EP3594587A1

EP3594587A1 - Heat pump hot water supply device

Info

Publication number: EP3594587A1
Application number: EP17899425.7A
Authority: EP
Inventors: Toru Koide
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2017-03-09
Filing date: 2017-03-09
Publication date: 2020-01-15
Anticipated expiration: 2037-03-09
Also published as: JP6704505B2; EP3594587B1; JPWO2018163345A1; EP3594587A4; WO2018163345A1

Abstract

The present invention is to reduce the maximum high pressure, as high-pressure suppression, by storing refrigerant in a refrigerant amount adjusting device at the time of inflow of water at high temperature and to avoid liquid compression by storing liquid back at the time of transition into the refrigerant amount adjusting device, thereby the reliability of a compressor being ensured. At the time of boiling, the opening degree of an expansion valve is adjusted such that a difference between a hot water target temperature and an inlet refrigerant temperature is equal to a temperature difference set in advance. When the temperature of fluid sent from a hot water tank to a condenser is high, the temperature difference is changed to adjust the valve opening degree of the expansion valve in an opening direction, so that concentration of refrigerant on a high-pressure side can be reduced and high-pressure suppression can thus be achieved. In contrast, concentration of refrigerant on a low-pressure side increases, and excess liquid refrigerant is thus stored in the refrigerant amount adjusting device. Furthermore, after an operation stops, in the case where restarting is performed immediately after liquid refrigerant is stored in the evaporator, if no refrigerant amount adjusting device is provided, liquid back to the compressor may occur, resulting in liquid compression. Thus, due to storage of refrigerant in the refrigerant amount adjusting device, liquid compression can be avoided, and the reliability of the compressor can thus be ensured.

Description

Technical Field

The present invention relates to a heat pump hot water supply apparatus that includes a refrigerant amount adjusting device.

Background Art

For a heat pump cycle including a compressor, a condenser, an expansion valve, an evaporator, and a refrigerant amount adjusting device, a technique for changing the storage amount of liquid refrigerant in the refrigerant amount adjusting device to attain a predetermined capacity at optimal efficiency has been suggested (for example, Patent Literature 1). The capacity of the heat pump cycle is controlled by changing the amount of refrigerant in the condenser and adjusting pressure on a high-pressure side. The amount of refrigerant in the condenser increases by temporarily decreasing the opening degree of the expansion valve. With this increase, the storage amount of liquid refrigerant in the refrigerant amount adjusting device at an outlet of the evaporator decreases. As the amount of refrigerant on the high-pressure side increases, the pressure increases and the capacity increases. In contrast, by opening the expansion valve, the storage amount of liquid refrigerant in the refrigerant amount adjusting device at the outlet of the evaporator increases, and the amount of refrigerant on the high-pressure side decreases. When the pressure on the high-pressure side decreases, the capacity decreases. As described above, operation at the optimal efficiency can be achieved by adjusting the storage amount of liquid refrigerant in the refrigerant amount adjusting device as a cycle.
Furthermore, for a heat pump cycle including a compressor, a condenser, an expansion valve, an evaporator, and an internal heat exchanger, but not including a refrigerant amount adjusting device, a technique for reducing, using the internal heat exchanger, an increase in pressure on a high-pressure side at a time of inflow of water at high temperature while reducing cost by not including the refrigerant amount adjusting device, has been suggested (for example, Patent Literature 2). In the case where the temperature of fluid sent to the condenser by a hot water circulating pump from a bottom part of a hot water tank is high (that is, at the time of inflow of water at high temperature), the concentration of refrigerant present in the condenser decreases, and the pressure increases abnormally. To reduce the abnormal increase in the pressure, refrigerant present in a region from an outlet of the condenser to an inlet of the expansion valve is cooled down. Therefore, the concentration of refrigerant on the high-pressure side is increased, and the abnormal increase in the pressure on the high-pressure side is reduced. The refrigerant present in the region from the outlet of the condenser to the inlet of the expansion valve is cooled down by refrigerant present in a region from an outlet of the evaporator to the compressor. As described above, by reducing the pressure on the high-pressure side by the internal heat exchanger without using the refrigerant amount adjusting device, cost reduction can be achieved.

Citation List

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 7-18602
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2005-164103

Summary of Invention

Technical Problem

In Patent Literature 1, efficiency can be improved by adjusting, using the refrigerant amount adjusting device, the amount of refrigerant and pressure on the high-pressure side. However, the refrigerant amount adjusting device needs to have a large capacity to store liquid refrigerant. Therefore, there is a problem that the size of equipment increases and cost is thus increased. In Patent Literature 2, no refrigerant amount adjusting device is provided. Therefore, an increase in the size of equipment can be avoided. However, in place of the refrigerant amount adjusting device, the internal heat exchanger is used as means for reducing an increase in the pressure on the high-pressure side at the time of inflow of water at high temperature. In such a case, there are problems described below. Immediately after an operation of an apparatus stops, refrigerant flows into the evaporator with a low heat capacity and is stored in the evaporator as liquid refrigerant. Then, when a certain period of time has passed, liquid refrigerant is stored in the compressor with a high heat capacity. However, if the apparatus is restarted immediately after the liquid refrigerant is stored in the evaporator, liquid back of the refrigerant to the compressor may occur because no refrigerant amount adjusting device is provided. If liquid compression of the liquid-back refrigerant is performed by the compressor, malfunction may occur.
The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a heat pump hot water supply apparatus that guarantees the reliability of an apparatus by reducing high pressure at the time of inflow of water at high temperature and avoiding liquid compression caused by liquid back at the time of transition while reducing increases in the size and cost of equipment.

Solution to Problem

A heat pump hot water supply apparatus of an embodiment of the present invention includes a refrigerant circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a refrigerant amount adjusting device are connected sequentially; a hot water tank storing hot water heated by the condenser; a hot water circulating pump circulating hot water in a region between the condenser and the hot water tank; an inlet refrigerant temperature detection unit detecting an inlet refrigerant temperature of the condenser; an inlet water temperature detection unit detecting an inlet water temperature of the condenser; and a heat source unit control unit adjusting a valve opening degree of the expansion valve such that a difference between a hot water target temperature transmitted from a tank control unit provided at the hot water tank and the inlet refrigerant temperature is equal to a temperature difference set in advance. When the inlet water temperature reaches a threshold value or more, the heat source unit control unit changes the temperature difference to adjust the valve opening degree of the expansion valve in an opening direction.

Advantageous Effects of Invention

A heat pump hot water supply apparatus of an embodiment of the present invention performs, in a case where the temperature of fluid sent from a hot water tank to a condenser by a hot water circulating pump is high (that is, at the time of inflow of water at high temperature), high-pressure suppression such that a valve opening degree of an expansion valve is adjusted in an opening direction so that concentration of refrigerant on a high-pressure side is reduced not to exceed a fixed pressure. In contrast, since concentration of refrigerant on a low-pressure side increases, and the refrigerant is thus stored in a refrigerant amount adjusting device as excess liquid refrigerant. Even if an apparatus is restarted immediately after liquid refrigerant is stored in an evaporator, the liquid-back refrigerant returned from the evaporator can be stored as liquid refrigerant in the refrigerant amount adjusting device. With this configuration, the refrigerant is stored in the refrigerant amount adjusting device so that liquid compression can be avoided, and the reliability of the compressor can thus be ensured. Furthermore, in the case where a suction muffler that includes a space in which liquid refrigerant can be stored is used as the refrigerant amount adjusting device, increases in the size and cost of equipment can also be reduced.
Furthermore, a heat pump hot water supply apparatus of an embodiment of the present invention controls the valve opening degree of an expansion valve such that a difference between a hot water target temperature from a tank control unit provided at a hot water tank and a temperature detected by an inlet refrigerant detection unit of a condenser (hereinafter, referred to as an inlet refrigerant temperature) is equal to a temperature difference set in advance (hereinafter, referred to as a set temperature difference). The opening degree of the expansion valve may be controlled based only on a detection temperature obtained by a water inlet detection unit of the condenser and a target value for the inlet refrigerant detection unit of the condenser. However, depending on the operation environmental condition, there may be a relationship that the hot water target temperature is higher than the target value, and water may not boil. In contrast, according to an embodiment of the present invention, the temperature difference is set in advance such that the relationship that a value obtained by subtracting the hot water target temperature from the inlet refrigerant temperature is more than 0 is obtained and the opening degree of the expansion valve is adjusted to achieve the set temperature difference. Therefore, water can be made to boil reliably irrespective of environmental conditions.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a circuit diagram of a heat pump hot water supply apparatus according to the present invention.
[Fig. 2] Fig. 2 is a block diagram of a heat source unit control unit and a memory unit.
[Fig. 3] Fig. 3 is a cross-sectional view of a compressor and a refrigerant amount adjusting device.
[Fig. 4] Fig. 4 is a flowchart illustrating boiling operation control by the heat source unit control unit.
[Fig. 5] Fig. 5 is a schematic diagram illustrating transition of the temperature of hot water stored in a hot water tank.
[Fig. 6] Fig. 6 is a time chart of an inlet water temperature and an inlet refrigerant temperature of a condenser, the amount of refrigerant stored in the refrigerant amount adjusting device, a hot water target temperature of a tank control unit, and the valve opening degree of an expansion valve.
[Fig. 7] Fig. 7 is a circuit diagram of a heat pump hot water supply apparatus according to the present invention that includes an internal heat exchanger.
[Fig. 8] Fig. 8 is a pressure-enthalpy chart illustrating effects in high pressure suppression.
[Fig. 9] Fig. 9 is a pressure-enthalpy chart illustrating effects in improvement of a coefficient of performance (hereinafter, referred to as a COP).

Description of Embodiments

Embodiment

1.

Hereinafter, an outdoor unit 100 of an air-conditioning apparatus according to Embodiment 1 of the present invention will be explained with reference to drawings.
Fig. 1 is a circuit diagram of a heat pump hot water supply apparatus 100 according to Embodiment 1 of the present invention. The heat pump hot water supply apparatus 100 includes a heat source unit 200 and a tank unit 300.
The heat source unit 200 includes a refrigerant circuit in which a compressor 1 that compresses refrigerant and discharges the compressed refrigerant, a condenser 2 that exchanges heat between refrigerant and water, an expansion valve 3 of an electronic control type whose opening degree is variable to decompress high-pressure refrigerant into low-pressure refrigerant, an evaporator 4 that exchanges heat between air and refrigerant, and a refrigerant amount adjusting device 6 that is able to temporarily store liquid refrigerant are connected by a refrigerant pipe 19 in a ring shape. Furthermore, the heat source unit 200 also includes an inlet water temperature detection unit 9 that detects the temperature of water at the inlet of the condenser 2, an outlet water temperature detection unit 10 that detects the temperature of water at the outlet of the condenser 2, an outside air temperature detection unit 16 that detects the outside air temperature, an inlet refrigerant temperature detection unit 17 that detects the temperature of refrigerant at the inlet of the condenser 2, and an outlet refrigerant temperature detection unit 18 that detects the temperature of refrigerant at the outlet of the evaporator 4. Each of the above-mentioned detection units may include a temperature sensor. A fan 8 that promotes heat exchange between refrigerant and air in the evaporator 4 is installed in the vicinity of the evaporator 4. The fan 8 is rotated by driving of a fan motor 7, and air flow passing through the evaporator 4 is generated by the rotation. Carbon dioxide (CO₂) may be used as refrigerant. An operation of the heat source unit 200 is controlled by a heat source unit control unit 13.
The tank unit 300 includes a hot water tank 14 that stores hot water heated by the condenser 2 and a hot water circulating pump 11 that is arranged between the condenser 2 and the hot water tank 14 and circulates hot water in a region between the condenser 2 and the hot water tank 14. The condenser 2 and the hot water tank 14 are connected by a hot water circulating pipe 15. An operation of the tank unit 300 is controlled by a tank control unit 12. The tank control unit 12 is able to transmit a hot water target temperature to the heat source unit control unit of the heat source unit 200.
Fig. 2 is a block diagram of the heat source unit control unit 13. The heat source unit control unit 13 includes a compressor rotation speed control part 21 that controls the rotation speed of the compressor 1, a fan rotation speed control part 22 that controls the rotation speed of the fan motor 7, a pump rotation speed control part 23 that controls the rotation speed of the hot water circulating pump 11, a detection temperature reception part 24 that receives a detection temperature such as an inlet refrigerant temperature of the condenser 2, an expansion valve opening degree adjustment part 25 that adjusts the opening degree of the expansion valve 3, and a hot water target temperature reception part 26 that receives a hot water target temperature transmitted from the tank control unit 12. The expansion valve opening degree adjustment part 25 adjusts the valve opening degree of the of the expansion valve 3 such that a difference between the hot water target temperature and the inlet refrigerant temperature becomes equal to a set temperature difference. When the inlet water temperature reaches a predetermined threshold value or more, the expansion valve opening degree adjustment part 25 changes the set temperature difference and adjusts the valve opening degree of the expansion valve 3 in an opening direction. The set temperature difference is stored in advance in a memory unit 30 in the heat source unit 200. The heat source unit control unit 13 includes, for example, a microchip. The memory unit 30 includes, for example, a semiconductor memory.
Fig. 3 is a cross-sectional view of the compressor 1 and the refrigerant amount adjusting device 6. In the case where refrigerant in a two-phase gas-liquid state flows from the evaporator 4 through a suction pipe 31 into the refrigerant amount adjusting device 6, gas refrigerant flows through a relay pipe 32 into the compressor 1, and liquid refrigerant is stored as excess refrigerant in a liquid refrigerant storage part 33 of the refrigerant amount adjusting device 6. The compressor 1 compresses the gas refrigerant, causes the compressed gas refrigerant to be discharged through a discharge pipe 34, and sends the discharged gas refrigerant to the condenser 2. The liquid refrigerant storage part 33 is an internal space provided at a bottom part of the refrigerant amount adjusting device 6, which is a tube shape. A so-called suction muffler achieving a muffling effect may be used as the refrigerant amount adjusting device 6. In this case, the suction muffler serves as both muffling means and excess refrigerant storing means. Refrigerating machine oil, along with refrigerant, flows through the suction pipe 31 into the refrigerant amount adjusting device 6. An oil return hole 35 through which refrigerating machine oil stored at the bottom of the liquid refrigerant storage part 33 returns to the compressor 1 is provided at the relay pipe 32. Refrigerant and refrigerating machine oil may be temporarily stored in a mixed or separate state at the bottom of the liquid refrigerant storage part 33.
Fig. 4 is a flowchart of boiling operation control by the heat source unit control unit 13. Boiling operation control for the heat pump hot water supply apparatus 100 will be explained below with reference to Fig. 4.
First, when receiving a boiling operation instruction from the tank control unit 12 provided in the tank unit 300, the heat source unit control unit 13 provided in the heat source unit 200 starts a boiling operation (step S11). The heat source unit control unit 13 receives a hot water target temperature, along with the boiling operation instruction. Next, the heat source unit control unit 13 receives an inlet water temperature of the condenser 2 (step S12). In the case where the inlet water temperature is equal to or higher than a predetermined temperature, the heat source unit control unit 13 ends the operation control, without performing the boiling operation (step S13). In the case where the inlet water temperature is lower than the predetermined temperature, the heat source unit control unit 13 controls the rotation frequency of the compressor 1 in accordance with the inlet water temperature detected by the outside air temperature detection unit 16 and the inlet water temperature detection unit 9 (step S14).
Next, the heat source unit control unit 13 determines whether or not the inlet water temperature detected by the inlet water temperature detection unit 9 of the condenser 2 is equal to or more than a predetermined threshold value (step S15). In the case where the inlet water temperature is less than the predetermined threshold value, the heat source unit control unit 13 reads a first temperature difference stored in the memory unit 30, and defines the read first temperature difference as a set temperature difference (step S16). In the case where the inlet water temperature is equal to or more than the predetermined threshold value, the heat source unit control unit 13 reads a second temperature difference stored in the memory unit 30, and defines the read second temperature difference as a set temperature difference (step S17). The second temperature difference is smaller than the first temperature difference.
After setting a temperature difference, the heat source unit control unit 13 performs processing described below. First, the heat source unit control unit 13 receives an inlet refrigerant temperature detected by the inlet refrigerant detection unit 17 of the condenser 2 (step S18). Next, the heat source unit control unit 13 calculates a difference between the hot water target temperature and the inlet refrigerant temperature (step S19). Hereinafter, this difference will be referred to as a calculated temperature difference. Next, the heat source unit control unit 13 adjusts the opening degree of the expansion valve 3 such that the calculated temperature difference becomes equal to the set temperature difference (step S20). When the inlet water temperature of the condenser 2 reaches the predetermined threshold value or more, the valve opening degree is adjusted based on the second temperature difference, which is smaller than the first temperature difference. Accordingly, the valve opening degree is adjusted in an opening direction.
The first temperature difference may be set such that an optimal COP can be obtained under environmental conditions such as, for example, certain outside air temperature conditions and inlet water temperature conditions (winter standard heating conditions, mid-term standard heating conditions, or other conditions defined by JIS). The second temperature difference is set to a value smaller than the first temperature difference such that pressure on the high-pressure side at the time of inflow of water at high temperature does not exceed the designed upper limit. These temperature differences are fixed values under certain fixed conditions such as the above-mentioned outside air temperature or inlet water temperature. These temperature differences may be set to fixed values, for example, within a range from 15 degrees C to 30 degrees C. The opening degree of the expansion valve 3 may be controlled based only on the outside air temperature, the inlet water temperature detected by the inlet water temperature detection unit 9 of the condenser 2, a target value for the inlet refrigerant temperature detected by the inlet refrigerant detection unit 17 of the condenser 2, and the hot water target temperature from the tank control unit 12. However, depending on the environmental condition, there may be a relationship that the hot water target temperature is higher than the target value for the inlet refrigerant temperature, and water may not boil. For example, in the case where, at the time of inflow of water at high temperature, to suppress the pressure on the high-pressure side, processing for uniformly decreasing the target value for the inlet refrigerant temperature is performed, regardless of the hot water target temperature, the relationship that the hot water target temperature is higher than the target value for the inlet refrigerant temperature may be obtained. In contrast, in the heat pump hot water supply apparatus 100 according to Embodiment 1, temperature differences satisfying the relationship that a value obtained by subtracting the hot water target temperature from the inlet refrigerant temperature is more than 0 are stored in advance as first and second temperature differences in the memory unit 30. Then, the opening degree of the expansion valve 3 is adjusted such that the calculated temperature difference becomes equal to a set temperature difference by defining the first temperature difference as the set temperature difference in the case where the inlet water temperature is less than the predetermined threshold value and defining the second temperature difference, which is smaller than the first temperature difference, as the set temperature difference in the case where the inlet water temperature reaches the predetermined threshold value or more. With the above processing, a failure in which water does not boil can be avoided while performing adjustment such that the pressure on the high-pressure side does not exceed the designed upper limit pressure at the time of inflow of water at high temperature.
Fig. 5 is a schematic diagram illustrating transition of the temperature of hot water stored in the hot water tank 14. During a period of a boiling operation from the start of boiling, the temperature of water supplied to the heat source unit 200 is low (for example, 5 degrees C). However, the inlet water temperature of the condenser 2 increases before boiling is completed (for example, 5 to 60 degrees C). For example, in the case where the city water minimum temperature is 5 degrees C and the hot water tapping maximum temperature is 90 degrees C, the temperature of water in the hot water tank 14 before the boiling operation is about 5 degrees C, the temperature of hot water in an upper part of the hot water tank 14 during the boiling operation is 90 degrees C, and the temperature of hot water in a lower part of the hot water tank 14 during the boiling operation is 5 degrees C. The temperature of hot water in the upper part of the hot water tank 14 before boiling is completed is 90 degrees C, and the temperature of hot water in the lower part of the hot water tank 14 before boiling is completed is 60 degrees C, which is medium temperature water.
When the inlet water temperature increases, concentration of refrigerant present in the condenser 2 decreases. At this time, if the first temperature difference set in advance to achieve the optimal COP under certain environmental conditions is maintained, the pressure abnormally increases. Thus, under certain environmental conditions that may cause the pressure on the high-pressure side to exceed a designed pressure (for example, under conditions where, at a low outside air temperature, the maximum boiling temperature and the maximum heating capacity are required, the inlet refrigerant temperature of the condenser 2 is high, and the rotation speed of the compressor 1 reaches the maximum), the second temperature difference, which is smaller than the first temperature difference, is defined as the set temperature difference. The second temperature difference is smaller than the first temperature difference. Therefore, when the inlet water temperature reaches the predetermined temperature or more, the set temperature difference decreases. Then, the opening degree of the expansion valve 3 is set such that the difference between the hot water target temperature from the tank control unit 12 and the detection temperature obtained by the inlet refrigerant detection unit 17 of the condenser 2 becomes equal to the changed set temperature difference. With such control, high-pressure suppression can be performed such that the concentration of refrigerant on the high-pressure side can be reduced and the pressure on the high-pressure side does not exceed the designed pressure.
Fig. 6 is a time chart illustrating an inlet water temperature 41 of the condenser 2, an inlet refrigerant temperature 42 of the condenser 2, a hot water target temperature 43 of the tank control unit 12, a stored refrigerant amount 44 in the refrigerant amount adjusting device 6, and the valve opening degree of the expansion valve. The pressure on the high-pressure side is reduced by adjustment of the opening degree of the expansion valve 3 mentioned above, whereas the concentration of refrigerant on the low-pressure side increases. During a period up to a time point T1 at which the inlet water temperature 41 detected by the inlet water temperature detection unit 9 of the condenser 2 reaches a predetermined threshold value 41 (for example, 50 degrees C), refrigerant is used up under the designed pressure or below, and there is no excess liquid refrigerant. Therefore, no liquid refrigerant is stored in the refrigerant amount adjusting device 6. During this period, the inlet refrigerant temperature 42 and the hot water target temperature 43 are constant. After the inlet water temperature 41 detected by the inlet water temperature detection unit 9 of the condenser 2 exceeds the predetermined threshold value 41a, to achieve an operation at the designed pressure or below, liquid storage of excess liquid refrigerant into the refrigerant amount adjusting device 6 is performed, and high-pressure suppression is thus performed. That is, at the time point T1 at which the inlet water temperature exceeds the predetermined threshold value 41, adjustment of the valve opening degree in steps S17 to S20 starts. At this time, a valve opening degree 45 is adjusted such that the difference between the inlet refrigerant temperature 42 and the hot water target temperature 43 becomes equal to a fixed set temperature difference (second temperature difference). The valve opening degree 45 starts increasing at the time point T1. Accordingly, the actual temperature difference decreases. For example, the temperature difference between the inlet refrigerant temperature 42 and the hot water target temperature 43 during the period up to the time point T1 at which the inlet water temperature 41 reaches the predetermined threshold value 41a is 30 degrees C, and the temperature difference at or later than the time point T1 at which the inlet water temperature 41 reaches the predetermined threshold value 41a is 25 degrees C. At a time point T2 at which the inlet water temperature 41 reaches a predetermined temperature 41b, the boiling operation ends (step S13). The amount of refrigerant filled in the entire refrigeration circuit may be, for example, about 1000 grams. A target value 44a for the stored refrigerant amount 44 in the refrigerant amount adjusting device 6 may be, for example, about 30 grams. In the case where a suction muffler is used as the refrigerant amount adjusting device 6, excess liquid refrigerant is stored at the bottom part of the suction muffler.
Soon after the boiling operation stops, the heat source unit control unit 13 may start a boiling operation. After the operation stops, the expansion valve 3 is fully opened, and the pressure on the high-pressure side and the pressure on the low-pressure side are balanced. At this time, by being affected by the outside air temperature, refrigerant flows into the evaporator 4 that has a low heat capacity (easily transfers heat), and is stored as liquid refrigerant. When a fixed time has passed, liquid refrigerant is stored in the compressor 1, which has a high heat capacity. If restarting is performed immediately after the entire liquid refrigerant is stored in the evaporator 4, the liquid refrigerant stored in the evaporator 4 flows into the compressor 1 at one time. In the case where the refrigerant amount adjusting device 6 is not provided unlike Embodiment 1, liquid back of liquid refrigerant to the compressor 1 may occur, resulting in liquid compression by the compressor 1. In contrast, in the heat pump hot water supply apparatus 100 according to Embodiment 1, liquid refrigerant from the evaporator 4 at the time of start of the apparatus is temporarily stored in the refrigerant amount adjusting device 6. Therefore, liquid compression of refrigerant by the compressor 1 can be avoided, and the reliability of the compressor 1 can thus be ensured.
As described above, in the heat pump hot water supply apparatus 100 according to Embodiment 1, in the case where the temperature of fluid sent from the bottom part of the hot water tank 14 to the condenser 2 by the hot water circulating pump 11 is high (that is, at the time of inflow of water at high temperature), concentration of refrigerant on the high-pressure side is reduced by adjusting the valve opening degree of the expansion valve 3 in the opening direction, and high-pressure suppression is thus performed such that a certain fixed pressure is not exceeded. In contrast, the concentration of refrigerant on the low-pressure side increases, and liquid storage of excess liquid refrigerant into the refrigerant amount adjusting device 6 is thus performed. Due to storage of excess liquid refrigerant in the refrigerant amount adjusting device 6, there is no need to provide an internal heat exchanger that allows heat exchange between high-pressure-side refrigerant and low-pressure-side refrigerant. Thus, cost can be reduced. After the operation stops, refrigerant flows into the evaporator 4 with a low heat capacity and is stored as liquid refrigerant in the evaporator 4. After that, when the fixed time has passed, liquid refrigerant is stored in the compressor 1 with a high heat capacity. In the case where the apparatus is restarted immediately after liquid refrigerant is stored in the evaporator 4, if no refrigerant amount adjusting device 6 is provided, liquid back to the compressor 1 may cause liquid compression. Thus, the refrigerant amount adjusting device 6 is provided in the heat pump hot water supply apparatus 100 according to Embodiment 1, and liquid refrigerant is stored in the refrigerant amount adjusting device 6. Therefore, liquid compression by the compressor 1 can be avoided, and the reliability of the compressor 1 can thus be ensured. A suction muffler may be used as the refrigerant amount adjusting device 6. The suction muffler serves as both muffling means and the refrigerant amount adjusting device 6. Therefore, there is no need to provide a separate refrigerant amount adjusting device. Thus, effects such as reduction of cost and reduction of the increase of capacity of an outdoor unit can be achieved.

Embodiment 2.

Hereinafter, an outdoor unit 100 of an air-conditioning apparatus according to Embodiment 2 of the present invention will be explained with reference to drawings.
Fig. 7 is a circuit diagram of the heat pump hot water supply apparatus 100 that includes an internal heat exchanger 5. For example, due to constraints on structure, the refrigerant amount adjusting device 6 with a certain size or more cannot be installed. In such a case, if a designed pressure on a high-pressure side may be exceeded, the internal heat exchanger 5, which allows heat exchange between refrigerant in a region from the outlet of a condenser 2 to the inlet of an expansion valve 3 and refrigerant in a region from the outlet of an evaporator 4 to the inlet of a compressor 1, may be provided, as illustrated in Fig. 7. In this case, the expansion valve 3 is provided at a refrigerant flow passage between the evaporator 4 and the internal heat exchanger 5.
Fig. 8 is a pressure-enthalpy chart illustrating effects in high-pressure suppression. Fig. 9 is a pressure-enthalpy chart illustrating effects in COP improvement. The internal heat exchanger 5 has two roles. One of the roles is, as illustrated in Fig. 8, to increase the concentration of refrigerant in the evaporator 4 and store the refrigerant in the evaporator when the inlet water temperature of the condenser 2 increases by heat exchange by the internal heat exchanger 5. In accordance with this, the concentration of refrigerant on the high-pressure side can be reduced, and high pressure can thus be suppressed. Signs 51 and 52 represent an enthalpy range on the low-pressure side and an enthalpy range on the high-pressure side, respectively, varied by heat exchange by the internal heat exchanger 5. The other role is, as illustrated in Fig. 9, to be able to provide superheat at the outlet of the evaporator 4 and thus improve the COP. A sign 54 in Fig. 9 represents an enthalpy range increased when superheat is provided at the outlet of the evaporator 4 by the internal heat exchanger 5. A sign 55 represents transition of state of refrigerant in the case where the internal heat exchanger 5 is provided. A sign 56 represents transition of state of refrigerant in the case where the internal heat exchanger 5 is not provided.
In the case where both the internal heat exchanger 5 and the refrigerant amount adjusting device 6 are used as in Embodiment 2, effects of high-pressure suppression and COP improvement mentioned above can be achieved. If the amount of liquid storage in the refrigerant amount adjusting device 6 can be increased to an extent not causing overflow, the internal heat exchanger 5 can be made compact, which leads to reduction in cost. Furthermore, by performing control such that the entire amount of excess liquid refrigerant can be stored only in the refrigerant amount adjusting device 6, the internal heat exchanger 5 can be removed as in Embodiment 1. Therefore, a further reduction in cost can be achieved.

Reference Signs List

1 compressor, 2 condenser, 3 expansion valve, 4 evaporator, 5 internal heat exchanger, 6 refrigerant amount adjusting device, 7 fan motor, 8 fan, 9 inlet water temperature detection unit, 10 outlet water temperature detection unit, 11 hot water circulating pump, 12 tank control unit, 13 heat source unit control unit, 14 hot water tank, 15 hot water circulating pipe, 16 outside air temperature detection unit, 17 inlet refrigerant temperature detection unit, 18 outlet refrigerant temperature detection unit, 19 refrigerant pipe, 21 compressor rotation speed control part, 22 fan rotation speed control part, 23 pump rotation speed control part, 24 detection temperature reception part, 25 expansion valve opening degree adjustment part, 26 temperature reception part, 30 memory unit, 31 suction pipe, 32 relay pipe, 33 liquid refrigerant storage part, 34 discharge pipe, 35 oil return hole, 100 heat pump hot water supply apparatus, 200 heat source unit, 300 tank unit

Claims

A heat pump hot water supply apparatus comprising: a refrigerant circuit in which a compressor, a condenser, an expansion valve, an evaporator, and a refrigerant amount adjusting device are connected sequentially; a hot water tank storing hot water heated by the condenser; a hot water circulating pump circulating hot water in a region between the condenser and the hot water tank; an inlet refrigerant temperature detection unit detecting an inlet refrigerant temperature of the condenser; an inlet water temperature detection unit detecting an inlet water temperature of the condenser; and a heat source unit control unit adjusting a valve opening degree of the expansion valve such that a difference between a hot water target temperature transmitted from a tank control unit provided at the hot water tank and the inlet refrigerant temperature is equal to a temperature difference set in advance, wherein when the inlet water temperature reaches a threshold value or more, the heat source unit control unit changes the temperature difference to adjust the valve opening degree of the expansion valve in an opening direction.
The heat pump hot water supply apparatus of claim 1, wherein refrigerant is stored in the refrigerant amount adjusting device when the inlet water temperature reaches the threshold value or more.
The heat pump hot water supply apparatus of claim 1 or 2, wherein the refrigerant amount adjusting device is provided at an inlet of the compressor.
The heat pump hot water supply apparatus of any one of claims 1 to 3, wherein the refrigerant amount adjusting device is a suction muffler that includes a space in which liquid refrigerant is able to be stored.
The heat pump hot water supply apparatus of any one of claims 1 to 4, further comprising an internal heat exchanger allowing heat exchange between refrigerant in a region from an outlet of the condenser to an inlet of the expansion valve and refrigerant in a region from an outlet of the evaporator to an inlet of the compressor.
The heat pump hot water supply apparatus of any one of claims 1 to 5, further comprising a memory unit storing the temperature difference set in advance,
wherein the temperature difference set in advance is equal to a temperature difference represented by a relationship that a value obtained by subtracting the hot water target temperature from the inlet refrigerant temperature is more than 0.