JP2015117902A - Refrigeration cycle device - Google Patents

Abstract

A refrigeration cycle apparatus capable of efficient operation even at a low outside air temperature is provided. A refrigeration cycle apparatus 1 is provided in which a compressor 2, a condenser 4, an expansion valve 5, and an evaporator 6a are sequentially connected by a refrigerant pipe 8. In addition, a bypass valve 12 is provided for increasing the maximum flow rate of refrigerant flowing through the expansion valve 5 at the maximum opening when the outside temperature is low. For this reason, the liquid refrigerant radiated and condensed by the condenser 4 flows through the opened bypass valve 12 and the expansion valve 5, respectively, so that the flow rate of refrigerant flowing to the evaporator 6a of the hydrothermal exchanger 6 is expanded. The maximum refrigerant flow rate that flows when the valve 5 is at the maximum opening degree is increased. Thereby, the suction-side superheat degree SH of the compressor 2 can be adjusted within a predetermined range, and the flow rate of the refrigerant circulating in the refrigeration cycle apparatus 1 can be ensured even at a low outside air temperature. As a result, it is possible to suppress a decrease in the suction side pressure, thereby improving COP. [Selection] Figure 1

Description

  Embodiments described herein relate generally to a refrigeration cycle apparatus, and more particularly, to a refrigeration cycle apparatus that can perform an efficient operation even at a low outside air temperature.

  In a conventional refrigeration cycle apparatus, in order to secure a pressure difference between a high pressure side and a low pressure side at a low outside air temperature, a device that performs control to increase the high pressure side pressure by reducing the rotation speed of the condenser fan is known. (For example, refer to Patent Document 1).

Japanese Patent No. 4215543

  The conventional refrigeration cycle apparatus has a problem that the coefficient of performance (COP) decreases because the high-pressure side pressure is kept high at low outside air temperatures.

  The problem to be solved by the present invention is to provide a refrigeration cycle apparatus capable of efficient operation even at a low outside air temperature.

  The refrigeration cycle apparatus according to the embodiment includes a refrigeration cycle apparatus in which a compressor, a condenser, an expansion unit, and an evaporator are sequentially connected by refrigerant piping, and a unit that increases the maximum refrigerant flow rate of the expansion unit at a low outside air temperature. ing.

The refrigeration cycle figure which shows the structure of the refrigeration cycle apparatus of 1st Embodiment. (A) increases the high-pressure side pressure in the conventional refrigeration cycle apparatus indicated by the alternate long and short dash line corresponding to the low outside air temperature, and increases the high-pressure side pressure in the conventional refrigeration cycle apparatus indicated by the solid line at the low outside temperature. (B) is a Ph diagram showing the relative relationship between the refrigerant pressure P and the specific enthalpy h, and (b) shows the water in the water heat exchanger during operation indicated by the alternate long and short dash line in FIG. And a diagram showing the relative relationship between the temperature T of the refrigerant and the specific enthalpy h. (A) is a Ph diagram showing the relative relationship between the refrigerant pressure P and the specific enthalpy h of the first embodiment indicated by a broken line together with the conventional example indicated by the solid line in FIG. FIG. 5B is a diagram showing a relative relationship between water and refrigerant temperatures T and specific enthalpy h in the water heat exchanger and the liquid-gas heat exchanger of the first embodiment. (A) in the first embodiment shown in FIG. 1, the temperature T and the specific enthalpy h of the water and refrigerant in the water heat exchanger and the liquid-gas heat exchanger when the return water temperature is low. The Th diagram showing the relationship, (b) shows a high return water temperature indicated by a solid line when the flow direction of water inside the water heat exchanger is set to the opposite direction (parallel flow) in the first embodiment. And a Th diagram showing a relationship between water and refrigerant temperature T and specific enthalpy h in the water heat exchanger and in the liquid-gas heat exchanger when the return water temperature indicated by the dotted line is low. The refrigeration cycle figure which shows the structure of the refrigeration cycle apparatus which is a modification of 1st Embodiment. The refrigeration cycle figure which shows the structure of the refrigeration cycle apparatus which is another modification of 1st Embodiment. The refrigeration cycle figure which shows the structure of the refrigeration cycle apparatus of 2nd Embodiment. (A) is a Ph diagram showing the relative relationship between the refrigerant pressure P and the specific enthalpy h in the second embodiment indicated by a broken line together with the conventional example indicated by the solid line in FIG. b) A Th diagram showing the relationship between the water and refrigerant temperatures T and the specific enthalpy h in the water heat exchanger and the gas-gas heat exchanger of the second embodiment.

  Hereinafter, the refrigeration cycle apparatus of the embodiment will be described with reference to the drawings.

  In addition, the same code | symbol is attached | subjected to the same or an equivalent part in several drawings.

(First embodiment)
FIG. 1 is a refrigeration cycle diagram showing the configuration of the refrigeration cycle apparatus of the first embodiment. As shown in FIG. 1, the refrigeration cycle apparatus 1 according to the first embodiment is, for example, an air-cooled chiller, and is rotated at a rotational speed by a refrigerant discharge port 2a of a compressor 2 such as a hermetic rotary compressor and an inverter not shown. A condenser 4 comprising an air heat exchanger having a condenser fan 3 that can be controlled, a liquid refrigerant flow path 20a of the liquid-gas heat exchanger 20, an expansion valve 5 as an example of an expansion means, and a water heat exchanger 6 The refrigerant 6a, the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20, the accumulator 7, and the refrigerant suction port 2b of the compressor 2 are connected in this order by the refrigerant pipe 8 to circulate the refrigerant.

  The compressor 2 includes a hermetic container such as a high-pressure case, and is configured such that the rotational speed can be controlled by an inverter not shown. The expansion valve 5 is constituted by, for example, a PMV (pulse motor valve) or the like, and the opening degree is controlled by the number of pulses of the opening degree control pulse signal inputted.

  The water heat exchanger 6 includes an evaporator 6a that is connected to the refrigerant pipe 8 and passes the refrigerant, and a water flow path 6b that is connected to the water pipe 10 provided with the circulation pump 9 and passes the circulating water so as to exchange heat. The circulating water passing through the water flow path 6b is cooled to generate cold water. This cold water is used for cooling and the like.

  The refrigerant pipe 8 includes a bypass pipe 11 that allows the refrigerant inlet side and the outlet side of the expansion valve 5 to communicate with each other. The bypass pipe 11 is provided with a bypass valve 12 that is an open / close valve such as an electromagnetic valve. ing.

  The bypass valve 12 is configured as a maximum refrigerant flow rate increasing means for flowing a refrigerant flow rate higher than the maximum flow rate flowing through the expansion valve 5 that is controlled to the maximum opening degree at a low outside air temperature. Each is electrically connected to the controller 15 via a signal line (not shown).

  The liquid-gas heat exchanger 20 has a liquid refrigerant flow path 20a through which high-temperature and high-pressure liquid refrigerant from the condenser 4 passes, and a gas refrigerant flow through which low-temperature and low-pressure suction gas refrigerant from the evaporator 6a of the water heat exchanger 6 passes. The passage 20b is provided so that heat can be exchanged, the liquid refrigerant flowing out of the condenser 4 is cooled, and the suction gas immediately before the accumulator 7 is heated.

  The refrigeration cycle apparatus 1 detects the discharge pressure sensor 13 that detects the discharge side pressure Pd of the compressor 2, the suction pressure sensor 14 that detects the suction side pressure Ps of the compressor 2, and the discharge temperature Td of the compressor 2. A discharge temperature sensor 34 and a suction temperature sensor 35 for detecting the suction temperature Ts of the compressor 2 are provided, and these sensors are connected to the controller 15 via signal lines (not shown).

  The controller 15 is connected to each inverter (not shown) of the compressor 2, the condenser fan 3 for promoting heat exchange, and the circulation pump 9 via a signal line (not shown).

  The controller 15 includes, for example, a microcomputer and includes a CPU, ROM, RAM, and other memories, and calculates the suction side superheat degree SH, the discharge side superheat degree DSH, and the saturation temperature of the compressor 2, respectively. A means for calculating the degree of superheat, an expansion valve opening control means for controlling the opening of the expansion valve 5, a bypass valve opening / closing control means for controlling the opening / closing of the bypass valve 12, the compressor 2, the condenser fan 3, and the circulation pump 9. A rotation speed control means for controlling the operation rotation speed is provided.

  The superheat degree calculation means includes a refrigerant saturation temperature based on the suction side pressure Ps and the discharge side pressure Pd of the compressor 2 read from the discharge pressure sensor 13 and the suction pressure sensor 14, respectively, a discharge temperature sensor 34, and a suction temperature sensor. The suction side superheat degree SH and the discharge side superheat degree DSH are calculated from the discharge temperature Td and the suction temperature Ts of the compressor 2 read from 35.

  The expansion valve opening control means controls the opening of the expansion valve 5 by controlling the number of pulses of the control pulse signal given to the expansion valve 5 made of PMV, while the pulse of the maximum opening of the expansion valve 5 is controlled. The number is stored in a memory, and the opening degree of the expansion valve 5 is constantly monitored.

  The controller 15 is configured to flow a refrigerant flow rate higher than the maximum flow rate that flows through the expansion valve 5 that is controlled to the maximum opening degree during low compression operation at low outside temperatures such as in the intermediate season (spring / autumn) or winter season. The maximum refrigerant flow rate increasing control means for controlling the opening of the bypass valve 12 is provided.

  Here, the low outside air temperature refers to a case where the outside air temperature is lower than the outlet water temperature of the evaporator 6a of the water heat exchanger 6 (outside air temperature <outlet water temperature) in the case of a chiller or refrigerator that uses water on the use side. Say. In the case of an air conditioner that uses air on the use side, it means that the outside air temperature is lower than the temperature of the air blown into the room (that is, the set temperature) (outside air temperature <set temperature).

  In a normal refrigeration cycle apparatus, the opening degree of the expansion valve 5 is controlled in order to control the suction side superheat degree SH within a certain range. Since the expansion valve 5 causes the refrigerant to flow due to the pressure difference between the inlet side and the outlet side, when the condensing pressure decreases as the outside air temperature decreases, the refrigerant flow rate is secured and the suction side superheat degree SH is kept within a certain range. Therefore, the opening degree tends to increase.

  In the conventional refrigeration cycle apparatus that does not include the bypass valve 12, the refrigerant flow rate is insufficient even when the expansion valve 5 is fully opened at a low outside air temperature, so that the suction pressure, that is, the saturation evaporation temperature is lowered, and the COP (coefficient of performance) is lowered. There was a problem to do. The cause of the COP decrease is that the rotation speed of the compressor 2 increases to compensate for an increase in input (electric power) of the compressor 2 due to an increase in the compression ratio and a decrease in cooling capacity due to a decrease in the density of refrigerant sucked by the compressor 2. It is done. As a result, the suction side superheat degree SH becomes excessive. The dashed-dotted line in FIG. 2 (a), (b) has shown the Ph diagram and Th diagram at this time.

  Therefore, in the conventional example shown by the solid line in FIGS. 2A and 2B, the expansion valve 5 is increased by decreasing the rotation speed of the condenser fan 3 and increasing the condensing pressure on the high pressure side at a low outside air temperature. The refrigerant pressure was secured by securing the differential pressure, and the suction side pressure and the suction side superheat degree SH were controlled within a certain range. However, even in this case, there is a problem that the COP is lowered due to an increase in the compression ratio due to the high condensation pressure.

  Therefore, in the first embodiment, the condensing temperature is lowered in accordance with the outside air temperature without increasing the condensing pressure on the high pressure side by decreasing the rotation speed of the condenser fan 3 at the low outside air temperature. The maximum refrigerant flow rate increase control means of the controller 15 is at a low outside air temperature, that is, the suction side superheat degree SH (calculated value) of the compressor 2 is larger than a predetermined value (for example, 3K), and the expansion valve 5 is opened. When the degree is the maximum opening, it is determined that the refrigerant flow rate of the expansion valve 5 is insufficient, and the bypass valve 12 of the maximum refrigerant flow rate increasing means is opened. At the same time, the opening degree of the expansion valve 5 is adjusted so that the suction side superheat degree SH of the compressor 2 is within a predetermined range.

  For this reason, the liquid refrigerant radiated and condensed by the condenser 4 flows through the opened bypass valve 12 and the expansion valve 5, respectively, so that the flow rate of refrigerant flowing to the evaporator 6a of the hydrothermal exchanger 6 is expanded. The maximum refrigerant flow rate that flows when the valve 5 is at the maximum opening degree is increased. Thereby, the suction-side superheat degree SH of the compressor 2 can be adjusted within a predetermined range, and the flow rate of the refrigerant circulating in the refrigeration cycle apparatus 1 can be ensured even at a low outside air temperature. As a result, it is possible to suppress a decrease in the suction side pressure, thereby improving COP.

  On the other hand, when the bypass valve 12 is opened and the low compression operation is performed, the discharge-side superheat degree DSH is greatly reduced due to the low compression. Therefore, the lower the compression ratio, the easier it is to liquefy because the high-temperature and high-pressure gas refrigerant discharged into the high-pressure case, which is a sealed container of the compressor 2, radiates heat in the high-pressure case because the degree of superheat is low. . For this reason, the refrigerant liquefied in the high-pressure case may drop on the refrigerating machine oil stored in the lower bottom of the high-pressure case, and the refrigerating machine oil may be diluted.

  In general, a rotary compressor having a high-pressure case is set with a lower limit value of the discharge side superheat degree DSH, and the discharge side superheat degree DSH is made larger than the lower limit value by largely controlling the suction side superheat degree SH. This is possible on the refrigeration cycle, but as shown in FIG. 2 (a), if the temperature of the return water of the water heat exchanger 6 is the same, it is necessary to greatly reduce the evaporation temperature. Cycle efficiency is reduced (power consumption is increased).

  Therefore, according to the first embodiment, as shown in FIGS. 3A and 3B, in the liquid-gas heat exchanger 20, the suction gas immediately before the accumulator 7 by the high-temperature liquid refrigerant from the condenser 4. By increasing the temperature by heating the suction side, it is possible to increase both the suction side superheat degree SH and the discharge side superheat degree DSH.

  Since the suction side superheat degree SH can be secured by the liquid refrigerant having a temperature higher than the temperature of the return water of the water heat exchanger 6, the evaporation temperature of the evaporator 6a is desired as shown in FIGS. 3 (a) and 3 (b). The value can be maintained. In addition, in FIG. 3A, the broken line is a Ph diagram at the time of low outside air temperature of the refrigeration cycle apparatus 1 according to the first embodiment.

  Further, as shown in FIGS. 4A and 4B, the suction-side superheat degree SH can be ensured by the heat exchanger of the liquid refrigerant and the suction-side gas refrigerant by providing the liquid-gas heat exchanger 20. Therefore, in all the operations of the year including the low compression operation, when the use-side load decreases and the return water temperature decreases, the desired evaporation temperature can be maintained. That is, high-efficiency operation at partial load is possible.

  Further, as shown in FIG. 4 (b), when the flow direction of the water in the water flow path 6b of the water heat exchanger 6 and the flow direction of the refrigerant in the evaporator 6a are parallel flows (parallel flow), Since the temperature difference at the refrigerant outlet becomes small, the performance of the evaporator 6a can be fully exhibited, and high-efficiency operation is possible regardless of outside air conditions.

(Modification of the first embodiment)
FIG. 5 is a configuration diagram of a refrigeration cycle of a refrigeration cycle apparatus 1A according to a modification of the first embodiment. The refrigeration cycle apparatus 1A includes a first on-off valve 31 and a first switch 31 for switching whether to use the liquid-gas heat exchanger 20 of the refrigeration cycle apparatus 1 shown in FIG. 1 according to the operating state of the refrigeration cycle. It is characterized in that two on-off valves 32 are interposed. Further, a condensation temperature sensor 36 is provided between the outlet side of the liquid refrigerant flow path 20 a of the liquid-gas heat exchanger 20 and the expansion valve 5.

  The first on-off valve 31 is interposed in the middle of the inlet-side refrigerant pipe portion 8a that connects the inlet side of the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20 and the outlet side of the evaporator 6a. . The second on-off valve 32 is interposed in the middle of the outlet side refrigerant pipe portion 8b that connects the outlet side of the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20 and the outlet side of the evaporator 6a. . These first and second on-off valves 31 and 32 are connected to the controller 15 via signal lines (not shown) and are controlled to be opened and closed by the controller 15.

  Therefore, when the first on-off valve 31 is fully open and the second on-off valve 32 is fully closed, the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20 is conducted, and the liquid-gas heat exchanger 20 is Inserted into the refrigeration cycle. On the other hand, when the first on-off valve 31 is fully closed and the second on-off valve 32 is fully open, the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20 becomes non-conductive, and the liquid-gas heat exchanger 20 Bypassed.

  In the case of an ultra-low pressure operation in which the temperature of the liquid refrigerant has decreased with a further decrease in the outside air temperature, a phenomenon may occur in which the temperatures of the condensate and the evaporated gas are reversed.

  If the evaporative gas temperature is higher than the condensate temperature and heat is exchanged in the liquid-gas heat exchanger 20, the refrigerant liquefied in the condenser 4 may be two-phased.

  Therefore, the controller 15 compares the condensate temperature detected by the condensing temperature sensor 36 with the evaporating gas temperature detected by the suction temperature sensor 35, and when the evaporating gas temperature is higher than the condensate temperature, The first on-off valve 31 is fully closed and the second on-off valve 32 is fully opened so as to bypass the gas heat exchanger 20.

(Other variations of the first embodiment)
FIG. 6 is a configuration diagram of a refrigeration cycle of a refrigeration cycle apparatus 1B according to another modification of the first embodiment. This refrigeration cycle apparatus 1B is characterized in that the first on-off valve 31 and the second on-off valve 32 of the refrigeration cycle apparatus 1A shown in FIG.

  The four-way valve 33 has four connection ports 33 a to 33 d, the first connection port 33 a is the outlet side of the evaporator 6 a, and the second connection port 33 b is the inlet side of the gas refrigerant flow path 20 b of the liquid-gas heat exchanger 20. The third connection port 33c is connected to the outlet side of the gas refrigerant flow path 20b of the liquid-gas heat exchanger 20, and the fourth connection port 33d is connected to the inlet side of the accumulator 7.

  When the liquid-gas heat exchanger 20 is used, the four-way valve 33 is configured such that the first connection port 33a and the second connection port 33b communicate with each other, and the third connection port 33c and the fourth connection port 33d communicate with each other. It is switched by the controller 15 (solid line in FIG. 6).

  On the other hand, when the liquid-gas heat exchanger 20 is not used (bypassed), the four-way valve 33 communicates with the first connection port 33a and the fourth connection port 33d, and the second connection port 33b and the third connection port 33c. Is switched by the controller 15 (broken line in FIG. 6).

  Then, similarly to the refrigeration cycle apparatus 1A shown in FIG. 5, the controller 15 compares the condensate temperature detected by the condensing temperature sensor 36 with the evaporating gas temperature detected by the suction temperature sensor 35, and the condensate temperature. When the evaporative gas temperature is higher than that, the four-way valve 33 is switched and controlled so as to bypass the liquid-gas heat exchanger 20.

(Second Embodiment)
FIG. 7 is a configuration diagram of the refrigeration cycle of the refrigeration cycle apparatus 1C according to the second embodiment. This refrigeration cycle apparatus 1C replaces the liquid-gas heat exchanger 20 of the refrigeration cycle apparatus 1 shown in FIG. 1 with a gas-gas heat exchanger 30, and uses this gas-gas heat exchanger 30 or not. This is characterized in that a first on-off valve 31 and a second on-off valve 32 for switching according to the operating state of the refrigeration cycle are interposed.

  That is, the gas-gas heat exchanger 30 includes a discharge gas passage 30a through which high-temperature and high-pressure discharge gas discharged from the compressor 2 flows, and a low-temperature and low-pressure suction gas immediately before the accumulator 7 sucked into the suction side of the compressor 2. The high-temperature and high-pressure discharge gas flowing through the discharge gas flow channel 30a and the low-temperature and low-pressure suction gas are configured to be capable of heat exchange.

  That is, the high temperature and high pressure discharge gas is characterized in that the low temperature and low pressure suction gas can be heated.

  The first on-off valve 31 is interposed in the middle of the inlet-side refrigerant piping portion 8a that connects the inlet side of the suction gas passage 30b of the gas-gas heat exchanger 30 and the outlet side of the evaporator 6a. ing. The 2nd on-off valve 32 is interposed in the middle of the exit side refrigerant piping part 8b which connects the exit side of the suction gas flow path 30b of the gas-gas heat exchanger 30, and the exit side of the evaporator 6a. . These first and second on-off valves 31 and 32 are connected to the controller 15 via signal lines (not shown) and are controlled to be opened and closed by the controller 15.

  Therefore, when the first on-off valve 31 is fully open and the second on-off valve 32 is fully closed, the suction gas flow path 30b of the gas-gas heat exchanger 30 is conducted, and the gas-gas heat exchanger 30 is Inserted into the refrigeration cycle. On the other hand, when the first on-off valve 31 is fully closed and the second on-off valve 32 is fully open, the suction gas passage 30b of the gas-gas heat exchanger 30 becomes non-conductive, and the gas-gas heat exchanger 30 Bypassed.

  That is, in the liquid-gas heat exchanger 20 of the refrigeration cycle apparatus 1 according to the first embodiment, the suction temperature of the compressor can be heated only to a temperature lower than the temperature of the liquid refrigerant. In the case of an ultra-low pressure operation in which the temperature is lowered, it is necessary to secure the discharge side superheat degree DSH by lowering the evaporation temperature and securing a large suction side superheat degree SH. As a result, the suction-side pressure decreases to ensure the discharge-side superheat degree DSH, and the efficiency during the low compression operation decreases due to the increase in the compression ratio.

  However, according to the refrigeration cycle apparatus 1C of the second embodiment, the low-temperature and low-pressure suction gas is converted into the high-temperature and high-pressure discharge gas by the gas-gas heat exchanger 30 on the downstream side of the evaporator 6a and immediately before the accumulator 7. Since heating is performed, it is possible to secure a large suction side superheat degree SH for securing a required discharge side superheat degree DSH while maintaining a desired evaporation temperature even during an ultra-low pressure operation.

  Then, the controller 15 determines the saturation temperature and the suction from the discharge side pressure Pd of the compressor 2 detected by the discharge pressure sensor 13 and the suction side pressure Ps of the compressor 2 immediately before the accumulator 7 detected by the suction pressure sensor 14. The side superheat degree SH and the discharge side superheat degree DSH are calculated, and normally the opening degree of the expansion valve 5 is controlled so that the suction side superheat degree SH falls within a predetermined range, and at the same time, the discharge side superheat degree DSH is also monitored.

  If the discharge-side pressure decreases due to a decrease in the outside air temperature, and the suction-side pressure begins to decrease despite the expansion valve 5 being controlled to the maximum opening, the bypass valve 12 is first set to increase the maximum refrigerant flow rate. Control valve opening. The subject of control of the opening degree of the expansion valve 5 remains the suction side superheat degree SH. This suppresses a decrease in suction side pressure, that is, evaporation temperature. Thereafter, when the discharge side superheat degree DSH decreases below a predetermined threshold due to a further decrease in the outside air temperature, the controller 15 fully opens the first on-off valve 31 and fully closes the second on-off valve 32. Then, the control proceeds to the opening degree control of the expansion valve 5 for which the discharge side superheat degree DSH is controlled.

  During this time, the suction side superheat degree SH is monitored by the suction pressure sensor 14 and the suction temperature sensor 35. If the suction side superheat degree SH falls within a predetermined range, the controller 15 controls the first on-off valve. 31 is fully closed, and the second on-off valve 32 is controlled to be fully opened, and the control returns to the normal suction side superheat degree SH.

  As shown in FIGS. 8A and 8B, according to the refrigeration cycle apparatus 1C, the gas-gas heat exchanger 30 causes the low-temperature and low-pressure by the high-temperature and high-pressure discharge gas on the downstream side of the evaporator 6a. Since the suction gas is heated, it is possible to obtain a large suction side superheat degree SH for securing a desired discharge side superheat degree DSH while maintaining a desired evaporation temperature even during an ultra-low pressure compression operation. . In addition, in Fig.8 (a), a broken line is a Ph diagram at the time of the low external temperature of 1 C of refrigeration cycle apparatuses which concern on 2nd Embodiment.

  In the gas-gas heat exchanger 30 except when the ultra-low pressure compression operation is performed, the suction gas is heated by the discharge gas, so that the discharge gas temperature is lowered and the heat radiation performance in the condenser 4 is reduced. In this case, the gas-gas heat exchanger 30 is made non-conductive by the open / close control of the first and second on-off valves 31 and 32, and this gas-gas heat exchange is performed. Since the device 30 is not used by bypass, the efficiency of the refrigeration cycle can be maintained equivalent to that of a normal refrigeration cycle.

  That is, according to the refrigeration cycle apparatus 1C according to the second embodiment, it is possible to expand the outside air temperature range in which the low-pressure compression operation can be performed more efficiently than the refrigeration cycle apparatus 1 according to the first embodiment. At the same time, it is possible to suppress a decrease in efficiency by bypassing the gas-gas heat exchanger 30 and not using it during the year-round cooling operation including partial load.

  In the above-described embodiment, the case where the bypass valve 12 is controlled to open when the suction side superheat degree SH is excessive and the opening degree of the expansion valve 5 is the maximum opening degree has been described, but the present invention is not limited to this. For example, the bypass valve 12 may be controlled to open when the temperature of the evaporator 6a (that is, the evaporation temperature) falls below a predetermined value.

  Further, instead of the bypass valve 12, an expansion valve with a different capacity of the expansion valve 5 may be provided. For example, if an expansion valve having a smaller capacity is connected to the expansion valve 5 in parallel, fine refrigerant flow control is possible, and if an expansion valve having a larger capacity than the expansion valve 5 is connected in parallel, the refrigerant flow rate can be controlled. The range of control can be increased. Further, instead of the bypass valve 12, a flow rate adjustment valve capable of adjusting the flow rate may be provided.

  In the above embodiment, the case where the present invention is applied to a cooling chiller has been described. However, the present invention is not limited to this. For example, a heat pump chiller or a water heat exchanger that switches between cooling and heating using a four-way valve. Instead of 6, a refrigeration cycle apparatus provided with an air heat exchanger may be used.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of this invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the scope of the present invention. These embodiments and modifications thereof are included in the scope and gist of the present invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C ... Refrigeration cycle apparatus, 2 ... Compressor, 4 ... Condenser, 5 ... Expansion valve, 6 ... Hydrothermal exchanger, 6a ... Evaporator, 11 ... Bypass pipe, 12 ... Bypass valve, 13 DESCRIPTION OF SYMBOLS ... Discharge pressure sensor, 14 ... Suction pressure sensor, 15 ... Controller, 20 ... Liquid-gas heat exchanger, 30 ... Gas-gas heat exchanger, 31 ... 1st on-off valve, 32 ... 2nd on-off valve, 33 ... Four-way valve, 34 ... Discharge temperature sensor, 35 ... Suction temperature sensor, 36 ... Condensation temperature sensor.

Claims (4)

In a refrigeration cycle apparatus in which a compressor, a condenser, expansion means, and an evaporator are sequentially connected by a refrigerant pipe,
A refrigeration cycle apparatus comprising means for increasing the maximum refrigerant flow rate of the expansion means at a low outside air temperature. The maximum refrigerant flow rate increasing means is constituted by a bypass path that connects the refrigerant inlet side and the outlet side of the expansion means, and an on-off valve or an expansion valve interposed in the bypass path. The refrigeration cycle apparatus according to claim 1. 3. The refrigeration cycle apparatus according to claim 1, further comprising liquid-gas heat exchange means for exchanging heat between the liquid refrigerant from the condenser and the suction gas refrigerant of the compressor. The refrigeration cycle apparatus according to claim 1 or 2, further comprising gas-gas heat exchange means for exchanging heat between the suction gas refrigerant and the discharge gas refrigerant of the compressor.

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