JP2006138611A - Heat pump system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a cooling/heating (hot water supply) system by using supercritical refrigerant without using a four-way switch valve, and to realize reduction of liquid back in starting by liquefied refrigerant (flooded refrigerant) condensed and accumulated in a heat source-side heat exchanger in stopping the operation. <P>SOLUTION: When a heating or hot water supplying operation is started, a switch valve 7 between the heat source-side heat exchanger 11 and a high-pressure gas pipe 3 is opened, a switch valve 8 between the heat source-side heat exchanger 11 and a low-pressure gas pipe 6 is closed, a switch valve 9 between a use-side heat exchanger 12 and the high-pressure gas pipe 3 is closed, a switch valve 10 between the use-side heat exchanger 12 and the low-pressure gas pipe 6 is opened, and expansion valves 15, 16 respectively between each of heat exchangers 11, 12 and a liquid pipe 17 are opened. An inverse cycle is started for a short time, a pressure of the refrigerant is raised to a supercritical state by using a high-pressure sensor 21, and then the operation is switched to a normal operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat pump system such as an air conditioning (including hot water supply) system, and more particularly to a heat pump system using a supercritical refrigerant such as carbon dioxide as a refrigerant.

  Conventionally, in a cooling / heating system using a fluorocarbon (fluorocarbon) refrigerant, switching control between cooling and heating is performed by a four-way switching valve attached to a compressor discharge pipe and a suction pipe. On the other hand, supercritical refrigerants such as carbon dioxide (carbon dioxide) are 3 to 4 times higher on the high pressure side than fluorocarbon refrigerants, and the differential pressure between the high pressure side and the low pressure side is very large. If the pressure difference between the high-pressure side and the low-pressure side increases, problems such as leakage will inevitably occur and the sealing technology will become very difficult. There is no switching valve.

  Therefore, using a supercritical refrigerant such as carbon dioxide refrigerant, heat source side heat exchange via a switching valve to the high pressure gas pipe connected to the discharge pipe of the compressor and the low pressure gas pipe connected to the suction pipe of the compressor And one end of each heat exchanger are connected to each other, and the other end of each heat exchanger is connected to a liquid pipe via an expansion valve, and the compressor, each switching valve, each expansion valve, etc. are controlled by control means. Thus, there has already been proposed a heat pump system (refrigeration apparatus) that performs cooling operation, heating operation, or hot water supply operation (see, for example, Patent Document 1).

The thing of the said patent document 1 uses a supercritical refrigerant | coolant, such as a carbon dioxide refrigerant | coolant, and uses the switching valve by an electromagnetic on-off valve not using a four-way switching valve, but a high pressure gas pipe, a low pressure gas pipe, and a liquid pipe. In this refrigeration system, an outdoor unit having an outdoor heat exchanger as a heat source side heat exchanger, a plurality of indoor units having an indoor heat exchanger as a use side heat exchanger, and a hot water supply unit In addition, while operating the hot water supply unit, a plurality of indoor units can be cooled or heated at the same time, or these cooling and heating operations can be performed in combination, and the inside of the high-pressure gas pipe can be operated as a refrigeration system. Since the inside is operated at a supercritical pressure, the refrigerant does not condense in the high-pressure gas pipe and does not liquefy and stagnate (condensate and stay) in the high-pressure gas pipe like the chlorofluorocarbon refrigerant.
JP 2004-226018 A

  However, even in a system using a supercritical refrigerant as described in Patent Document 1, when the operation is stopped, the refrigerant condenses and stays in the heat source side heat exchanger (sleeps) if the outdoor temperature is lower than the room. In this state, when starting in the heating or hot water supply operation mode as it is, the condensed liquefied refrigerant in the heat source side heat exchanger is backed up at once, and even if an accumulator (gas-liquid separator) is provided in the suction pipe of the compressor, Since it overflows and flows into the compressor, the oil behavior of the compressor becomes unstable and adversely affects durability. In addition, when the liquid back occurs, the start-up of the heating operation or the like is delayed accordingly.

  Accordingly, the present invention has been made to solve such problems, and can use a supercritical refrigerant to realize a cooling / heating (hot water supply) system without using a four-way switching valve, and can also provide a heat source when the operation is stopped. It is an object of the present invention to provide a heat pump system that can realize a reduction in the amount of liquid back at the time of startup by a liquefied refrigerant (stagnation refrigerant) that condenses and stays in the side heat exchanger.

  In order to achieve the above object, the present invention uses a supercritical refrigerant and switches to a high pressure gas pipe connected to the discharge pipe of the compressor and a low pressure gas pipe connected to the suction pipe of the compressor. One end side of the heat source side heat exchanger and the use side heat exchanger is connected via a valve, and the other end side of each heat exchanger is connected to a liquid pipe via an expansion valve, and the compressor, each switching valve, and each In a heat pump system in which an expansion valve or the like is controlled by a control means to perform cooling operation, heating operation or hot water supply operation, a switching valve between the heat source side heat exchanger and the high pressure gas pipe at the start of heating or hot water supply operation Is opened, the switching valve between the low pressure gas pipe is closed, the switching valve between the use side heat exchanger and the high pressure gas pipe is closed, and the switching valve between the low pressure gas pipe is opened. And open the expansion valve between both heat exchangers and the liquid pipe for a short time. Cycles started, is characterized in that the switching to normal operation.

  In addition, a detection unit that detects a supercritical state of the refrigerant is provided, and the refrigerant is boosted to the supercritical state using the detection unit, and then switched to a normal operation.

  Furthermore, an intermediate pressure receiver is provided for gas-liquid separation of the refrigerant flowing in the liquid pipe and supplying the separated gas-phase refrigerant to the compressor.

  Further, a pressure sensor is used as detection means for detecting the supercritical state of the refrigerant.

  In addition, a carbon dioxide refrigerant is used as the supercritical refrigerant.

  According to the present invention, it is possible to realize a cooling / heating (hot water supply) system using a supercritical refrigerant without using a four-way switching valve, and at the start of heating or hot water supply operation, a short-cycle reverse cycle is activated to switch to normal operation. As a result, it is possible to reduce the amount of liquid back at the time of start-up by the liquefied refrigerant (sleeping refrigerant) that condenses and stays in the heat source side heat exchanger when the operation is stopped.

  Also, a liquefied refrigerant (condensed and retained in the heat source side heat exchanger when the operation is stopped) is provided by detecting means for detecting the supercritical state of the refrigerant, boosting the refrigerant to the supercritical state, and switching to normal operation. It is possible to more reliably realize a reduction in the amount of liquid back at the time of start-up due to the stagnation refrigerant.

  Furthermore, the liquid pipe is provided with an intermediate pressure receiver for gas-liquid separation of the refrigerant and supplying the separated gas-phase refrigerant to the compressor, so that the liquid pipe has a saturated liquid line enthalpy from the liquid pipe to the expansion valve. Since the phase refrigerant flows in, when the use side heat exchanger or the heat source side heat exchanger functions as an evaporator, the compression work of the compressor is reduced while the enthalpy difference between the inlet and the outlet is increased. It is possible to increase the refrigeration capacity of the refrigeration cycle with the carbon dioxide refrigerant and improve the coefficient of performance.

  Further, by using the pressure sensor as the detecting means for detecting the supercritical state of the refrigerant, the supercritical state of the refrigerant can be detected almost certainly.

  In addition, since carbon dioxide refrigerant is used as a supercritical refrigerant, carbon dioxide refrigerant is not toxic or flammable among natural refrigerants, and there is an advantage that it is not necessary to provide an abatement facility.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a refrigerant circuit diagram of a heat pump system according to an embodiment of the present invention, and FIG. 2 is a Mollier diagram (pressure-enthalpy diagram) showing its operation.

  In the refrigerant circuit shown in FIG. 1, a carbon dioxide (carbon dioxide) refrigerant that is a natural refrigerant and is operated in a supercritical state on the high pressure side is used as the refrigerant. The carbon dioxide refrigerant is not less than about 73 atm and not less than about 31 ° C. and is neither a liquid nor a gas, but is in a supercritical state having both of these characteristics.

  The compressor 1 for compressing the carbon dioxide refrigerant is of a two-stage compression type capable of high-pressure compression. The discharge pipe 2 on the high-stage compression element side is connected to the high-pressure gas pipe 3 and the suction on the low-stage compression element side. The pipe 4 is connected to a low-pressure gas pipe 6 via an accumulator (gas-liquid separator) 5.

  One end side of the heat source side heat exchanger 11 and the use side heat exchanger 12 is connected to the high pressure gas pipe 3 and the low pressure gas pipe 6 through switching valves (electromagnetic on-off valves) 7, 8, 9, 10 respectively. . The heat source side heat exchanger 11 is specifically an outdoor heat exchanger or the like, and is provided with a blower fan 13 for promoting heat exchange with the outside air. Moreover, the use side heat exchanger 12 is specifically an indoor heat exchanger or the like, and is provided with a blower fan 14 for promoting heat exchange with room air and blowing out cold air and hot air.

  The other end side of each of the heat exchangers 11 and 12 is connected to a liquid pipe (narrow pipe) 17 via expansion valves (reducing valves) 15 and 16 each consisting of an electronic control valve. Each switching valve 7-10, each fan 13, 14, each expansion valve 15, 16, etc. are controlled by a control means comprising a microcomputer (not shown) so that a cooling operation or a heating operation can be performed. ing. In addition, if the use side heat exchanger 12 includes a plurality of indoor units and a hot water supply unit having an indoor heat exchanger as described in Patent Document 1 described above, a plurality of indoor units can be operated while operating the hot water supply unit. The unit can be cooled or heated at the same time, or these cooling and heating operations can be mixed.

  Further, in the present embodiment, an intermediate pressure receiver 18 for separating the refrigerant flowing in the liquid pipe 17 into gas and liquid and supplying the separated gas-phase refrigerant to the compressor 1 is provided. This intermediate pressure receiver 18 corresponds to the bidirectional flow of the gas-liquid mixed refrigerant flowing through the liquid pipe 17. For example, bidirectional gas-liquid separation can be realized by the partition plate 19 in which a large number of through holes are formed. The gas phase refrigerant separated by the intermediate pressure receiver 18 is configured to be supplied to the suction side of the high-stage compression element in the two-stage compression compressor 1.

  The discharge pipe 2 of the compressor 1 is provided with a high-pressure sensor 21 for detecting the supercritical state of the carbon dioxide refrigerant, and the detection output of the high-pressure sensor 21 is supplied to a microcomputer constituting control means (not shown). It is designed to be entered.

  In the above configuration, during the cooling operation, the high pressure side switching valve 7 of the heat source side heat exchanger 11 of FIG. 1 is opened, the low pressure side switching valve 8 is closed, and the high pressure side switching valve 9 of the use side heat exchanger 12 is closed. The low pressure side switching valve 10 is opened, and the expansion valves 15 and 16 are operated by a throttle action.

  As a result, the refrigerant that has been compressed by the compressor 1 and becomes high temperature and high pressure is in a supercritical state (abcd in FIG. 2), and passes from the discharge pipe 2 through the high pressure gas pipe 3 to the high pressure side switching valve. 7 flows into the heat source side heat exchanger 11. The refrigerant flowing into the heat source side heat exchanger 11 is cooled by exchanging heat with the outside air by the air blown by the fan 13, but is not condensed because it is in a supercritical state (de in FIG. 2).

  The supercritical refrigerant cooled by the heat source side heat exchanger 11 is decompressed and expanded through the expansion valve 15 having a throttle action, and flows into the intermediate pressure receiver 18 (ef in FIG. 2). During this time, the refrigerant passes through the saturated liquid gland SL, gets out of the supercritical state, partially liquefies and becomes a gas-liquid mixed refrigerant and flows into the intermediate pressure receiver 18. The gas-liquid mixed refrigerant flowing into the intermediate pressure receiver 18 is separated into a gas-phase refrigerant and a liquid-phase refrigerant here, and the separated gas-phase refrigerant is supplied to the suction side of the high-stage compression element of the compressor 1 (FIG. 2). Fc). On the other hand, in the liquid phase refrigerant from which the gas phase refrigerant has been separated, the enthalpy content of the gas phase refrigerant is lost and the enthalpy is reduced to the saturated liquid gland SL (fg in FIG. 2).

  The liquid-phase refrigerant from which the gas-phase refrigerant has been separated by the intermediate-pressure receiver 18 is decompressed and expanded via the expansion valve 16 having a throttle action, and flows into the use-side heat exchanger 12 (gh in FIG. 2). In the use-side heat exchanger 12, the liquid-phase refrigerant exchanges heat with room air by blowing air from the fan 14 to evaporate, and the cooled air is blown into the room as cold air, while exceeding the saturated vapor line SV. The refrigerant that is completely in the gas phase is sucked into the compressor 1 through the accumulator 5 provided in the low pressure gas pipe 6 and the suction pipe 4 from the use side heat exchanger 12 through the low pressure side switching valve 10 (FIG. 2). H-a). And the refrigeration cycle mentioned above is repeated.

  On the other hand, in the case of heating (or hot water supply) operation, as a measure for preventing liquid back of the liquefied refrigerant (sleeping refrigerant) condensing and staying in the heat source side heat exchanger 11 during operation stop, the heat source side heat shown in FIG. The high pressure side switching valve 7 of the exchanger 11 is opened, the low pressure side switching valve 8 is closed, the high pressure side switching valve 9 of the use side heat exchanger 12 is closed, the low pressure side switching valve 10 is opened, and the expansion valves 15 and 16 are Operate in the open state (reverse cycle start). During the reverse cycle startup, the fan 13 of the heat source side heat exchanger 11 is stopped, and the fan 14 of the use side heat exchanger 12 is stopped or operated with a light breeze that does not blow cold air.

  Thereby, the refrigerant discharged from the compressor 1 passes through the high pressure gas pipe 3 from the discharge pipe 2 and flows into the heat source side heat exchanger 11 via the high pressure side switching valve 7, and stagnation in the heat source side heat exchanger 11. The refrigerant is expelled. The purged sleeping refrigerant flows through the expansion valve 15 in the open state, flows into the liquid pipe 17 and the intermediate pressure receiver 18, and then flows into the use-side heat exchanger 12 through the expansion valve 16 in the open state. If the operation of the compressor 1 is continued as it is, the discharge pressure of the compressor 1 gradually increases, and the refrigerant in the heat source side heat exchanger 11 enters a supercritical state.

  Therefore, there is almost no condensate in the heat source side heat exchanger 11, and the amount of internal refrigerant decreases. Excess refrigerant is held in the intermediate pressure receiver 18. The supercritical state of the refrigerant in the heat source side heat exchanger 11 is detected by the high pressure sensor 21 provided in the compressor discharge pipe 2 when the discharge pressure of the compressor 1 is increased, and is approximately the supercritical pressure of the carbon dioxide refrigerant. The supercritical state of the refrigerant can be detected almost certainly by detecting that the pressure is 73 atm or higher by the microcomputer constituting the control means.

  Thereafter, the compressor 1 is stopped once, the switching valves 7 to 10 are closed, and the expansion valves 15 and 16 are in an open state to balance the pressure, and then enter a normal operation. The reason why the normal operation is started after the pressure is balanced is to prevent generation of a large switching refrigerant sound due to a collision between the high-pressure refrigerant and the low-pressure refrigerant.

  Even during the pressure balance, the refrigerant in the heat source side heat exchanger 11 passes through the expansion valve 15 in the open state, flows into the liquid pipe 17 and the intermediate pressure receiver 18, and further passes through the expansion valve 16 in the open state to use side heat. Since the refrigerant flows into the exchanger 12, the amount of the internal refrigerant in the heat source side heat exchanger 11 is further reduced, the amount of liquid back to the compressor 1 is further reduced, the durability of the compressor 1 is improved, and the rising speed is also increased.

  When entering the normal heating (or hot water supply) operation, the high pressure side switching valve 7 of the heat source side heat exchanger 11 in FIG. 1 is closed, the low pressure side switching valve 8 is opened, and the high pressure side switching valve 9 of the use side heat exchanger 12 is opened. Is opened, the low-pressure side switching valve 10 is closed, and the expansion valves 15 and 16 are operated by a throttle action.

  As a result, the refrigerant that has been compressed by the compressor 1 and becomes high temperature and high pressure is in a supercritical state (abcd in FIG. 2), and passes from the discharge pipe 2 through the high pressure gas pipe 3 to the high pressure side switching valve. It flows into the use side heat exchanger 12 through 9. In the use-side heat exchanger 12, the air heated by air exchanged with the room air by the fan 14 is heated and blown into the room while the refrigerant is cooled but condensed in a supercritical state. (De in FIG. 2).

  The supercritical refrigerant cooled by the heat source side heat exchanger 12 is decompressed and expanded through the expansion valve 16 having a throttle action and flows into the intermediate pressure receiver 18 (ef in FIG. 2). During this time, the refrigerant passes through the saturated liquid gland SL, gets out of the supercritical state, partially liquefies and becomes a gas-liquid mixed refrigerant and flows into the intermediate pressure receiver 18. The gas-liquid mixed refrigerant flowing into the intermediate pressure receiver 18 is separated into a gas-phase refrigerant and a liquid-phase refrigerant here, and the separated gas-phase refrigerant is supplied to the suction side of the high-stage compression element of the compressor 1 (FIG. 2). Fc). On the other hand, in the liquid phase refrigerant from which the gas phase refrigerant has been separated, the enthalpy content of the gas phase refrigerant is lost and the enthalpy is reduced to the saturated liquid gland SL (fg in FIG. 2).

  The liquid-phase refrigerant from which the gas-phase refrigerant has been separated by the intermediate pressure receiver 18 is decompressed and expanded via the expansion valve 15 having a throttle action, and flows into the heat source side heat exchanger 11 (gh in FIG. 2). In the heat source side heat exchanger 12, the liquid phase refrigerant exchanges heat with the outside air by blowing air from the fan 13 to evaporate, and the refrigerant that has completely changed to the vapor phase beyond the saturated vapor line SV is transferred from the heat source side heat exchanger 11. It is sucked into the compressor 1 through the accumulator 5 provided in the low pressure gas pipe 6 and the suction pipe 4 through the low pressure side switching valve 8 (ha in FIG. 2). And the refrigeration cycle mentioned above is repeated.

  Thus, in the present system, at the start of the heating (or hot water supply) operation, the reverse refrigerant is activated for a short time as described above, so that the sleeping refrigerant in the heat source side heat exchanger 11 passes through the liquid pipe 17, It is held in the use side heat exchanger 12 from the intermediate pressure receiver 18 and the amount of refrigerant in the heat source side heat exchanger 11 can be reduced at the time of startup. Then, by using the pressure sensor 21 to increase the refrigerant pressure to the supercritical state, the heat source side heat exchanger 11 is almost free of condensate, and the amount of refrigerant retained is further reduced. It is possible to surely reduce the amount of liquid back at the time of starting the hot water supply, improving the durability of the compressor 1 and increasing the startup speed.

  In the present embodiment, since the liquid pipe 17 is provided with the bidirectional intermediate pressure receiver 18 as described above, a saturated liquid is provided from the liquid pipe 17 to the expansion valves 15 and 16 as shown in FIG. Since the liquid refrigerant having the enthalpy of the line SL flows in, when the use side heat exchanger 12 or the heat source side heat exchanger 11 functions as an evaporator, the difference in enthalpy between the inlet and the outlet is increased. Can do. Further, since the gas-phase refrigerant having the intermediate pressure separated by the intermediate pressure receiver 18 is guided to the suction side of the high-stage compression element in the two-stage compression compressor 1, the compression work of the compressor 1 is reduced. Can do.

  Therefore, when the use side heat exchanger 12 or the heat source side heat exchanger 11 functions as an evaporator, the compression work of the compressor 1 is reduced while the enthalpy difference between the inlet and the outlet is increased. Therefore, the refrigeration capacity of the refrigeration cycle with the carbon dioxide refrigerant can be increased and the coefficient of performance can be improved.

  Further, since the two-stage compression type compressor 1 is used, the above-described operation and effect can be realized by a single compressor, and space saving and cost reduction can be achieved.

  In the above embodiment, the supercritical state can be detected almost certainly by using the high-pressure sensor 21 as the detecting means for detecting the supercritical state of the refrigerant. It is also conceivable that the elapsed time is measured in advance by an experiment or the like, and a supercritical state is detected by a temperature sensor or timer with a certain margin in the value.

  In addition to the carbon dioxide refrigerant, for example, ethylene, diborane, ethane, nitric oxide and the like are listed as refrigerants operated on the high pressure side in a supercritical state. Among natural refrigerants, carbon dioxide refrigerant is toxic and flammable. Therefore, there is an advantage that it is not necessary to install a detoxification facility.

The refrigerant circuit figure of the heat pump system which concerns on one Embodiment of this invention. The Mollier diagram which shows the effect | action.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Discharge pipe 3 High pressure gas pipe 4 Suction pipe 5 Accumulator 6 Low pressure gas pipe 7-10 Switching valve 11 Heat source side heat exchanger 12 Use side heat exchanger 13, 14 Blower fan 15, 16 Expansion valve 17 Liquid pipe 18 Intermediate pressure receiver 21 High pressure sensor

Claims (5)

A heat source side heat exchanger and a use side heat exchanger are connected to the high pressure gas pipe connected to the discharge pipe of the compressor and the low pressure gas pipe connected to the suction pipe of the compressor via a switching valve, respectively. One end side of each heat exchanger is connected, and the other end side of each heat exchanger is connected to a liquid pipe via an expansion valve, and the compressor, each switching valve, each expansion valve, etc. are controlled by a control means to perform cooling operation or heating operation Alternatively, in a heat pump system designed to perform hot water supply operation,
At the start of heating or hot water supply operation, the switching valve between the heat source side heat exchanger and the high pressure gas pipe is opened, the switching valve between the low pressure gas pipe is closed, and the use side heat exchanger and the high pressure gas pipe are closed. Close the switching valve to the gas pipe, open the switching valve to the low-pressure gas pipe, open the expansion valve between both heat exchangers and the liquid pipe, start a reverse cycle for a short time, A heat pump system characterized by switching to operation.   The heat pump system according to claim 1, further comprising a detection unit that detects a supercritical state of the refrigerant, wherein the refrigerant is boosted to a supercritical state using the detection unit and then switched to a normal operation.   3. The heat pump system according to claim 1, further comprising an intermediate pressure receiver configured to gas-liquid separate the refrigerant flowing in the liquid pipe and supply the separated gas-phase refrigerant to the compressor.   The heat pump system according to claim 2, wherein a pressure sensor is used as a detection means for detecting a supercritical state of the refrigerant. The heat pump system according to any one of claims 1 to 4, wherein a carbon dioxide refrigerant is used as the supercritical refrigerant.