EP2645019A1

EP2645019A1 - Heat pump hot-water supply device

Info

Publication number: EP2645019A1
Application number: EP10859908.5A
Authority: EP
Inventors: Takeshi Sugimoto; Masayuki Okazaki; Tomoyoshi Obayashi; Toshiro Abe; Kensuke Inoue
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2010-11-24
Filing date: 2010-11-24
Publication date: 2013-10-02
Anticipated expiration: 2030-11-24
Also published as: EP2645019B1; WO2012070082A1; JP5653451B2; EP2645019A4; JPWO2012070082A1

Abstract

A heat pump type hot water supply apparatus 100 performs a reverse defrosting operation in which a refrigerant discharged from a compressor 1 is conducted to a pass 31 other than a pass 33 located at a lowermost position of an evaporator 13. After completion of the reverse defrosting operation, when the outside air temperature is a predetermined temperature or less and thereafter a predetermined time has elapsed and a difference between a shell temperature of the compressor 1 and a low pressure saturation temperature becomes a predetermined value or less, the refrigerant discharged from the compressor 1 is branched off between the compressor 1 and the four-way valve 2, and is conducted to the pass 33 located at the lowermost position of the evaporator 13 such that the refrigerant flows in parallel to the water heat exchanger 3 until the predetermined time has elapsed.

Description

Technical Field

The present invention relates to a heat pump type hot water supply apparatus using a heat pump which circulates a refrigerant, and particularly to a heat pump type hot water supply apparatus which performs a defrosting operation of removing frost attached to a heat exchanger functioning as an evaporator even when an outdoor air temperature is low (for example, 0 degrees C or less).

Background Art

There is a conventional heat pump type hot water supply apparatus which uses a heat pump for circulating a refrigerant and is capable of performing a defrosting operation for removing frost attached to an evaporator. As such, "a method for controlling a heat pump type hot water supply apparatus having a refrigeration cycle which includes a water heat exchanger that heats water to generate hot water, wherein if an outside air temperature is lower than or equal to a predetermined temperature, a preset high limit temperature of hot water generated by the water heat exchanger is regulated" has been proposed (for example, refer to Patent Literature 1).
In the technology described in Patent Literature 1, a defrosting operation is carried out in which by conducting a refrigerant (hot gas) discharged from a compressor into a heat source side heat exchanger, frost attached to the heat source side heat exchanger is melted. During a normal defrosting operation, it is determined that a water heat exchanger may be in danger of freezing when the water temperature becomes low or if the temperature of the water heat exchanger becomes lower. In this case, by opening a bypass circuit so as to prevent a refrigerant from flowing into the water heat exchanger, or by letting the refrigerant to flow into the bypass circuit in parallel to the water heat exchanger so as to reduce an amount of the refrigerant circulating in the water heat exchanger, freezing of the water heat exchanger is prevented. Then, when the outside air temperature becomes lower than or equal to a predetermined temperature (for example, -5 degrees C), a desired high limit temperature of hot water is decreased (for example, the temperature is lowered from 65degrees C to 58degrees C).

Citation List

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-41860 (refer to page7, Fig. 1 and the like)

Summary of Invention

Technical Problem

The technology described in Patent Literature 1 is established for the purpose of reducing the load for a compressor, such that if the outside air temperature becomes lower than or equal to a predetermined temperature, a preset high limit temperature of hot water generated by a water heat exchanger is regulated. This lowers the hot water temperature in a hot water storage tank below 60 degrees C, and therefore, there is a possibility that the hot water temperature in the hot water storage tank cannot be maintained at 60 degrees C that is required for preventing outbreak of Legionaires' disease. The recommended temperature of hot water stored in the hot water storage tank so as to suppress bleeding of Legionella bacteria is 60 degrees C or higher.
The invention has been made to overcome the above-described problems, and an object of the invention is to provide a heat pump type hot water supply apparatus which can maintain the hot water temperature (for example, 65degrees C) required even when the outside air temperature is low (for example, when the outside air temperature is 0degrees C or less) and perform a defrosting operation of an evaporator with high efficiency.

Solution to Problems

A heat pump type hot water supply apparatus according to the invention includes a main circuit in which a compressor, a flow switching device, a water heat exchanger, an expansion device and an evaporator are connected by pipes, and this apparatus performs a reverse defrosting operation in which a refrigerant discharged from the compressor is made to flow into the evaporator by switching the flow of the refrigerant by the flow switching device. Further, this apparatus performs the reverse defrosting operation in which the refrigerant discharged from the compressor is conducted to passes other than a pass located at a lower portion of the evaporator. Furthermore, after completion of the reverse defrosting operation, when an outside air temperature is a predetermined temperature or less and thereafter a predetermined time has elapsed or a difference between a compressor shell temperature and a low pressure saturation temperature becomes a predetermined value or less, the refrigerant discharged from the compressor is branched off between the compressor and the flow switching device, and is conducted to the pass located at the lower portion of the evaporator such that the refrigerant flows in parallel to the water heat exchanger until the predetermined time has elapsed.

Advantageous Effects of Invention

A heat pump type hot water supply apparatus according to the invention is configured such that, after completion of a reverse defrosting operation, when an outside air temperature is a predetermined temperature or less and thereafter a predetermined time has elapsed or a difference between a compressor shell temperature and a low pressure saturation temperature becomes a predetermined value or less, a refrigerant discharged from a compressor is branched off between the compressor and a flow switching device, and is conducted to a pass located at a lower portion of the evaporator such that the refrigerant flows in parallel to a water heat exchanger until the predetermined time has elapsed. Therefore, the hot water temperature (for example, 65 degrees C) which is required even when the outside air temperature is low can be maintained, and at the time of a hot water supply operation, and it becomes possible to prevent the refrigerant from being stored in the pass located in the lower portion of the evaporator, and thus this apparatus can perform the defrosting operation with high efficiency without decreasing a heating capacity for removing frost which is caused by a refrigerant shortage during the defrosting operation.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a refrigerant circuit diagram illustrating an exemplary refrigerant circuit configuration of a heat pump type hot water supply apparatus according to Embodiment of the invention.
[Fig. 2] Fig. 2 is a schematic diagram illustrating an exemplary pass pattern of an evaporator of the heat pump type hot water supply apparatus according to Embodiment of the invention.
[Fig. 3] Fig. 3 is a flow chart showing the flow of a control operation during a defrosting operation of the heat pump type hot water supply apparatus according to Embodiment of the invention.
[Fig. 4] Fig. 4 is a refrigerant circuit diagram illustrating another exemplary refrigerant circuit configuration of the heat pump type hot water supply apparatus according to Embodiment of the invention.

Description of Embodiment

Embodiment of the invention will be described below with reference to the drawings.
Fig. 1 is a refrigerant circuit diagram illustrating an exemplary refrigerant circuit configuration of a heat pump type hot water supply apparatus 100 according to Embodiment of the invention. With reference to Fig. 1, an exemplary circuit configuration of the heat pump type hot water supply apparatus 100 will be described below. The heat pump type hot water supply apparatus 100 is configured to perform a hot water supply operation by use of a refrigeration cycle for circulating a refrigerant (a heat pump cycle). There are cases that in Fig. 1 and subsequent figures, the relationships of sizes between each component may be different from the actual sizes.
As shown in Fig. 1, the heat pump type hot water supply apparatus 100 is provided with a refrigerant circuit, as a main circuit, in which a compressor 1, a four-way valve 2 serving as a flow switching valve, a water heat exchanger 3 (for example, a load side heat exchanger which exchanges heat between a refrigerant circulating in the refrigerant circuit and a heat medium such as water circulating in a water circuit), a liquid receiver 6, a double pipe heat exchanger 7, an expansion device 11, and an evaporator 13 are connected by a refrigerant pipe 20. That is to say, due to the refrigerant being circulated in the main circuit, the heat pump type hot water supply apparatus 100 can be configured to perform a hot water supply operation.
Further, the heat pump type hot water supply apparatus 100 includes an injection pipe 21 formed by branching off a liquid pipe at an outlet side of the liquid receiver 6 and connecting the pipe to the compressor 1 via a secondary side of the double pipe heat exchanger 7. As a result, it becomes possible to suppress decrease of the heating capacity of the apparatus in a cold district as well. An injection electronic expansion valve 8 is provided between a branch point of the injection pipe 21 and the double pipe heat exchanger 7. An injection solenoid valve 9 is provided on the injection pipe 21 between the double pipe heat exchanger 7 and the compressor 1. Moreover, the heat pump type hot water supply apparatus device 100 includes a first bypass pipe 23 formed by branching off the refrigerant pipe 20 at an outlet side of the water heat exchanger 3 and connected to an outlet side of the double pipe heat exchanger 7. The first bypass pipe 23 is provided with a first check valve 10.
The heat pump type hot water supply apparatus 100 includes a second bypass pipe 24 which bypasses the expansion device 11. The second bypass pipe 24 is provided with a second check valve 12. Further, the heat pump type hot water supply apparatus 100 also includes a hot gas conducting pipe 22 used to conduct a refrigerant (hot gas) discharged from the compressor 1 to the evaporator 13. The hot gas conducting pipe 22 is provided with a hot gas solenoid valve 14. Incidentally, a high pressure sensor 15 is provided in a discharge portion of the compressor 1, a low pressure sensor 16 is provided in a suction portion of the compressor 1, a shell temperature sensor 17 is provided in a lower portion of the compressor 1, and an outside air temperature sensor 18 is provided in the vicinity of the evaporator 13.
The compressor 1 is used to compress a refrigerant suctioned from the suction portion, the injection pipe 21 and the hot gas conducting pipe 22 into a high temperature, high pressure state. The compressor 1 may be, for example, a capacity controllable compressor of which rotation speed can be controlled by an inverter. The compressor 1 is configured so as to be capable of injecting the refrigerant passing through the injection pipe 21 into a compression chamber inside of the compressor 1. Further, the compressor 1 is also configured so as to be capable of letting the refrigerant passing through the hot gas conducting pipe 22 flow into the compression chamber of the compressor 1.
The four-way valve 2 is used to switch the flow direction of the refrigerant between the reverse defrosting operation and the hot water supply operation. The water heat exchanger 3 is used to receive and pass heating energy stored in the refrigerant to a water circuit side. An inlet of a water circuit connected to the water heat exchanger 3 is referred to as a water circuit inlet 4, and an outlet of the water circuit is referred to as a water circuit outlet 5. The water circuit inlet 4 and the water circuit outlet 5 are each connected to a hot water storage tank, which is not illustrated, and thereby form the water circuit. Incidentally, the hot water storage tank is configured to store therein hot water boiled by the water heat exchanger 3.
The liquid receiver 6 is provided at the outlet side of the water heat exchanger 3 and is used to store therein excess refrigerant. The heat is exchanged between the refrigerant flowing out from the double pipe heat exchanger 7 and from the liquid receiver 6 and passing through the injection pipe 21, and the refrigerant flowing through the refrigerant pipe 20. The double pipe heat exchanger 7 is formed by a liquid pipe (referred to as a liquid pipe 20a) through which a liquid refrigerant flowing out from the liquid receiver 6 passes, the injection pipe 21 of which pipe diameter is larger than that of the liquid pipe 20a and which is disposed so as to cover the liquid pipe 20a, and a pipe unit (not illustrated) of which pipe diameter is larger than that of the injection pipe 21 and which forms an enclosed space. Incidentally, in the following description, the liquid pipe 20a side of the double pipe heat exchanger 7 is referred to as a primary side, and the injection pipe 21 side thereof is referred to as a secondary side.
The expansion device 11 serves as a reducing valve or an expansion valve and is used to decompress and expand a refrigerant. The expansion device 11 may be, for example, an electronic expansion valve having a variably controllable opening degree. The evaporator 13 exchanges heat between air (outside air) supplied from a fan which is not illustrated or the like, and the refrigerant, so as to evaporate and gasify the refrigerant. The refrigerant pipe 20 is used to link various component devices. Each of the liquid pipe 20a, the injection pipe 21, the hot gas conducting pipe 22, the first bypass pipe 23, and the second bypass pipe 24 is a component which forms a part of the refrigerant pipe 20.
The injection electronic expansion valve 8 is used to decompress and expand the refrigerant flowing through the injection pipe 21. The injection electronic expansion valve 8 may be, for example, an electronic expansion valve having a variably controllable opening degree. The injection solenoid valve 9 is controlled so as to open and close and is used to control flowing of the refrigerant into the injection pipe 21. The first check valve 10 permits the flow of the refrigerant in one direction (from the expansion device 11 to the water heat exchanger 3 side). The second check valve 12 permits the flow of the refrigerant in one direction (from the evaporator 13 to the inlet side of the first bypass pipe 23). The hot gas solenoid valve 14 is controlled so as to open and close, and is used to control flowing of the refrigerant into the hot gas conducting pipe 22.
The high pressure sensor 15 is used to detect the pressure of the refrigerant discharged from the compressor 1. The low pressure sensor 16 is used to detect the pressure of the refrigerant to be suctioned into the compressor 1. The shell temperature sensor 17 is used to detect the shell temperature of the compressor 1. The outside air temperature sensor 18 is used to detect the temperature of outside air which exchanges heat with the evaporator 13. Information detected by these sensors (pressure information, temperature information) is transmitted to a controller 50 and is used for a driving frequency of the compressor 1, switching of the four-way valve 2, the opening degree of the expansion device 11, the opening degree of the injection electronic expansion valve 8, opening and closing of the injection solenoid valve 9, opening and closing of the hot gas solenoid valve 14, and the like.
Fig. 2 is a schematic diagram illustrating an exemplary pass pattern of the evaporator 13 of the heat pump type hot water supply apparatus 100. With reference to Fig. 2, the evaporator 13 will be further described below in detail. As shown in Fig. 2, the evaporator 13 is configured in such a manner that the refrigerant is branched off at an inlet header 31 provided at an inlet side of the evaporator and flows into plural passes, and the refrigerant which has flowed out of the plural passes is merged at an outlet header 32 provided at the outlet side of the evaporator. Fig. 2 illustrates a state in which the pass of the evaporator 13 is branched into eight ways, that is, passes 30a to 30h.
However, a pass 33 located at the lowermost position of the evaporator 13 does not communicate with the other passes (the passes 31 a to 31 h). In other words, the pass 33 does not communicate with the inlet header 31 or with the outlet header 32. The pass 33 is configured in such a manner that the inlet side thereof is made to communicate with the hot gas solenoid valve 14 and the outlet side thereof is made to communicate with the suction portion of the compressor 1 via another pipe (the hot gas conducting pipe 22). Accordingly, the hot gas solenoid valve 14 is controlled so as to close during the water heating operation (at the time of the heating operation), and therefore, the refrigerant does not flow in the pass 33. A unit base 34 is provided at a lower side of the evaporator 13. That is to say, the evaporator 13 is disposed above the unit base 34. Further, in Fig. 2, as a suitable example, a case in which the pass 33 located at the lowermost position alone does not communicate with the other passes (the passes 31 a to 31 h) is shown. However, a plurality of passes disposed at the lower portion of the evaporator 13 (further at the lower side of the evaporator 13 than the center in the height direction of the evaporator 13) each may be made to function as in the pass 33.
As the refrigerant circulating in the refrigerant circuit which constitutes the heat pump type hot water supply apparatus 100, for example, a single refrigerant such as R-22, R-134a, R-32, a near-azeotropic refrigerant mixture such as R-410A, R-404A, a non-azeotropic refrigerant mixture such as R-407C, tetrafluoropropene (HFO-1234yf or HFO-1234ze) that is a refrigerant which contains a double bond in its chemical formula and is expressed in the chemical formula C3H2F4 and has a relatively low global warming potential, a mixture containing the refrigerant, or a natural refrigerant, such as CO2 or propane, can be used. Considering the global environment, it is preferable to use R-32 having a low global warming potential or, for example, a refrigerant mixture containing R-32 and tetrafluoropropene (HFO-1234yf or HFO-1234ze). Further, in order to meet a demand of supplying high temperature hot water (for example, hot water of 65degrees C is stored in the hot water storage tank), refrigerants such as R407C, R134a, HFO-1234yf, HFO-1234ze are particularly preferable.
Next, the operation of the heat pump type hot water supply apparatus 100 will be described.

[Hot water supply operation]

During the hot water supply operation, the refrigerant discharged from the compressor 1 is made to flow via the four-way valve 2 to the water heat exchanger 3. The refrigerant which has flowed into the water heat exchanger 3 exchanges heat with a heat medium such as water which has flowed from the water circuit inlet 4, and heats the water. Then, the heated heat medium (in this case, hot water) is made to flow from the water circuit outlet 5 to the hot water storage tank and is stored therein. Incidentally, the pipe from the hot water storage tank communicates with the water circuit inlet 4, and therefore, the heat medium circulates between the water heat exchanger 3 and the hot water storage tank.
The refrigerant that has heated the heat medium flows out from the water heat exchanger 3 and passes through the liquid receiver 6, and thereafter, is branched off. A part of the refrigerant flows into the liquid pipe 20a and the remaining part thereof flows into the injection pipe 21. The double pipe heat exchanger 7 exchanges heat between the primary side refrigerant flowing through the liquid pipe 20a, and the secondary side refrigerant flowing in the injection pipe 21 and pressed by the injection electronic expansion valve 8. In other words, the double pipe heat exchanger 7 exchanges heat between the refrigerant flowing through the liquid pipe 20a led to a closed space, and the refrigerant flowing through the injection pipe 21. Then, the liquid refrigerant subcooled by the secondary side refrigerant is conducted to the expansion device 11, and thereafter, it flows into the evaporator 13.
At this moment, in the evaporator 13, the refrigerant passes through the passes 30a to 30h other than the lowermost pass 33, and exchanges heat with the outside air. The refrigerant which has exchanged heat with the outside air is made to merge at the outlet header 32, and is again suctioned into the compressor 1 via the four-way valve 2. Further, during the hot water supply operation, the hot gas solenoid valve 14 is controlled so as to close, so that the refrigerant does not flow into the pass 33 located at the lowermost position of the evaporator 13.
The refrigerant which has flowed into the injection pipe 21 passes through the injection electronic expansion valve 8, and thereafter, exchanges heat with the liquid refrigerant at the primary side in the double pipe heat exchanger 7. The refrigerant flows out of the double pipe heat exchanger 7, and thereafter, flows through the injection solenoid valve 9 which is controlled so as to open when the injection is required, and is further made to flow to an intermediate portion (an injection port) of the compression chamber in the compressor 1, thereby cooling gas discharged from the compressor 1.
Note that when the hot water supply operation is continuously performed in a cold district or the like, frost is attached to the evaporator 13. If the frost attached to the evaporator 13 is left as it is, the heat exchange capacity of the evaporator 13 may become degraded. In this case, a desired capacity of the hot water supply operation cannot be exhibited. Accordingly, in the heat pump type hot water supply apparatus 100, a defrosting operation for removing frost attached to the evaporator 13 is appropriately performed. As the defrosting operation performed by the heat pump type hot water supply apparatus 100, there are two types of operation as follows: a reverse defrosting operation in which the refrigerant flow is reversed so that the refrigerant discharged from the compressor 1 is made to flow into the evaporator 13; and a hot gas defrosting operation in which a part of the refrigerant (hot gas) discharged from the compressor 1 is branched off and is made to flow into the evaporator 13. The defrosting operation will be described below in detail.

[Defrosting operation (reverse defrosting operation plus hot gas defrosting operation)]

Next, the refrigerant circuit during the defrosting operation will be described.
During the reverse defrosting operation, the refrigerant discharged from the compressor 1 is led to the evaporator 13 by switching the four-way valve 2. In this case, in the evaporator 13, the refrigerant passes through the passes 30a to 30h other than the pass 33, and frost attached to the evaporator 13 is melted. The refrigerant which has exchanged heat with the frost attached to the evaporator 13 is merged at the outlet header 32, and flows in the second bypass pipe 24 and the first bypass pipe 23, and bypasses the expansion device 11, and the double pipe heat exchanger 7 and the liquid receiver 6, respectively, and also passes through the water heat exchanger 3, and is suctioned again into the compressor 1 via the four-way valve 2. During the reverse defrosting operation, the heat medium is circulated in the water heat exchanger 3, so as not to be frozen.
Further, after completion of the reverse defrosting operation, the hot gas defrosting operation can be performed by controlling the hot gas solenoid valve 14 to be open. The refrigerant thus can be made to flow into the hot gas conducting pipe 22 in parallel with the refrigerant circuit for the hot water supply operation. In other words, by opening the hot gas solenoid valve 14, a part of the refrigerant discharged from the compressor 1 is branched off from between the compressor 1 and the four-way valve 2, and flows into the pass 33 located at the lowermost position of the evaporator 13 via the hot gas solenoid valve 14. Another part of the refrigerant discharged from the compressor 1 flows into the water heat exchanger 3 via the four-way valve 2. The refrigerant which has flowed into the pass 33 exchanges heat with the frost attached to the lowermost position of the evaporator 13, and thereafter, flows from the evaporator 13 and is led to the suction side of the compressor 1.
Fig. 3 is a flow chart showing the flow of a control operation during the defrosting operation (the reverse defrost operation and the hot gas defrosting operation). With reference to Fig. 3, the control operation during the defrosting operation will be described below. The controller 50 starts the defrosting operation when it is determined that predetermined conditions (for example, a cumulative operation time of the compressor 1, a drop in the outside air temperature, and the like) have been satisfied (step S101). The controller 50 performs the reverse defrosting operation by, at first, switching the four-way valve 2 to flow hot gas into the passes 30a to 30h of the evaporator 13 (step S102).
When it is determined that the predetermined conditions (for example, passing of a predetermined time, and the like) have been satisfied, the controller 50 terminates the reverse defrosting operation (step S103). Subsequently, the controller makes a determination as to whether the outside air is lower than or equal to a predetermined temperature (for example, 0 degrees C or less) (step S104). When the outside air is not less than or equal to the predetermined temperature (step S104: NO), the controller 50 switches the four-way valve 2 and performs the hot water supply operation (step S110).
On the other hand, when the outside air is less than or equal to the predetermined temperature (step S104: YES), the controller 50 is in a standby state until a predetermined time (for example, 10 seconds) elapses after completion of the reverse defrosting operation (step S105). When the predetermined time has elapsed after completion of the reverse defrosting operation (step S105: YES), the controller 50 controls the hot gas solenoid valve 14 to be open, and starts the hot gas defrosting operation (step S106). In this case, the reason for the controller 50 to be in a standby state for the predetermined time is so that, when the four-way valve 2 is switched after completion of the reverse defrosting operation, the controller 50 can change to the hot gas defrosting operation after the four-way valve 2 is reliably switched by the pressure difference between the front and rear sides of the four-way valve 2.
The controller 50 makes a determination as to whether a predetermined time (for example, five minutes or thereabouts) has elapsed after the start of the hot gas defrosting operation (step S107). When it is determined that the predetermined has elapsed after the start of the hot gas defrosting operation (step S107: YES), the controller 50 finishes the hot gas defrosting operation (step S108), and controls the hot gas solenoid valve 14 to be closed and switches to the hot water supply operation (step S110).
To the contrary, if it is determined that the predetermined time has not elapsed after the start of the hot gas defrosting operation (step S107: NO), there is a possibility that the liquid refrigerant may return to the compressor 1 and therefore, the controller 50 converts the shell temperature of the compressor 1 detected by the shell temperature sensor 17 and the low pressure value detected by the low pressure sensor 16 into a low pressure saturated gas temperature, and makes a determination as to whether a value (given by subtracting the low pressure saturated gas temperature from the compressor shell temperature) is a predetermined value or less (step S109).
When it is determined that the value (given by subtracting the low pressure saturated gas temperature from the compressor shell temperature) is not less than or equal to the predetermined value (step S109: NO), the controller 50 returns to a determination as to whether the predetermined time has elapsed after the start of the hot gas defrosting operation (step S107). On the other hand, when it is determined that the value (given by subtracting the low pressure saturated gas temperature from the compressor shell temperature) is the predetermined value or less (step S109: YES), the controller 50 makes a determination that the refrigerant may return to the compressor in a liquid state, and even when the predetermined time has not elapsed after the start of the hot gas defrosting operation, the hot gas defrosting operation is finished so as to protect the compressor 1 (step S108). Then, the controller controls the hot gas solenoid valve 14 to be closed and switches to the hot water supply operation (step S110).
When the outside air temperature is low and the evaporator 13 is severely frosted due to snowfall or the like, or the lower part of the evaporator is covered with snow, the refrigerant may be accumulated in the pass 33 located at the lowermost position of the evaporator 13. In such cases, the refrigerant cannot be used at the defrosting operation, the amount of refrigerant therefore becomes insufficient and the heating capacity may become degraded. Further, the pass 33 located at the lowermost position of the evaporator 13 is provided in the vicinity of the unit base 34, and therefore, snow piled in the unit base 34 or the cold unit base 34 draws heat required for removing frost during the defrosting operation.
Hence, in the heat pump type hot water supply apparatus 100, the evaporator 13 is configured such that the pass 33 located at the lowermost position in the vicinity of the unit base 34 is separated from the other passes 30a to 30h. Accordingly, during the hot water supply operation, the refrigerant is not allowed to be accumulated in the pass 33 located at the lowermost position of the evaporator 13, thereby making it possible to prevent deterioration of the heating capacity for removing frost caused by the refrigerant shortage during the defrosting operation. Further, even when the outside air temperature is low, deterioration of the hot water supplying ability can be suppressed and the hot water supplying temperature can be maintained at a high value (for example, 65degrees C). Accordingly, breeding of Legionella bacteria or the like in the hot water storage tank can be suppressed.
In addition, the heat pump type hot water supply apparatus 100 is configured to perform the reverse defrosting operation via the passes 30a to 30h of the evaporator 13 and thereafter, let the hot gas flow into the pass 33 located at the lowermost position of the evaporator 13. Accordingly, at the time of defrosting in the other passes than the pass 33 located at the lowermost position of the evaporator 13, the hot gas defrosting operation can be performed without excessively heating water which has been generated by melting frost by the reverse defrosting operation and has dropped down in the pass 33, and also without letting the dropped water deprive of the heating capacity. For this reason, by the hot gas defrosting operation, it becomes possible to reliably remove frost from the part in the vicinity of the unit base 34 and the lower portion of the evaporator 13 which could be a source of remaining ice.
Fig. 4 is a refrigerant circuit diagram illustrating another exemplary refrigerant circuit configuration of the heat pump type hot water supply apparatus according to Embodiment of the invention. With reference to Fig. 4, another exemplary circuit configuration of the heat pump type hot water supply apparatus 100 will be described below.
When the hot gas defrosting operation is performed, the low pressure of the refrigerant suctioned into the compressor 1 and the high pressure of the refrigerant discharged from the compressor 1 both rise during removing frost from the lowermost portion of the evaporator 13. Consequently, in Fig. 4, in order to maintain designed pressure of the evaporator 13 at a low value, a first hot gas expansion device 25 is provided between the compressor 1 and the hot gas solenoid valve 14, and a second hot gas expansion device 26 is provided between the pass 33 of the evaporator 13 and a suction port of the compressor 1.
Since the first hot gas expansion device 25 and the second hot gas expansion device 26 are provided, even during the hot gas defrosting operation, there is no possibility that the low pressure of the refrigerant suctioned into the compressor 1 and the high pressure of the refrigerant discharged from the compressor 1 each may rise extraordinarily. For this reason, the designed pressure of the evaporator 13 can be maintained at a low value, thereby making it possible to make a contribution to further improvement of reliability. Fig. 4 illustrates a case in which the first hot gas expansion device 25 and the second hot gas expansion device 26 each includes a capillary, but the configuration is not limited to this case. These expansion devices each may also be an expansion device such as an expansion valve.
Incidentally, the refrigerant to be used, the number of the water heat exchangers 3, the respective number of the temperature sensors and pressure sensors may also be determined in accordance with intended purposes and uses for which the heat pump type hot water supply apparatus 100 is applied. Further, the controller 50 may be configured by a microcomputer or the like, which is capable of performing the integrated control of the heat pump type hot water supply apparatus 100.

Reference Signs List

1: compressor, 2: four-way valve, 3: water heat exchanger, 4: water circuit inlet, 5: water circuit outlet, 6: liquid receiver, 7: double pipe heat exchanger, 8: injection electronic expansion valve, 9: injection solenoid valve, 10: first check valve, 11: expansion device, 12: second check valve, 13: evaporator, 14: hot gas solenoid valve, 15: high pressure sensor, 16: low pressure sensor, 17: shell temperature sensor, 18: outside air temperature sensor, 20: refrigerant pipe, 20a: liquid pipe, 21: injection pipe, 22: hot gas conducting pipe, 23: first bypass pipe, 24: second bypass pipe, 25: first hot gas expansion device, 26: second hot gas expansion device, 30a: pass, 30b: pass, 30c: pass, 30d: pass, 30e: pass, 30f: pass, 30g: pass, 31: inlet header, 32: outlet header, 33: pass, 34: unit base, 50: controller, 100: heat pump type hot water supply apparatus.

Claims

A heat pump type hot water supply apparatus comprising:
a main circuit in which a compressor, a flow switching device, a water heat exchanger, an expansion device and an evaporator are connected by pipes, the apparatus performing a reverse defrosting operation in which a refrigerant discharged from the compressor is made to flow into the evaporator by switching a flow of the refrigerant by the flow switching device,

wherein the reverse defrosting operation is performed in which the refrigerant discharged from the compressor is conducted to passes other than a pass located at a lower portion of the evaporator, and

wherein, after completion of the reverse defrosting operation, when an outside air temperature is a predetermined temperature or less; and thereafter a predetermined time has elapsed, or a difference between a compressor shell temperature and a low pressure saturation temperature becomes a predetermined value or less, the refrigerant discharged from the compressor is branched off between the compressor and the flow switching device, and is conducted to the pass located at the lower portion of the evaporator such that the refrigerant flows in parallel to the water heat exchanger until the predetermined time has elapsed.
The heat pump type hot water supply apparatus of claim 1, further comprising:
a hot gas conducting pipe which branches off a pipe between the compressor and the flow switching device and which is connected to a suction side of the compressor via the pass located at the lower portion of the evaporator; and

a hot gas solenoid valve disposed in the hot gas conducting pipe,

wherein by opening and closing the hot gas solenoid valve, the refrigerant discharged from the compressor is conducted to the pass located at the lower portion of the evaporator via the hot gas conducting pipe.
The heat pump type hot water supply apparatus of claim 1 or claim 2, further comprising:
a liquid receiver disposed between the water heat exchanger and the expansion device;

a double pipe heat exchanger disclosed between the expansion device and the liquid receiver;

an injection pipe which branches off a refrigerant pipe between the double pipe heat exchanger and the liquid receiver and which is connected to an injection port of the compressor via the double pipe heat exchanger;

an injection electronic expansion valve disposed at an upstream side of the injection pipe from the double pipe heat exchanger; and

an injection solenoid valve disposed in the injection pipe between the double pipe heat exchanger and the compressor.
The heat pump type hot water supply apparatus of claim 3, further comprising:
a first bypass pipe which bypasses the double pipe heat exchanger and the liquid receiver;

a second bypass pipe which bypasses the expansion device;

a first check valve disposed in the first bypass pipe; and

a second check valve disposed in the second bypass pipe,

wherein during the reverse defrosting operation, the refrigerant which has flowed out of the evaporator is suctioned into the compressor via the second bypass pipe and the first bypass pipe.
The heat pump type hot water supply apparatus of any one of claims 1 to 4, further comprising:
a first hot gas expansion device disposed on a hot gas conducting pipe between the compressor and a hot gas solenoid valve; and

a second hot gas expansion device disposed on the hot gas conducting pipe between the evaporator and the compressor.