EP2241829A2

EP2241829A2 - Heat pump type hot water supply system

Info

Publication number: EP2241829A2
Application number: EP10008096A
Authority: EP
Inventors: Shinichi Sakamoto; Hidehiko Kataoka
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2001-09-28
Filing date: 2002-09-27
Publication date: 2010-10-20
Anticipated expiration: 2022-09-27
Also published as: EP1298395B1; ATE498803T1; EP1298395A3; EP1298395A2; EP2241829A3; JP2003106653A; EP2241829B1; DE60239177D1

Abstract

A heat pump type hot water supply system includes a hot water storage tank (3), and a circulation line (12) connecting a water outlet (10) at the lower part of the storage tank (3) and a hot water inlet (11) at the upper part thereof. The circulation line (12) is provided partway therealong with a heat exchange line (14) to be heated by a heat pump heat source. The system is configured to return hot water heated up in the heat exchange line (14) to the hot water storage tank (3) through the hot water inlet (11) When the heated water temperature of the heat exchange line (14) is equal to or below a set point, the return of the water to the hot water storage tank (3) through the hot water inlet (11) is hindered, and when the heated temperature of the heat exchange line (14) is above the set point, the outgoing water from the heat exchange line (14) is returned to the hot water storage tank (3) through the hot water inlet (11).

Description

This invention relates to heat pump type hot water supply systems.
As an example of conventional heat pump type hot water supply systems, there is known one, as shown in Figure 8 , which includes a hot water storage tank 50, and a circulation line 53 connecting between a water outlet 51 and a hot water inlet 52 each formed in the hot water storage tank 50. In addition, a heat exchange line 54 is provided partway along the circulation line 53 and can be heated by a heat pump type heating source. This heat pump type hot water supply system performs a hot water return operation in which unheated water from the water outlet 51 is heated up to a predetermined temperature in the heat exchange line 54 and the water heated up to the predetermined temperature is returned to the storage tank 50 through the hot water inlet 52. The heat pump type hot water supply system is composed of a tank unit 55 and a heat source unit 56, and the tank unit 55 includes the above-mentioned hot water storage tank 50. The heat source unit 56 includes a compressor 57, a water heat exchanger 58 (forming the heat exchange line 54), an expansion valve 59, and a heat exchanger 60.
With the above configuration, when the compressor 57 is driven, refrigerant flows from the compressor 57 to the water heat exchanger 58, the expansion valve 59 and the heat exchanger 60 in this order. During the time, the heat exchanger 60 functions as an evaporator, and the water heat exchanger 58 functions as a condenser. On the other hand, a pump 61 is provided in the circulation line 53, and the driving of the pump 61 enables circulation of water through the circulation line 53. Therefore, the water passing through the water heat exchanger 58, which is acting as a condenser, is heated up therein and then returns to the hot water storage tank 50 through the hot water inlet 52.
Heated water being stored in the hot water storage tank 50, however, exists at high temperatures in the upper part of the tank and at low temperatures in the lower part thereof. If water is returned from the circulation line 53 directly to the storage tank 50 in the above-described manner at the start-up or in similar cases, cold water or low-temperature hot water will be undesirably sent to the upper part of the storage tank 50 because the water to be returned does not reach a desired high temperature. To cope with this, there is proposed a solution as shown in the dash-double-dot line in Figure 8 . In this solution, a three way valve 62 is provided in the circulation line 53 and the circulation line 53 is connected at the three way valve 62 to a bypass line 63 to form a bypass circuit that bypasses the storage tank 50. When the water heated up in the heat exchange line 54 has a low temperature, the bypass line 63 is put into the on state so that the heated water circulates through the bypass circuit so as not to return to the storage tank 50, resulting in heating the water up to a predetermined high temperature.
However, for the conventional heat pump type hot water supply system described above, when the bypass line 63 is in the on state (in bypass operation), the temperature of the water heated up in the heat exchange line 54 is substantially equal to that of the water incoming to the heat exchange line 54 as shown in Figure 9 (a graph showing the relationship between the incoming water temperature and the outgoing water temperature of the water heat exchanger 58). In this case, the heat source unit of heat pump type can no longer operate because of its performance limit. Therefore, the heat source unit stops the bypass operation and performs a normal hot water return operation in which the heated water is returned to the tank through the hot water inlet 52. This results in the return of the hot water at a low temperature (in this case, 60°C) not reaching a desired temperature (in this case, 85°C) to the upper part of the hot water storage tank 50. At this time, as can be seen from the graph of Figure 9 , the incoming water temperature of the heat exchange line 54 abruptly changes, which makes it difficult to maintain the temperature of water heated up by the heat exchange line 54 (hereinafter, referred to as the heated water temperature of the heat exchange line 54) constant. To solve this problem, conventional systems require improved start-up performance and a complicated control system for storage of hot water at a constant temperature, resulting in its complicated entire configuration and design difficulties.
Furthermore, as shown in Figure 8 , the conventional heat pump type hot water supply system may be provided with a bypass line 65 that is interposed between a connection line connecting the compressor 57 and the water heat exchanger 58 and a connection line connecting the expansion valve 59 and the heat exchanger 60 and that has a defrost valve 64 placed in the bypass line 65 to perform a defrosting operation. Here, the defrosting operation means the operation in which the expansions valve 59 is fully closed, hot gas discharged from the compressor 57 is supplied to the heat exchanger 60 through the bypass line 65, and the heat exchanger 60 is thereby heated with heat of the hot gas. In this case, when the outside air temperature is low, such as in winter, the defrosting operation is repeatedly conducted, i.e., the start-up operating condition is repeated, so that the average storage hot water temperature in the storage tank drops. Therefore, in order to raise the average storage hot water temperature to the degree as in the cases other than the defrosting operation, it is necessary to raise the heated water temperature of the heat exchange line 54. If it is done, the COP may in turn drop as shown in Figure 10 (a graph showing the relationship between the heated water temperature and the COP). Alternatively, if the heated water temperature of the heat exchange line is not raised as expected, the amount of heat of the stored hot water cannot be sufficiently ensured by counting on only night-time hot water storage operation which is low in electricity cost. The system is therefore required to perform a day-time reheating operation which is high in electricity cost, resulting in increased cost.
The present invention has been made in view of the foregoing problems, and therefore its object is to provide a heat pump type hot water supply system which prevents drop in the average storage hot water temperature of the hot water storage tank and enables to avoid day-time reheating operation and to achieve reduced cost owing to energy conservation.
To solve the above problems, a first heat pump type hot water supply system is directed to a heat pump type hot water supply system which includes a hot water storage tank 3, and a circulation line 12 connecting a water outlet 10 at the lower part of the storage tank 3 and a hot water inlet 11 at the upper part thereof, the circulation line 12 being provided partway therealong with a heat exchange line 14 to be heated by a heat pump heat source, and in which water heated up in the heat exchange line 14 is returned to the hot water storage tank 3 through the hot water inlet 11. The first heat pump type hot water supply system is characterised in that when the heated water temperature of the heat exchange line 14 is equal to or below a set point, the return of the water to the hot water storage tank 3 through the hot water inlet 11 is hindered, and when the heated water temperature of the heat exchange line 14 is above the set point, the outgoing water from the heat exchange line 14 is returned to the hot water storage tank 3 through the hot water inlet 11.
With the first heat pump type hot water supply system, when the heated water temperature of the heat exchange line 14 is above the set point, water having flowed out of the storage tank 3 through the water outlet 10 flows through the circulation line 12 and then returns to the storage tank 3 through the hot water inlet 11. On the other hand, when the water outgoing from the heat exchange line 14 has a temperature equal to or below the set point because it has been insufficiently heated in the heat exchange line 14, the return of the water to the storage tank 3 through the hot water inlet 11 is hindered. As a result, low-temperature water or low-temperature hot water is not returned to the upper part of the storage tank 3 and is therefore not mixed with the hot water existing at high temperatures in the upper part of the storage tank 3, thereby preventing temperature drop of the high-temperature storage water.
A second heat pump type hot water supply system is characterised in that when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water from the heat exchange line 14 is returned to the hot water storage tank 3 through a supply water inlet 5 formed in the bottom of the hot water storage tank 3.
With the second heat pump type hot water supply system, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water from the heat exchange line 14 is returned to the hot water storage tank 3 through the supply water inlet 5 in the bottom of the hot water storage tank 3. As a result, low-temperature water or low-temperature hot water from the heat exchange line 14 is mixed with the low-temperature storage water in the lower part of the storage tank 3 without being mixed with the high-temperature storage water in the upper part of the storage tank 3. In particular, since a baffle (baffle plate) is generally provided near to the supply water inlet 5 inside of the storage tank 3, low-temperature water or low-temperature hot water entering the storage tank 3 through the supply water inlet 5 will impinge on the baffle and therefore will not reach the high-temperature storage water in the upper part of the storage tank 3. Thereafter, when the heated water temperature of the heat exchange line 14 rises and exceeds the set point, the system returns to its normal operation in which the outgoing water at a sufficiently high temperature from the heat exchange line 14 is returned to the storage tank 3 through the hot water inlet 11. Regardless of whether the system is in the normal operating condition or in a circulation condition (bypass operation) using the supply water inlet 5, the storage water in the storage tank 3 flows out through the water outlet 10 to the heat exchange line 14. Accordingly, as shown in Figure 3 (a graph showing the relationship between the incoming and outgoing water temperatures of the heat exchange line), the incoming waters to the heat exchange line 14 in both the cases have no temperature difference, so that the heated water temperature of the heat exchange line 14 is kept substantially constant.
A third heat pump type hot water supply system is characterised in that a flow return port 43 is formed in a portion of the outer wall of the hot water storage tank 3 located below the vertically middle of the hot water storage tank 3, wherein the outgoing water from the heat exchange line 14 is returned to the hot water storage tank 3 through the flow return port 43 when the heated water temperature of the heat exchange line 14 is equal to or below the set point.
With the third heat pump type hot water supply system, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water at a low temperature from the heat exchange line 14 is returned to the hot water storage tank 3 through the flow return port 43 located in a portion of the outer wall of the hot water storage tank 3 below the vertically middle of the hot water storage tank 3. Therefore, low-temperature water or low-temperature hot water is not mixed with the high-temperature storage water in the upper part of the storage tank 3. Thereafter, when the heated water temperature of the heat exchange line 14 rises and exceeds the set point, the system returns to its normal operation in which the water having reached a sufficiently high temperature is returned to the storage tank 3 through the hot water inlet 11. Also with this configuration, the temperature of the incoming water to the heat exchange line 14 is not different from that of the incoming water in the other operating conditions, so that the heated water temperature of the heat exchange line 14 is kept substantially constant.
A fourth heat pump type hot water supply system is characterised in that the water outlet 10 is composed of a supply water inlet 5 formed in the bottom of the hot water storage tank 3, the storage water in the hot water storage tank 3 is allowed to flow out to the circulation line 12 through the supply water inlet 5, and when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the water heated up in the heat exchange line 14 is returned to the hot water storage tank 3 through a port 10 formed in the bottom of the hot water storage tank 3.
With the fourth heat pump type hot water supply system, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water at a low temperature from the heat exchange line 14 is returned to the hot water storage tank 3 through the port 10 in the bottom of the storage tank 3. Therefore, low-temperature water or low-temperature hot water is not mixed with the high-temperature storage water in the upper part of the storage tank 3. Thereafter, when the heated water temperature of the heat exchange line 14 rises and exceeds the set point, the system returns to its normal operation in which the water having reached a sufficiently high temperature is returned to the storage tank 3 through the hot water inlet 11. Accordingly, also with this configuration, the incoming water temperature of the heat exchange line 14 has not difference between various operating conditions, so that the heated water temperature of the heat exchange line 14 is kept substantially constant. In addition, since this configuration avoids the need to additionally provide a flow return port, it has the advantage of allowing use of existing hot water storage tanks.
A fifth heat pump type hot water supply system is characterised in that when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water from the heat exchange line 14 is drained from the circulation line 12 to the outside.
With the fifth heat pump type hot water supply system, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, the outgoing water at a low temperature from the heat exchange line 14 is drained to the outside without being returned to the storage tank 3. Therefore, if this operation is continued, the heated water temperature of the heat exchange line 14 rises with time and then exceeds the set point. When the heated water temperature of the heat exchange line 14 exceeds the set point, the operation to drain the water to the outside is cancelled. As a result, the hot water that has been heated up to a sufficiently high temperature in the heat exchange line 14 can be returned to the storage tank 3 through the hot water inlet 11.
As described so far, according to the heat pump type hot water supply system of the present invention, when the water has not been sufficiently heated up in the heat exchange line, the low-temperature water or low-temperature hot water is not returned to the upper part of the storage tank and therefore is not mixed with the high-temperature storage water in the upper part of the storage tank. This prevents drop of the average storage hot water temperature and avoids a day-time reheating operation, resulting in reduced cost owing to energy conservation.
According to the second heat pump type hot water supply system, since a baffle is generally provided near to the supply water inlet inside of the storage tank, low-temperature water or low-temperature hot water returned therein impinges on the baffle so as not to reach the high-temperature storage water in the upper part of the storage tank, which provides the average storage hot water temperature with further stability. Furthermore, since the storage water in the tank is taken to the heat exchange line through the water outlet in both the normal operating condition and the circulation operating condition (bypass operation) using the supply water inlet, there is no difference in the incoming water temperature of the heat exchange line between both the operating conditions. Therefore, the heated water temperature of the heat exchange line can be kept substantially constant. In other words, even if the system has switched from the bypass operation to the normal operation, there is no substantial variation in the incoming water temperature between both the operations and therefore the heated water temperature of the heat exchange line can be kept substantially constant. Accordingly, the start-up performance of the system can be improved with a simple control system, and the outgoing water temperature can be kept stably at a high temperature.
According to the third or fourth heat pump type hot water supply system, like the second heat pump type hot water supply system, the incoming water temperature of the heat exchange line does not vary substantially even at the switchover from the bypass operation to the normal operation, and therefore the heated water temperature of the heat exchange line can be kept substantially constant. As a result, as compared with conventional hot water supply systems of this kind, the start-up performance can be improved with a simple control system. In addition, the fourth heat pump type hot water supply system avoids the need to additionally provide a flow return port or the like and allows use of existing (already installed) hot water storage tanks, which contributes to cost reduction.
According to the fifth heat pump type hot water supply system, since no low-temperature water is returned to the storage tank, variations in the average storage hot water temperature can certainly be reduced, which ensures achievement of energy conservation.

Figure 1 is a circuit diagram schematically showing a heat pump type hot water supply system according to an embodiment of the present invention.
Figure 2 is a block diagram of a control section of the above heat pump type hot water supply system.
Figure 3 is a graph showing the relationship between the incoming water temperature and the outgoing water temperature in the above heat pump type hot water supply system.
Figure 4 is a circuit diagram schematically showing a modified example of a selector means in the above heat pump type hot water supply system.
Figure 5 shows another embodiment of the heat pump type hot water supply system of the present invention, wherein Figure 5A is a circuit diagram schematically showing an essential part, and Figure 5B is a circuit diagram schematically showing the essential part using the selector means shown in Figure 4 .
Figure 6 shows still another embodiment of the heat pump type hot water supply system of the present invention, wherein Figure 6A is a circuit diagram schematically showing an essential part, and Figure 6B is a circuit diagram schematically showing the essential part using the selector means shown in Figure 4 .
Figure 7 shows still another embodiment of the heat pump type hot water supply system of the present invention, wherein Figure 7A is a circuit diagram schematically showing an essential part, and Figure 7B is a circuit diagram schematically showing the essential part using the selector means shown in Figure 4 .
Figure 8 is a circuit diagram schematically showing a conventional heat pump type hot water supply system.
Figure 9 is a graph showing the relationship between the incoming water temperature and the outgoing water temperature in the conventional heat pump type hot water supply system.
Figure 10 is a graph showing the relationship between the heated water temperature and the COP in the conventional heat pump type hot water supply system.

Description will be made in detail about embodiments of the present invention with reference to the drawings. Figure 1 is a schematic circuit diagram of a heat pump type hot water supply system according to an embodiment of the present invention. The hot water supply system includes a tank unit 1 and a heat source unit 2, and is configured to heat water (warm water) in the tank unit 1 with the heat source unit 2.
The tank unit 1 includes a hot water storage tank 3. The hot water stored in the storage tank 3 is supplied to a bath tub and so on. For this purpose, the storage tank 3 has a supply water inlet 5 formed in the bottom wall thereof and a hot water outlet 6 formed in the top wall thereof, so that water is fed to the storage tank 3 through the supply water inlet 5 and high-temperature hot water goes out through the hot water outlet 6. In this case, the supply water inlet 5 is connected to a supply water line 8 having a check valve 7, and a baffle 9 is provided near to the supply water inlet 5 inside of the storage tank 3. Furthermore, a water outlet 10 is formed in the bottom wall of the storage tank 3, and a hot water inlet 11 is formed in the upper part of the side wall (peripheral wall) of the storage tank 3.
The water outlet 10 and the hot water inlet 11 are connected together through a circulation line 12. In the circulation line 12, a pump 13 and a heat exchange line 14 are provided. Furthermore, a three-way valve 16 as a selector means 15 described later is provided in a portion of the circulation line 12 close to the hot water inlet 11. The three-way valve 16 is connected to a bypass line 17 connecting in return to the supply water line 8. Therefore, this heat pump type hot water supply system can perform two operations: a normal operation in which water (warm water) flows through the water outlet 10 into the circulation line 12 and passes through the circulation line 12, and the water heated up in the circulation line 12 then returns to the storage tank 3 through the hot water inlet 11 without flowing through the bypass line 17; and a bypass operation in which the water (warm water) flows through the water outlet 10 into the circulation line 12, passes through the circulation line 12, flows into the bypass line 17 through the three-way valve 16 and then returns from the bypass line 17 through the supply water inlet 5 to the storage tank 3.
Furthermore, the storage tank 3 includes four remaining water amount sensors 18a, 18b, 18c and 18d vertically spaced at regular pitches on the side wall thereof, and a temperature sensor 19 on the top wall thereof. Each of the remaining water amount sensors 18a, 18b, 18c and 18d and the temperature sensor 19 is formed of a thermistor, for example. Moreover, the circulation line 12 is provided with an incoming water thermistor 20 at its side upstream of the heat exchange line 14 (more specifically, upstream of the pump 13), and an outgoing water thermistor 21 (forming a sensor 22 for sensing the temperature of water heated up by the heat exchange line 14 (i.e., heated water temperature)) at its side downstream of the heat exchange line 14.
Referring to Figure 2 , a control section of the heat pump type hot water supply system is provided with a controller 23 for controlling the selector means 15 according to the heated water temperature sensed by the sensor 22. Specifically, when the heated water temperature sensed by the sensor 22 is equal to or below a set point (e.g., 85°C) preset by a setting means 24, the controller 23 causes the three-way valve 16 as the selector means 15 to change to the position for the bypass operation in which the water flows through the bypass line 17. On the other hand, when the heated water temperature exceeds the set point, the controller 23 causes the three-way valve 16 to change to the position for the normal operation in which the hot water does not flow through the bypass line 17. Here, the set point means a high temperature substantially equal to the temperature of the hot water in the upper part of the storage tank 3. The controller 23 and the other means in the control section are each formed using, for example, a microcomputer containing a CPU, a memory, and an input/output interface.
Referring again to Figure 1 , the heat source unit 2 includes a refrigerant circuit, and the refrigerant circuit includes a compressor 25, a water heat exchanger 26 constituting the heat exchange line 14, a subcooling heat exchanger 27, a receiver 28, an expansion valve 29, and a heat exchanger 30. The refrigerant circuit further includes a refrigerant line 31 through which the compressor 25 and the water heat exchanger 26 are connected, and another refrigerant line 32 through which the expansion valve 29 and the heat exchanger 30 are connected. A bypass line 33 is connected between both the refrigerant lines 31 and 32, and is provided with a defrosting valve 34. The refrigerant circuit 31 is provided with a thermistor 35, an HPS 36 as a pressure protective switch, and a pressure sensor 37, while the heat exchanger 30 is provided with a heat exchanger thermistor 38. Furthermore, a supercritical refrigerant for use in a supercritical state, such as carbon dioxide (CO2), is used as a refrigerant. In Figure 1 , the reference numeral 39 indicates an outside air thermistor.
The bypass line 33 is for performing a defrosting operation to supply a hot gas discharged from the compressor 25 to the heat exchanger 30 for defrosting of the heat exchanger 30. For this purpose, the heat source unit 2 includes a defrosting controller (not shown) for changeover between a normal water heating operation and the defrosting operation. Specifically, in the normal water heating operation, the water heat exchanger 26 and the heat exchanger 30 act as a condenser and an evaporator, respectively, thereby heating the water passing through the heat exchange line 14. In the defrosting operation, the hot gas flows through the heat exchanger 30 so that it heats up the heat exchanger 30. The defrosting controller is formed using, for example, a microcomputer containing a CPU, a memory, and an input/output interface, like the controller 23.
Next, description will be made about operations of the heat pump type hot water supply system having the above-described configuration. First, the compressor 25 is driven, so that the water heat exchanger 26 acts as a condenser and the heat exchanger 30 acts as an evaporator. Next, the pump 13 is driven (operated). Thereby, storage water (warm water) flows out of the storage tank 3 through the water outlet 10 in the tank bottom, and then flows through the heat exchange line 14 of the circulation line 12. During the time, the water is heated up by the water heat exchanger 26 functioning as a condenser. Thereafter, the heated water returns to the upper part of the storage tank 3 through the three-way valve 16 and the hot water inlet 11. This operation is conducted repeatedly so that high-temperature hot water is stored in the storage tank 3. It is to be noted that this operation is preferably conducted in late night hours when the electricity rates are low for the purpose of cost reduction.
During start-up or in like conditions, water heating in the heat exchange line 14 may not be sufficiently conducted and therefore the heated water temperature of the heat exchange line 14 may not reach the set point. In the heat pump type hot water supply system of this embodiment, however, if the heated water temperature of the heat exchange line 14 is equal to or below the set point, the sensor 22 senses that and the controller 23 causes the three-way valve 16 as the selector means 15 to change the position so that the water in the circulation line 12 flows through the bypass line 17. In other words, when the heated water temperature is equal to or below the set point, the system performs the bypass operation to return the hot water at a low temperature below the set point to the storage tank 3 through the supply water line 8 and the supply water inlet 5 without returning it to the storage tank 3 through the hot water inlet 11. Thereafter, when the heated water temperature exceeds the set point, the controller 23 allows the selector means 15 to change the position so that the system enters into the normal operating condition in which the hot water does not flow through the bypass line 17. In short, the hot water reaching a desired high temperature can be returned to the storage tank 3 through the hot water inlet 11.
As can be seen from the above, in the heat pump type hot water supply system of this embodiment, when the heated water temperature of the heat exchange line 14 is at a low temperature, the outgoing water is returned to the lower side of the storage tank 3. Therefore, as shown in Figure 3 (a graph showing the relationship between the incoming water temperature and the outgoing water temperature of the water heat exchanger 26), the temperature of water incoming from the tank lower side water outlet 10 to the heat exchange line 14 is kept low. Accordingly, even if the system is changed from the bypass operation to the normal water heating operation (i.e., even if the system is turned to a bypass OFF operating condition), the incoming water temperature of the heat exchange line 14 substantially does not change and the heated water temperature thereof can be kept substantially constant. Furthermore, as a result of the bypass operation, the heated water temperature can be raised to a sufficiently high temperature. This makes it possible to keep hot water fed from the storage tank 3 at a stable high temperature. Consequently, improvement in the start-up performance and hot water storage at a constant temperature can be achieved with a simple control system.
Furthermore, when the outside air is at low temperatures, such as in winter, the system performs a defrosting operation by the defrosting controller. Specifically, when the temperature of the heat exchanger thermistor 38 is equal to or below a reference value, the defrosting controller fully closes the expansion valve 29 and opens the defrosting valve 34. Here, the reference value is the temperature indicating that it is undesirable to continue the normal operation any more, because temperature drop beyond the reference value invites the frosting of the heat exchanger 30 and eventually performance drop. In such a case, a hot gas discharged from the compressor 25 is supplied to the heat exchanger 30 to defrost the heat exchanger 30 by the heat from the hot gas. When the temperature of the heat exchanger 30 exceeds the reference value, the defrosting controller fully closes the defrosting valve 34 and opens the expansion valve 29, thereby returning the system to the normal operation. Thereafter, the same switchover from normal to defrosting operation is made at appropriate times so as not to frost the heat exchanger 30. Then, when the defrosting operation is completed, the system enters into the same state as in the start-up, i.e., in the state where the water returned from the circulation line 12 to the storage tank 3 has a low temperature. Even in this case, however, the water is not returned to the storage tank 3 through the hot water inlet 11 to avoid drop in the average storage hot water temperature until the outgoing water from the heat exchange line 14 reaches a high temperature by the bypass operation. In this manner, the heated water temperature of the heat exchange line 14 can be sufficiently raised to ensure a sufficient outgoing water temperature by night-hours operation (off-peak operation). This avoids the need for reheating operation in day hours when the electricity rates are high, resulting in cost reduction.
As described above, the heat pump type hot water supply system of this embodiment includes the receiver 28 and the subcooling heat exchanger 27. The receiver 28 is for keeping the amount of circulation of the refrigerant in the refrigerant circuit at an adequate amount. The subcooling heat exchanger 27 is for adjusting the amount of refrigerant charged into the receiver 28. Provision of these elements enables a proper refrigeration cycle and a stable heated water temperature of the heat exchange line 14 to be kept.
Next, Figure 4 shows a modified example of the selector means 15. In this example, the selector means 15 is composed of two two- way valves 40 and 41 without using the three-way valve 16. Specifically, one of the two-way valves 40 is disposed near to the hot water inlet 11 in the circulation line 12, while the other two-way valve 41 is disposed in the bypass line 17. During the normal operation, the two-way valve 40 is opened while the two-way valve 41 closed. During the bypass operation, the two-way valve 40 is closed while the two-way valve 41 opened. In these manners, the two- way valves 40 and 41 have the same function as the three-way valve 16. Therefore, also when the system uses the selector means 15 shown in Figure 4 , the outgoing water from the heat exchange line 14 is not returned to the storage tank 3 through the hot water inlet 11 to avoid drop in the average storage hot water temperature until the heated water temperature of the heat exchange line 14 reaches a high temperature. It is to be noted that the opening/closing operations on the two- way valves 40 and 41 are made of course by the controller 23 according to the temperature sensed by the sensor 22.
Next, Figure 5 shows a heat pump type hot water supply system according to another embodiment of the present invention. Figure 5A is a schematic circuit diagram of an essential part, and Figure 5B is a schematic circuit diagram of the essential part using the selector means 15 shown in Figure 4 . In these cases, the supply water inlet 5 of the storage tank 3 in Figure 1 is used as a water outlet 10, and the water outlet 10 of the storage tank 3 in Figure 1 is used as a flow return port 43. Specifically, in the normal operation, the low-temperature storage water flows out of the storage tank 3 through the water outlet 10 doubling as the supply water inlet 5 to the circulation line 12 and is heated up by the heat exchange line 14 in the circulation line 12, and the water heated up to a high temperature is returned to the storage tank 3 through the selector means 15 and the hot water inlet 11. On the other hand, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, such as at the start-up or during the defrosting operation, the controller 23 (not shown in this embodiment), like the heat pump type hot water supply system of Figure 1 , causes the selector means 15 to change to the position in which the water in the circulation line 12 flows through the bypass line 17. In this case, the opening which functions as the water outlet 10 in Figure 1 is used as the flow return port 43 so that the water is returned to the storage tank 3 through the bypass line 17. Since the heat pump type hot water supply system shown in Figure 5B uses the two- way valves 40 and 41 instead of the three-way valve 16, it can perform the same operations as the heat pump type hot water supply system shown in Figure 5A .
Next, Figure 6 shows a heat pump type hot water supply system according to still another embodiment of the present invention. Figure 6A is a schematic circuit diagram of an essential part, and Figure 6B is a schematic circuit diagram of the essential part using the selector means 15 shown in Figure 4 . In the case of Figure 6A , the flow return port 43 is formed in the vertically intermediate portion of the side wall of the storage tank 3, and is connected to the bypass line 17 connecting to the selector means 15. Therefore, in the normal operation, the low-temperature storage water flows out of the storage tank 3 through the water outlet 10 to the circulation line 12 and is heated up by the heat exchange line 14 in the circulation line 12, and the water heated up to a high temperature is returned to the storage tank 3 through the selector means 15 and the hot water inlet 11. On the other hand, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, such as at the start-up or during the defrosting operation, the controller 23 (not shown in this embodiment), like the heat pump type hot water supply system shown in Figure 1 , causes the selector means 15 to change positions. As a result, the water in the circulation line 12 flows through the bypass line 17, and is returned to the storage tank 3 through the bypass line 17 and the flow return port 43. Since the heat pump type hot water supply system shown in Figure 6B uses the two- way valves 40 and 41 instead of the three-way valve 16, it can perform the same operations as the heat pump type hot water supply system shown in Figure 6A .
As can be seen from the above, the heat pump type hot water supply systems shown in Figures 5 and 6 can also have the same effect as the heat pump type hot water supply system shown in Figure 1 , i.e., the effect of preventing drop in the average storage hot water temperature by avoiding the return of the water from the heat exchange line 14 to the storage tank 3 through the hot water inlet 11 until the heated water temperature of the heat exchange line 14 reaches a high temperature.
Next, Figure 7 shows a heat pump type hot water supply system according to still another embodiment of the present invention. Figure 7A is a schematic circuit diagram of an essential part, and Figure 7B is a schematic circuit diagram of the essential part using the selector means 15 shown in Figure 4 . In the case of Figure 7A , the bypass line 17 is not connected to the storage tank 3, but the water entering the bypass line 17 is drained (discharged) to the outside. Specifically, in the normal operation, the low-temperature storage water flows out of the storage tank 3 through the water outlet 10 to the circulation line 12 and is heated up by the heat exchange line 14 in the circulation line 12, and the water heated up to a high temperature is returned to the storage tank 3 through the selector means 15 and the hot water inlet 11. On the other hand, when the heated water temperature of the heat exchange line 14 is equal to or below the set point, such as at the start-up or during the defrosting operation, the controller 23 (not shown in this embodiment), like the heat pump type hot water supply system shown in Figure 1 , causes the selector means 15 to change positions. As a result, the water in the circulation line 12 flows through the bypass line 17, and is then drained to the outside through the bypass line 17. In this case, the drained water may be discharged directly to sewers or may be discharged after being used for washing or any other purposes.
Accordingly, the heat pump type hot water supply system shown in Figure 7 can also have the same effect, i.e., the effect of preventing drop in the average storage hot water temperature by avoiding the return of the water from the heat exchange line 14 to the storage tank 3 through the hot water inlet 11 until the heated water temperature of the heat exchange line 14 reaches a high temperature. Since the heat pump type hot water supply system shown in Figure 7B uses the selector means 15 shown in Figure 4 , it can perform the same operations as the heat pump type hot water supply system shown in Figure 7A .
The embodiments of the present invention have been described so far. The present invention, however, is not limited to the above-described embodiments but can be put into practice also in the form of various changes and modifications which fall within the scope of this invention. For example, the set point as a reference for the changeover between the normal water heating operation and the bypass operation can be freely preset. However, the set point is preferably set around the temperature in the upper part of the storage tank 3, and more preferably set at about 85°C. Furthermore, the position of the flow return port 43 can be freely changed so long as it is not above the vertically middle point of the side wall of the storage tank 3. Furthermore, the subcooling heat exchanger 27 and/or the receiver 28 may be omitted from the heat source unit 2.
Accordingly, the above-described embodiments should be considered in all respects as illustrative only and not restrictive of the invention. The scope of the invention is defined by the scope of the appended claims and is not restricted to the description. Furthermore, all changes and modifications belonging to equivalents of the scope of the invention fall within the scope of the invention.

Claims

A heat pump type hot water supply system which includes a hot water storage tank (3), a bypass line (17), and a circulation line (12) connecting a water outlet (10) at the lower part of the storage tank (3) and a hot water inlet (11) at the upper part thereof, the circulation line (12) being provided partway therealong with a heat exchange line (14) to be heated by a heat pump heat source, and in which water heated up in the heat exchange line (14) is returned to the hot water storage tank (3) through the hot water inlet (11),
characterised in that
the hot water storage tank (3) includes a flow return port (43) formed in a portion of the outer wall of the hot water storage tank (3) located below the vertically middle of the hot water storage tank (3), wherein the outgoing water from the bypass line (17) is returned to the hot water storage tank (3) through the flow return port (43) when the heated water temperature of the heat exchange line (14) is equal to or below the set point in the flow return port (43) connected to the bypass line (17), and the outgoing water from the heat exchange line (14) is returned to the hot water storage tank (3) through the hot water inlet (11) when the heated water temperature of the heat exchange line (14) is above the set point.