STORAGE TYPE HEAT PUMP HOT WATER SUPPLYING APPARATUS

Abstract

A storage type heat pump hot water supplying apparatus includes: control circuitry to control a compressor frequency and a pump rotational speed, the compressor frequency being an operating frequency of the compressor, the pump rotational speed being a rotational speed of a water pump. The control circuitry is configured to control, in a heat accumulating operation for accumulating hot water in the hot water storage tank, the pump rotational speed so that the actual hot water discharge temperature becomes equal to a target hot water discharge temperature. The heat accumulating operation includes a first operation and a second operation after the first operation. The compressor frequency in the first operation is higher than the compressor frequency in the second operation. The target hot water discharge temperature in the first operation is lower than the target hot water discharge temperature in the second operation.

Description

FIELD

The present disclosure relates to a storage type heat pump hot water supplying apparatus.

BACKGROUND

PTL 1 described below discloses a technique in which, in a storage type heat pump hot water supplying apparatus, after a heat pump apparatus is started up, a control device first controls either one of or both the heat pump apparatus and a circulation pump so that a hot water discharge temperature becomes equal to an intermediate target temperature. The intermediate target temperature is a temperature lower than a target hot water discharge temperature. The control device continues, for a predetermined time period, an operation of causing the hot water discharge temperature to be equal to the intermediate target temperature. Thereafter, the control device controls either one of or both the heat pump apparatus and the circulation pump so that the hot water discharge temperature becomes equal to the target hot water discharge temperature.

CITATION LIST

Patent Literature

[PTL 1] JP 2017-207234 A

SUMMARY

Technical Problem

A lower hot water discharge temperature allows the amount of power consumption of a storage type heat pump hot water supplying apparatus to be reduced more. In the above-described technique, it is difficult to increase the quantity of accumulated heat at the intermediate target temperature, being a relatively low hot water discharge temperature, and hence, there is a problem that it is difficult to reduce the amount of power consumption.

The present disclosure has been made to solve the above-described problem, and it is an object of the present disclosure to provide a storage type heat pump hot water supplying apparatus that has an advantage in increasing the quantity of accumulated heat at a relatively low temperature.

Solution to Problem

A storage type heat pump hot water supplying apparatus according to the present disclosure includes: a heat source machine including a compressor to compress refrigerant and a water heat exchanger to exchange heat between water and the refrigerant compressed by the compressor; a hot water storage tank to store hot water heated by the heat source machine; a water circuit including a feed path connecting a lower part of the hot water storage tank to a water inlet of the water heat exchanger, a return path connecting a water outlet of the water heat exchanger to an upper part of the hot water storage tank, and a water pump provided in the feed path or the return path; a temperature sensor to detect an actual hot water discharge temperature, the actual hot water discharge temperature being a temperature of hot water flowing out of the water heat exchanger; and control circuitry to control a compressor frequency and a pump rotational speed, the compressor frequency being an operating frequency of the compressor, the pump rotational speed being a rotational speed of the water pump. The control circuitry is configured to control, in a heat accumulating operation for accumulating hot water in the hot water storage tank, the pump rotational speed so that the actual hot water discharge temperature becomes equal to a target hot water discharge temperature. The heat accumulating operation includes a first operation and a second operation after the first operation. The compressor frequency in the first operation is higher than the compressor frequency in the second operation. The target hot water discharge temperature in the first operation is lower than the target hot water discharge temperature in the second operation.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a storage type heat pump hot water supplying apparatus that has an advantage in increasing the quantity of accumulated heat at a relatively low temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a storage type heat pump hot water supplying apparatus according to an embodiment 1.

FIG. 2 is a diagram showing an example of a temporal change in hot water discharge temperature in an heat accumulating operation.

FIG. 3 is a diagram showing an example of a temporal change in COP during a period shown in FIG. 2.

FIG. 4 is a diagram showing the relationship between an input (W) and capacity (Q) in a winter-season hot water supplying and heat retaining mode efficiency test.

FIG. 5 is a diagram showing the summary of effects that occur when a low temperature heat accumulating operation time period is increased.

FIG. 6 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of the storage type heat pump hot water supplying apparatus according to the embodiment 1 in the heat accumulating operation.

FIG. 7 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of a storage type heat pump hot water supplying apparatus according to an embodiment 2 in the heat accumulating operation.

FIG. 8 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of a storage type heat pump hot water supplying apparatus according to an embodiment 3 in the heat accumulating operation.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described with reference to drawings. In the respective drawings, the identical or corresponding elements are given the same reference symbols, and the description of such elements will be simplified or omitted.

Embodiment 1

FIG. 1 is a diagram showing a storage type heat pump hot water supplying apparatus according to an embodiment 1. As shown in FIG. 1, a storage type heat pump hot water supplying apparatus 1 according to the embodiment 1 includes a heat source machine 2 and a tank unit 3. The heat source machine 2 is disposed outdoors. The tank unit 3 may be disposed outdoors, or may be disposed in the room. The heat source machine 2 and the tank unit 3 are connected with each other via a water pipe and an electric cable (not shown in the drawing).

A hot water storage tank 4, a water pump 5, and a control device 6 are provided in the tank unit 3, the hot water storage tank 4 storing hot water heated by the heat source machine 2. Hereinafter, the rotational speed of the water pump 5 will be referred to as “pump rotational speed”. The control device 6 can control a pump rotational speed. The control device 6 may be configured to change a pump rotational speed by inverter control, for example. The control device 6 may include at least one processor and at least one memory.

The heat source machine 2 includes a refrigerant circuit in which a compressor 7, a water heat exchanger 8, an expansion valve 9, and an air heat exchanger 10 are connected in a ring shape via refrigerant pipes 12. The heat source machine 2 further includes a blower 11 and a control device 13, the blower 11 being configured to send outdoor air to the air heat exchanger 10. The heat source machine 2 performs the operation of a refrigeration cycle, that is, a heat pump cycle, using the refrigerant circuit. The compressor 7 compresses refrigerant gas. Refrigerant may be any one of a carbon dioxide, an ammonia, a propane, an isobutane, a fluorocarbon, such as an HFC, an HFO-1123, and an HFO-1234yf, for example.

The control device 13 controls the action of the compressor 7. The action speed of the compressor 7 is variable. By allowing the operating frequency of an electric motor included in the compressor 7 to be variably controlled by inverter control, the control device 13 can variably control the action speed of the compressor 7. A higher operating frequency of the compressor 7 causes a higher action speed of the compressor 7. A higher action speed of the compressor 7 causes a larger circulation amount of refrigerant, thus increasing heating capacity. Hereinafter, the operating frequency of the compressor 7 will be referred to as “compressor frequency”. The control device 13 may include at least one processor and at least one memory.

The control device 6 and the control device 13 are capable of communication with each other. In the present embodiment, the control device 6 and the control device 13 cooperate with each other to control the action of the storage type heat pump hot water supplying apparatus 1. The control device 6 and the control device 13 correspond to control circuitry. In the description made hereinafter, either one or both the control device 6 and the control device 13 may be referred to as “control circuitry”. In the present disclosure, the configuration is not limited to the configuration in which the control device 6 and the control device 13 cooperate with each other to control the action of the storage type heat pump hot water supplying apparatus 1, and may be a configuration in which a single control device controls the action of the storage type heat pump hot water supplying apparatus 1.

The hot water storage tank 4 stores hot water heated by the heat source machine 2 and low temperature water that is to be heated by the heat source machine 2. In the hot water storage tank 4, due to a difference in the density of water caused by a temperature difference, a temperature stratification is formed in which the upper layer has a high temperature and the lower layer has a low temperature. The hot water storage tank 4 is covered by a heat insulating material (not shown in the drawing) that prevents dissipation of heat. Although the shape of the hot water storage tank 4 is not particularly limited, the shape of the hot water storage tank 4 may be a cylindrical shape that uses the vertical direction as the axial direction, for example.

The water heat exchanger 8 includes a refrigerant flow passage and a water flow passage, refrigerant compressed by the compressor 7 flowing through the refrigerant flow passage, water from the hot water storage tank 4 flowing through the water flow passage. The water heat exchanger 8 causes refrigerant flowing through the refrigerant flow passage to exchange heat with water flowing through the water flow passage, thus heating the water.

The expansion valve 9 causes high pressure refrigerant that passes through the water heat exchanger 8 to expand, thus reducing the pressure of the high pressure refrigerant. The control device 13 may control the degree of opening of the expansion valve 9. The expansion valve 9 may be a linear expansion valve the degree of opening of which can be continuously controlled.

The air heat exchanger 10 exchanges heat between outdoor air and low pressure refrigerant that passes through the expansion valve 9, thus causing the low pressure refrigerant to evaporate. Low pressure refrigerant gas that passes through the air heat exchanger 10 flows into the compressor 7.

The lower part of the hot water storage tank 4 is connected to the inlet of the water flow passage of the water heat exchanger 8 via a feed path 14. The outlet of the water flow passage of the water heat exchanger 8 is connected to the upper part of the hot water storage tank 4 via a return path 15. The water pump 5 is provided to the feed path 14. Instead of adopting the example shown in the drawing, the water pump 5 may be provided to the return path 15. The water pump 5, the feed path 14, and the return path 15 form a water circuit for performing a heat accumulating operation. The heat accumulating operation is an operation of accumulating heat in the hot water storage tank 4 by accumulating hot water in the hot water storage tank 4.

A water supply pipe 16 is connected to the lower part of the hot water storage tank 4. A hot water supply pipe 17 for supplying hot water from the hot water storage tank 4 is connected to the upper part of the hot water storage tank 4. When the storage type heat pump hot water supplying apparatus 1 is used, low temperature water supplied from a water source, such as a water supply, for example, flows into the lower part of the hot water storage tank 4 through the water supply pipe 16, so that the inside of the hot water storage tank 4 is always maintained in a state of being fully filled with water. In supplying hot water, hot water in the hot water storage tank 4 flows out to the hot water supply pipe 17 due to water pressure from the water supply pipe 16. With such outflow of water, the same amount of low temperature water flows into the lower part of the hot water storage tank 4 from the water supply pipe 16.

When the water pump 5 is operated, water circulates through the water circuit. The storage type heat pump hot water supplying apparatus 1 can execute the heat accumulating operation. In the heat accumulating operation, water is caused to circulate through the water circuit to accumulate, in the hot water storage tank 4, hot water heated by the water heat exchanger 8. In the heat accumulating operation, the control circuitry performs control as follows. The heat source machine 2 and the water pump 5 are operated. Water that flows out of the lower part of the hot water storage tank 4 is sent to the water heat exchanger 8 through the feed path 14. Hot water heated by the water heat exchanger 8 returns to the tank unit 3 through the return path 15, and flows into the upper part of the hot water storage tank 4. By performing such a heat accumulating operation, in the hot water storage tank 4, hot water is gradually stored from the upper part toward the lower part, so that the temperature boundary layer between hot water and low temperature water gradually moves downward.

In the description made hereinafter, the temperature of hot water that flows out of the water heat exchanger 8 will be referred to as “hot water discharge temperature”. The heat source machine 2 includes a hot water discharge temperature sensor 18 that detects a hot water discharge temperature. In the description made hereinafter, an actual hot water discharge temperature detected by the hot water discharge temperature sensor 18 will be referred to as “actual hot water discharge temperature”. The hot water discharge temperature sensor 18 is installed at the outlet of the water flow passage of the water heat exchanger 8 or in the return path 15. In the heat accumulating operation, the control circuitry controls the pump rotational speed so that the actual hot water discharge temperature detected by the hot water discharge temperature sensor 18 becomes equal to a target hot water discharge temperature.

Hereinafter, the flow rate of water flowing through the water circuit will be simply referred to as “water flow rate”. In the case in which the actual hot water discharge temperature is lower than the target hot water discharge temperature, the control circuitry reduces the pump rotational speed to reduce the water flow rate. With such an operation, the actual hot water discharge temperature rises, thus approaching the target hot water discharge temperature. In the case in which the actual hot water discharge temperature is higher than the target hot water discharge temperature, the control circuitry increases the pump rotational speed to increase the water flow rate. The actual hot water discharge temperature is reduced, thus approaching the target hot water discharge temperature.

In general, there is a tendency for a lower hot water discharge temperature to cause a higher COP (Coefficient Of Performance), leading to a reduction in the amount of power consumption of the storage type heat pump hot water supplying apparatus 1. FIG. 2 is a diagram showing an example of a temporal change in hot water discharge temperature in the heat accumulating operation. FIG. 3 is a diagram showing an example of a temporal change in COP during the period shown in FIG. 2.

A first stage in FIG. 2 and FIG. 3 corresponds to a low temperature heat accumulating operation in which hot water is accumulated in the hot water storage tank 4 at a relatively low hot water discharge temperature. A second stage in FIG. 2 and FIG. 3 corresponds to a high temperature heat accumulating operation in which hot water is accumulated in the hot water storage tank 4 at a relatively high hot water discharge temperature. A refrigerant pressure on the high-pressure side of the refrigerant circuit in the low temperature heat accumulating operation is lower than a refrigerant pressure on the high-pressure side of the refrigerant circuit in the high temperature heat accumulating operation. As a result, the COP in the low temperature heat accumulating operation is higher than the COP in the high temperature heat accumulating operation.

The time period (time period from tp to tc) of control in the first stage in FIG. 2 and FIG. 3 will be referred to as “low temperature heat accumulating operation time period”. Under the operating conditions for winter-season hot water supplying and heat retaining mode efficiency specified in JIS (Japanese Industrial Standards), a longer low temperature heat accumulating operation time period improves winter-season hot water supplying and heat retaining mode efficiency more.

In the description made hereinafter, hours including the daytime of a day will be referred to as “daytime hours”, and hours other than the daytime hours of a day will be referred to as “nighttime hours”. The daytime hours may be hours from 7:00 to 23:00, for example. In such a case, hours from 23:00 to 7:00 of the next day correspond to the nighttime hours. A heat accumulating operation performed in the daytime hours will be referred to as “daytime heat accumulating operation”. A heat accumulating operation performed in the nighttime hours will be referred to as “nighttime heat accumulating operation”. The quantity of heat accumulated in the hot water storage tank 4 due to the heat accumulating operation will be referred to as “quantity of accumulated heat”.

FIG. 4 is a diagram showing the relationship between an input (W) and capacity (Q) in a winter-season hot water supplying and heat retaining mode efficiency test. FIG. 5 is a diagram showing the summary of effects that occur when the low temperature heat accumulating operation time period is increased.

In the description made hereinafter, the temperature of water that flows into the water heat exchanger 8 will be referred to as “inflow water temperature”, and the flow rate of water that flows into the water heat exchanger 8 will be referred to as “inflow water flow rate”. Further, the quantity of heat applied per hour to water by the heat source machine 2 will be referred to as “heating capacity”. The unit of heating capacity is the watt, for example. The heating capacity corresponds to the quantity of heat provided per hour to water by refrigerant in the water heat exchanger 8.

As described above, when a hot water discharge temperature is low, the COP is high. Before the end of the nighttime heat accumulating operation, the temperature boundary layer reaches the lower part of the hot water storage tank 4, so that there may be a case in which an inflow water temperature rises. Therefore, in hours before the end of the nighttime heat accumulating operation, there may be a case in which the COP reduces due to a rise in inflow water temperature.

As can be understood from FIG. 3 to FIG. 5, as the quantity of accumulated heat at a low temperature is increased, the COP at the time of startup is improved more. Further, the quantity of accumulated heat in daytime hours can be increased and hence, the quantity of accumulated heat in nighttime hours reduces. When the quantity of accumulated heat in nighttime hours reduces, losses of heat energy dissipating from the hot water storage tank 4 reduce. Due to the above, a longer low temperature heat accumulating operation time period can reduce the larger amount of power consumption.

In the course of the execution of the heat accumulating operation, there may be a case in which the heat accumulating operation is stopped to perform, for example, a heat retaining operation that uses the heat source machine 2. The heat retaining operation that uses the heat source machine 2 is, for example, an operation in which hot water is supplied to a reheating heat exchanger (not shown in the drawing) from the heat source machine 2, the reheating heat exchanger heating bathtub water circulated from a bathtub to maintain heat of bathtub water in the bathtub.

There is a possibility that, in the course of the execution of the low temperature heat accumulating operation, the heat retaining operation that uses the heat source machine 2 is required. Therefore, there may be a case in which, in the course of the execution of the low temperature heat accumulating operation, the low temperature heat accumulating operation is stopped due to the execution of the heat retaining operation that uses the heat source machine 2. As described above, as there are hours in which the low temperature heat accumulating operation is stopped due to the heat retaining operation, the low temperature heat accumulating operation time period is limited. For this reason, there is a limit to effects of reducing the amount of power consumption brought about by increasing the low temperature heat accumulating operation time period.

FIG. 6 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of the storage type heat pump hot water supplying apparatus 1 according to the embodiment 1 in the heat accumulating operation. As shown in FIG. 6, the heat accumulating operation according to the present disclosure includes a first operation and a second operation after the first operation. For example, after startup of the compressor 7 of the heat source machine 2, the control circuitry first executes the first operation and, after the end of the first operation, the control circuitry executes the second operation. The control circuitry is configured to set the compressor frequency in the first operation to be higher than the compressor frequency in the second operation. Further, the control circuitry is configured to set the target hot water discharge temperature in the first operation to be lower than the target hot water discharge temperature in the second operation. As described above, the control circuitry controls the pump rotational speed so that the actual hot water discharge temperature detected by the hot water discharge temperature sensor 18 becomes equal to the target hot water discharge temperature. Therefore, the actual hot water discharge temperature in the first operation takes a value corresponding to the target hot water discharge temperature in the first operation, and the actual hot water discharge temperature in the second operation takes a value corresponding to the target hot water discharge temperature in the second operation.

A higher compressor frequency causes higher heating capacity. Therefore, heating capacity in the first operation is higher than heating capacity in the second operation. In the description made hereinafter, the quantity of accumulated heat brought about by the first operation will be referred to as “quantity of low-temperature accumulated heat”, and the quantity of accumulated heat brought about by the second operation will be referred to as “quantity of high-temperature accumulated heat”. In the present embodiment, the heating capacity in the first operation is higher than the heating capacity in the second operation and hence, even when a limitation is imposed on the time period of the first operation, it is possible to increase the quantity of low-temperature accumulated heat. The COP in the first operation is higher than the COP in the second operation. Therefore, a larger quantity of low-temperature accumulated heat increases the COP as a whole more. For this reason, the present embodiment has an advantage in reducing the amount of power consumption of the storage type heat pump hot water supplying apparatus 1.

The control circuitry is configured to set the pump rotational speed in the first operation to be higher than the pump rotational speed in the second operation. With such a configuration, it is possible to set the actual hot water discharge temperature in the first operation to be lower than the actual hot water discharge temperature in the second operation. In the case in which there is a fluctuation in pump rotational speed, it is sufficient to configure the control circuitry such that the average pump rotational speed in the first operation is set to be higher than the average pump rotational speed in the second operation.

The control circuitry may be configured to execute, in the daytime heat accumulating operation performed in daytime hours, the heat accumulating operation including the first operation and the second operation. With such a configuration, it is possible to increase the quantity of accumulated heat in daytime hours and it is possible to reduce the quantity of accumulated heat in nighttime hours. Accordingly, such a configuration has a further advantage in reducing the amount of power consumption for a day.

The control circuitry may be configured to execute, in the nighttime heat accumulating operation performed in nighttime hours, the second operation by omitting the first operation. In nighttime hours, there may be a case in which the quantity of heat larger than that in daytime hours is required to be accumulated in the hot water storage tank 4. Therefore, there is a possibility that, immediately before the end of the nighttime heat accumulating operation, the temperature boundary layer in the hot water storage tank 4 reaches the lower part of the hot water storage tank 4, so that an inflow water temperature rises. A longer time period of the first operation tends to cause the inflow water temperature to rise more immediately before the end of the nighttime heat accumulating operation. In view of the above, in the nighttime heat accumulating operation, the second operation is executed by omitting the first operation. With such a configuration, it is possible to prevent an inflow water temperature from rising immediately before the end of the nighttime heat accumulating operation. As a result, it is possible to avoid a reduction in COP caused by a rise in inflow water temperature. Accordingly, such a configuration has a further advantage in reducing the amount of power consumption for a day.

In the present embodiment, the control circuitry is configured to keep the target hot water discharge temperature constant within a period from the start of the first operation to the end of the first operation. With such a configuration, it is possible to make the actual hot water discharge temperature more stable within the period from the start of the first operation to the end of the first operation and hence, the COP is further increased.

In the present embodiment, the control circuitry is configured to keep a compressor frequency constant within the period from the start of the first operation to the end of the first operation. With such a configuration, heating capacity is stabilized within the period from the start of the first operation to the end of the first operation and hence, it is possible to make the actual hot water discharge temperature more stable, leading to a further increase in COP.

As described above, when the heat accumulating operation including the first operation and the second operation is executed, there is a tendency, even when the quantity of accumulated heat in the hot water storage tank 4 is the same, for a larger ratio of the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat to increase the COP as a whole more. However, a larger ratio of the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat causes the volume of hot water stored in the hot water storage tank 4 to increase and hence, before the end of the heat accumulating operation, the temperature boundary layer tends to approach the lower part of the hot water storage tank 4. As a result, there is a possibility that, before the end of the heat accumulating operation, the inflow water temperature rises, thus reducing the COP.

The control circuitry may detect, by using a hot water supply flow rate sensor (not shown in the drawing) and a hot water supply temperature sensor (not shown in the drawing), the hot water supply load to learn daily hot water supply loads, the hot water supply flow rate sensor detecting the flow rate of hot water passing through the hot water supply pipe 17, the hot water supply temperature sensor detecting the temperature of hot water passing through the hot water supply pipe 17. The control circuitry may determine a target quantity of accumulated heat by performing statistical processing on the hot water supply loads of a plurality of past days (of the past 14 days, for example). When the target quantity of accumulated heat is large, the volume of hot water that is necessary to be stored in the hot water storage tank 4 increases. Therefore, in such a case, there is a possibility that, before the end of the heat accumulating operation, the temperature boundary layer approaches the lower part of the hot water storage tank 4, so that the inflow water temperature rises, thus reducing the COP. To more surely avoid such a situation, when the control circuitry executes the heat accumulating operation including the first operation and the second operation, the control circuitry may change, according to the target quantity of accumulated heat, the ratio of the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat. For example, when the target quantity of accumulated heat is relatively large, the control circuitry may set a relatively small ratio for the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat. When the target quantity of accumulated heat is relatively small, the control circuitry may set a relatively large ratio for the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat. With such a configuration, even in the case in which the target quantity of accumulated heat is large, it is possible to prevent a situation in which an inflow water temperature rises before the end of the heat accumulating operation and hence a reduction in COP can be avoided more surely. Further, in the case in which the target quantity of accumulated heat is small, that is, there is a condition that the inflow water temperature is less likely to rise before the end of the heat accumulating operation, when the ratio of the quantity of low-temperature accumulated heat to the quantity of high-temperature accumulated heat is further increased, the COP as a whole is further increased.

Embodiment 2

Next, an embodiment 2 will be described with reference to FIG. 7. However, points that make the embodiment 2 different from the above-described embodiment 1 will be mainly described, and the repeated description will be simplified or omitted. Further, elements identical or corresponding to the above-described elements are given the same reference symbols. FIG. 7 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of a storage type heat pump hot water supplying apparatus 1 according to the embodiment 2 in the heat accumulating operation.

As shown in FIG. 7, a control circuitry according to the embodiment 2 is configured to increase a target hot water discharge temperature in a stepwise manner within the period from the start of the first operation to the end of the first operation. With such a configuration, a change in target hot water discharge temperature at the time of the transition from the first operation to the second operation is lower than that in the embodiment 1. For this reason, when transition is made from the first operation to the second operation, it is possible to make the actual hot water discharge temperature more stable than that in the embodiment 1 and hence, losses at the time of the transition are reduced, thus further increasing the COP.

The control circuitry according to the embodiment 2 is configured to reduce a compressor frequency in a stepwise manner within the period from the start of the first operation to the end of the first operation. With such a configuration, a change in compressor frequency and a change in heating capacity at the time of the transition from the first operation to the second operation are lower than those in the embodiment 1. For this reason, when the transition is made from the first operation to the second operation, it is possible to make the actual hot water discharge temperature more stable than that in the embodiment 1 and hence, losses at the time of the transition are reduced, thus further increasing the COP.

In the example shown in the drawing, the control circuitry is configured to reduce, in the first operation, the compressor frequency simultaneously with an increase in target hot water discharge temperature. That is, the control circuitry is configured to reduce, in the first operation, the compressor frequency as the target hot water discharge temperature rises.

In the example shown in the drawing, the control circuitry is configured to increase the target hot water discharge temperature in three stages in the first operation. However, the configuration is not limited to the example shown in the drawing and, in the first operation, the control circuitry may increase the target hot water discharge temperature in two stages, or may increase the target hot water discharge temperature in four stages or multiple stages of five or more.

In the example shown in the drawing, the control circuitry is configured to reduce the compressor frequency in three stages in the first operation. However, the configuration is not limited to the example shown in the drawing and, in the first operation, the control circuitry may reduce the compressor frequency in two stages, or may reduce the compressor frequency in four stages or multiple stages of five or more.

Embodiment 3

Next, an embodiment 3 will be described with reference to FIG. 8. However, points that make the embodiment 3 different from the above-described embodiment 1 will be mainly described, and the repeated description will be simplified or omitted. Further, elements identical or corresponding to the above-described elements are given the same reference symbols. FIG. 8 is a diagram showing an example of temporal changes in the target hot water discharge temperature, the compressor frequency, and the heating capacity of a storage type heat pump hot water supplying apparatus 1 according to the embodiment 3 in the heat accumulating operation.

As shown in FIG. 8, a control circuitry according to the embodiment 3 is configured to continuously increase the target hot water discharge temperature within the period from the start of the first operation to the end of the first operation. That is, the control circuitry according to the embodiment 3 is configured to change the target hot water discharge temperature on a gradient within the period from the start of the first operation to the end of the first operation. In the present embodiment, losses at the time of the transition from the first operation to the second operation are even smaller than those in the embodiment 2, thus further increasing the COP.

In the example shown in the drawing, the control circuitry is configured to cause the target hot water discharge temperature at the end of the first operation to be equal to the target hot water discharge temperature in the second operation.

The control circuitry according to the embodiment 3 is configured to continuously reduce the compressor frequency within the period from the start of the first operation to the end of the first operation. That is, the control circuitry according to the embodiment 3 is configured to change the compressor frequency on a gradient within the period from the start of the first operation to the end of the first operation. In the present embodiment, losses at the time of the transition from the first operation to the second operation are even smaller than those in the embodiment 2, thus further increasing the COP.

In the example shown in the drawing, the control circuitry is configured to cause the compressor frequency at the end of the first operation to be equal to the compressor frequency in the second operation.

Embodiment 4

Next, an embodiment 4 will be described. However, points that make the embodiment 4 different from the above-described embodiments will be mainly described, and the repeated description will be simplified or omitted. Further, elements identical or corresponding to the above-described elements are given the same reference symbols.

The present embodiment 4 may be implemented in combination with any one of the above-described embodiments 1 to 3. In the present embodiment 4, a control circuitry is configured to set the rotational speed of the blower 11 in the first operation to be higher than the rotational speed of the blower 11 in the second operation.

As described above, the action speed of the compressor 7 in the first operation is higher than the action speed of the compressor 7 in the second operation and hence, the refrigerant pressure on the low-pressure side of the refrigerant circuit in the first operation may be lower than the refrigerant pressure on the low-pressure side of the refrigerant circuit in the second operation. Therefore, depending on conditions, such as the temperature and humidity of outside air, there is a possibility of frost forming on the air heat exchanger 10 during the first operation. In contrast, in the present embodiment, the rotational speed of the blower 11 in the first operation is set to be higher than the rotational speed of the blower 11 in the second operation and hence, it is possible to surely suppress a situation in which frost forms on the air heat exchanger 10 during the first operation.

Of the items described in the above-described respective embodiments, a plurality of items that can be combined may be implemented in combination.

Claims

1. A storage type heat pump hot water supplying apparatus, comprising:

a heat source machine including a compressor to compress refrigerant and a water heat exchanger to exchange heat between water and the refrigerant compressed by the compressor;

a hot water storage tank to store hot water heated by the heat source machine;

a water circuit including a feed path connecting a lower part of the hot water storage tank to a water inlet of the water heat exchanger, a return path connecting a water outlet of the water heat exchanger to an upper part of the hot water storage tank, and a water pump provided in the feed path or the return path;

a temperature sensor to detect an actual hot water discharge temperature, the actual hot water discharge temperature being a temperature of hot water flowing out of the water heat exchanger; and

control circuitry to control a compressor frequency and a pump rotational speed, the compressor frequency being an operating frequency of the compressor, the pump rotational speed being a rotational speed of the water pump,

wherein the control circuitry is configured to control, in a heat accumulating operation for accumulating hot water in the hot water storage tank, the pump rotational speed so that the actual hot water discharge temperature becomes equal to a target hot water discharge temperature,

wherein the heat accumulating operation includes a first operation and a second operation after the first operation,

wherein the compressor frequency in the first operation is higher than the compressor frequency in the second operation, and

wherein the target hot water discharge temperature in the first operation is lower than the target hot water discharge temperature in the second operation.

2. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the pump rotational speed in the first operation is higher than the pump rotational speed in the second operation.

3. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the target hot water discharge temperature is kept constant within a period from a start of the first operation to an end of the first operation.

4. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the target hot water discharge temperature is increased in a stepwise manner within a period from a start of the first operation to an end of the first operation.

5. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the target hot water discharge temperature is continuously increased within a period from a start of the first operation to an end of the first operation.

6. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the compressor frequency is kept constant within the period from the start of the first operation to the end of the first operation.

7. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the compressor frequency is reduced in a stepwise manner within the period from the start of the first operation to the end of the first operation.

8. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the compressor frequency is continuously reduced within the period from the start of the first operation to the end of the first operation.

9. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the heat source machine further includes an air heat exchanger to exchange heat between outdoor air and the refrigerant, and a blower to send air to the air heat exchanger,

wherein the control circuitry sets a rotational speed of the blower in the first operation to be higher than a rotational speed of the blower in the second operation.

10. The storage type heat pump hot water supplying apparatus according to claim 1, wherein the heat accumulating operation including the first operation and the second operation is a daytime heat accumulating operation performed in daytime hours being hours including daytime of a day, and

in a nighttime heat accumulating operation performed in nighttime hours being hours other than the daytime hours of the day, the control circuitry executes the second operation by omitting the first operation.