EP3130868A1

EP3130868A1 - Heat pump system

Info

Publication number: EP3130868A1
Application number: EP16178654.6A
Authority: EP
Inventors: Hiroyuki Yamada; Kenichi Murakami; Takashi Inaba; Tetsuji Fujino
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2015-08-10
Filing date: 2016-07-08
Publication date: 2017-02-15
Also published as: JP2017036882A

Abstract

Provided is a heat pump system capable of reliably preventing freezing and damage of a water heat exchanger in a reverse cycle type defrosting operation and eliminating occurrence of heat loss on a water circuit side.

In the heat pump system, a single-line refrigerant circuit 42 is configured such that a first utilization unit 3 including a utilization-side heat exchanger 28 and a second utilization unit 4 including a water heat exchanger 35 configured to generate hot water are connected in parallel to a heat source unit 2 including a heat-source-side heat exchanger 7, and a defrosting control means 45 configured to switch the refrigerant circuit 42 from an air-heating cycle to an air-cooling cycle by a four-way switching valve 6 to remove the frost adhering to the heat-source-side heat exchanger 7 is provided. The defrosting control means 45 includes means 33, 34 configured to block, in the defrosting operation, a refrigerant flow toward the water heat exchanger 35 of the second utilization unit 4 and to allow refrigerant to flow only toward the utilization-side heat exchanger 28 of the first utilization unit 3.

Description

{Technical Field}

The present invention relates to a heat pump system including both of a unit configured to heat or cool indoor air by heat exchange with refrigerant to perform air-heating/cooling and a unit configured to generate hot water for hot water supply or for air-heating by heat exchange with refrigerant.

{Background Art}

As described in, e.g., PTLs 1 and 2, the following heat pump system has been known as a heat pump system capable of heating or cooling indoor air by heat exchange with refrigerant to perform air-conditioning in a room while generating hot water for hot water supply or for air-heating by heat exchange with refrigerant. In the heat pump system, a single-line refrigerant circuit (a heat pump cycle) is configured such that a first utilization unit including a direct expansion type utilization-side heat exchanger configured to exchange heat between refrigerant and indoor air and a second utilization unit including a direct expansion type water heat exchanger configured to exchange heat between refrigerant and water to generate hot water for hot water supply or for air-heating are connected in parallel to a heat source unit including a compressor, a four-way switching valve, and a heat-source-side heat exchanger configured to exchange heat between refrigerant and external air.
It has been known that in the above-described heat pump system, frost is caused on the heat-source-side heat exchanger configured to exchange heat with heat-source-unit-side external air in the operation in an air-heating cycle, i.e., in the operation in, e.g., a hot water generation operation mode for generating hot water for hot water supply or for air-heating, an air-heating operation mode, or a hot water generation air-heating operation mode. A so-called reverse cycle type defrosting control means is employed, which is configured to switch, when frost on the heat-source-side heat exchanger is detected, the refrigerant circuit from the air-heating cycle to an air-cooling cycle by the four-way switching valve to remove the frost (perform defrosting).
PTLs 1 and 2 each disclose the system employing the reverse cycle type defrosting control means. In a defrosting operation, when the temperature of water circulating in the water heat exchanger of the second utilization unit is equal to or higher than a predetermined temperature, defrosting is performed by the refrigerant supplied only to the water heat exchanger of the second utilization unit or supplied to both of the water heat exchanger of the second utilization unit and the utilization-side heat exchanger of the first utilization unit. When the water temperature reaches equal to or lower than the predetermined temperature, switching is performed such that the refrigerant flowing toward the water heat exchanger is blocked and that refrigerant is supplied only to the utilization-side heat exchanger of the first utilization unit. That is, in the air-source heat pump system incorporating the water heat exchanger, a defrosting method employing a logic different from that of a typical air-to-air heat pump system is employed to prevent freezing of water in the water heat exchanger.

{Citation List}

{Patent Literature}

{PTL 1}
Japanese Unexamined Patent Application, Publication No. 2006-46692
{PTL 2}
Japanese Unexamined Patent Application, Publication No. 2010-196950

{Summary of Invention}

{Technical Problem}

In the operation in the air-heating cycle such as the hot water generation operation mode, the air-heating operation mode, or the hot water generation air-heating operation, frost is caused on the heat-source-side heat exchanger of the heat source unit in the above-described heat pump system. In this state, low-pressure refrigerant is supplied to the water heat exchanger of the second utilization unit to perform defrosting. This is because the defrosting operation is performed using the heat absorbed from hot water of a water circuit connected to the water heat exchanger, and therefore, a defrosting operation time is shortened.
However, the defrosting operation is typically performed with the maximum rotational speed of the compressor. Thus, a low pressure rapidly drops in the moment of switching to the defrosting operation, and easily reaches a lower pressure. For this reason, a hot water temperature on a water circuit side decreases due to a heat absorption effect of low-pressure refrigerant. This might lead to freezing of water in the water heat exchanger. Thus, there is a risk of damaging the water heat exchanger. Particularly in the case where the water heat exchanger is a plate type heat exchanger, tendency shows that the above-described case carries a high risk of causing damage due to easy detachment of a joint portion between plates.
For this reason, it is required that when the monitored water-circuit-side temperature reaches equal to or lower than the predetermined temperature, switching is performed to block the refrigerant flowing toward the water heat exchanger and to allow refrigerant to flow only toward the utilization-side heat exchanger of the first utilization unit, as described above. This leads to a complicated control system. Moreover, since defrosting is performed using the heat absorbed from hot water, the defrosting operation time can be shortened, but the hot water temperature decreases. Thus, when the operation mode is switched back to the hot water generation operation mode or the hot water generation air-heating operation mode after completion of the defrosting operation, the operation of recovering the heat loss caused due to a decrease in the hot water temperature is required, for example.
The present invention has been made to solve the above-described problems, and is intended to provide a heat pump system capable of reliably preventing freezing and damage of a water heat exchanger in a reverse cycle type defrosting operation and eliminating occurrence of heat loss on a water circuit side.

{Solution to Problem}

In order to solve the above-described problem, the heat pump system of the present invention employs the following solution.
According to a first aspect of the present invention, there is provided the heat pump system apparatus including a heat source unit including a compressor, a four-way switching valve, and a heat-source-side heat exchanger configured to exchange heat between refrigerant and external air; a first utilization unit including a utilization-side heat exchanger configured to exchange heat between refrigerant and indoor air; a second utilization unit including a water heat exchanger configured to exchange heat between refrigerant and water to generate hot water for hot water supply or for air-heating; a single-line refrigerant circuit configured such that the first and second utilization units are connected in parallel to the heat source unit; and a defrosting control means configured to switch, when frost is caused on the heat-source-side heat exchanger, the refrigerant circuit from an air-heating cycle to an air-cooling cycle by the four-way switching valve to perform defrosting. The defrosting control means includes a means configured to block, in a defrosting operation, a refrigerant flow toward the water heat exchanger of the second utilization unit and to allow refrigerant to flow only toward the utilization-side heat exchanger of the first utilization unit.
According to the configuration of the aspect, in the operation in the air-heating operation mode or the hot water generation operation mode in which the utilization-side heat exchanger of the first utilization unit and the water heat exchanger of the second utilization unit function as condensers (heat radiators) and the heat-source-side heat exchanger of the heat source unit functions as an evaporator or in the operation in the hot water generation air-heating operation mode, i.e., in the operation of the refrigerant circuit in the air-heating cycle, when the defrosting control means detects frost on the heat-source-side heat exchanger, the refrigerant circuit is switched to the defrosting operation mode by switching from the air-heating cycle to the air-cooling cycle. In this mode, the means configured to block the refrigerant flow toward the water heat exchanger of the second utilization unit blocks the refrigerant flow toward the water heat exchanger, and allows refrigerant to circulate only in the utilization-side heat exchanger of the first utilization unit. Accordingly, high-temperature high-pressure refrigerant discharged from the compressor is introduced into the heat-source-side heat exchanger through the four-way switching valve, and then, dissipates heat to melt the frost. After the refrigerant is condensed and liquefied, the pressure of the refrigerant is reduced, and then, the refrigerant is guided to the utilization-side heat exchanger of the first utilization unit. After the refrigerant is evaporated, the refrigerant is sucked into the compressor. In this manner, refrigerant circulates in the air-cooling cycle, and the defrosting operation is performed. When the defrosting control means detects completion of defrosting, the air-cooling cycle is switched to the air-heating cycle, and the operation mode is switched back to the original operation mode. Thus, even if the reverse cycle type defrosting control means is employed, low-pressure refrigerant does not circulate in the water heat exchanger of the second utilization unit in the defrosting operation. Consequently, it can be ensured that the risk of damaging the water heat exchanger due to freezing of water in the water heat exchanger is eliminated. Moreover, e.g., the control of monitoring, in the defrosting operation, a water temperature on a water circuit side to switch the defrosting operation mode is no longer required, and therefore, a control system can be simplified. In addition, occurrence of the heat loss due to utilization of heat of hot water on the water circuit side in the defrosting operation is eliminated, and as a result, energy can be saved.
In the heat pump system apparatus, the means configured to block the refrigerant flow toward the water heat exchanger may include a refrigerant circuit shutoff valve provided at one or both of an outlet and an inlet of a refrigerant circuit connected to the water heat exchanger.
The means configured to block the refrigerant flow toward the water heat exchanger is the refrigerant circuit shutoff valve provided at one or both of the outlet and inlet of the refrigerant circuit connected to the water heat exchanger. Thus, when the defrosting control means detects frost on the heat-source-side heat exchanger to switch the operation to the defrosting operation, the refrigerant circuit shutoff valve provided at part of the refrigerant circuit provided with the water heat exchanger is closed to block the refrigerant flow. This prevents low-pressure refrigerant from circulating in the water heat exchanger, and therefore, freezing of water in the water heat exchanger and damage of the water heat exchanger due to freezing can be prevented. With a simple configuration in which the shutoff valve is merely provided at part of the refrigerant circuit provided with the water heat exchanger, freezing and damage of the water heat exchanger can be prevented, and the degree of freedom in selection of the water heat exchanger increases so that, e.g., a plate type heat exchanger which is easily frozen and damaged can be used.
The heat pump system may be configured such that in the case of a system including a dedicated electronic expansion valve at part of the refrigerant circuit provided with the second utilization unit, the electronic expansion valve is also used as the refrigerant circuit shutoff valve.
In the case of the system including the dedicated electronic expansion valve at part of the refrigerant circuit provided with the second utilization unit, the electronic expansion valve is also used as the refrigerant circuit shutoff valve. Thus, even if no dedicated shutoff valve is provided at the refrigerant circuit to shut off the circuit, the function of fully closing the electronic expansion valve is utilized so that part of the refrigerant circuit provided with the water heat exchanger can be shut off in the defrosting operation. Thus, the shutoff valves to be placed at the refrigerant circuit can be reduced, leading to a simple configuration and a lower cost.
The heat pump system may be configured such that the means configured to block the refrigerant flow toward the water heat exchanger is closed to block the refrigerant flow at the same time that the four-way switching valve is switched by a signal of detection of frost caused on the heat-source-side heat exchanger or when a detection value of a low-pressure sensor provided at the heat source unit or a detection value of a pressure sensor provided at the second utilization unit falls below a predetermined value after switching of the four-way switching valve.
The means configured to block the refrigerant flow toward the water heat exchanger is closed to block the refrigerant flow at the same time that the four-way switching valve is switched by the signal of detection of the frost caused on the heat-source-side heat exchanger or when the detection value of the low-pressure sensor provided at the heat source unit or the detection value of the pressure sensor provided at the second utilization unit falls below the predetermined value after switching of the four-way switching valve. Thus, when the four-way switching valve is switched to perform the defrosting operation, it can be ensured that the means (the refrigerant circuit shutoff valve) configured to block the refrigerant flow toward the water heat exchanger is closed to block the refrigerant flow toward the water heat exchanger. Consequently, freezing and damage of the water heat exchanger can be prevented, and the control system can be simplified. In addition, occurrence of the heat loss on the water circuit side is eliminated, and as a result, energy can be saved.

{Advantageous Effects of Invention}

According to the present invention, even if the reverse cycle type defrosting control means is employed, low-pressure refrigerant does not circulate in the water heat exchanger of the second utilization unit in the defrosting operation. Consequently, it can be ensured that the risk of damaging the water heat exchanger due to freezing of water in the water heat exchanger is eliminated. Moreover, e.g., the control of monitoring, in the defrosting operation, the water temperature on the water circuit side to switch the defrosting operation mode is no longer required, and therefore, the control system can be simplified. In addition, occurrence of the heat loss due to utilization of heat of hot water on the water circuit side in the defrosting operation is eliminated, and as a result, energy can be saved.

{Brief Description of Drawings}

{Fig. 1}
Fig. 1 is a system diagram of a heat pump system of an embodiment of the present invention.

{Description of Embodiments}

Embodiments of the present invention will be described below with reference to drawings.

(First Embodiment)

A first embodiment of the present invention will be described below with reference to Fig. 1.
Fig. 1 illustrates a system diagram of a heat pump system of the first embodiment of the present invention.
A heat pump system 1 includes a heat source unit 2, a first utilization unit 3, and a second utilization unit 4. The heat pump system 1 is configured such that the first utilization unit 3 and the second utilization unit 4 are connected in parallel to the heat source unit 2.

(Heat Source Unit)

The heat source unit 2 includes a heat-source-side refrigerant circuit 15 (i.e., the heat source unit 2 is an outdoor unit). The heat-source-side refrigerant circuit 15 is configured such that a compressor 5 configured to compress refrigerant, a four-way switching valve 6 configured to switch a refrigerant flow direction, a heat-source-side heat exchanger 7 configured to exchange heat between refrigerant and external air, an air-heating electronic expansion valve (EEVH) 8 configured to insulate and expand refrigerant in an air-heating cycle, a receiver 9 configured to store liquid refrigerant, an air-cooling electronic expansion valve (EEVC) 10 configured to insulate and expand refrigerant in an air-cooling cycle, an accumulator 11 configured to separate liquid from the refrigerant sucked into the compressor 5 to suck only gas, and liquid- and gas-operated valves 12, 13 connected respectively to liquid and gas pipes 16, 17 connected between the first utilization unit 3 and the second utilization unit 4 are connected together via a refrigerant pipe 14 as in a known technique, for example.
Moreover, the heat source unit (the outdoor unit) 2 is also provided with an outdoor fan 18 configured to send external air to the heat-source-side heat exchanger 7. The heat source unit (the outdoor unit) 2 further includes a discharge temperature sensor 19 configured to detect the temperature of high-pressure refrigerant discharged from the compressor 5, a high-pressure sensor 20 configured to detect the pressure of high-pressure refrigerant discharged from the compressor 5, a suction temperature sensor 21 configured to detect the temperature of low-pressure refrigerant sucked into the compressor 5, a low-pressure sensor 22 configured to detect the pressure of low-pressure refrigerant sucked into the compressor 5, heat exchange temperature sensors 23, 24 configured to detect the temperature of the heat-source-side heat exchanger 7 at each position, and an external temperature sensor 25 configured to detect an external temperature, for example.

(First Utilization Unit)

The first utilization unit 3 is an indoor unit provided for air-conditioning (air-cooling/heating) in a room. In the first utilization unit 3, a utilization-side heat exchanger 28 is, via refrigerant circuit shutoff valves 26, 27, connected to a branched liquid pipe 16A and a branched gas pipe 17A, the pipes 16A, 17A being branched respectively from the liquid and gas pipes 16, 17 connected to the liquid- and gas-operated valves 12, 13 of the heat source unit 2. The utilization-side heat exchanger 28 is a direct expansion type heat exchanger configured to exchange heat between refrigerant and indoor air sent by a not-shown indoor fan to heat or cool the indoor air.
The first utilization unit (the indoor unit) 3 is also provided with a suction temperature sensor 29 configured to detect the temperature of air sucked from the room and heat exchange temperature sensors 30, 31, 32 configured to detect temperature at both ends and the center of the utilization-side heat exchanger 28.

(Second Utilization Unit)

The second utilization unit 4 is a hot water indoor unit configured to generate hot water for hot water supply or for air-heating. The second utilization unit 4 includes a water heat exchanger (a refrigerant/water heat exchanger) 35 connected, via refrigerant circuit shutoff valves 33, 34, to a branched liquid pipe 16B and a branched gas pipe 17B, the pipes 16B, 17B being branched respectively from the liquid and gas pipes 16, 17 connected to the liquid- and gas-operated valves 12, 13 of the heat source unit 2. The water heat exchanger (the refrigerant/water heat exchanger) 35 is a direct expansion type heat exchanger configured to exchange heat between refrigerant and water, and examples of such a heat exchanger includes a plate type heat exchanger.
A water circuit 36 including a water inlet pipe 36A and a water outlet pipe 36B is connected to a water flow path side of the water heat exchanger (the refrigerant/water heat exchanger) 35. Thus, the water supplied to a tank configured to store hot water or the water flowing through a hot water load circulates via a water circulation pump 37 provided at the water inlet pipe 36A.
The second utilization unit (the hot water indoor unit) 4 is also provided with an inlet water temperature sensor 38 configured to detect the inlet water temperature of the water heat exchanger 35, an outlet water temperature sensor 39 configured to detect the outlet water temperature of the water heat exchanger 35, an outlet liquid pipe sensor 40 configured to detect the refrigerant temperature at the outlet of the water heat exchanger 35, and a pressure sensor 41 configured to detect the refrigerant pressure of the water heat exchanger 35.
The first utilization unit (the indoor unit) 3 and the second utilization unit (the hot water indoor unit) 4 are, via the liquid pipe 16, the gas pipe 17, the branched liquid pipes 16A, 16B, and the branched gas pipes 17A, 17B, connected in parallel to the liquid- and gas-operated valves 12, 13 provided respectively at both ends of the heat-source-side refrigerant circuit 15 of the heat source unit (the outdoor unit) 2. This forms a single-line refrigerant circuit (a heat pump cycle) 42.
The heat source unit 2 is also provided with a heat-source-side controller 43 configured to control operation of the heat pump system 1. The heat-source-side controller 43 includes an operation control means 44. Based on, e.g., detection values and set values of various sensors provided at the heat source unit 2, the first utilization unit 3, and the second utilization unit 4, the operation control means 44 optionally controls switching of the four-way switching valve 6 according to the rotational speed of the compressor 5 and the operation mode, the rotational speed of the outdoor fan 18, the opening degrees of the air-heating electronic expansion valve (EEVH) 8 and the air-cooling electronic expansion valve (EEVC) 10, opening/closing of the refrigerant circuit shutoff valves 26, 27, 33, 34, and the rotational speed of the water circulation pump 37, for example. Thus, the operation control means 44 suitably controls the heat pump system 1 according to each operation mode.
In addition to the above-described operation control means 44, the heat-source-side controller 43 is provided with a defrosting control means 45 configured to remove (defrost) front adhering to the heat-source-side heat exchanger 7 when the heat pump system 1 operates in the air-heating cycle.
That is, the heat pump system 1 can perform the air-cooling/heating operation of operating only the first utilization unit (the indoor unit) 3, the hot water generation operation of operating only the second utilization unit (the hot water indoor unit) 4 to generate hot water for hot water supply or for air-heating, and the hot water generation air-heating operation of simultaneously operating both of the first utilization unit (the indoor unit) 3 and the second utilization unit (the hot water indoor unit) 4, for example. Any of the air-heating operation mode, the hot water generation operation mode, and the hot water generation air-heating operation mode is performed in the air-heating cycle. In the air-heating cycle, the heat-source-side heat exchanger 7 functions as an evaporator, and the utilization-side heat exchanger 28 and the water heat exchanger (the refrigerant/water heat exchanger) 35 function as condensers (heat radiators).
In this case, when an external temperature is low, frost is caused on the heat-source-side heat exchanger 7 functioning as the evaporator for absorbing heat from external air to evaporate refrigerant, and for this reason, heat exchange is disturbed. Thus, in the case where frost is caused on the heat-source-side heat exchanger 7, the defrosting operation of removing such frost is performed. The defrosting operation employs a reverse cycle type defrosting method. In such a method, when the defrosting control means 45 detects frost on the heat-source-side heat exchanger 7, the refrigerant circuit 42 is switched from the air-heating cycle to the air-cooling cycle by the four-way switching valve 6 such that high-temperature high-pressure refrigerant gas discharged from the compressor 5 is introduced into the heat-source-side heat exchanger 7 by the four-way switching valve 6. Heat of such refrigerant gas melts the frost.
As described above, in the reverse cycle type defrosting method, the refrigerant circuit 42 is switched from the air-heating cycle to the air-cooling cycle, and hot gas refrigerant is introduced into the heat-source-side heat exchanger 7 to melt frost. In this method, the refrigerant used for defrosting in the heat-source-side heat exchanger 7 dissipates heat, and therefore, is condensed and liquefied. After the pressure of the refrigerant is reduced by the air-cooling electronic expansion valve (EEVC) 10, the refrigerant is evaporated and gasified while circulating through the utilization-side heat exchanger 28 of the first utilization unit 3 and the water heat exchanger 35 of the second utilization unit 4. Then, the refrigerant is sucked into the compressor 5 through the four-way switching valve 6. In the defrosting operation, when low-pressure refrigerant is supplied to the water heat exchanger 35 and is evaporated by exchanging heat with water, water is frozen in the water heat exchanger 35, leading to the risk of damaging the water heat exchanger 35.
For this reason, in the present embodiment, a control system configured to close the refrigerant circuit shutoff valves 33, 34 provided at part of the refrigerant circuit 42 provided with the water heat exchanger 35 of the second utilization unit 4 to block the flow of refrigerant toward the water heat exchanger 35 and to open the refrigerant circuit shutoff valves 26, 27 to allow refrigerant to flow only toward the utilization-side heat exchanger 28 of the first utilization unit 3 in the defrosting operation is added to the defrosting control means 45.
That is, the defrosting control means 45 has the following function. In the operation in the above-described air-heating operation mode, the hot water generation operation mode, and the hot water generation air-heating operation mode, when the temperature of the heat-source-side heat exchanger 7 detected by the heat exchange temperature sensor 23 is equal to or lower than a predetermined value, it is determined that frost is caused on the heat-source-side heat exchanger 7. The operation mode is switched to the defrosting operation mode by switching of the four-way switching valve 6 to the air-cooling cycle and control of the rotational speed of the compressor 5. In addition, the refrigerant circuit shutoff valves 33, 34 are closed, and the refrigerant circuit shutoff valves 26, 27 are opened. Thus, the flow of refrigerant toward the water heat exchanger 35 is blocked, and refrigerant flows only toward the utilization-side heat exchanger 28 of the first utilization unit 3. In this manner, the defrosting operation is performed. When the detection value of the heat exchange temperature sensor 23 reaches equal to or greater than the predetermined temperature and completion of defrosting is detected, the operation mode is switched back to the original operation mode.
According to the configuration of the present embodiment described above, the following features and advantageous effects are provided.
(Air-Cooling/Heating Operation Using First Utilization Unit)
In this case, operation is performed in the state in which the refrigerant circuit shutoff valves 26, 27 are opened and the refrigerant circuit shutoff valves 33, 34 are closed.
In air-cooling, the four-way switching valve 6 is switched to an air-cooling cycle side, and the high-temperature high-pressure refrigerant discharged from the compressor 5 is guided to the heat-source-side heat exchanger 7 by the four-way switching valve 6. In the refrigerant circuit 42, such refrigerant circulates back to the compressor 5 in way of the receiver 9, the air-cooling electronic expansion valve (EEVC) 10, the utilization-side heat exchanger 28, the four-way switching valve 6, and the accumulator 11. Thus, the heat-source-side heat exchanger 7 acts as a condenser, and the utilization-side heat exchanger 28 acts as an evaporator. Accordingly, the air cooled by the utilization-side heat exchanger 28 is discharged into the room, and is used for air-cooling.
Needless to say, the following system may be used in air-cooling. In the system, air-cooling in the room is performed in such a manner that the refrigerant circuit shutoff valves 26, 27 are opened to supply refrigerant to the utilization-side heat exchanger 28 to cool indoor air. In addition, air-cooling using chilled water is performed in such a manner that the refrigerant circuit shutoff valves 33, 34 are opened to generate chilled water at the water heat exchanger 35 to supply the chilled water to an air-cooling load side.
On the other hand, in air-heating, the four-way switching valve 6 is switched to an air-heating cycle side, and the high-temperature high-pressure refrigerant discharged from the compressor 5 is guided to the utilization-side heat exchanger 28 by the four-way switching valve 6. In the refrigerant circuit 42, such refrigerant circulates back to the compressor 5 in way of the receiver 9, the air-heating electronic expansion valve (EEVH) 8, the heat-source-side heat exchanger 7, the four-way switching valve 6, and the accumulator 11. Thus, the utilization-side heat exchanger 28 acts as a condenser, and the heat-source-side heat exchanger 7 acts as an evaporator. Accordingly, the air heated by heat dissipation in the utilization-side heat exchanger 28 is discharged into the room, and is used for air-heating.
(Hot Water Generation Operation Using Second Utilization Unit)
In this case, operation is performed in the state in which the refrigerant circuit shutoff valves 26, 27 are closed and the refrigerant circuit shutoff valves 33, 34 are opened. In such operation, hot water for hot water supply or for air-heating is generated at the water heat exchanger 35.
Since such operation is performed in the air-heating cycle, the four-way switching valve 6 is switched to the air-heating cycle side.
The high-temperature high-pressure refrigerant discharged from the compressor 5 is first guided to the water heat exchanger 35 by the four-way switching valve 6. In the refrigerant circuit 42, such refrigerant circulates back to the compressor 5 in way of the receiver 9, the air-heating electronic expansion valve (EEVH) 8, the heat-source-side heat exchanger 7, the four-way switching valve 6, and the accumulator 11. Thus, the water heat exchanger 35 acts as a condenser, and the heat-source-side heat exchanger 7 acts as an evaporator. Accordingly, the water circulating in the water circuit 36 is heated by heat dissipation in the water heat exchanger 35, and as a result, hot water having a predetermined temperature is generated. Such hot water is supplied to the hot water storage tank or the hot water load, and is used for hot water supply or air-heating using hot water.
(Hot Water Generation Air-Heating Operation Using First and Second Utilization Units)
In this case, operation is performed in the state in which the refrigerant circuit shutoff valves 26, 27, 33, 34 are opened, and the four-way switching valve 6 is switched to the air-heating cycle side.
The first utilization unit 3 and the second utilization unit 4 are connected in parallel to the heat-source-side refrigerant circuit 15 of the heat source unit 2. Thus, the high-temperature high-pressure refrigerant discharged from the compressor 5 is simultaneously guided to both of the utilization-side heat exchanger 28 and the water heat exchanger 35 by the four-way switching valve 6.
The refrigerant simultaneously guided to the utilization-side heat exchanger 28 and the water heat exchanger 35 dissipates heat, and is condensed and liquefied in the utilization-side heat exchanger 28 and the water heat exchanger 35. Then, the refrigerant from the utilization-side heat exchanger 28 and the refrigerant from the water heat exchanger 35 are joined together at the liquid pipe 16, and are introduced into the receiver 9. In the refrigerant circuit 42, such refrigerant circulates back to the compressor 5 in way of the air-heating electronic expansion valve (EEVH) 8, the heat-source-side heat exchanger 7, the four-way switching valve 6, and the accumulator 11. In this operation, indoor air is heated by the utilization-side heat exchanger 28 to perform air-heating. Meanwhile, hot water is generated at the water heat exchanger 35, and is used for hot water supply or air-heating using hot water.

(Defrosting Operation)

In the above-described air-heating operation mode using the first utilization unit 3, the above-described hot water generation operation mode using the second utilization unit 4, and the above-described hot water generation air-heating operation mode using both of the first utilization unit 3 and the second utilization unit 4, the refrigerant circuit 42 operates in the air-heating cycle. Thus, depending on operational conditions, frost might be caused on the heat-source-side heat exchanger 7 of the heat source unit 2 exchanging heat with external air. Such frost can be detected by the defrosting control means 45 in such a manner that the heat exchange temperature sensor 23 provided at the heat-source-side heat exchanger 7 detects a temperature equal to or lower than a predetermined temperature.
When the defrosting control means 45 detects frost on the heat-source-side heat exchanger 7, the refrigerant circuit 42 is switched to the air-cooling cycle by the four-way switching valve 6, and the rotational speed of the compressor 5 is changed to the rotational speed for the defrosting operation. Meanwhile, the refrigerant circuit shutoff valves 26, 27 are opened, and the refrigerant circuit shutoff valves 33, 34 are closed. Accordingly, the flow of refrigerant toward the water heat exchanger 35 is blocked, and refrigerant flows only toward the utilization-side heat exchanger 28 of the first utilization unit 3. In this manner, the defrosting operation is started.
The high-temperature high-pressure refrigerant gas discharged from the compressor 5 is guided to the heat-source-side heat exchanger 7 via the four-way switching valve 6. After such refrigerant is condensed and liquefied by heat dissipation, the refrigerant circulates, in the refrigerant circuit 42, back to the compressor 5 in way of the receiver 9, the air-cooling electronic expansion valve (EEVC) 10, the utilization-side heat exchanger 28, the four-way switching valve 6, and the accumulator 11. Frost is melted by heat dissipation in the heat-source-side heat exchanger 7. In this operation, since the utilization-side heat exchanger 28 acts as an evaporator, chilled air is discharged into the room, and might disturb air-heating environment. For this reason, operation may be performed with the indoor fan of the first utilization unit 3 being stopped.
After the frost adhering to the heat-source-side heat exchanger 7 is melted and removed, the temperature of the heat-source-side heat exchanger 7 increases. Thus, the defrosting control means 45 detects completion of defrosting when the detection value of the heat exchange temperature sensor 23 exceeds a predetermined temperature, and terminates the defrosting operation. The defrosting control means 45 switches, e.g., the four-way switching valve 6 and the refrigerant circuit shutoff valves 26, 27, 33, 34 back to the state prior to the defrosting operation. Thus, the operation mode is switched back to the original operation mode, and operation in such an original mode is resumed.
According to the present embodiment, even if the reverse cycle type defrosting control means is employed, low-pressure refrigerant does not circulate in the water heat exchanger 35 of the second utilization unit 4 in the defrosting operation. Thus, it can be ensured that the risk of damaging the water heat exchanger 35 due to freezing of water in the water heat exchanger 35 is eliminated. In addition, e.g., the control of monitoring, during the defrosting operation, the water temperature in the water circuit 36 to switch the defrosting operation mode is no longer required, and therefore, the control system can be simplified.
Moreover, occurrence of the heat loss caused due to utilization of heat of hot water stored in the water circuit 36 in the defrosting operation is eliminated, and therefore, energy can be saved.
The means configured to block the flow of refrigerant toward the water heat exchanger 35 includes the refrigerant circuit shutoff valves 33, 34 provided at the outlet and inlet of the refrigerant circuit 42 connected to the water heat exchanger 35. Thus, when the defrosting control means 45 switches the operation mode to the defrosting operation in response to detection of frost on the heat-source-side heat exchanger 7, the refrigerant circuit shutoff valves 33, 34 provided at part of the refrigerant circuit 42 provided with the water heat exchanger 35 are closed such that the flow of refrigerant toward the water heat exchanger 35 is blocked. This can prevent freezing of water in the water heat exchanger 35 and damage of the water heat exchanger 35 due to freezing.
With such a configuration, freezing and damage of the water heat exchanger 35 can be prevented by such a simple configuration that the shutoff valves 33, 34 are merely provided at part of the refrigerant circuit 42 provided with the water heat exchanger 35. Thus, the degree of freedom in selection of the water heat exchanger 35 increases so that, e.g., a plate type heat exchanger which is easily frozen and damaged can be used.
As described above, the reverse cycle type defrosting control of switching the cycle to the air-cooling cycle (i.e., the defrosting cycle), in which the direct expansion type utilization-side heat exchanger (the indoor heat exchanger) 28 configured to exchange heat between refrigerant and indoor air serves as an evaporator, to remove the frost adhering to the heat-source-side heat exchanger 7 configured to exchange heat with external air is a defrosting control method employed for a typical air-to-air heat pump type air conditioner. Such a typical method can be used as it is. For an air-source heat pump system incorporating a water heat exchanger, development of a new defrosting control method can be skipped.
According to the above-described embodiment, in the defrosting operation mode, the refrigerant circuit shutoff valves 26, 27 are opened, and the refrigerant circuit shutoff valves 33, 34 are closed. In this manner, the flow of refrigerant toward the water heat exchanger 35 is blocked, and refrigerant flows only toward the utilization-side heat exchanger 28 of the first utilization unit 3. Needless to say, the refrigerant circuit shutoff valves 26, 27, 33, 34 provided in the refrigerant circuit 42 are not provided only for refrigerant circuit switching in the defrosting operation, but are also used for refrigerant circuit switching in other operation modes.

(Other Embodiments)

The present invention is not limited to the aspect of the above-described first embodiment, and may have the following embodiments.

(1) In the first embodiment, based on the detection value of the heat exchange temperature sensor 23 provided at the heat-source-side heat exchanger 7, the defrosting control means 45 detects frost on the heat-source-side heat exchanger 7, and terminates defrosting. However, regardless of a combination with the detection value of the external temperature sensor 25 configured to detect external temperature and the detection value of the temperature sensor, the operation time in the air-heating cycle may be counted such that the defrosting operation is periodically performed every predetermined period of time.
(2) In the first embodiment, the refrigerant circuit shutoff valves 33, 34 are provided respectively at both of the outlet and inlet of the refrigerant circuit (the branched liquid pipe 16B and the branched gas pipe 17B) 42 connected to the water heat exchanger 35. However, in order to block refrigerant circulation in the defrosting operation, the refrigerant circuit shutoff valve 33, 34 may be provided at either one of the outlet or inlet of the refrigerant circuit 42. In this case, the number of refrigerant circuit shutoff valves is decreased so that a cost can be reduced.
(3) In the first embodiment, the air-heating electronic expansion valve (EEVH) 8 and the air-cooling electronic expansion valve (EEVC) 10 are provided at the heat source unit (the outdoor unit) 2. However, the air-cooling electronic expansion valves (EEVC) 10 may be separately arranged at the branched liquid pipes 16A, 16B of the first utilization unit (the indoor unit) 3 and the second utilization unit (the hot water indoor unit) 4.
In this case, the function of fully closing each of the separately-arranged air-cooling electronic expansion valves (EEVC) 10 is utilized so that each electronic expansion valve (EEVC) 10 can be also used as the refrigerant circuit shutoff valve (the shutoff valve 33) configured to block the flow of refrigerant toward the water heat exchanger 35 in the defrosting operation. Thus, the number of refrigerant circuit shutoff valves can be decreased. Consequently, the configuration of the refrigerant circuit 42 can be simplified, and a cost can be reduced.
(4) In the first embodiment, the presence or absence of frost is determined (detected) by the defrosting control means 45 based on the detection value of the heat exchange temperature sensor 23 provided at the heat-source-side heat exchanger 7. With such a signal, the four-way switching valve 6 is switched to the air-cooling cycle, and the refrigerant circuit shutoff valves 33, 34 are closed. However, when the four-way switching valve 6 is, for defrosting, switched in response to detection of frost, a low-pressure is rapidly dropped. Thus, the low-pressure sensor 22 or the pressure sensor 41 may detect that such a pressure falls below a predetermined value, and then, the refrigerant circuit shutoff valves 33, 34 may be closed.

Note that the present invention is not limited to the aspects of the above-described embodiments, and modification can be optionally made without departing from the scope of the present invention. For example, in the above-described embodiments, the case where the single first utilization unit (the indoor unit) 3 is connected has been described as an example. A multi-type heat pump system may be employed, which is configured such that a plurality of first utilization units (indoor units) 3 are connected in parallel.

{Reference Signs List}

1: heat pump system
2: heat source unit
3: first utilization unit
4: second utilization unit
5: compressor
6: four-way switching valve
7: heat-source-side heat exchanger
28: utilization-side heat exchanger
33, 34: refrigerant circuit shutoff valve (means configured to block refrigerant flow toward water heat exchanger)
35: water heat exchanger
42: refrigerant circuit
45: defrosting control means

Claims

A heat pump system (1) comprising:
a heat source unit (2) including a compressor, a four-way switching valve (6), and a heat-source-side heat exchanger (7) configured to exchange heat between refrigerant and external air;

a first utilization unit (3) including a utilization-side heat exchanger (28) configured to exchange heat between refrigerant and indoor air;

a second utilization unit (4) including a water heat exchanger (35) configured to exchange heat between refrigerant and water to generate hot water for hot water supply or for air-heating;

a single-line refrigerant circuit (42) configured such that the first and second utilization units (3, 4) are connected in parallel to the heat source unit (2); and

a defrosting control means (45) configured to switch, when frost is caused on the heat-source-side heat exchanger (7), the refrigerant circuit (42) from an air-heating cycle to an air-cooling cycle by the four-way switching valve (6) to perform defrosting,

wherein the defrosting control means (45) includes a means configured to block, in a defrosting operation, a refrigerant flow toward the water heat exchanger (35) of the second utilization unit (4) and to allow refrigerant to flow only toward the utilization-side heat exchanger (28) of the first utilization unit (3).
The heat pump system of claim 1, wherein
the means configured to block the refrigerant flow toward the water heat exchanger includes a refrigerant circuit shutoff valve (33, 34) provided at one or both of an outlet and an inlet of a refrigerant circuit connected to the water heat exchanger (35).
The heat pump system of claim 2, wherein
in a case of a system including a dedicated electronic expansion valve at part of the refrigerant circuit provided with the second utilization unit (4), the electronic expansion valve is also used as the refrigerant circuit shutoff valve.
The heat pump system of any one of claims 1 to 3, wherein
the means configured to block the refrigerant flow toward the water heat exchanger (35) is closed to block the refrigerant flow
at the same time that the four-way switching valve (6) is switched by a signal of detection of frost caused on the heat-source-side heat exchanger (7) or

when a detection value of a low-pressure sensor (22) provided at the heat source unit (2) or a detection value of a pressure sensor (41) provided at the second utilization unit (4) falls below a predetermined value after switching of the four-way switching valve (6).