇ T is agreement with the actual temperature difference ⁇ T 0 . When it is determined that the set target temperature difference ⁇ T is agreement with the actual temperature difference ⁇ T 0 , the control routine moves to step S 170 . On the other hand, when it is determined that the set target temperature difference ⁇ T is not agreement with the actual temperature difference ⁇ T 0 , the control routine moves to step S 110 .
- step S 170 it is determined whether or not a water heating capacity reaches a target water heating capacity. When it is determined that the water heating capacity reaches the target water heating capacity, the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity, the rotation speed of the motor 6 a of the compressor 6 is increased at step S 180 for obtaining the target water heating capacity. Thereafter, the control routine moves to step S 10 .
- the target temperature difference ⁇ T is set to be larger than a general control based on the refrigerant evaporation temperature Ts. Therefore, the opening degree of the expansion valve 8 becomes larger, the refrigerant pressure discharged from the compressor 6 becomes lower, and refrigerant temperature Td discharged from the compressor 6 can be decreased to the operation temperature area. As a result, it can prevent a problem affected to the compressor 6 in the heat pump cycle 4 .
- the predetermined temperature Ts 1 protection control start temperature
- a third preferred embodiment of the present invention will be now described with reference to FIGS. 6, 7A and 7 B.
- the third embodiment it is determined whether or not the load applied to the compressor 6 is excessive (i.e., larger than an upper limit value), and the target temperature difference ⁇ T is set larger when the load of the compressor 6 is excessive.
- an operation state of a protection circuit (not shown), which restricts output current for protecting the inverter circuit 16 , is detected.
- the output current is restricted by the protection circuit, it is determined that the load of the compressor 6 is larger than the upper limit value. That is, in this case, it is determined that the load of the compressor 6 is excessive.
- FIG. 6 is a flow diagram showing a control process of the ECU 15 according to the third embodiment.
- Step S 210 the high-pressure side refrigerant pressure of the heat pump cycle 4 is controlled by controlling the valve opening degree of the expansion valve 8 , so that a set target temperature difference ⁇ T can be obtained.
- step S 220 it is determined whether or not a current restriction due to the inverter circuit 16 is performed in the compressor 6 .
- the target temperature difference ⁇ T is changed to become larger (e.g., 15° C.) at step S 230 , and thereafter, the control routine moves to step S 210 .
- the water heating capacity can be determined based on a heat quantity of hot water that is heated by refrigerant in the water heat exchanger 7 and is stored in the tank 2 .
- the heat quantity of hot water is calculated in accordance with a hot water temperature and a hot water flow amount. Specifically, when the heat quantity transmitted into water for a predetermined time is equal to or larger than a predetermined value, it is determined that the target water heating capacity is obtained.
- step S 210 When it is determined that the water heating capacity reaches the target water heating capacity, the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity, the rotation speed of the motor 6 a of the compressor 6 is increased at step S 250 for obtaining the target water heating capacity. Thereafter, the control routine moves to step S 210 .
- the high-pressure side refrigerant pressure is controlled so that the set target temperature difference ⁇ T (e.g., 10° C.) can be obtained, and a suitable heat-exchanging state of the water heat exchanger 7 can be obtained.
- the target temperature difference ⁇ T e.g., 10° C.
- the heat pump cycle operates with a high-pressure side refrigerant pressure lower than that in the normal operation state.
- the current restriction due to the inverter circuit 16 can be canceled by increasing the target temperature difference ⁇ T, and it can prevent the refrigerant flow amount from being decreased due to a reduce of the rotation speed of the compressor 6 .
- a necessary water heating capacity can be obtained in the heat-pump water heater 1 without throttling the valve opening degree of the expansion valve 8 more than a necessary degree.
- the present invention is typically applied to the heat-pump water heater 1 for heating water.
- the present invention may be applied to a heat-pump fluid heater for heating a fluid using the heat pump cycle 4 as a heating source.
- the valve opening degree of the expansion valve 8 is controlled so that the set target temperature difference ⁇ T can be obtained.
- a water discharge amount of the electrical pump 3 may be controlled, so that the flow amount of water flowing into the water heat exchanger 7 is changed and the target temperature difference ⁇ T is obtained.
- the excessive load of the compressor 6 is determined based on the current restriction due to the inverter circuit 16 .
- electrical current applied to the motor 6 a of the compressor 6 from the inverter circuit 16 is detected, and the load of the compressor 6 may be determined based on the applied electrical current. For example, as shown in FIG. 8, when electrical current applied to the motor 6 a is equal to or larger than a determination value, it is determined that the load of the compressor 6 is equal to or larger than a set upper limit value, and the target temperature difference ⁇ T is changed to be larger.
- the excessive load of the compressor 6 may be determined based on at least one physical amount relative to the load of the compressor, such as a target heating temperature of water, an outside air temperature and a rotation speed of the compressor 6 .
- the target temperature difference when the target temperature difference ⁇ T is changed, the target temperature difference may be stepwise changed or may be gradually continuously changed.
- the target temperature difference ⁇ T can be changed stepwise based on a combination of the outside air temperature and a target water temperature to be heated.
- a determination range of the target temperature difference ⁇ T may be changed in accordance with the rotation speed of the compressor 6 . That is, as the rotation speed of the compressor 6 is higher, the target temperature difference ⁇ T is corrected to become larger.
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Heat-Pump Type And Storage Water Heaters (AREA)
Abstract
Description
- This application is related to Japanese Patent Applications No. 2000-118394 filed on Apr. 19, 2000, and No. 2000-311142 filed on Oct. 11, 2000, the contents of which are hereby incorporated by reference.
- 1. Field of the Invention
- The present invention relates to a heat-pump water heater that heats water using a super-critical (transcritical) heat pump cycle as a heating source.
- 2. Description of Related Art
- In a conventional heat-pump water heater, low-temperature water is heat-exchanged with high-temperature refrigerant in a water heat exchanger, and high-temperature water heated in the water heat exchanger is stored in a water tank to be supplied to a user after being temperature-adjusted. In the heat-pump water heater, a target temperature difference ΔT between water flowing into the water heat exchanger and refrigerant discharged from the water heat exchanger is set, and high-pressure side refrigerant pressure of the heat pump cycle is controlled based on the target temperature difference ΔT for increasing a cycle efficiency of the heat pump cycle. Generally, the high-pressure side refrigerant pressure is controlled by adjusting a valve opening degree of the expansion valve.
- However, when the high-pressure side refrigerant pressure is controlled based on the target temperature difference ΔT when the heat-pump water heater is used under a low temperature, a low-pressure side refrigerant pressure (e.g., evaporation pressure) of the heat pump cycle is decreased, and temperature of refrigerant discharged from a compressor may exceed a normal operation temperature area of the compressor.
- On the other hand, when the high-pressure side refrigerant pressure of the heat pump cycle is increased due to an outside air increase, a water temperature increase, a rotation speed increase of the compressor or a deterioration of operation performance of the water heat exchanger, load of the compressor increases, and a normal operation of the heat pump cycle may be affected. In this case, when the rotation speed of the compressor is decreased for preventing the overload of the compressor, it is difficult to obtain a necessary heating capacity in the water heater only by controlling the valve opening degree of the expansion valve.
- In view of the foregoing problems, it is an object of the present invention to provide a heat-pump fluid heater for heating a fluid (e.g., water) using a heat pump cycle as a heating source, in which a refrigerant temperature discharged from a compressor can be controlled in an operation temperature area even when the heat pump cycle is used under a low temperature.
- It is an another object of the present invention to provide a heat-pump fluid heater which prevents a problem of a heat pump cycle due to a load increase of a compressor, while obtaining a desired water-heating capacity in a water supply system.
- According to the present invention, in a heat pump fluid heater for heating a fluid (e.g., water) using a heat pump cycle as a heating source, a control unit for controlling operation of the heat pump cycle controls a high-pressure side refrigerant pressure from the compressor and before being decompressed in the heat pump cycle, so that a temperature difference between the fluid flowing into a heat exchanger and refrigerant discharged from the heat exchanger becomes a set target temperature difference. Further, the control unit has a detection member for detecting one of a refrigerant temperature and a physical amount relative to the refrigerant temperature discharged from the compressor, and the control unit changes the target temperature difference to be increased when a detection value of the detection member is more than a predetermined value. When the target temperature difference is changed and becomes larger, a heat-exchanging efficiency of the heat exchanger is decreased, and a heat-exchanging amount in the heat exchanger is reduced. That is, in this case, because the refrigerant pressure discharged from the compressor is controlled to be decreased, the refrigerant temperature discharged from the compressor is decreased. Accordingly, even when the heat pump cycle is used under a low temperature condition, the refrigerant temperature discharged from the compressor can be controlled in an operation temperature area.
- Preferably, the control unit sets the target temperature difference larger as a low-pressure side refrigerant pressure after being decompressed in the heat pump cycle becomes lower, when the low-pressure side refrigerant pressure in the heat pump cycle is lower than a predetermined pressure. When the low-pressure side refrigerant pressure (e.g., evaporation pressure) of the heat pump cycle is decreased due to a decrease of outside air temperature, for example, load of the compressor is increased and refrigerant temperature discharged from the compressor is increased. Accordingly, by setting the target temperature difference larger as the low-pressure side refrigerant pressure becomes lower, it can effectively restrict the refrigerant temperature discharged from the compressor from being increased.
- On the other hand, the control unit determines whether or not a load of the compressor is excessive, and the control unit changes the target temperature difference to be increased to a value when it is determined that the load of the compressor is excessive. In this case, when the target temperature difference is made larger, the compressor continuously operates with a relatively lower high-pressure. Accordingly, is can prevent a problem of a heat pump cycle due to an increased load of the compressor. Further, when the fluid is water in a hot water supply system, a desired water-heating capacity can be obtained.
- According to the present invention, the control unit has a temperature detection sensor for detecting a refrigerant temperature discharged from the compressor, and the control unit controls a high-pressure side refrigerant pressure from the compressor and before being decompressed in the heat pump cycle, so that a temperature difference between the fluid flowing into the heat exchanger and refrigerant discharged from the heat exchanger becomes a target temperature difference when the refrigerant temperature detected by the temperature sensor is lower than a predetermined temperature. On the other hand, when the refrigerant temperature detected by the temperature sensor is higher than the predetermined temperature, the control unit controls the high-pressure side refrigerant pressure of the heat pump cycle so that the refrigerant temperature detected by the temperature sensor becomes lower than the predetermined temperature. Accordingly, the refrigerant temperature discharged from the compressor can be directly controlled without changing the target temperature difference.
- Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings, in which:
- FIG. 1 is a schematic diagram of a heat-pump water heater according to a first preferred embodiment of the present invention;
- FIG. 2 is a graph (T-H diagram) showing a relationship between temperature and enthalpy in a heat pump cycle using carbon dioxide as refrigerant, according to the first embodiment;
- FIG. 3 is a flow diagram showing a control process of an electronic control unit (ECU) according to the first embodiment;
- FIG. 4 is a flow diagram showing a control process of the ECU according to a second preferred embodiment of the present invention;
- FIG. 5 is a characteristic view showing a relationship between an evaporation temperature Ts of refrigerant and a target temperature difference ΔT, according to the second embodiment;
- FIG. 6 is a flow diagram showing a control process of the ECU according to a third preferred embodiment of the present invention;
- FIGS. 7A and 7B are graphs (T-H diagrams), respectively, each showing a relationship between temperature and enthalpy in a heat pump cycle using carbon dioxide as refrigerant, according to the third embodiment;
- FIG. 8 is a graph showing a relationship between a driving current and a load of a compressor according to a modification of the present invention; and
- FIG. 9 is a graph showing a stepwise change of the target temperature difference ΔT according to an another modification of the present invention.
- Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
- A first preferred embodiment of the present invention will be now described with reference to FIGS.1-3. As shown in FIG. 1, a heat-
pump water heater 1 is a hot water supply system, in which heated hot water is stored in atank 2 and is supplied to a user after being temperature-adjusted. The heat-pump water heater 1 includes thetank 2, anelectrical pump 3 forcibly circulating water in a water cycle, and a super-critical (trans-critical) heat pump cycle 4. - The
tank 2 is made of a metal having a corrosion resistance, such as a stainless steel, and has a heat insulating structure so that high-temperature hot water can be stored for a long time. Hot water stored in thetank 2 can be supplied to a kitchen, a bath or the like, and can be used as a heating source for a floor heater or a room heater or the like. - The
electrical pump 3, thetank 2 and awater heat exchanger 7 of the heater pump cycle 4 are connected by a water pipe 5 to form the water cycle. Therefore, water circulates between thetank 2 and thewater heat exchanger 7, and water circulating amount in the water cycle can be adjusted in accordance with a rotation speed of a motor disposed in theelectrical pump 3. - The super-critical heat pump cycle4 uses carbon dioxide having a low-critical pressure as refrigerant, for example, so that a high-pressure side refrigerant pressure becomes equal to or greater than the critical pressure of carbon dioxide. As shown in FIG. 1, the heater pump cycle 4 includes a
compressor 6, thewater heat exchanger 7, an expansion valve 8, an air heat exchanger 9 and anaccumulator 10. - The
compressor 6 includes anelectrical motor 6 a which is driven by aninverter circuit 16. Thecompressor 6 compresses sucked gas refrigerant by the rotation of theelectrical motor 6 a, so that refrigerant discharged from thecompressor 6 has the pressure equal to or greater than the critical pressure of refrigerant. Thewater heat exchanger 7 is disposed to perform a heat exchange between high-pressure gas refrigerant discharged from thecompressor 6 and water pumped from theelectrical pump 3. In thewater heat exchanger 7, a flow direction of refrigerant is set opposite to a flow direction of water. - The expansion valve8 is constructed so that a valve opening degree can be electrically adjusted. The expansion valve 8 is disposed at a downstream side of the
water heat exchanger 7 in a refrigerant flow direction, and decompresses refrigerant cooled in thewater heat exchanger 7 in accordance with a valve opening degree. Afan 11 for blowing air (i.e., outside air) toward the air heat exchanger 9 is disposed so that refrigerant decompressed in the expansion valve 8 is heat-exchanged with air in the air heat exchanger 9. Therefore, refrigerant is evaporated in the air heat exchanger 9 by absorbing heat from air. - Refrigerant from the air heat exchanger9 flows into the
accumulator 10 and is separated into gas refrigerant and liquid refrigerant in theaccumulator 10. Only separated gas refrigerant in theaccumulator 10 is sucked into thecompressor 6, and surplus refrigerant in the heat pump cycle 4 is stored in theaccumulator 10. - The heat-
pump water heater 1 has an electrical control unit (hereinafter, referred to as ECU) 15, and plural sensors 12-14. Specifically, the plural sensors 12-14 are a firstrefrigerant temperature sensor 12 for detecting a temperature Td of refrigerant discharged from thecompressor 6, awater temperature sensor 13 for detecting temperature Tw of water flowing into thewater heat exchanger 7, and the secondrefrigerant temperature sensor 14 for detecting temperature Tr of refrigerant flowing out from thewater heat exchanger 7. Detection signals from the sensors 12-14 are input into theECU 15, and theECU 15 controls operation of the heat pump cycle 4. - The
ECU 15 controls a high-pressure side refrigerant pressure in the heat pump cycle 4 based on a temperature difference between water flowing into thewater heat exchanger 7 and refrigerant flowing out from thewater heat exchanger 7, so that the heat pump cycle 4 can be operated with a high efficiency. That is, a target temperature difference ΔT between water flowing into thewater heat exchanger 7 and refrigerant flowing out from thewater heat exchanger 7 is set as an index of the cycle efficiency, and the valve opening degree of the expansion valve 8 is electrically controlled so that the target temperature difference ΔT is obtained. - Next, the control process of the
ECU 15 according to the first embodiment will be now described with reference to FIG. 3. First, at step S10, the high-pressure side refrigerant pressure of the heat pump cycle 4 is controlled by controlling the valve opening degree of the expansion valve 8, so that a set target temperature difference ΔT (e.g., 10° C.) is obtained. Next, at step S20, the refrigerant temperature Td discharged from thecompressor 6 is detected by the firstrefrigerant temperature sensor 12. - At step S30, it is determined whether or not the refrigerant temperature Td discharged from the
compressor 6 is equal to or higher than a predetermined value Tdp. In the first embodiment, the predetermined value Tdp is set based on a permissible upper limit temperature of thecompressor 6. When it is determined that the refrigerant temperature Td discharged from thecompressor 6 is equal to or higher than the predetermined value Tdp at step S30, the target temperature difference ΔT is increased at step S40. Thereafter, the control routine returns to step S10. Accordingly, the target temperature difference ΔT is gradually increased until the refrigerant temperature Td discharged from thecompressor 6 becomes smaller than the predetermined value Tdp. On the other hand, when it is determined that the refrigerant temperature Td discharged from thecompressor 6 is lower than the predetermined value Tdp at step S30, it is determined whether or not a water heating capacity reaches a target water heating capacity at step S50. For example, the water heating capacity can be determined based on a heat quantity of hot water that is heated by refrigerant in thewater heat exchanger 7 and is stored in thetank 2. Here, the heat quantity of hot water is calculated in accordance with a hot water temperature and a hot water flow amount. Specifically, when the heat quantity transmitted into water for a predetermined time is equal to or larger than a predetermined value, it is determined that the target water heating capacity is obtained. - When it is determined that the water heating capacity reaches the target water heating capacity at step S50, the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity at step S50, the rotation speed of the
motor 6 a of thecompressor 6 is increased for obtaining the target water heating capacity. Thereafter, the control routine moves to step S10. - According to the first embodiment of the present invention, when the refrigerant temperature Td discharged from the
compressor 6 is higher than the predetermined value Tdp, the target temperature difference ΔT is changed to be increased, and therefore, the opening degree of the expansion valve 8 becomes larger. FIG. 2 shows both states of the heat pump cycle 4, before and after the valve opening degree of the expansion valve 8 becomes larger. In FIG. 2, Q′ indicates a heat radiating capacity of thewater heat exchanger 7 before the valve opening degree of the expansion valve 8 becomes larger, Q indicates the heat radiating capacity of thewater heat exchanger 7 after the valve opening degree of the expansion valve 8 becomes larger, L′ indicates a compression operation amount (i.e., consumed power) before the valve opening degree of the expansion valve 8 becomes larger, and L indicates the compression operation amount after the valve opening degree of the expansion valve 8 becomes larger. Before the valve opening degree of the expansion valve 8 becomes larger, the target temperature difference ΔT′ is in a permissle range, but the refrigerant temperature Td′ discharged from thecompressor 6 is higher than the predetermined value Tdp. This cycle state is readily caused when the outside air temperature becomes lower and the low-pressure side refrigerant pressure of the heat pump cycle 4 becomes lower. - After the valve opening degree of the expansion valve8 becomes larger, because the high-pressure side refrigerant pressure of the heat pump cycle 4 decreases, the compression operation amount of the
compressor 6 is decreased (L′→L), and the heat radiating amount of thewater heat exchanger 7 is decreased (Q′→Q). As a result, the refrigerant temperature Td discharged from thecompressor 6 decreases. Until the refrigerant temperature Td discharged from thecompressor 6 is decreased to the operation temperature area of thecompressor 6, the target temperature difference ΔT is changed to be increased. According to the first embodiment, because the refrigerant temperature Td discharged from thecompressor 6 can be decreased to be in the operation temperature area, a problem affected to thecompressor 6 can be prevented. - In the above-described first embodiment, instead of the refrigerant temperature Td detected by the first
refrigerant temperature sensor 12, a physical amount relative to the refrigerant temperature Td, such as an evaporation pressure, an evaporation temperature and a refrigerant pressure discharged from thecompressor 6, may be used. Further, when the refrigerant temperature Td discharged from thecompressor 6 is higher than the predetermined temperature Tdp, the valve opening degree of the expansion valve 8 can be directly controlled so that the refrigerant temperature Td becomes lower than the target temperature Tdp, without changing the target temperature difference ΔT or without firstly setting the target temperature difference ΔT. - A second preferred embodiment of the present invention will be now described with reference to FIGS. 4 and 5. In the second embodiment, the target temperature difference ΔT is set based on a low-pressure side refrigerant temperature (e.g., evaporation temperature TS of refrigerant). In the second embodiment, the other parts are similar to those of the above-described first embodiment.
- FIG. 4 is a flow diagram showing a control process of the
ECU 15 according to the second embodiment. First, at step S110, the valve opening degree of the expansion valve 8 is controlled so that a set target temperature difference ΔT can be obtained. Next, an evaporation temperature Ts of refrigerant is detected at step S120, and it is determined whether or not the evaporation temperature Ts is equal to or lower than a predetermined temperature Ts1 (i.e., protection control start temperature) at step S130. When the evaporation temperature Ts of refrigerant is equal to or lower than the predetermined temperature Ts1 at step S130, the target temperature difference ΔT is determined based on the evaporation temperature Ts of refrigerant in accordance with the graph of FIG. 5. In FIG. 5, Tp indicates a protection control start point. On the other hand, when the evaporation temperature Ts of refrigerant is higher than the predetermined temperature Ts1 at step S130, the control routine moves to step S170. - After the target temperature difference ΔT is determined at step S140, an actual temperature difference ΔT0 is detected at step S150, and the set target temperature difference ΔT is compared with the actual temperature difference ΔT0 at step S160. That is, at step S160, it is determined whether or not the set target temperature difference ΔT is agreement with the actual temperature difference ΔT0. When it is determined that the set target temperature difference ΔT is agreement with the actual temperature difference ΔT0, the control routine moves to step S170. On the other hand, when it is determined that the set target temperature difference ΔT is not agreement with the actual temperature difference ΔT0, the control routine moves to step S110.
- At step S170, it is determined whether or not a water heating capacity reaches a target water heating capacity. When it is determined that the water heating capacity reaches the target water heating capacity, the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity, the rotation speed of the
motor 6 a of thecompressor 6 is increased at step S180 for obtaining the target water heating capacity. Thereafter, the control routine moves to step S10. - According to the second embodiment of the present invention, when the refrigerant evaporation temperature Ts is lower than the predetermined temperature Ts1, the target temperature difference ΔT is set to be larger than a general control based on the refrigerant evaporation temperature Ts. Therefore, the opening degree of the expansion valve 8 becomes larger, the refrigerant pressure discharged from the
compressor 6 becomes lower, and refrigerant temperature Td discharged from thecompressor 6 can be decreased to the operation temperature area. As a result, it can prevent a problem affected to thecompressor 6 in the heat pump cycle 4. In the second embodiment, when the refrigerant temperature Td discharged from thecompressor 6 becomes lower due to a decrease of water temperature, the predetermined temperature Ts1 (protection control start temperature) may be set at a low value. - A third preferred embodiment of the present invention will be now described with reference to FIGS. 6, 7A and7B. In the third embodiment, it is determined whether or not the load applied to the
compressor 6 is excessive (i.e., larger than an upper limit value), and the target temperature difference ΔT is set larger when the load of thecompressor 6 is excessive. In the third embodiment, for determining the load of thecompressor 6, an operation state of a protection circuit (not shown), which restricts output current for protecting theinverter circuit 16, is detected. When the output current is restricted by the protection circuit, it is determined that the load of thecompressor 6 is larger than the upper limit value. That is, in this case, it is determined that the load of thecompressor 6 is excessive. - FIG. 6 is a flow diagram showing a control process of the
ECU 15 according to the third embodiment. First, at Step S210, the high-pressure side refrigerant pressure of the heat pump cycle 4 is controlled by controlling the valve opening degree of the expansion valve 8, so that a set target temperature difference ΔT can be obtained. Next, at step S220, it is determined whether or not a current restriction due to theinverter circuit 16 is performed in thecompressor 6. When the current restriction is performed at step S220, the target temperature difference ΔT is changed to become larger (e.g., 15° C.) at step S230, and thereafter, the control routine moves to step S210. - On the other hand, when the current restriction is not performed at step S220, it is determined whether or not a water heating capacity reaches a target water heating capacity at step S240. For example, the water heating capacity can be determined based on a heat quantity of hot water that is heated by refrigerant in the
water heat exchanger 7 and is stored in thetank 2. Here, the heat quantity of hot water is calculated in accordance with a hot water temperature and a hot water flow amount. Specifically, when the heat quantity transmitted into water for a predetermined time is equal to or larger than a predetermined value, it is determined that the target water heating capacity is obtained. - When it is determined that the water heating capacity reaches the target water heating capacity, the control routine is finished. On the other hand, when it is determined that the water heating capacity does not reach the target water heating capacity, the rotation speed of the
motor 6 a of thecompressor 6 is increased at step S250 for obtaining the target water heating capacity. Thereafter, the control routine moves to step S210. - According to the third embodiment, in a normal operation of the heat pump cycle4, as shown in FIG. 7A, the high-pressure side refrigerant pressure is controlled so that the set target temperature difference ΔT (e.g., 10° C.) can be obtained, and a suitable heat-exchanging state of the
water heat exchanger 7 can be obtained. On the other hand, when the load of thecompressor 6 becomes excessive due to some reason, the target temperature difference ΔT (e.g., 10° C.) is changed to be increased by a value (e.g., 5° C.) as compared with the normal operation state, as shown in FIG. 7B. Even in this case, the heat pump cycle operates with a high-pressure side refrigerant pressure lower than that in the normal operation state. - In the third embodiment, even when the current restriction due to the
inverter circuit 16 is performed, the current restriction can be canceled by increasing the target temperature difference ΔT, and it can prevent the refrigerant flow amount from being decreased due to a reduce of the rotation speed of thecompressor 6. As a result, a necessary water heating capacity can be obtained in the heat-pump water heater 1 without throttling the valve opening degree of the expansion valve 8 more than a necessary degree. - Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.
- For example, In the above-described embodiments, the present invention is typically applied to the heat-
pump water heater 1 for heating water. However, the present invention may be applied to a heat-pump fluid heater for heating a fluid using the heat pump cycle 4 as a heating source. - In the above-described first and second embodiments, the valve opening degree of the expansion valve8 is controlled so that the set target temperature difference ΔT can be obtained. However, a water discharge amount of the
electrical pump 3 may be controlled, so that the flow amount of water flowing into thewater heat exchanger 7 is changed and the target temperature difference ΔT is obtained. - In the above-described third embodiment, the excessive load of the
compressor 6 is determined based on the current restriction due to theinverter circuit 16. However, electrical current applied to themotor 6 a of thecompressor 6 from theinverter circuit 16 is detected, and the load of thecompressor 6 may be determined based on the applied electrical current. For example, as shown in FIG. 8, when electrical current applied to themotor 6 a is equal to or larger than a determination value, it is determined that the load of thecompressor 6 is equal to or larger than a set upper limit value, and the target temperature difference ΔT is changed to be larger. - Further, the excessive load of the
compressor 6 may be determined based on at least one physical amount relative to the load of the compressor, such as a target heating temperature of water, an outside air temperature and a rotation speed of thecompressor 6. - Further, in the third embodiment, when the target temperature difference ΔT is changed, the target temperature difference may be stepwise changed or may be gradually continuously changed. For example, as shown in FIG. 9, the target temperature difference ΔT can be changed stepwise based on a combination of the outside air temperature and a target water temperature to be heated. In this case, a determination range of the target temperature difference ΔT may be changed in accordance with the rotation speed of the
compressor 6. That is, as the rotation speed of thecompressor 6 is higher, the target temperature difference ΔT is corrected to become larger. - Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.
Claims (20)
Applications Claiming Priority (4)
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JP2000-311142 | 2000-10-11 |
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- 2001-04-18 DE DE60102313T patent/DE60102313T2/en not_active Expired - Lifetime
- 2001-04-18 US US09/837,107 patent/US6430949B2/en not_active Expired - Fee Related
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Also Published As
Publication number | Publication date |
---|---|
DE60102313D1 (en) | 2004-04-22 |
DE60102313T2 (en) | 2005-03-17 |
EP1148307A3 (en) | 2002-01-16 |
US6430949B2 (en) | 2002-08-13 |
EP1148307A2 (en) | 2001-10-24 |
EP1148307B1 (en) | 2004-03-17 |
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