JP2008241065A - Refrigerating device and oil returning method of refrigerating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently return a refrigerating machine oil accumulated from evaporators 34, 37 to a compressor 30, to the compressor 30 in a refrigerating device 10 using the weak phase-soluble refrigerating machine oil for lubrication in the compressor 30. <P>SOLUTION: In this refrigerating device using the weak phase-soluble refrigerating machine oil for lubrication in the compressor 30, a control means 50 is disposed to perform oil-returning control for controlling an operating state of a refrigerating cycle so that a temperature of the refrigerant at outlets of the evaporators 34, 37 reach an upper limit corresponding temperature corresponding to a time when the quantity of refrigerant dissolved in the refrigerating machine oil reaches an upper limit value under a pressure of the refrigerant at the outlets of the evaporators 34, 37 to return the refrigerating machine oil accumulated from the evaporators 34, 37 to the compressor 30, to the compressor 30 with the refrigerant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a refrigeration apparatus that performs control for returning refrigeration oil accumulated between an evaporator and a compressor to the compressor, and an oil return method in the refrigeration apparatus.

  Conventionally, a refrigeration apparatus that performs lubrication of a compressor using refrigeration oil is known. In this type of refrigeration apparatus, the refrigeration oil discharged together with the refrigerant from the compressor is dissolved in the liquid refrigerant, flows through the refrigerant circuit, and flows into the evaporator. In the evaporator, the liquid refrigerant evaporates but the refrigerating machine oil does not evaporate, so that the refrigerating machine oil is separated from the refrigerant. The refrigerating machine oil separated from the refrigerant accumulates between the evaporator and the evaporator and the compressor.

  In this type of refrigerating apparatus, if the amount of refrigerating machine oil accumulated between the evaporator and the compressor increases, the refrigerating machine oil in the compressor may decrease, resulting in poor lubrication. Therefore, conventionally, a refrigeration apparatus that performs control for returning refrigeration oil accumulated between the evaporator and the compressor to the compressor is known. This type of refrigeration apparatus is disclosed in Patent Document 1.

Specifically, the refrigeration apparatus of Patent Document 1 is configured to detect the amount of oil in the compressor and perform an oil return operation (oil return operation). This refrigeration apparatus is controlled so that the refrigerant superheat degree at the evaporator outlet is, for example, 10 ° C. during normal operation, while the refrigerant superheat degree at the evaporator outlet is 0 ° C. during oil return operation. It is controlled to become. In this oil return operation, the amount of liquid refrigerant increases as the degree of superheat of the refrigerant decreases, so the amount of liquid refrigerant dissolved in the refrigeration oil increases and the kinematic viscosity of the refrigeration oil decreases. Then, the refrigerating machine oil having a reduced kinematic viscosity is washed away by the refrigerant and returns to the compressor (30).
JP 2002-257427 A

  By the way, the oil return operation of the conventional refrigeration apparatus can efficiently return the refrigeration oil to the compressor in the refrigeration apparatus using the compatible refrigeration oil having the property that the liquid refrigerant easily dissolves, but the property that the liquid refrigerant hardly dissolves. In the refrigeration apparatus using the weakly compatible refrigerating machine oil, the refrigerating machine oil cannot be efficiently returned to the compressor.

  Specifically, unlike the compatible refrigerator oil, the weakly compatible refrigerator oil has an upper limit in the amount of liquid refrigerant dissolved in the refrigerator oil per unit amount. For this reason, as the degree of superheat (temperature) of the refrigerant at the outlet of the evaporator decreases and the amount of liquid refrigerant increases, the amount of liquid refrigerant that dissolves in the refrigerating machine oil increases and the kinematic viscosity of the refrigerating machine oil decreases. However, when the amount of the liquid refrigerant that dissolves in the refrigerating machine oil reaches the upper limit, the kinematic viscosity of the refrigerating machine oil does not decrease even if the superheat degree of the refrigerant is further reduced. On the other hand, as the degree of superheat of the refrigerant decreases, the amount of gas refrigerant decreases and the flow rate of the gas refrigerant decreases, so the shearing force acting on the refrigeration machine oil decreases.

  Therefore, in the conventional oil return method that adjusts the superheat degree (temperature) of the refrigerant only in consideration of lowering the kinematic viscosity of the refrigerating machine oil, the superheat degree (temperature) of the refrigerant at the outlet of the evaporator determines the dynamics of the refrigerating machine oil. There is a possibility that the value may be adjusted to a value smaller than the value of the superheat degree of the refrigerant at which the viscosity does not decrease. In such a case, since the flow rate of the gas refrigerant is reduced due to a decrease in the degree of superheat of the refrigerant, the shearing force acting on the refrigeration oil is reduced, and the refrigeration oil is difficult to return.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a refrigerating machine oil that accumulates between an evaporator and a compressor in a refrigerating apparatus that uses a weakly compatible refrigerating machine oil for lubrication in a compressor. Is to be efficiently returned to the compressor.

  The first invention includes a refrigerant circuit (20) for performing a refrigeration cycle in which the refrigerant compressed by the compressor (30) is radiated by the radiator (34, 37) and evaporated by the evaporator (34, 37). The refrigeration apparatus (10) that uses weakly compatible refrigerating machine oil for lubrication in the compressor (30) is an object. The refrigeration apparatus (10) includes the evaporator in order to return the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) to the compressor (30) together with the refrigerant. The temperature of the refrigerant at the outlet of (34, 37) reaches an upper limit corresponding temperature corresponding to the temperature at which the amount of refrigerant dissolved in the refrigeration oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37). Control means (50) for performing oil return control for controlling the operating state of the refrigeration cycle is provided.

  In the first invention, oil return control is performed to return the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) to the compressor (30) together with the refrigerant. In the oil return control, the operating state of the refrigeration cycle is controlled so that the temperature of the refrigerant at the outlet of the evaporator (34, 37) becomes the upper limit corresponding temperature. The upper limit temperature corresponds to the temperature at which the amount of refrigerant that dissolves in the refrigeration oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37), that is, the operation of the refrigeration oil even if the refrigerant temperature is further reduced. It corresponds to the temperature at which the viscosity does not decrease. That is, in the oil return control of the first invention, the refrigerant temperature at the outlet of the evaporator (34, 37) further reduces the refrigerant temperature at the refrigerant pressure at the outlet of the evaporator (34, 37). However, the operating state of the refrigeration cycle is controlled so that the upper limit temperature corresponding to the temperature at which the kinematic viscosity of the refrigeration oil does not decrease.

  According to a second aspect of the present invention, in the first aspect of the invention, the control means includes a superheat degree adjusting means (12, 14, 36) for adjusting the superheat degree of the refrigerant at the outlet of the evaporator (34, 37). (50), in the oil return control, the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is such that the temperature of the refrigerant at the outlet of the evaporator (34, 37) becomes the upper limit corresponding temperature. The superheat degree adjusting means (12, 14, 36) is controlled so as to reach the target value of the superheat degree determined.

  In the second aspect of the invention, the target value of the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is set to a value such that the temperature of the refrigerant at the outlet of the evaporator (34, 37) becomes the above upper limit corresponding temperature. It has been. When the control means (50) controls the superheat degree adjusting means (12, 14, 36) so that the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) becomes this target value, the evaporator (34, 37) The temperature of the refrigerant at the outlet is adjusted to the upper limit temperature.

  According to a third invention, in the second invention, the evaporation side expansion valve (36) for adjusting the refrigerant flow rate of the evaporator (34, 37) is provided with the superheat degree adjusting means (12, 14, 36). The control means (50) controls the opening of the evaporation side expansion valve (36) in the oil return control.

  In 3rd invention, a control means (50) adjusts the opening degree of the evaporation side expansion valve (36) as a superheat degree adjustment means (12,14,36). The opening degree of the evaporation side expansion valve (36) is adjusted so that the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) becomes the target value of the superheat degree.

  According to a fourth aspect of the present invention, in the second or third aspect, the evaporation side fan (12, 14) for sending air to the evaporator (34, 37) includes the superheat degree adjusting means (12, 14, 36), and the control means (50) controls the air flow rate of the evaporation side fans (12, 14) in the oil return control.

  In 4th invention, a control means (50) adjusts the ventilation volume of the evaporation side fan (12,14) as a superheat degree adjustment means (12,14,36). The amount of air blown from the evaporation side fans (12, 14) is adjusted so that the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) becomes the target value of the superheat degree.

  In a fifth aspect of the present invention based on any one of the second to fourth aspects, the refrigerant circuit (20) uses carbon dioxide as the refrigerant and polyalkylene glycol as the refrigerating machine oil. The target value is a value in the range of 3 ° C. or more and 5 ° C. or less.

  In the fifth invention, carbon dioxide is used as the refrigerant, and polyalkylene glycol (PAG) is used as the refrigerating machine oil for lubrication in the compressor (30). Polyalkylene glycol is a refrigerating machine oil with low compatibility with carbon dioxide. Here, the amount of carbon dioxide refrigerant dissolved in the polyalkylene glycol reaches the upper limit when the temperature of the refrigerant is approximately −37 ° C. as shown in FIG. 2 under a pressure of 1 MPa. In this state, the degree of superheat of the refrigerant is 5 ° C. Further, when the pressure is 7 MPa, the temperature of the refrigerant is approximately 30 ° C. In this state, the degree of superheat of the refrigerant is 3 ° C. In the fifth aspect of the invention, assuming that the refrigerant pressure at the outlet of the evaporator (34, 37) when carbon dioxide is used as the refrigerant is in the range of 1 MPa to 7 MPa, the kinematic viscosity of the refrigerating machine oil is The target value corresponding to the value of the superheat degree of the refrigerant that does not decrease is set to a value in the range of 3 ° C. or more and 5 ° C. or less.

  According to a sixth invention, in any one of the first to fifth inventions, the normal operation for adjusting the temperature of the target space, and from the evaporator (34, 37) to the compressor (30). An oil return operation for forcibly returning the refrigeration oil accumulated therebetween to the compressor (30) is selectively executable, and the control means (50) is configured to perform the oil return operation in the oil return operation. Take control.

  In the sixth aspect of the invention, the refrigeration apparatus is configured to selectively execute normal operation and oil return operation. Then, oil return control is performed in the oil return operation. In oil return operation, the upper limit temperature corresponding to the temperature at which the refrigerant viscosity at the outlet of the evaporator (34,37) does not decrease the kinematic viscosity of the refrigerating machine oil at the refrigerant pressure at the outlet of the evaporator (34,37). Thus, the operating state of the refrigeration cycle is controlled.

  In a seventh aspect based on the sixth aspect, the control means (50) performs the oil return control in the oil return operation and sets the operating capacity of the compressor (30) to start the oil return operation. Increase than before.

  In the seventh aspect of the invention, oil return control is performed in the oil return operation, and the operating capacity of the compressor (30) is increased from immediately before the start of the oil return operation. For this reason, compared to immediately before the start of the oil return operation, the amount of refrigerant flowing through the refrigerant circuit (20) increases and the flow rate of the refrigerant increases, so that the evaporator (34, 37) changes to the compressor (30). The shearing force that acts on the refrigeration oil that accumulates in the meantime increases.

  An eighth invention comprises the evaporation side pressure detection means (52) for detecting the pressure of the refrigerant at the outlet of the evaporator (34, 37) in any one of the second to fourth inventions, The control means (50) performs the oil return control in a normal operation for adjusting the temperature of the target space, and uses the detected pressure of the evaporation side pressure detection means (52) in the oil return control during the normal operation. Set the target value.

  In the eighth invention, oil return control is performed in the normal operation for adjusting the temperature of the target space. In this oil return control during normal operation, the target value of the degree of superheat determined so that the temperature of the refrigerant at the outlet of the evaporator (34, 37) becomes the upper limit corresponding temperature is the evaporation side pressure detection means during normal operation. It is set according to the refrigerant pressure at the outlet of the evaporator (34, 37) detected by (52).

  The ninth invention comprises a refrigerant circuit (20) for performing a refrigeration cycle in which the refrigerant compressed by the compressor (30) is radiated by the radiator (34, 37) and evaporated by the evaporator (34, 37), In the refrigeration apparatus (10) that uses weakly compatible refrigeration oil for lubrication in the compressor (30), the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) is combined with the refrigerant. An oil return method for a refrigeration apparatus for returning to the compressor (30) is an object. In this oil return method, the refrigerant temperature at the outlet of the evaporator (34, 37) is such that the amount of refrigerant dissolved in the refrigeration oil at the refrigerant pressure at the outlet of the evaporator (34, 37) reaches the upper limit. An oil return process is provided for controlling the operating state of the refrigeration cycle so that the temperature reaches an upper limit temperature corresponding to the temperature when the temperature reaches.

  In the ninth aspect of the invention, in the oil return stroke, the operating state of the refrigeration cycle is controlled so that the state of the refrigerant at the outlet of the evaporator (34, 37) becomes the target state. The upper limit temperature corresponds to the temperature at which the amount of refrigerant that dissolves in the refrigeration oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37), that is, the operation of the refrigeration oil even if the refrigerant temperature is further reduced. It corresponds to the temperature at which the viscosity does not decrease. That is, in the oil return method according to the ninth aspect of the invention, the refrigerant temperature at the outlet of the evaporator (34, 37) further reduces the refrigerant temperature at the refrigerant pressure at the outlet of the evaporator (34, 37). However, the operating state of the refrigeration cycle is controlled so that the upper limit temperature corresponding to the temperature at which the kinematic viscosity of the refrigeration oil does not decrease.

  In the present invention, in the oil return control or the oil return process, the kinematic viscosity of the refrigerating machine oil decreases at the refrigerant temperature at the outlet of the evaporator (34, 37) and the refrigerant pressure at the outlet of the evaporator (34, 37). The operating state of the refrigeration cycle is controlled so that the upper limit corresponding temperature corresponding to the temperature that disappears is reached. Therefore, unlike the conventional refrigeration apparatus, there is no possibility that the refrigerant temperature at the outlet of the evaporator (34, 37) is adjusted to a value smaller than the refrigerant temperature value at which the kinematic viscosity of the refrigeration oil does not decrease. The refrigeration oil does not easily return to the compressor (30) due to a decrease in the flow rate of the gas refrigerant. In the oil return control or the oil return stroke, the flow rate of the gas refrigerant increases to some extent in the state where the kinematic viscosity of the refrigerating machine oil is the smallest or close to this state. Therefore, since sufficient shearing force acts on the refrigeration oil in a state in which the kinematic viscosity is lowered, the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) is efficiently stored in the compressor ( 30).

  In the fifth aspect of the invention, assuming that the refrigerant pressure at the outlet of the evaporator (34, 37) when carbon dioxide is used as the refrigerant is in the range of 1 MPa to 7 MPa, The target value corresponding to the value of the superheat degree of the refrigerant at which the viscosity does not decrease is set to a value in the range of 3 ° C. to 5 ° C. Here, when the refrigerant and the refrigerating machine oil are combined in the fifth invention, in the conventional oil return operation in which the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) is adjusted to 0 ° C., the evaporator The superheat degree of the refrigerant at the outlet of (34, 37) is smaller than the value of the superheat degree of the refrigerant at which the kinematic viscosity of the refrigerating machine oil does not decrease. The gas at the outlet of the evaporator (34, 37) is compared to a state where the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) becomes a value of the superheat degree of the refrigerant at which the kinematic viscosity of the refrigeration oil does not decrease. The flow rate of the refrigerant is reduced. Therefore, in the conventional oil return operation, the refrigerating machine oil accumulated between the evaporator (34, 37) and the compressor (30) cannot be efficiently returned to the compressor (30). On the other hand, in the fifth invention, the kinematic viscosity of the refrigerating machine oil is about the same as in the conventional case, but the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) is adjusted to a value larger than the conventional one. Accordingly, the flow rate of the gas refrigerant at the outlet of the evaporator (34, 37) increases. Therefore, more refrigeration oil can be returned to the compressor (30) than in the case of the conventional oil return operation.

  In the seventh aspect of the invention, the operating capacity of the compressor (30) in the oil return operation is increased from immediately before the start of the oil return operation, so that the evaporator (34, 37) reaches the compressor (30). The shearing force acting on the refrigerating machine oil that accumulates until is increased. Therefore, since the refrigerating machine oil accumulated between the evaporator (34, 37) and the compressor (30) is more easily returned to the compressor (30), more refrigerating machine oil is returned to the compressor (30). be able to.

  In the eighth aspect of the invention, the target value of the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) is set according to the pressure of the refrigerant at the outlet of the evaporator (34, 37) during normal operation. Is done. Here, the upper limit value of the amount of the liquid refrigerant dissolved in the refrigerating machine oil changes according to the temperature and pressure of the refrigerant. Therefore, the upper limit value changes depending on the change in refrigerant pressure at the outlet of the evaporator (34, 37) during normal operation. In the eighth aspect of the invention, the target value of the superheat degree is set reflecting the refrigerant pressure at the outlet of the evaporator (34, 37) during normal operation, so the evaporator (34, 37) at that time It becomes a value corresponding to the upper limit value of the refrigerant pressure at the outlet. Accordingly, during normal operation, the temperature of the refrigerant at the outlet of the evaporator (34, 37) can be adjusted to a temperature at which the kinematic viscosity of the refrigerating machine oil does not decrease or close to that temperature. Refrigerating machine oil accumulated between (34, 37) and the compressor (30) can be returned to the compressor (30) more efficiently.

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

  This embodiment is an air conditioner (10) configured by a refrigeration apparatus (10) according to the present invention. The air conditioner (10) of this embodiment is provided with the outdoor unit (11) and the indoor unit (13), as shown in FIG. A plurality of indoor units (13) may be provided.

  The air conditioner (10) includes a refrigerant circuit (20) filled with a refrigerant. Carbon dioxide refrigerant is used as the refrigerant. The refrigerant circuit (20) includes an outdoor circuit (21) accommodated in the outdoor unit (11) and an indoor circuit (22) accommodated in the indoor unit (13). The outdoor circuit (21) and the indoor circuit (22) are connected by a liquid side communication pipe (23) and a gas side communication pipe (24).

《Outdoor circuit configuration》
The outdoor circuit (21) is provided with a compressor (30), a four-way switching valve (33), an outdoor heat exchanger (34) that is a heat source side heat exchanger, and an expansion valve (36). At one end of the outdoor circuit (21), a liquid side shut-off valve (25) to which the liquid side communication pipe (23) is connected is provided. The other end of the outdoor circuit (21) is provided with a gas side shut-off valve (26) to which the gas side communication pipe (24) is connected.

  The compressor (30) is configured as a variable-pressure high-pressure dome type compressor. The compressor (30) can change the operating capacity in a plurality of stages by changing the output frequency of the inverter and changing the rotational speed of the electric motor. Refrigerating machine oil used for lubricating the sliding portion is collected at the bottom of the casing of the compressor (30). Polyalkylene glycol is used for refrigerating machine oil. Polyalkylene glycol is a weakly compatible refrigerating machine oil that is difficult to dissolve carbon dioxide refrigerant.

  The discharge side of the compressor (30) is connected to the first port (P1) of the four-way switching valve (33) via the discharge pipe (42). The suction side of the compressor (30) is connected to the third port (P3) of the four-way switching valve (33) via the suction pipe (41).

  The outdoor heat exchanger (34) is configured as a cross fin type fin-and-tube heat exchanger. An outdoor fan (12) is provided in the vicinity of the outdoor heat exchanger (34). In the outdoor heat exchanger (34), heat is exchanged between the outdoor air sent by the outdoor fan (12) and the circulating refrigerant. One end of the outdoor heat exchanger (34) is connected to the fourth port (P4) of the four-way switching valve (33). The other end of the outdoor heat exchanger (34) is connected to the liquid side shut-off valve (25) via the liquid pipe (43). The liquid pipe (43) is provided with a variable opening expansion valve (36) constituted by an electronic expansion valve. The second port (P2) of the four-way switching valve (33) is connected to the gas side shut-off valve (26).

  The four-way selector valve (33) is in a first state in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other (FIG. 1). And a second state (FIG. 1) in which the first port (P1) and the fourth port (P4) communicate with each other and the second port (P2) and the third port (P3) communicate with each other. The state indicated by a broken line) can be switched.

  The outdoor circuit (21) is provided with one set of temperature sensor (45) and pressure sensor (46) on one end side and the other end side of the compressor (30). Specifically, the suction pipe (41) is provided with a pair of suction temperature sensors (45a) and a suction pressure sensor (46a). The discharge pipe (42) is provided with a pair of discharge temperature sensors (45b) and a discharge pressure sensor (46b). An outdoor liquid temperature sensor (45e) is provided on the liquid side of the outdoor heat exchanger (34), and an outdoor gas temperature sensor (45f) is provided on the gas side of the outdoor heat exchanger (34). In addition, an outdoor temperature sensor (18) is provided in the vicinity of the outdoor fan (12).

《Indoor circuit configuration》
The indoor circuit (22) is provided with an indoor heat exchanger (37) which is a use side heat exchanger. The indoor heat exchanger (37) is configured as a cross-fin type fin-and-tube heat exchanger. An indoor fan (14) is provided in the vicinity of the indoor heat exchanger (37). In the indoor heat exchanger (37), heat is exchanged between the indoor air sent by the indoor fan (14) and the circulating refrigerant.

  The indoor circuit (22) is provided with temperature sensors (45) on one end side and the other end side of the indoor heat exchanger (37), respectively. Specifically, an indoor liquid temperature sensor (45c) is provided between the liquid side end of the indoor circuit (22) and the indoor heat exchanger (37). An indoor gas temperature sensor (45d) is provided between the indoor heat exchanger (37) and the gas side end of the indoor circuit (22). An indoor temperature sensor (19) is provided in the vicinity of the indoor fan (14).

<Control part>
The refrigeration apparatus (10) can selectively execute a normal operation and an oil return operation. The normal operation is an operation for adjusting the temperature of the indoor space that is the target space. As normal operation, heating operation and cooling operation can be performed. The oil return operation is an operation to forcibly return the refrigeration oil accumulated between the heat exchanger (34, 37), which is an evaporator, during normal operation to the compressor (30) and return it to the compressor (30). is there.

  The refrigeration apparatus (10) is provided with a control unit (50) for controlling normal operation and oil return operation. The control unit (50) constitutes a control means, and includes an operation capacity control unit (47), an expansion valve control unit (48), and an oil return control unit (51).

  The operating capacity control unit (47) is configured to control the operating capacity of the compressor (30). Specifically, the operating capacity control unit (47) includes an initial value of a high pressure target value, which is a target value of the refrigerant pressure discharged from the compressor (30) during the heating operation, and the compressor (30) during the cooling operation. The initial value of the low pressure target value, which is the target value of the pressure of the suction refrigerant, is set. The operating capacity control unit (47) is configured such that the detected value of the suction pressure sensor (46a) becomes the low pressure target value during the cooling operation so that the detected value of the discharge pressure sensor (46b) becomes the high pressure target value during the heating operation. The operating capacity of the compressor (30) is controlled so that

  The expansion valve control unit (48) is configured to control the opening degree of the expansion valve (36) constituting the superheat degree adjusting means. Specifically, an initial value (for example, 10 ° C.) of a target superheat degree during heating operation and an initial value (for example, 10 ° C.) of a target superheat degree during cooling operation are set in the expansion valve control unit (48). Has been. The expansion valve control unit (48) is configured to start from the indoor heat exchanger (37) during the cooling operation so that the superheat degree of the refrigerant flowing out of the outdoor heat exchanger (34) becomes the target superheat degree during the heating operation. The opening degree of the expansion valve (36) is adjusted so that the superheat degree of the refrigerant that has flowed out becomes the target superheat degree.

  During the cooling operation, the expansion valve control unit (48) determines the absolute value of the difference between the detected value of the indoor liquid temperature sensor (45c) and the detected value of the indoor gas temperature sensor (45d) as the indoor heat exchanger (37 ) Is detected as the degree of superheat of the refrigerant that has flowed out. During heating operation, the absolute value of the difference between the detected value of the outdoor liquid temperature sensor (45e) and the detected value of the outdoor gas temperature sensor (45f) is detected as the degree of superheat of the refrigerant flowing out of the outdoor heat exchanger (37). .

  In the cooling operation, the expansion valve control unit (48) expands the opening of the expansion valve (36) when the absolute value of the difference is larger than the target superheat degree, and the absolute value of the difference is larger than the target superheat degree. Is smaller, the opening of the expansion valve (36) is reduced. On the other hand, in the heating operation, the expansion valve control unit (48) expands the opening of the expansion valve (36) when the absolute value of the difference is larger than the target superheat degree, and the absolute value of the difference becomes the target overheat. If it is smaller than the degree, the opening of the expansion valve (36) is reduced.

  The expansion valve control unit (48) has a target value for oil return (4 ° C.) as a target value for the degree of superheat of the refrigerant at the outlet of the heat exchanger (34, 37) serving as an evaporator during the oil return operation. Is set. During the oil return operation, the expansion valve control unit (48) controls the expansion valve (36) so that the superheat degree of the refrigerant at the outlet of the heat exchanger (34, 37) serving as an evaporator becomes the oil return target value. Adjust the opening. The outdoor heat exchanger (34) becomes an evaporator as it is when the oil return operation is performed during the heating operation, and the indoor heat exchanger (37) remains as it is when the oil return operation is performed during the cooling operation. It becomes an evaporator.

  Here, the target value for oil return (4 ° C.) is obtained when the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) is adjusted to the target value for oil return. The refrigerant temperature is determined to be an upper limit temperature corresponding to the temperature at which the amount of refrigerant dissolved in the refrigerating machine oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37).

  Specifically, in the refrigeration apparatus using carbon dioxide as the refrigerant, the low pressure of the refrigeration cycle, that is, the pressure of the refrigerant at the outlet of the evaporator (34, 37) is in the range of 1 MPa to 7 MPa. Under a pressure of 1 MPa, for example, as shown in FIG. 2, when the temperature of the refrigerant is approximately −37 ° C., the amount of carbon dioxide refrigerant dissolved in the polyalkylene glycol reaches the upper limit. The concentration of the carbon dioxide refrigerant when reaching the upper limit is 60%. The superheat degree of the refrigerant in this state is 5 ° C. Therefore, the degree of superheating of the refrigerant becomes 4 ° C. when the temperature of the refrigerant becomes approximately −38 ° C. That is, when the refrigerant superheat degree at the outlet of the evaporator (34, 37) is adjusted to 4 ° C. with the refrigerant pressure at the outlet of the evaporator (34, 37) being 1 MPa, the temperature of the refrigerant is increased. It will be approximately -38 ° C. When the pressure is 1 MPa, this −38 ° C. becomes the upper limit temperature corresponding to the temperature (−37 ° C.) when the amount of the refrigerant dissolved in the refrigerating machine oil reaches the upper limit.

  In addition, when the pressure is, for example, 7 MPa, when the refrigerant temperature is approximately 30 ° C., the amount of carbon dioxide refrigerant dissolved in the polyalkylene glycol reaches the upper limit. The superheat degree of the refrigerant in this state is 3 ° C. The degree of superheat of the refrigerant becomes 4 ° C. when the temperature of the refrigerant becomes approximately 31 ° C. That is, when the refrigerant superheat degree at the outlet of the evaporator (34, 37) is adjusted to 4 ° C. in a state where the refrigerant pressure at the outlet of the evaporator (34, 37) is 7 MPa, the temperature of the refrigerant is It will be about 31 ° C. When the pressure is 7 MPa, this 31 ° C. becomes the upper limit temperature corresponding to the temperature (30 ° C.) when the amount of the refrigerant dissolved in the refrigerating machine oil reaches the upper limit.

  Similarly, when the pressure of the refrigerant at the outlet of the evaporator (34, 37) becomes a value other than 1 MPa and 7 MPa in the range of 1 MPa to 7 MPa, the refrigerant at the outlet of the evaporator (34, 37) is also the same. The temperature at which the amount of refrigerant dissolved in the refrigerating machine oil reaches the upper limit is determined from the point on the line where the concentration of carbon dioxide refrigerant in FIG. The temperature at which the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) reaches 4 ° C. is determined as the upper limit temperature corresponding to that temperature.

  The oil return control unit (51) can execute oil return control for returning the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) to the compressor (30) together with the refrigerant. It is configured. The oil return control unit (51) of this embodiment performs oil return control in the oil return operation.

  Specifically, the oil return control unit (51) is configured to determine the execution of the oil return operation when, for example, the accumulated operation time from the previous oil return operation reaches a predetermined time. When the oil return control unit (51) determines the execution of the oil return operation, the oil return control unit (51) instructs the expansion valve control unit (48) to change the target superheat degree to the oil return target value as the oil return control. It is configured.

  In addition, the oil return control unit (51) controls the operation capacity control unit (47) so that the operation capacity of the compressor (30) increases during the oil return operation as well as immediately before the oil return operation. A command is issued to change the low pressure target value or the high pressure target value. When shifting to the oil return operation during the cooling operation, the oil return control unit (51) issues a command to the operation capacity control unit (47) to change the low pressure target value to a value smaller than the initial value. When shifting to the oil return operation during the heating operation, the operation capacity control unit (47) is instructed to change the high pressure target value to a value larger than the initial value.

-Air conditioner operation-
The operation of the air conditioner (10) of this embodiment will be described. In the air conditioner (10), the cooling operation and the heating operation are switched by the four-way switching valve (33).

<Heating operation>
In the heating operation, the four-way switching valve (33) is set to the first state. When the compressor (30) is operated in this state, a vapor compression refrigeration cycle in which the outdoor heat exchanger (34) serves as an evaporator and the indoor heat exchanger (37) serves as a radiator in the refrigerant circuit (20). Done.

  Specifically, the refrigerant having a pressure higher than the critical pressure of carbon dioxide discharged from the compressor (30) exchanges heat with indoor air in the indoor heat exchanger (37). In this heat exchange, the refrigerant dissipates heat to the room air and is cooled. The refrigerant cooled by the indoor heat exchanger (37) is depressurized when passing through the expansion valve (36), and thereafter evaporates by exchanging heat with outdoor air in the outdoor heat exchanger (34). The refrigerant evaporated in the outdoor heat exchanger (34) is sucked into the compressor (30) and compressed.

<Cooling operation>
In the cooling operation, the four-way switching valve (33) is set to the second state. When the compressor (30) is operated in this state, in the refrigerant circuit (20), the outdoor heat exchanger (34) becomes a radiator and the indoor heat exchanger (37) becomes an evaporator (34, 37). A vapor compression refrigeration cycle is performed.

  Specifically, the refrigerant having a pressure higher than the critical pressure of carbon dioxide discharged from the compressor (30) exchanges heat with outdoor air in the outdoor heat exchanger (34). In this heat exchange, the refrigerant dissipates heat to the outdoor air and is cooled. The refrigerant cooled in the outdoor heat exchanger (34) is depressurized when passing through the expansion valve (36), and then evaporates by exchanging heat with indoor air in the indoor heat exchanger (37). The refrigerant evaporated in the indoor heat exchanger (37) is sucked into the compressor (30) and compressed.

-Control unit operation-
Of the operations of the control unit (50), the operation during the oil return operation will be described. Hereinafter, the oil return operation in the case of shifting to the oil return operation during the cooling operation will be described.

  When the oil return control unit (51) determines, for example, that the accumulated operation time from the previous oil return operation has reached a predetermined time and the execution of the oil return operation is performed, a capacity increasing process is performed. In the capacity increasing process, the oil return control unit (51) instructs the operation capacity control unit (47) to decrease the low pressure target value. When receiving the command from the oil return control unit (51), the operating capacity control unit (47) changes the low pressure target value to a value smaller than the initial value. When the low pressure target value is changed, the operating capacity of the compressor (30) is increased.

  In the oil return operation, the oil return process is performed simultaneously with the capacity increasing process. In the oil return stroke, the oil return control unit (51) instructs the expansion valve control unit (48) to change the target superheat degree to the oil return target value (4 ° C.). When receiving the command from the oil return control unit (51), the expansion valve control unit (48) changes the target superheat degree to the oil return target value (4 ° C.). When the target superheat degree is changed to the oil return target value, the opening degree of the expansion valve (36) is adjusted so that the superheat degree of the refrigerant at the outlet of the indoor heat exchanger (37) becomes the oil return target value. The When the degree of superheat of the refrigerant at the outlet of the indoor heat exchanger (37) is adjusted to the oil return target value, the temperature of the refrigerant at the outlet of the indoor heat exchanger (37) becomes the above-mentioned upper limit temperature.

  This upper limit corresponding temperature is a temperature corresponding to a temperature at which the amount of the refrigerant dissolved in the refrigerating machine oil reaches the upper limit value, that is, a temperature at which the kinematic viscosity of the refrigerating machine oil does not decrease even if the refrigerant temperature is further reduced. For this reason, in the oil return operation, the temperature of the refrigerant at the outlet of the indoor heat exchanger (37) becomes a temperature at which the kinematic viscosity of the refrigerating machine oil reaches or reaches a minimum value.

  The oil return operation is performed for a predetermined time. When the oil return operation is completed, the control unit (50) restarts the cooling operation.

-Effect of the embodiment-
In the present embodiment, in the oil return operation, the temperature of the refrigerant at the outlet of the evaporator (34, 37) becomes a temperature at which the kinematic viscosity of the refrigerating machine oil does not decrease due to the pressure of the refrigerant at the outlet of the evaporator (34, 37). The degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is adjusted so that the corresponding upper limit temperature is reached. For this reason, like the conventional refrigeration apparatus, the refrigerant superheat degree at the outlet of the evaporator (34, 37) may be adjusted to a value smaller than the refrigerant superheat value at which the kinematic viscosity of the refrigerating machine oil does not decrease. Therefore, the refrigeration oil does not easily return to the compressor (30) due to a decrease in the flow rate of the gas refrigerant. In the oil return operation, the flow rate of the gas refrigerant is increased to some extent in a state where the kinematic viscosity of the refrigerating machine oil is the smallest or close to this state. Therefore, since sufficient shearing force acts on the refrigeration oil in a state in which the kinematic viscosity is lowered, the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) is efficiently stored in the compressor ( 30).

  In this embodiment, assuming that the pressure of the refrigerant at the outlet of the evaporator (34, 37) when carbon dioxide is used as the refrigerant is in the range of 1 MPa to 7 MPa, the kinematic viscosity of the refrigerating machine oil is The target value corresponding to the value of the superheat degree of the refrigerant that does not decrease is set to a value in the range of 3 ° C. or more and 5 ° C. or less. Here, when the refrigerant and the refrigerating machine oil are combined in the present embodiment, in the conventional oil return operation in which the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) is adjusted to 0 ° C., the evaporator (34 37), the refrigerant superheat degree at the outlet becomes smaller than the refrigerant superheat value at which the kinematic viscosity of the refrigerating machine oil does not decrease. The gas at the outlet of the evaporator (34, 37) is compared to a state where the superheat degree of the refrigerant at the outlet of the evaporator (34, 37) becomes a value of the superheat degree of the refrigerant at which the kinematic viscosity of the refrigeration oil does not decrease. The flow rate of the refrigerant is reduced. Therefore, in the conventional oil return operation, the refrigerating machine oil accumulated between the evaporator (34, 37) and the compressor (30) cannot be efficiently returned to the compressor (30). On the other hand, in this embodiment, the kinematic viscosity of the refrigeration oil is about the same as in the conventional case, but the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is adjusted to a value larger than the conventional one. Therefore, the flow rate of the gas refrigerant at the outlet of the evaporator (34, 37) increases. Therefore, more refrigeration oil can be returned to the compressor (30) than in the case of the conventional oil return operation.

  Moreover, in this embodiment, by increasing the operating capacity of the compressor (30) in the oil return operation from immediately before the start of the oil return operation, the operation from the evaporator (34, 37) to the compressor (30) is performed. The shearing force acting on the refrigerating machine oil accumulated in between is increased. Therefore, since the refrigerating machine oil accumulated between the evaporator (34, 37) and the compressor (30) is more easily returned to the compressor (30), more refrigerating machine oil is returned to the compressor (30). be able to.

-Modification of the embodiment-
A modification of the embodiment will be described. In this modification, the oil return control unit (51) is configured to perform oil return control in normal operation.

  Specifically, as shown in FIG. 3, the controller (50) is provided with an evaporation side pressure detector (52) which is an evaporation side pressure detector. The evaporation side pressure detection unit (52) is configured to detect the pressure of the refrigerant at the outlet of the heat exchanger (34, 37) serving as an evaporator during normal operation. The evaporation side pressure detector (52) detects the same value as the measured value of the suction pressure sensor (46a) as the refrigerant pressure at the outlet of the evaporator (34, 37).

  The oil return control unit (51) is configured to change the set value for oil return using the detection pressure of the evaporation side pressure detection unit (52) during normal operation. The oil return control unit (51) receives information on the detected pressure from the evaporation side pressure detection unit (52), for example, at predetermined time intervals. When the oil return control unit (51) receives the detected pressure information from the evaporation side pressure detection unit (52), the degree of superheat of the refrigerant when the amount of refrigerant that dissolves in the refrigeration oil at the detected pressure reaches the upper limit value. Is set to the set value for oil return. For example, when the detected pressure is 1 MPa, the set value for oil return is set to 5 ° C., and when the detected pressure is 7 MPa, the set value for oil return is set to 3 ° C.

  In this modification, the target value of the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is set according to the pressure of the refrigerant at the outlet of the evaporator (34, 37) during normal operation. Here, the upper limit value of the amount of the liquid refrigerant dissolved in the refrigerating machine oil changes according to the temperature and pressure of the refrigerant. Therefore, the upper limit value changes depending on the change in refrigerant pressure at the outlet of the evaporator (34, 37) during normal operation. In this modification, the target value is set to reflect the refrigerant pressure at the outlet of the evaporator (34, 37) during normal operation, so that the refrigerant at the outlet of the evaporator (34, 37) at that time is set. It becomes the upper limit in pressure. Therefore, the refrigerant temperature at the outlet of the evaporator (34, 37) can be adjusted to a temperature at which the kinematic viscosity of the refrigerating machine oil does not decrease during normal operation. The refrigerating machine oil accumulated up to the machine (30) can be returned to the compressor (30) more efficiently.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

  In the above embodiment, the refrigeration apparatus (10) may be a refrigeration apparatus other than the air conditioner (for example, a refrigeration apparatus for refrigeration or freezing).

  Moreover, about the said embodiment, values (for example, 5 degreeC) other than 4 degreeC in the range whose oil return target value is 3 degreeC or more and 5 degrees C or less may be sufficient.

  Moreover, about the said embodiment, the combination with a refrigerant | coolant and weak compatibility refrigerating machine oil different from the said embodiment may be sufficient.

  Moreover, about the said embodiment, the fan (12, 14) which sends air to the heat exchanger (34, 37) used as an evaporator may comprise a superheat degree adjustment means. Specifically, in the oil return control related to the heating operation, the outdoor fan (12) constitutes a superheat degree adjusting means, and in the oil return control related to the cooling operation, the indoor fan (14) constitutes a superheat degree adjusting means. In this case, the fans (12, 14) constituting the superheat degree adjusting means are configured to have a variable air volume, and the air volume controller (53) for controlling the air flow of the fans (12, 14) is provided in the controller (50). Provided. In the oil return control, the air volume control unit (53) configures the superheat degree adjusting means so that the superheat degree of the refrigerant at the outlet of the heat exchanger (34, 37) serving as an evaporator becomes the oil return target value. Control the fans (12, 14). When the refrigerant superheat degree at the outlet of the evaporator (34, 37) is larger than the target value for oil return, the air volume control unit (53) decreases the air flow of the fan (12, 14), and the evaporator ( If the degree of superheat of the refrigerant at the outlet of (34, 37) is smaller than the target value for oil return, the air flow rate of the fan (12, 14) is increased. The superheat degree adjusting means may be constituted by both the expansion valve (36) and the fans (12, 14).

  Moreover, about the said embodiment, it comprises the refrigeration apparatus (10) so that the quantity of the refrigerating machine oil in a compressor (30) can be estimated, and the quantity of the refrigerating machine oil in the estimated compressor (30) is less than predetermined value. In some cases, an oil return operation may be performed.

  In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  As described above, the present invention is useful for a refrigeration apparatus that performs control for returning refrigeration oil accumulated between the evaporator and the compressor to the compressor, and an oil return method in the refrigeration apparatus.

FIG. 1 is a schematic configuration diagram of a refrigeration apparatus according to an embodiment of the present invention. FIG. 2 is a chart showing the relationship between the kinematic viscosity of the refrigeration oil and the concentration of the refrigerant dissolved in the refrigeration oil with respect to temperature and pressure in the combination of the refrigerant and the refrigeration oil used in the refrigeration apparatus according to the embodiment of the present invention. FIG. 3 is a schematic configuration diagram of a refrigeration apparatus according to a modification of the embodiment of the present invention.

Explanation of symbols

10 Air conditioner (refrigeration equipment)
12 Outdoor fan (superheat degree adjustment means, evaporation side fan)
14 Indoor fan (superheater, evaporative fan)
20 Refrigerant circuit
30 Compressor
34 Outdoor heat exchanger (evaporator, radiator)
36 Expansion valve (superheat degree control means, evaporation side control valve)
37 Indoor heat exchanger (evaporator, radiator)
50 Control unit (control means)
52 Evaporation side pressure detector (evaporation side pressure detection means)

Claims (9)

A refrigerant circuit (20) that performs a refrigeration cycle in which the refrigerant compressed by the compressor (30) is radiated by the radiator (34, 37) and evaporated by the evaporator (34, 37);
A refrigerating apparatus that uses weakly compatible refrigerating machine oil for lubrication in the compressor (30),
In order to return the refrigeration oil accumulated between the evaporator (34, 37) and the compressor (30) to the compressor (30) together with the refrigerant, the refrigerant at the outlet of the evaporator (34, 37) Controls the operating state of the refrigeration cycle so that the temperature reaches the upper limit temperature corresponding to the temperature at which the amount of refrigerant dissolved in the refrigeration oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37) A refrigeration apparatus comprising control means (50) for performing oil return control. In claim 1,
A superheat degree adjusting means (12, 14, 36) for adjusting the superheat degree of the refrigerant at the outlet of the evaporator (34, 37);
In the oil return control, the control means (50) is configured so that the degree of superheat of the refrigerant at the outlet of the evaporator (34, 37) is equal to the temperature of the refrigerant at the outlet of the evaporator (34, 37). A refrigeration apparatus, wherein the superheat degree adjusting means (12, 14, 36) is controlled to achieve a target value of the superheat degree determined to be. In claim 2,
The evaporation side expansion valve (36) for adjusting the refrigerant flow rate of the evaporator (34, 37) constitutes the superheat degree adjusting means (12, 14, 36),
The said control means (50) controls the opening degree of the said evaporation side expansion valve (36) in the said oil return control, The freezing apparatus characterized by the above-mentioned. In claim 2 or 3,
The evaporation side fan (12, 14) for sending air to the evaporator (34, 37) constitutes the superheat degree adjusting means (12, 14, 36),
The said control means (50) controls the ventilation volume of the said evaporation side fan (12,14) in the said oil return control, The freezing apparatus characterized by the above-mentioned. In any one of Claims 2 thru | or 4,
In the refrigerant circuit (20), carbon dioxide is used as the refrigerant, and polyalkylene glycol is used as the refrigerating machine oil.
The refrigerating apparatus according to claim 1, wherein the target value of the superheat degree is a value in a range of 3 ° C to 5 ° C. In any one of claims 1 to 5,
Oil for forcibly returning the refrigeration oil accumulated between the normal operation to adjust the temperature of the target space and the evaporator (34, 37) to the compressor (30) to the compressor (30) The return operation can be executed selectively,
The refrigeration apparatus, wherein the control means (50) performs the oil return control in the oil return operation. In claim 6,
In the oil return operation, the control means (50) performs the oil return control and increases the operating capacity of the compressor (30) from immediately before the start of the oil return operation. In any one of Claims 2 thru | or 4,
Evaporation side pressure detection means (52) for detecting the pressure of the refrigerant at the outlet of the evaporator (34, 37),
The control means (50) performs the oil return control in a normal operation for adjusting the temperature of the target space, and uses the detected pressure of the evaporation side pressure detection means (52) in the oil return control during the normal operation. A refrigeration apparatus characterized by setting a target value of the superheat degree. The compressor (30) includes a refrigerant circuit (20) for performing a refrigeration cycle in which the refrigerant compressed by the compressor (30) is radiated by the radiator (34, 37) and evaporated by the evaporator (34, 37). In the refrigerating apparatus (10) using the weakly compatible refrigerating machine oil for lubrication in the refrigerating machine, the refrigerating machine oil accumulated between the evaporator (34, 37) and the compressor (30) is combined with the refrigerant in the compressor (30). An oil return method for a refrigeration apparatus for returning to
The upper limit of the refrigerant temperature at the outlet of the evaporator (34, 37) corresponding to the temperature at which the amount of refrigerant dissolved in the refrigerating machine oil reaches the upper limit at the refrigerant pressure at the outlet of the evaporator (34, 37) An oil return method for a refrigeration apparatus, comprising an oil return process for controlling an operating state of a refrigeration cycle so as to achieve a corresponding temperature.

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