GB2618030A

GB2618030A - Refrigeration cycle device

Info

Publication number: GB2618030A
Application number: GB2312113.0A
Authority: GB
Inventors: Ono Hideki; Yashiro Takanori; Ishihara Nobuya; Nishiyama Takumi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2021-02-26
Filing date: 2021-02-26
Publication date: 2023-10-25
Anticipated expiration: 2041-02-26
Also published as: GB202312113D0; JPWO2022180821A1; GB2618030B; WO2022180821A1

Abstract

A refrigeration cycle device (100) comprises: a first refrigerant circuit (RC1); a second refrigerant circuit (RC2); a heat exchanger (30) that performs heat exchange between a first refrigerant of a condenser (12) of the first refrigerant circuit (RC1) and a second refrigerant of an evaporator (23) of the second refrigerant circuit (RC2); and a control device 40. The control device (40) stops operation of the second refrigerant circuit (RC2) in response to the evaporation temperature of the first refrigerant and an operation frequency value of a compressor (10) of the first refrigerant circuit (RC1) being within a first range. The first range includes a lower limit value for the evaporation temperature and a lower limit value for the operation frequency.

Description

DESCRIPTION

TITLE OF INVENTION

Refrigeration Cycle Device

TECHNICAL FIELD

[0001] The present disclosure relates to a refrigeration cycle apparatus. BACKGROUND ART [0002] In recent years, refrigeration cycle apparatuses using carbon dioxide (CO2). which is a natural refrigerant (a substance that originally exists in nature) with less environmental load, are known. Since working pressure is high in a refrigeration cycle apparatus using CO, as refrigerant, it is necessary to improve pressure resistance of parts, increase pipe thickness, and the like, which leads to high cost. Accordingly, refrigeration cycle apparatuses including a low-stage side refrigerant circuit using a CO, refrigerant and a high-stage side refrigerant circuit using a refrigerant such as chlorofluorocarbon, ammonia, hydrocarbon, or the like have been developed.

[0003] For example, the refrigeration cycle apparatus described in WO 2015/132964 (PTL 1) includes a low-stage side refrigeration cycle and a high-stage side refrigeration cycle. The low-stage side refrigeration cycle includes a low-stage side compressor, a heat-source side heat exchanger, a low-stage side condenser, a low-stage side expansion valve, and a utilization side heat exchanger. The high-stage side refrigeration cycle includes a high-stage side compressor, a high-stage side condenser, a high-stage side expansion valve, and a high-stage side evaporator. The low-stage side condenser performs heat exchange with the high-stage side evaporator. When either a heat source temperature of a heat source that exchanges heat with refrigerant flowing through the heat source side heat exchanger, or a utilization temperature of a utilization side heat source that exchanges heat with the refrigerant flowing through the utilization side heat exchanger is lower than a predetermined temperature, the refrigeration cycle apparatus promotes heat exchange on a side having a temperature lower than the predetermined temperature.

CITATION LIST

PATENT LITERATURE

[0004] PTL 1: WO 2015/132964 SUMMARY OF INVENTION

TECHNICAL PROBLEM

[0005] In the refrigeration cycle apparatus described in WO 2015/132964, the heat source side heat exchanger and the high-stage side condenser arc arranged within a case of an outdoor unit. When the heat source side heat exchanger and the high-stage side condenser are heat exchangers of an air-cooled type, the heat source side heat exchanger and the high-stage side condenser are mutually influenced by blowers. As a result, an evaporation temperature decreases in the high-stage side refrigeration cycle, and there may occur a phenomenon in which liquid refrigerant is suctioned into the high-stage side compressor (a liquid back). The liquid back causes failure of the compressor.

[0006] An objcct of the present disclosure is to provide a refrigeration cycle apparatus including two refrigerant circuits, capable of suppressing occurrence of failure of a compressor due to a liquid back.

SOLUTION TO PROBLEM

[0007] A refrigeration cycle apparatus in the present disclosure includes a first refrigerant circuit and a second refrigerant circuit. The first refrigerant circuit includes a first compressor, a first heat exchanger of an air-cooled type, a first condenser, a first expansion device, and a first evaporator, and circulates a first refrigerant in order of the first compressor, the first heat exchanger, the first condenser, the first expansion device, and the first evaporator. The second refrigerant circuit includes a second compressor, a second condenser of the air-cooled type, a second expansion device, and a second evaporator, and circulates a second refrigerant in order of the second compressor, the second condenser, the second expansion device, and the second evaporator. The refrigeration cycle apparatus further includes a second heat exchanger to perform heat exchange between the first refrigerant in the first evaporator and the second refrigerant in the second condenser, and a controller. The controller stops operation of the second refrigerant circuit in response to values of an evaporation temperature of the first refrigerant in the first evaporator and an operation frequency of the first compressor being within a first range. The first range includes a lower limit value of the evaporation temperature and a lower limit value of the operation frequency.

ADVANTAGEOUS EFFECTS OF INVENTION

[0008] According to the present disclosure, the first range including the lower limit value of the evaporation temperature and the lower limit value of the operation frequency is a range in which a load is smaller than that in a remaining range. When the load is small, the amount of heat exchange in the second heat exchanger decreases, and an evaporation temperature in the second refrigerant circuit is likely to decrease. Accordingly, the controller stops operation of the second refrigerant circuit in response to the values of the evaporation temperature of the first refrigerant in the first evaporator and the operation frequency of the first compressor being within the first range. Thereby, occurrence of a liquid back in the second refrigerant circuit is suppressed. As a result, a refrigeration cycle apparatus including two refrigerant circuits, capable of suppressing occurrence of failure of a compressor due to a liquid back can be provided.

BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a view showing a configuration of a refrigeration cycle apparatus in accordance with a first embodiment.

Fig. 2 is a view showing flows of air within an outdoor unit.

Fig. 3 is a view showing an example of a two-dimensional map set beforehand in the first embodiment.

Fig. 4 is a view showing another example of the two-dimensional map set beforehand in the first embodiment.

Fig. 5 is a view showing an example of a two-dimensional map set beforehand in a second embodiment.

DESCRIPTION OF EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although a plurality of embodiments will be described below, it is originally intended from the time of filing the present application to combine configurations described in the embodiments as appropriate. It should be noted that identical or corresponding parts in the drawings will be designated by the same reference characters, and the description thereof will not be repeated.

[0011] First Embodiment <Configuration of Refrigeration Cycle Apparatus> Fig. 1 is a view showing a configuration of a refrigeration cycle apparatus 100 in accordance with a first embodiment. As shown in Fig. 1, it includes a low-stage side refrigerant circuit RC1, a high-stage side refrigerant circuit RC2, a heat exchanger 30, a controller 40, and sensors 50 and 51.

[0012] Refrigerant circuit RC1 includes a compressor 10, an auxiliary heat exchanger 11 of an air-cooled type, a condenser 12, an expansion device 13, and an evaporator 14.

Refrigerant circuit RC1 circulates a first refrigerant in order of compressor 10, auxiliary heat exchanger 11, condenser 12, expansion device 13, and evaporator 14.

[0013] Refrigerant circuit RC2 includes a compressor 20, a condenser 21 of the air-cooled type, an expansion device 22, and an evaporator 23. Refrigerant circuit RC2 circulates a second refrigerant in order of compressor 20, condenser 21 of the air-cooled type, expansion device 22, and evaporator 23.

[0014] Of refrigerant circuit RC1, expansion device 13 and evaporator 14 are arranged within an indoor unit 2 such as a showcase in a supermarket, for example.

Compressor 20, condenser 21, and expansion device 22 of refrigerant circuit RC1, and refrigerant circuit RC2 are arranged within an outdoor unit I. Outdoor unit 1 and indoor unit 2 arc connected by pipes 3 and 4. Accordingly, when a work such as changing connection of pipes 3 and 4 is performed to change the position of indoor unit 2, refrigerant circuit RC I may be opened. On this occasion, leakage of the first refrigerant may occur. On the other hand, refrigerant circuit RC2 is generally not opened.

[0015] Accordingly, in refrigeration cycle apparatus 100, as the first refrigerant charged into refrigerant circuit RC1, a CO, refrigerant or a mixed refrigerant containing CO2 having less impact on global warming is used in consideration of refrigerant leakage.

[0016] As the second refrigerant charged into refrigerant circuit RC2, it is desirable to use a refrigerant having less impact on global warming, such as an FIFO (hydrofluoroolefin) refrigerant (HF0-1234yf (CF3CF=CH2), HF0-1234ze (CF3-CH=CHF), an HC refrigerant, CO?, ammonia, water, or the like, for example.

However, since refrigerant circuit RC2 is not opened, for example, an HFC refrigerant having a high global warming potential, or the like may be used as the second refrigerant.

[0017] Heat exchanger 30 performs heat exchange between the first refrigerant in condenser 12 and the second refrigerant in evaporator 23. Heat exchanger 30 is, for example, a cascade heat exchanger of a plate type or the like.

[0018] Compressor 10 suctions the first refrigerant flowing through refrigerant circuit RC1, compresses the first refrigerant, and discharges the first refrigerant in a high temperature and high pressure state. Compressor 10 is, for example, a volumetric compressor equipped with an inverter and driven by a motor (not shown) controlled by the inverter. As compressor 10, for example, a compressor of a variety of types such as a reciprocating type, a rotary type, a scroll type, a screw type, and the like may be adopted.

[0019] Auxiliary heat exchanger 11 cools the first refrigerant in a gaseous state discharged from compressor 10, by heat exchange with air of the outdoors (outdoor air) used as a heat source. Auxiliary heat exchanger 11 has a blower 15 for promoting heat exchange. Blower 15 is a fan of a type capable of adjusting an air volume. [0020] Condenser 12 provides heat of the first refrigerant having passed through auxiliary heat exchanger 11, to the second refrigerant flowing through evaporator 23 of refrigerant circuit RC2, and thereby condenses and liquefies the first refrigerant.

[0021] Expansion device 13 decompresses and expands the first refrigerant having passed through condenser 12. Expansion device 13 is constituted for example by an electronic expansion valve, a capillary tube (capillary), a thermostatic expansion valve, or the like.

[0022] Evaporator 14 evaporates and gasifies the first refrigerant having passed through expansion device 13, by heat exchange with an object to be cooled, to maintain the object to be cooled at a set utilization temperature. By heat exchange with the first refrigerant, the object to be cooled is cooled directly or indirectly.

[0023] Compressor 20 suctions the second refrigerant flowing through refrigerant circuit RC2, compresses the second refrigerant, and discharges the second refrigerant in a high temperature and high pressure state. Compressor 20 is, for example, a volumetric compressor equipped with an inverter and driven by a motor (not shown) controlled by the inverter. As compressor 20, for example, a compressor of a variety of types such as a reciprocating type, a rotary type, a scroll type, a screw type, and the like may be adopted.

[0024] Condenser 21 performs heat exchange between the second refrigerant discharged from compressor 20 and the outdoor air, and condenses and liquefies the second refrigerant. Condenser 21 has a blower 24 for promoting heat exchange. Blower 24 is also constituted by a fan of a type capable of adjusting an air volume.

[0025] Expansion device 22 decompresses and expands the second refrigerant having passed through condenser 21. Expansion device 22 is constituted for example by an electronic expansion valve, a capillary tube (capillary), a thermostatic expansion valve, or the like.

[0026] Evaporator 23 evaporates and gasifies the second refrigerant having passed through expansion device 22, by heat exchange with the first refrigerant flowing through condenser 12.

[0027] Sensor 50 measures a temperature of the outdoor air. Sensor 51 measures a pressure of the first refrigerant having passed through evaporator 14. Sensors 50 and 51 output measurement results to controller 40.

[0028] Controller 40 includes a processor, a memory, and a communication interface. The processor controls operation frequencies (rotation speeds) of compressors 10 and 20, air volumes of blowers 15 and 24, and the like, according to data stored in the memory and information obtained via the communication interface (for example, the measurement results of sensors 50 and 51). The memory is constituted to include a ROM (Read Only Memory), a RAM (Random Access Memory), and a flash memory, for example. It should be noted that the flash memory stores an operating system, an application program, and a variety of data. Controller 40 is implemented by the processor executing the operating system and the application program stored in the memory. When the application program is executed, the variety of data stored in the memory is referred to.

[0029] <Flows of Air within Outdoor Unit> Fig. 2 is a view showing flows of air within outdoor unit 1. As shown in Fig. 2, within outdoor unit 1, auxiliary heat exchanger 11 and condenser 21 are arranged side by side. In the case of such an arrangement, a flow of the outdoor air generated by blower 24 for promoting heat exchange of condenser 21 has an impact also on auxiliary heat exchanger 11. Similarly, a flow of the outdoor air generated by blower 15 for promoting heat exchange of auxiliary heat exchanger 11 has an impact also on condenser 21.

[0030] When the outdoor air temperature is low, condensation capacity of auxiliary heat exchanger 11 increases. Accordingly, the amount of heat exchange in heat exchanger 30 decreases, and an evaporation temperature decreases excessively in refrigerant circuit RC2. As a result, there may occur a liquid back in which the second refrigerant in a liquid state flows into compressor 20. Especially when the condensation capacity of auxiliary heat exchanger 11 further increases by the flow of the outdoor air generated by blower 24 for promoting heat exchange of condenser 21, an excessive decrease of the evaporation temperature and a liquid back are likely to occur in refrigerant circuit RC2.

[0031] In order to suppress occurrence of such an excessive decrease of the evaporation temperature and a liquid back in refrigerant circuit RC2, controller 40 in accordance with the first embodiment performs control as described below.

[0032] <Control Method by Controller> Controller 40 controls operation of refrigerant circuit RC2, based on the outdoor air temperature measured by sensor 50, an evaporation temperature of the first refrigerant calculated from the pressure measured by sensor 51, and the operation frequency of compressor 10.

[0033] A plurality of two-dimensional maps are set beforehand in controller 40. A two-dimensional map is a map having axes representing the evaporation temperature of the first refrigerant and the operation frequency of compressor 10 in refrigerant circuit RC1. The plurality of two-dimensional maps are produced beforehand corresponding to outdoor air temperatures different from each other.

[0034] Fig. 3 is a view showing an example of a two-dimensional map 60 set beforehand in the first embodiment. Fig. 4 is a view showing another example of two-dimensional map 60 set beforehand in the first embodiment. Two-dimensional map shown in Fig. 3 is a map used when the outdoor air temperature is a temperature T1. Two-dimensional map 60 shown in Fig. 4 is a map used when the outdoor air temperature is a temperature T2. Temperature T1 is a lower limit value of a temperature range that the outdoor air may have. Temperature T2 is a temperature that is higher than temperature Ti and is slightly lower than a target value of a condensation temperature of the first refrigerant in refrigerant circuit RC 1.

[0035] As shown in Figs. 3 and 4, two-dimensional map 60 includes a first range 61 including a lower limit value of the evaporation temperature of the first refrigerant and a lower limit value of the operation frequency of compressor 10 in refrigerant circuit RC1, and a second range 62 including an upper limit value of the evaporation temperature and an upper limit value of the operation frequency. First range 61 and second range 62 are divided by a boundary line 63.

[0036] First range 61 is a region formed by a point 64 indicating the lower limit value of the evaporation temperature and the lower limit value of the operation frequency, a point 65 indicating the upper limit value of the evaporation temperature and the lower limit value of the operation frequency, a point 66 indicating the upper limit value of the evaporation temperature and a value selected from between the lower limit value and the upper limit value of the operation frequency, a point 68 indicating a value selected from between the lower limit value and the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, and a point 69 indicating the lower limit value of the evaporation temperature and the upper limit value of the operation frequency. That is, first range 61 is a region surrounded by a line connecting point 64 and point 65, a line connecting point 65 and point 66, boundary line 63 connecting point 66 and point 68, a line connecting point 68 and point 69, and a line connecting point 69 and point 64.

[0037] Second range 62 is a remaining region, that is, a region formed by point 66 indicating the upper limit value of the evaporation temperature and the value selected from between the lower limit value and the upper limit value of the operation frequency, a point 67 indicating the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, and point 68 indicating the value selected from between the lower limit value and the upper limit value of the evaporation temperature and the upper limit value of the operation frequency. Second range 62 is a region surrounded by a line connecting point 66 and point 67, a line connecting point 67 and point 68, and boundary line 63 connecting point 68 and point 66.

[0038] The upper limit value and the lower limit value of the operation frequency, the upper limit value and the lower limit value of the evaporation temperature, the value of the operation frequency at point 66, the value of the evaporation temperature at point 68, and boundary line 63 are determined according to the result of a test performed beforehand. Boundary line 63 is represented by an arbitrary function.

[0039] Controller 40 selects, from the plurality of two-dimensional maps 60, one two-dimensional map 60 corresponding to the outdoor air temperature measured by sensor 50. Specifically, controller 40 selects two-dimensional map 60 corresponding to a temperature closest to the outdoor air temperature measured by sensor 50.

[0040] Using selected two-dimensional map 60, controller 40 determines whether or not to operate refrigerant circuit RC2.

[0041] Specifically, controller 40 causes refrigerant circuit RC2 to operate in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within second range 62 of selected two-dimensional map 60. That is, controller 40 causes compressor 20 to operate and causes the second refrigerant to circulate in refrigerant circuit RC2 Furthermore, controller 40 causes blower 24 to operate.

[0042] Controller 40 stops operation of refrigerant circuit RC2 in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within first range 61 of selected two-dimensional map 60. That is, controller 40 stops operation of compressor 20 and stops circulation of the second refrigerant in refrigerant circuit RC2. Furthermore, controller 40 stops operation of blower 24.

[0043] It should be noted that controller 40 causes blower 15 to operate, regardless of which of first range 61 and second range 62 the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 are within.

[0044] The lower the evaporation temperature measured by sensor 51 is, the smaller a load is. The lower the operation frequency (rotation speed) of compressor 10 is, the smaller the load is. Accordingly, in two-dimensional map 60, first range 61 including the lower limit value of the evaporation temperature and the lower limit value of the operation frequency is a range in which the load is smaller than that in the remaining region (that is, second range 62 including the upper limit value of the evaporation temperature and the upper limit value of the operation frequency).

[0045] When the load is small, the condensation temperature of the first refrigerant in low-stage side refrigerant circuit RC1 is less likely to become higher. Accordingly, even if operation of high-stage side refrigerant circuit RC2 is stopped, the condensation temperature of the first refrigerant in refrigerant circuit RC1 can be maintained at the -10 -target value. Therefore, controller 40 stops operation of refrigerant circuit RC2 in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within first range 61. Thereby, power consumption required for refrigerant circuit RC2 is reduced, and operation sound is reduced. Furthermore, occurrence of a liquid back in refrigerant circuit RC2 is suppressed.

[0046] When the load is large, the condensation temperature of the first refrigerant in low-stage side refrigerant circuit RC1 is likely to become higher. Accordingly, controller 40 causes refrigerant circuit RC2 to operate in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor being within second range 62 Thereby, the condensation temperature of the first refrigerant in refrigerant circuit RC1 is adjusted to less than or equal to an upper limit value.

[0047] As shown in Figs. 3 and 4, first range 61 is set in two-dimensional map 60 to become larger as the outdoor air temperature becomes lower. Second range 62 is set in two-dimensional map 60 to become smaller as the outdoor air temperature becomes lower. That is, boundary line 63 between first range 61 and second range 62 is set to become closer to point 67 indicating the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, as the outdoor air temperature becomes lower.

[0048] As described above, when the outdoor air temperature is low, the condensation capacity of auxiliary heat exchanger 11 increases, and the amount of heat exchange in heat exchanger 30 decreases. Accordingly, an excessive decrease of the evaporation temperature or a liquid back in compressor 20 may occur in refrigerant circuit RC2.

Accordingly, by setting first range 61 to become larger as the outdoor air temperature becomes lower, a frequency at which operation of refrigerant circuit RC2 is stopped increases. Thereby, occurrence of a liquid back in refrigerant circuit RC2 is suppressed.

[0049] Second Embodiment When compared with refrigeration cycle apparatus 100 in accordance with the first embodiment, a refrigeration cycle apparatus in accordance with a second embodiment is different therefrom in that it uses two-dimensional map 60 including a third range.

[0050] Fig. 5 is a view showing an example of two-dimensional map 60 set beforehand in the second embodiment. As shown in Fig. 5, two-dimensional map 60 includes a third range 70 in addition to first range 61 and second range 62. Third range 70 is located between first range 61 and second range 62 in two-dimensional map 60. [0051] First range 61 is a region fornied by point 64 indicating the lower limit value of the evaporation temperature and the lower limit value of the operation frequency, point indicating the upper limit value of the evaporation temperature and the lower limit value of the operation frequency, a point 66a indicating the upper limit value of the evaporation temperature and a first value selected from between the lower limit value and the upper limit value of the operation frequency, a point 68a indicating a second value selected from between the lower limit value and the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, and point 69 indicating the lower limit value of the evaporation temperature and the upper limit value of the operation frequency. That is, first range 61 is a region surrounded by the line connecting point 64 and point 65, a line connecting point 65 and point 66a, a boundary line 63a connecting point 66a and point 68a, a line connecting point 68a and point 69, and the line connecting point 69 and point 64.

[0052] Second range 62 is a region formed by a point 66b indicating the upper limit value of the evaporation temperature and a third value selected from between the lower limit value and the upper limit value of the operation frequency, point 67 indicating the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, and a point 68b indicating a fourth value selected from between the lower limit value and the upper limit value of the evaporation temperature and the upper limit value of the operation frequency. Second range 62 is a region surrounded by a line connecting point 66b and point 67, a line connecting point 67 and point 68b, -12 -and a boundary line 63b connecting point 68b and point 66b. It should be noted that boundary line 63b is closer to point 67 than boundary line 63a. That is, the third value of the operation frequency at point 66b is higher than the first value of the operation frequency at point 66a. The fourth value of the evaporation temperature at point 68b is higher than the second value of the evaporation temperature at point 68a.

[0053] Third range 70 is a region formed by point 66a, point 66b, point 68b, and point 68a. That is, second range 62 is a region surrounded by a line connecting point 66a and point 66b, boundary line 63b connecting point 68b and point 66b, a line connecting point 68b and point 68a, and boundary line 63a connecting point 68a and point 66a.

[0054] The first value to the fourth value and boundary lines 63a and 63b are determined according to the result of a test performed beforehand. Boundary lines 63a and 63b are represented by arbitrary functions.

[0055] It should be noted that, also in the second embodiment, a plurality of two-dimensional maps 60 are set beforehand in controller 40. In addition, first range 61 is set in two-dimensional map 60 to become larger as the outdoor air temperature becomes lower. Second range 62 is set in two-dimensional map 60 to become smaller as the outdoor air temperature becomes lower. Two-dimensional map 60 shown in Fig. 5 is a map used when the outdoor air temperature is temperature TI.

[0056] As in the first embodiment, controller 40 selects, from the plurality of two-dimensional maps 60, one two-dimensional map 60 corresponding to the outdoor air temperature measured by sensor 50.

[0057] Controller 40 causes refrigerant circuit RC2 to operate and causes blower 15 to operate in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within second range 62 of selected two-dimensional map 60. That is, controller 40 causes the second refrigerant to circulate in refrigerant circuit RC2, and promotes heat exchange in auxiliary heat exchanger 11. Thereby, under a situation where the load is large, the condensation temperature of the first refrigerant in refrigerant circuit RC1 is adjusted to less than or equal to the upper limit value.

-13 - [0058] Controller 40 stops operation of refrigerant circuit RC2 and causes blower 15 to operate in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within first range 61 of selected two-dimensional map 60. Thereby, power consumption required for refrigerant circuit RC2 is reduced, and operation sound is reduced. Furthermore, occurrence of a liquid back in refrigerant circuit RC2 is suppressed.

[0059] Controller 40 causes refrigerant circuit RC2 to operate and stops operation of blower 15 in response to the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 being within third range 70 of selected two-dimensional map 60. By stopping operation of blower 15, condensation capacity of condenser 21 can be suppressed from becoming excessive in refrigerant circuit RC2. As a result, the number of times refrigerant circuit RC2 starts and stops decreases, and deterioration and failure of refrigerant circuit RC2 are suppressed. Furthermore, in refrigerant circuit RC1, stable operation can be performed while maintaining the condensation temperature of the first refrigerant at the target value.

[0060] Variation In the description of the first embodiment described above, it has been described that controller 40 determines which of first range 61 and second range 62 the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 belong to, using two-dimensional map 60. However, controller 40 may use a function representing boundary line 63, instead of two-dimensional map 60. For example, controller 40 uses a function y = f(x) representing boundary line 63, where x represents the operation frequency, and y represents the evaporation temperature. Controller 40 may determine, in response to y < f(x) being satisfied when the present operation frequency of compressor 10 and the evaporation temperature measured by sensor 51 are substituted into the function, that the evaporation temperature and the operation frequency belong to first range 61. Similarly, controller 40 may determine, in response to y f(x) being satisfied when the present operation frequency of compressor 10 and the evaporation temperature -14 -measured by sensor 51 are substituted into the function, that the evaporation temperature and the operation frequency belong to second range 62.

[0061] Similarly, in the description of the first embodiment described above, it has been described that controller 40 determines which of first range 61, second range 62, and third range 70 the evaporation temperature measured by sensor 51 and the present operation frequency of compressor 10 belong to, using two-dimensional map 60. However, controller 40 may use functions representing boundary lines 63a and 63b, instead of two-dimensional map 60. For example, controller 40 uses a function y = fa(x) representing boundary line 63a and a function y = fb(x) representing boundary line 63b, where x represents the operation frequency, and y represents the evaporation temperature. Controller 40 may determine, in response to y < fa(x) being satisfied when the present operation frequency of compressor 10 and the evaporation temperature measured by sensor 51 are substituted into the function, that the evaporation temperature and the operation frequency belong to first range 61.

Controller 40 may determine, in response to fa(x) y < fb(x) being satisfied when the present operation frequency of compressor 10 and the evaporation temperature measured by sensor 51 are substituted into the functions, that the evaporation temperature and the operation frequency belong to third range 70. Controller 40 may determine, in response to y fb(x) being satisfied when the present operation frequency of compressor 10 and the evaporation temperature measured by sensor 51 are substituted into the function, that the evaporation temperature and the operation frequency belong to second range 62.

[0062] It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the scope of the claims, rather than the description of the embodiments described above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

REFERENCE SIGNS LIST

[0063] 1: outdoor unit; 2: indoor unit; 3, 4: pipe; 10, 20: compressor; 11: auxiliary heat -15 -exchanger; 12, 21: condenser; 13, 22: expansion device; 14,23: evaporator; 15, 24: blower; 30: heat exchanger; 40: controller; 50, 51: sensor; 60: two-dimensional map; 61: first range; 62: second range; 63, 63a, 63b: boundary line; 64 to 69, 66a, 66b, 68a, 68b: point; 70: third range; 100: refrigeration cycle apparatus; Re..1, Rel: refrigerant circuit.

-16 -

Claims

CLAIMS[Claim 1] A refrigeration cycle apparatus comprising: a first refrigerant circuit including a first compressor, a first heat exchanger of an air-cooled type, a first condenser, a first expansion device, and a first evaporator, to circulate a first refrigerant in order of the first compressor, the first heat exchanger, the first condenser, the first expansion device, and the first evaporator; a second refrigerant circuit including a second compressor, a second condenser of the air-cooled type, a second expansion device, and a second evaporator, to circulate a second refrigerant in order of the second compressor, the second condenser, the second expansion device, and the second evaporator; a second heat exchanger to perform heat exchange between the first refrigerant in the first condenser and the second refrigerant in the second evaporator; and a controller, wherein the controller stops operation of the second refrigerant circuit in response to values of an evaporation temperature of the first refrigerant and an operation frequency of the first compressor in the first refrigerant circuit being within a first range, and the first range includes a lower limit value of the evaporation temperature and a lower limit value of the operation frequency.
[Claim 2] The refrigeration cycle apparatus according to claim 1, wherein the first heat exchanger and the second condenser are arranged within a case of an outdoor unit.
[Claim 3] The refrigeration cycle apparatus according to claim 1 or 2, wherein the controller causes the second refrigerant circuit to operate in response to the values of the evaporation temperature and the operation frequency being within a second range, and the second range includes an upper limit value of the evaporation temperature -17 -and an upper limit value of the operation frequency.
[Claim 4] The refrigeration cycle apparatus according to claim 3, wherein the first range is set to become larger as an outdoor air temperature becomes lower, and the second range is set to become smaller as the outdoor air temperature becomes lower.
[Claim 5] The refrigeration cycle apparatus according to claim 3 or 4, further comprising a blower to blow outdoor air into the first heat exchanger, wherein the controller causes the blower to operate in response to the values of the evaporation temperature and the operation frequency being within the first range or the second range, and causes the second refrigerant circuit to operate and stops operation of the blower in response to the values of the evaporation temperature and the operation frequency being within a third range, and the third range is located between the first range and the second range.
[Claim 6] The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the first range is a region formed by a first point indicating the lower limit value of the evaporation temperature and the lower limit value of the operation frequency, a second point indicating an upper limit value of the evaporation temperature and the lower limit value of the operation frequency, a third point indicating the upper limit value of the evaporation temperature and a value selected from between the lower limit value and an upper limit value of the operation frequency, a fourth point indicating a value selected from between the lower limit value -18 -and the upper limit value of the evaporation temperature and the upper limit value of the operation frequency, and a fifth point indicating the lower limit value of the evaporation temperature and the upper limit value of the operation frequency.
[Claim 7] The refrigeration cycle apparatus according to any one of claims 1 to 6, wherein the first refrigerant is a CO, refrigerant or a mixed refrigerant containing -19 -