GB2534510A

GB2534510A - Refrigeration cycle device

Info

Publication number: GB2534510A
Application number: GB1606526.0A
Authority: GB
Inventors: Ishikawa Tomotaka; Sumida Yoshihiro; Sugimoto Takeshi; Ikeda Takashi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2013-10-28
Filing date: 2013-10-28
Publication date: 2016-07-27
Anticipated expiration: 2033-10-28
Also published as: GB2534510B; WO2015063838A1; JPWO2015063838A1; CN105683681A

Abstract

This refrigeration cycle device has a heat-source unit, a cooling unit, a first connecting tube, and a second connecting tube. The heat-source unit has a compressor for compressing coolant, a high-pressure-side heat exchanger for cooling the coolant from the compressor, and a principal depressurization device for depressurizing the coolant from the condenser. The cooling unit has a low-pressure-side heat exchanger for vaporizing the coolant. The first connecting tube guides the coolant conveyed from the principal depressurization device to the low-pressure-side heat exchanger to the interval between the heat-source unit and the cooling unit. The second connecting tube guides the coolant conveyed from the low-pressure-side heat exchanger to the compressor to the interval between the heat-source unit and the cooling unit. The first connecting tube creates a coolant pressure loss in a range in which the saturation temperature of the coolant in the low-pressure-side heat exchanger does not fall below the use vaporization temperature of the low-pressure-side heat exchanger.

Description

Title of Invention: REFRIGERATION CYCLE APPARATUS

Technical Field

[0001] The present invention relates to a refrigeration cycle apparatus to be used for purposes of, for example, freezing and refrigeration.

Background Art

[0002] Hitherto, there is known a refrigerating machine obtained by connecting a heat source unit including a compressor and a condenser, and a cooling unit including an expansion valve and an evaporator, to each other, through a plurality of communication pipes, which is configured to circulate refrigerant between the heat source unit and the cooling unit through the communication pipes. In such a related-art refrigerating machine, use of CO2 being a high-pressure refrigerant has been attempted.

[0003] In the related-art refrigerating machine using such a high-pressure refrigerant, the communication pipe has a large material thickness due to a high operating pressure, and not only a cost of the communication pipe itself increases but also bending or connection work for the communication pipe becomes difficult, which increases time and labor for on-site installation work for the communication pipe as well. Further, when the above-mentioned related-art refrigerating machine is used for, for example, a showcase installed in a shop such as a convenience store or a supermarket, the cooling unit is often installed in a place away from the heat source unit, and hence a length of the communication pipe often increases (for example, a full length of the communication pipe becomes approximately 100 m). When the length of the communication pipe increases, a material cost for constructing the communication pipe on site increases. Therefore, a work time and a construction cost required to install the refrigerating machine increase.

[0004] Hitherto, in order to achieve reduction in material thickness of the communication pipe, there is proposed a refrigerating machine in which a pressure inside the communication pipe is lowered by arranging a main pressure reducing mechanism in a heat source unit and causing the refrigerant having been reduced in pressure by the main pressure reducing mechanism to flow through the communication pipe (see, for example, PTL 1).

Citation List Patent Literature [0005] [PTL 1] JP 2003-139422 A

Summary of Invention Technical Problem

[0006] However, in a related-art refrigerating machine disclosed in PTL 1, when the pressure loss of the refrigerant inside the communication pipe increases, a pressure of the refrigerant reduced by a main pressure reducing mechanism is lowered to a greater extent, and hence a saturation temperature of the refrigerant at an evaporator becomes liable to fall below an evaporating temperature used for the evaporator. Therefore, a proper operation of the refrigerating machine becomes hard to ensure.

[0007] The present invention has been made in order to solve such a problem as described above, and has an object to obtain a refrigeration cycle apparatus capable of alleviating time and labor for on-side installation work and avoiding reduction in proper operation range.

Solution to Problem [0008] According to one embodiment of the present invention, there is provided a refrigeration cycle apparatus, including: a heat source unit including: a compressor configured to compress refrigerant; a high-pressure-side heat exchanger configured to cool the refrigerant sent from the compressor; and a main pressure reducing device configured to reduce a pressure of the refrigerant sent from the high-pressure-side heat exchanger; a cooling unit including a low-pressure-side heat exchanger configured to evaporate the refrigerant; a first communication pipe configured to guide the refrigerant to be sent from the main pressure reducing device to the low-pressure-side heat exchanger between the heat source unit and the cooling unit; and a second communication pipe configured to guide the refrigerant to be sent from the low-pressure-side heat exchanger to the compressor between the heat source unit and the cooling unit, in which the first communication pipe is a communication pipe in which a pressure loss of the refrigerant occurs within a range that prevents a saturation temperature of the refrigerant at the low-pressure-side heat exchanger from falling below an in-use evaporating temperature of the low-pressure-side heat exchanger.

Advantageous Effects of Invention [0009] With the refrigeration cycle apparatus according to the one embodiment of the present invention, the pressure of the refrigerant inside the first communication pipe can be reduced by the pressure reduction of the refrigerant conducted by the main pressure reducing device, and reduction in material thickness of the first communication pipe can be achieved, which can alleviate time and labor for on-site installation work for the refrigeration cycle apparatus. Further, the pressure loss of the refrigerant inside the first communication pipe can be suppressed within the range that prevents the saturation temperature of the refrigerant at the low-pressure-side heat exchanger from falling below the in-use evaporating temperature of the low-pressure-side heat exchanger, which can avoid reduction in proper operation range of the refrigeration cycle apparatus.

Brief Description of Drawings

[0010] FIG. 1 is a block diagram for illustrating a refrigeration cycle apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram for illustrating an already-existing refrigeration cycle apparatus using an R410A refrigerant.

FIG. 3 is a graph for showing a relationship between a pressure loss of refrigerant inside a first communication pipe illustrated in FIG. 1 and an inner diameter of the first communication pipe.

FIG. 4 is a graph for showing a relationship between the pressure loss of the refrigerant inside the first communication pipe illustrated in FIG. 1 and a length of the first communication pipe.

FIG. 5 is a block diagram for illustrating a refrigeration cycle apparatus according to a second embodiment of the present invention.

FIG. 6 is a block diagram for illustrating a refrigeration cycle apparatus according to a third embodiment of the present invention.

FIG. 7 is a block diagram for illustrating a refrigeration cycle apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram for illustrating a refrigeration cycle apparatus according to a fifth embodiment of the present invention.

FIG. 9 is a graph for showing a relationship between the pressure loss of the refrigerant inside the first communication pipe to which a design pressure within a refrigeration cycle apparatus using an R404A refrigerant is applied and the inner diameter of the first communication pipe.

FIG. 10 is a graph for showing a relationship between the pressure loss of the refrigerant inside the first communication pipe to which the design pressure within the refrigeration cycle apparatus using the R404A refrigerant is applied and the length of the first communication pipe.

Description of Embodiments

[0011] Now, preferred embodiments of the present invention are described with reference to the accompanying drawings.

First Embodiment FIG. 1 is a block diagram for illustrating a refrigeration cycle apparatus according to a first embodiment of the present invention. In FIG. 1, the refrigeration cycle apparatus includes: a heat source unit 1; a cooling unit 2 arranged so as to be spaced apart from the heat source unit 1; and a first communication pipe 3 and a second communication pipe 4 connected between the heat source unit 1 and the cooling unit 2, which are configured to circulate refrigerant between the heat source unit 1 and the cooling unit 2. In this example, CO2 being a high-pressure refrigerant is used as the refrigerant of the refrigeration cycle apparatus, and a pressure on a high-pressure side of a refrigeration cycle is set to be equal to or smaller than a critical pressure of the refrigerant.

[0012] The heat source unit 1 includes a compressor 11, a condenser (high-pressure-side heat exchanger) 12, and a main pressure reducing device 13 (expansion valve) . The heat source unit 1 includes a plurality of connection pipes for connecting the second communication pipe 4, the compressor 11, the condenser 12, the main pressure reducing device 13, and the first communication pipe 3 in order. On the other hand, the cooling unit 2 includes an evaporator (low-pressure-side heat exchanger) 14. The cooling unit 2 includes a plurality of connection pipes for connecting the first communication pipe 3, the evaporator 14, and the second communication pipe 4 in order.

[0013] with this configuration, in the refrigeration cycle apparatus, when the compressor 11 is driven, the refrigerant is sent from the compressor 11 to the condenser 12, the main pressure reducing device 13, the first communication pipe 3, the evaporator 14, and the second communication pipe 4 in the stated order, and returns to the compressor 11.

[0014] The compressor 11 compresses a gaseous refrigerant. The refrigerant compressed by the compressor 11 is sent to the condenser 12.

[0015] The condenser 12 cools the gaseous refrigerant sent from the compressor 11 to make a liquid refrigerant. The condenser 12 cools and condenses the refrigerant by emitting heat from the gaseous refrigerant to coolant ( for example, air or water) . The refrigerant condensed by the condenser 12 is sent to the main pressure reducing device 13.

[0016] The main pressure reducing device 13 expands the refrigerant sent from the condenser 12 to reduce a pressure thereof. In this example, the main pressure reducing device 13 is set as an electric expansion valve capable of adjusting a flow rate of the refrigerant. The main pressure reducing device 13 is controlled by a control unit (not shown) . [0017] The first communication pipe 3 guides the refrigerant to be sent from the main pressure reducing device 13 to the evaporator 14 between the heat source unit 1 and the cooling unit 2.

[0018] The evaporator 14 evaporates the refrigerant sent from the first communication pipe 3. The evaporator 14 is provided to a container for cooling ( for example, showcase for cooling) installed in a shop such as a convenience store or a supermarket. The container for cooling is cooled when the refrigerant is evaporated by the evaporator 14.

[0019] The second communication pipe 4 guides the refrigerant to be sent from the evaporator 14 to the compressor 11 between the heat source unit 1 and the cooling unit 2. The gaseous refrigerant is guided inside the second communication pipe 4.

[0020] The first communication pipe 3 and the second communication pipe 4 are provided in a downstream of the main pressure reducing device 13 and an upstream of the compressor 11. Therefore, the first communication pipe 3 and the second communication pipe 4 are provided on a low-pressure side within the refrigeration cycle.

[0021] The main pressure reducing device 13 reduces the pressure of the refrigerant to a pressure equal to or smaller than a design pressure of the first communication pipe 3 and the second communication pipe 4. In this example, the design pressure of the first communication pipe 3 and the second communication pipe 4 is set to 4.15 MPa, and the main pressure reducing device 13 reduces the pressure of the refrigerant to be equal to or smaller than 4.15 MPa.

[0022] For example, in an already-existing refrigeration cycle apparatus using an R410A refrigerant, as illustrated in FIG. 2, the main pressure reducing device 13 is provided not to the heat source unit 1 but to the cooling unit 2, and the refrigerant sent from the condenser 12 is sent to the main pressure reducing device 13 after passing through the first communication pipe 3. That is, in the already-existing refrigeration cycle apparatus using the R410A refrigerant, the first communication pipe 3 is provided on the high-pressure side within the refrigeration cycle. A design pressure of the first communication pipe 3 of the already-existing refrigeration cycle apparatus using the R410A refrigerant illustrated in FIG. 2 is set to 4.15 MPa.

[0023] In the refrigeration cycle apparatus according to this embodiment that uses the high-pressure refrigerant (CO2), the main pressure reducing device 13 is provided to the heat source unit 1, and hence the pressure of the refrigerant is reduced by the main pressure reducing device 13, to thereby be able to set the pressure of the refrigerant inside the first communication pipe 3 and the second communication pipe 4 to be equal to or smaller than the design pressure of the first communication pipe 3 of the already-existing refrigeration cycle apparatus (that is, equal to or smaller than 4.15 MPa) . Therefore, the first communication pipe 3 and the second communication pipe 4 of the already-existing refrigeration cycle apparatus using the R410A refrigerant can be reused as the first communication pipe 3 and the second communication pipe 4 of the refrigeration cycle apparatus according to this embodiment that uses the high-pressure refrigerant (CO2)* [0024] Further, when the refrigerant that has exited from the main pressure reducing device 13 passes through the first communication pipe 3, a pressure loss of the refrigerant occurs. The pressure loss of the refrigerant inside the first communication pipe 3 becomes larger as the length of the first communication pipe 3 increases, and becomes larger as the inner diameter of the first communication pipe 3 decreases. In a case where the pressure loss of the refrigerant inside the first communication pipe 3 is large, when the refrigerant passes through the first communication pipe 3, the pressure of the refrigerant is greatly lowered, which raises a fear that a saturation temperature of the refrigerant at the evaporator 14 may fall below an evaporating temperature that the user wishes to use for the evaporator 14 (in-use evaporating temperature of the evaporator 14) (that is, fear that a proper operation of the refrigerating cycle apparatus cannot be conducted) . [0025] In order to prevent this, in the refrigeration cycle apparatus according to this embodiment, a magnitude of the pressure loss of the refrigerant inside the first communication pipe 3 is set within a range that prevents the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14. That is, the first communication pipe 3 is a communication pipe that causes the pressure loss of the refrigerant within the range that prevents the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14. The magnitude of the pressure loss of the refrigerant inside the first communication pipe 3 is set by adjusting the length and the inner diameter of the first communication pipe 3.

[0026] Normally, the evaporating temperature to be used for the evaporator 14 is from -4 0 °C to 0°C. Therefore, a proper operation of the refrigerating machine can be conducted by maintaining the pressure of the refrigerant at the evaporator 14 so as to prevent the saturation temperature of the refrigerant at the evaporator 14 from falling below -40°C (in-use evaporating temperature).

[0027] FIG. 3 is a graph for showing a relationship between the pressure loss of the refrigerant inside the first communication pipe 3 illustrated in FIG. 1 and the inner diameter of the first communication pipe 3. For example, when a refrigeration cycle apparatus installed in the shop such as a supermarket is assumed, a maximum length of the first communication pipe 3 is approximately m. In FIG. 3, each of an inlet pressure and an outlet pressure of the first communication pipe 3 exhibited when the length of the first communication pipe 3 is 100 m is shown.

[0028] As shown in FIG. 3, it is understood that, as the inner diameter of the first communication pipe 3 decreases, a difference between the inlet pressure and the outlet pressure of the first communication pipe 3 increases, and the pressure loss of the refrigerant inside the first communication pipe 3 increases. In the refrigeration cycle apparatus according to this embodiment, for example, assuming that the pressure of the refrigerant is reduced to 4.15 MPa (design pressure of the first communication pipe 3) by the main pressure reducing device 13, the inner diameter of the first communication pipe 3 for maintaining the outlet pressure of the first communication pipe 3 having a length of 100 m to be equal to or larger than 0.90MPa (pressure of the refrigerant corresponding to evaporating temperature of -40°C) is equal to or larger than 10.3 mm as understood from FIG. 3.

[0029] FIG. 4 is a graph for showing a relationship between the pressure loss of the refrigerant inside the first communication pipe 3 illustrated in FIG. 1 and the length of the first communication pipe 3. For example, when the refrigeration cycle apparatus of FIG. 2 installed in the shop such as a supermarket is assumed, the inner diameter of the first communication pipe 3 is approximately 12.7 mm. In FIG. 4, each of an inlet pressure and an outlet pressure of the first communication pipe 3 exhibited when the inner diameter of the first communication pipe 3 is 12.7 mm is shown.

[0030] As shown in FIG. 4, it is understood that, as the length of the first communication pipe 3 increases, a difference between the inlet pressure and the outlet pressure of the first communication pipe 3 increases, and the pressure loss of the refrigerant inside the first communication pipe 3 increases. In the refrigeration cycle apparatus according to this embodiment, for example, assuming that the pressure of the refrigerant is reduced to 4. 1 5MPa (designpressure of the first communication pipe 3) by the main pressure reducing device 13, the length of the first communication pipe 3 formaintaining the outlet pressure of the first communication pipe 3 having an inner diameter of 12.7 mm to be equal to or larger than 0.90 MPa (pressure of the refrigerant corresponding to evaporating temperature of -40°C) is equal to or smaller than 142 m as understood from FIG. 4.

[0031] In the refrigeration cycle apparatus according to this embodiment, the inner diameter of the first communication pipe 3 is set to be equal to or larger than 10.3 mm, or the length of the first communication pipe 3 is set to be equal to or smaller than 142m. This can suppress the pressure loss of the refrigerant inside the first communication pipe 3, and allows a proper operation of the refrigerating cycle apparatus. The pressure loss of the refrigerant is suppressed, and hence it suffices that the length of the first communication pipe 3 is equal to or larger than 0 m. Further, an upper limit of the inner diameter of the first communication pipe 3 is a size that allows the first communication pipe 3 to fit into a pipe installation space, or a size that causes immiscible refrigerating machine oil to exhibit a flow velocity of the refrigerant to an extent that allows the refrigerant to flow.

[0032] Further, in the refrigeration cycle apparatus according to this embodiment, the refrigerant having been reduced in pressure by the main pressure reducing device 13 passes through the first communication pipe 3, and hence the refrigerant inside the first communication pipe 3 is brought to a two-phase gas-liquid state. In the first communication pipe 3, as a quality in a two-phase gas-liquid refrigerant decreases, the refrigerant becomes closer to a single-phase liquid state, and hence the pressure loss of the refrigerant decreases. On the other hand, in the first communication pipe 3, as the pressure of the two-phase gas-liquid refrigerant decreases, the quality of the refrigerant increases. Based on such a fact, in this example, in order to reduce the pressure loss of the refrigerant inside the first communication pipe 3, a width of the pressure reduction of the refrigerant is adjusted by the main pressure reducing device 13 so that the pressure of the refrigerant inside the first communication pipe 3 becomes as high as possible within a range equal to or smaller than the design pressure of the first communication pipe 3. That is, in this example, the pressure of the refrigerant is reduced by the main pressure reducing device 13 so that the inlet pressure of the first communication pipe 3 becomes the design pressure of the first communication pipe 3.

[0033] In such a refrigeration cycle apparatus, the pressure of the refrigerant inside the first communication pipe 3 can be lowered by the pressure reduction of the refrigerant conducted by the main pressure reducing device 13, and hence pressure resistance performance of the first communication pipe 3 can be designed to be low. Accordingly, the communication pipe of the refrigeration cycle apparatus using a general refrigerant (for example, R410A) can be employed as the first communication pipe 3 of the refrigeration cycle apparatus using the high-pressure refrigerant (for example, CO2). For example, when the communication pipe of the already-existing refrigeration cycle apparatus using the general refrigerant is modified into the refrigeration cycle apparatus using the high-pressure refrigerant, the communication pipe of the already-existing refrigeration cycle apparatus canbe reused without a change, and alleviation of time and labor for modification work for the refrigeration cycle apparatus can be achieved. In addition, even when the refrigeration cycle apparatus using the high-pressure refrigerant is newly installed, the pressure inside the first communication pipe 3 can be lowered, and hence the material thickness of the first communication pipe 3 can be reduced. This facilitates bending and connection work for the first communication pipe 3, and can alleviate time and labor for on-site installation work for the refrigeration cycle apparatus.

[0034] Further, the pressure loss of the refrigerant inside the first communication pipe 3 is suppressed within the range that prevents the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14, and hence evaporation of the refrigerant can be prevented from failing to be properly conducted at the in-use evaporating temperature of the evaporator 14, which can avoid reduction in proper operation range of the refrigeration cycle apparatus.

[0035] That is, in the refrigeration cycle apparatus according to this embodiment, the alleviation of time and labor for installation work or modification work and the avoidance of the reduction in the proper operation range can be satisfied at the same time.

[0036] Further, the inner diameter of the first communication pipe 3 is equal to or larger than 10.3 mm or the length of the first communication pipe 3 is equal to or smaller than 142 if, and hence the pressure loss of the refrigerant inside the first communication pipe 3 can be easily suppressed with a simple configuration.

[0037] Note that, in the above-mentioned example, the pressure on the high-pressure side of the refrigeration cycle is set to be equal to or smaller than the critical pressure of the refrigerant, but the operation may be conducted within such a supercritical region that the pressure on the high-pressure side of the refrigeration cycle is higher than the critical pressure of the refrigerant.

[0038] Second Embodiment In the first embodiment, the refrigerant is sent from the first communication pipe 3 directly to the evaporator 14, but a degree of superheat of the refrigerant exiting from an outlet of the evaporator 14 may be controlled by providing a flow rate control unit 21 between the first communication pipe 3 and the evaporator 14 to send the refrigerant sent from the first communication pipe 3 to the evaporator 14 after adjusting the flow rate of the refrigerant by the flow rate control unit 21.

[0039] That is, FIG. 5 is a block diagram for illustrating a refrigeration cycle apparatus according to a second embodiment of the present invention. The cooling unit 2 further includes the flow rate control unit (cooling-unit-side pressure reducing device) 21. The flow rate control unit 21 is provided to the connection pipe for connecting the first communication pipe 3 and the evaporator 14 to each other. Further, the flow rate control unit 21 reduces the pressure of the refrigerant sent from the first communication pipe 3 to send the refrigerant to the evaporator 14. In this example, the flow rate control unit 21 is set as an electric expansion valve capable of adjusting the flow rate of the refrigerant. The flow rate control unit 21 is controlled by a control unit (not shown). The evaporator 14 evaporates the refrigerant having been reduced in pressure by the flow rate control unit 21.

[0040] The degree of superheat of the refrigerant at the outlet of the evaporator 14 is controlled by adjustment of the flow rate of the refrigerant conducted by the flow rate control unit 21. For example, after the pressure of the refrigerant is reduced by the main pressure reducing device 13 to set the pressure of the refrigerant inside the first communication pipe 3 to 4. 15 MPa (the design pressure of the first communication pipe 3) , the flow rate of the refrigerant is adjusted by the flow rate control unit 21, and the degree of superheat of the refrigerant exiting from the outlet of the evaporator 14 is set to from 5°C to 10°C. The other configuration is the same as that of the first embodiment.

[0041] In such a refrigeration cycle apparatus, the flow rate control unit 21 configured to reduce the pressure of the refrigerant sent from the first communication pipe 3 to send the refrigerant to the evaporator 14 is included in the cooling unit 2, and hence each of the pressure of the refrigerant inside the first communication pipe 3 and the evaporating temperature at the evaporator 14 can be controlled more positively. This allows the refrigerant to be evaporated sufficiently at the evaporator 14 while suppressing the increase in the pressure loss of the refrigerant inside the first communication pipe 3 more positively, which allows improvement in cooling performance at the evaporator 14 to be achieved. Therefore, the refrigerant returning from the evaporator 14 to the compressor 11 can be gasified more positively, and a failure or the like of the compressor 11 due to the returning of the liquid refrigerant to the compressor 11 can be avoided.

[0042] In this case, an adjustment width of the pressure reduction of the refrigerant used by the flow rate control unit 21 of the cooling unit 2 is equal to or smaller than approximately 0.3 MPa. Therefore, the maximum value of the pressure of the refrigerant inside the first communication pipe 3 can be set to a pressure higher than an evaporating pressure by 0. 3 MPa. Therefore, the pressure of the refrigerant inside the first communication pipe 3 can be increased within a range of the design pressure, and an increase in the pressure loss inside the first communication pipe 3 can be suppressed while achieving reduction in material thickness of the first communication pipe 3. Further, assuming that an upper limit of the pressure of the refrigerant inside the first communication pipe 3 is a design pressure of 4.15 MPa, an upper limit of the evaporating pressure becomes 3.85 MPa, and the evaporating temperature corresponding to the evaporating pressure of 3.85 MPa becomes 5°C. Normally, the evaporating temperature of the refrigeration cycle apparatus is from -40°C to 0°C, and hence the saturation temperature of the refrigerant at the evaporator 14 equal to or higher than the in-use evaporating temperature can be ensured, which can avoid the reduction in the proper operation range of the refrigeration cycle apparatus.

[0043] Note that, in the second embodiment, a plurality of cooling units 2 may be connected to a common first communication pipe 3 in parallel, and the refrigerant maybe sent from the common first communication pipe 3 to each of the cooling units 2. In this case, the pressure of the refrigerant is mainly reduced by the main pressure reducing device 13 of the heat source unit 1 so that the pressure of the refrigerant inside the first communication pipe 3 becomes equal to or smaller than the design pressure (4.15 MPa).

Further, in this case, the flow rate of the refrigerant is distributed to the respective evaporators 14 by the respective flow rate control units 21 based on the refrigeration capacities of the respective cooling units 2. That is, the flow rate of the refrigerant with respect to the respective evaporators 14 is adjusted by the respective flow rate control units 21 so that the evaporating temperatures at the respective evaporators 14 each become an in-use temperature. With this configuration, the refrigerant can be sufficiently evaporated by the respective cooling units 2 while suppressing the increase in the pressure loss of the refrigerant inside the first communication pipe 3 more positively, and improvement in cooling performance at each cooling unit can be achieved.

[0044] Third Embodiment FIG. 6 is a block diagram for illustrating a refrigeration cycle apparatus according to a third embodiment of the present invention. The heat source unit 1 further includes an internal heat exchanger 31. The internal heat exchanger 31 exchanges heat between the refrigerant sent from the second communication pipe 4 to the compressor 11 and the refrigerant sent from the condenser 12 to the main pressure reducing device 13. That is, the internal heat exchanger 31 exchanges heat between a gaseous refrigerant to be sucked into the compressor 11 and a liquid refrigerant that has exited from an outlet of the condenser 12. In the internal heat exchanger 31, heat is emitted from the refrigerant sent from the condenser 12 to the mainpressure reducing device 13 to the refrigerant sent from the second communication pipe 4 to the compressor 11. The other configuration is the same as that of the second embodiment.

[0045] In such a refrigeration cycle apparatus, the internal heat exchanger 31 configured to exchange heat between the refrigerant sent from the second communication pipe 4 to the compressor 11 and the refrigerant sent from the condenser 12 to the main pressure reducing device 13 is included in the heat source unit L, and hence a degree of subcooling of the liquid refrigerant to enter the main pressure reducing device 13 can be increased, and the quality of the refrigerant inside the first communication pipe 3 can be lowered. Therefore, the pressure loss of the refrigerant inside the first communication pipe 3 can be suppressed, and the outlet pressure of the first communication pipe 3 can be ensured so as to prevent the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14. Accordingly, a proper operation of the refrigerating cycle apparatus can be conducted more positively.

[0046] Note that, in the third embodiment, the internal heat exchanger 31 is applied to the heat source unit 1 according to the second embodiment, but the internal heat exchanger 31 may be applied to the heat source unit 1 according to the first embodiment.

[0047] Fourth Embodiment FIG. 7 is a block diagram for illustrating a refrigeration cycle apparatus according to a fourth embodiment of the present invention. The heat source unit 1 further includes a bypass circuit 41 and a bypass heat exchanger 42.

[0048] The bypass circuit 41 includes a bypass pressure reducing device 43 configured to reduce the pressure of a part of the refrigerant sent from the condenser 12 to the main pressure reducing device 13 and a bypass pipe 44 configured to send the refrigerant having been reduced in pressure by the bypass pressure reducing device 43 to a suction port of the compressor 11. In this example, the bypass pressure reducing device 43 is set as an electric expansion valve capable of adjusting the flow rate of the refrigerant.

[0049] The bypass heat exchanger 42 exchanges heat between the refrigerant sent from the condenser 12 to the main pressure reducing device 13 and the refrigerant having been reduced in pressure by the bypass pressure reducing device 43. That is, the bypass heat exchanger 42 exchanges heat between the liquid refrigerant that has exited from the outlet of the condenser 12 and the refrigerant in the two-phase gas-liquid state that has exited from the bypass pressure reducing device 43. In the bypass heat exchanger 42, heat is emitted from the refrigerant sent from the condenser 12 to the main pressure reducing device 13 to the refrigerant having been reduced in pressure by the bypass pressure reducing device 43. The other configuration is the same as that of the second embodiment.

[0050] In such a refrigeration cycle apparatus, the bypass heat exchanger 42 configured to exchange heat between the refrigerant sent from the condenser 12 to the main pressure reducing device 13 and the refrigerant having been reduced in pressure by the bypass pressure reducing device 43 is included in the heat source unit 1, and hence the degree of subcooling of the liquid refrigerant to enter the main pressure reducing device 13 can be increased, and the quality of the refrigerant inside the first communication pipe 3 can be lowered. Therefore, in the same manner as in the third embodiment, the pressure loss of the refrigerant inside the first communication pipe 3 can be suppressed. Further, a part of the refrigerant that has existed from the condenser 12 is sent to the compressor 11 by the bypass circuit 41, to thereby lower the flow rate of the refrigerant inside the first communication pipe 3, and hence the pressure loss of the refrigerant inside the first communication pipe 3 can be further suppressed. Therefore, a proper operation of the refrigerating cycle apparatus can be conducted more positively.

[0051] Note that, in the fourth embodiment, the bypass circuit 41 and the bypass heat exchanger 42 are applied to the heat source unit 1 according to the second embodiment, but the bypass circuit 41 and the bypass heat exchanger 42 maybe applied to the heat source unit 1 according to the first embodiment.

[0052] Further, the internal heat exchanger 31 according to the third embodiment may be applied to the heat source unit 1 according to the fourth embodiment. That is, both the internal heat exchanger 31 according to the third embodiment and the bypass circuit 41 and the bypass heat exchanger 42 according to the fourth embodiment may be applied to the heat source unit 1 according to the first embodiment or the second embodiment.

[0053] Fifth Embodiment FIG. 8 is a block diagram for illustrating a refrigeration cycle apparatus according to a fifth embodiment of the present invention. The heat source unit 1 further includes a liquid receiver 51. The liquid receiver 51 pools the liquid refrigerant that has exited from the condenser 12. With this configuration, the refrigerant at an outlet of the liquid receiver 51 is brought to a saturated liquid state. The liquid refrigerant pooled in the liquid receiver 51 is sent to the main pressure reducing device 13. The other configuration is the same as that of the second embodiment.

[0054] In such a refrigeration cycle apparatus, the liquid refrigerant that has exited from the condenser 12 is pooled in the liquid receiver 51, and the liquid refrigerant pooled in the liquid receiver 51 is sent to the main pressure reducing device 13, which can prevent the refrigerant to be sent to the main pressure reducing device 13 from being brought to a two-phase gas-liquid state. Therefore, the quality of the refrigerant inside the first communication pipe 3 can be lowered, and the increase in the pressure loss of the refrigerant inside the first communication pipe 3 can be suppressed. Accordingly, the outlet pressure of the first communication pipe 3 can be ensured so as to prevent the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14, and a proper operation of the refrigerating cycle apparatus can be conducted more positively.

[0055] Further, for example, when a plurality of cooling units 2 are installed, a large load fluctuation occurs due to switching in number of operation units among the respective cooling units 2. At this time, assuming that the liquid receiver 51 is not provided, the refrigerant at the outlet of the condenser 12 is brought to a two-phase gas-liquid state due to a lack of the refrigerant at the condenser 12, and the operation efficiency of the refrigeration cycle apparatus is lowered. In the fifth embodiment, the liquid refrigerant that has exited from the condenser 12 is pooled in the liquid receiver 51, which can avoid the lack of the refrigerant at the condenser 12, and can also avoid the lowering of the operation efficiency of the refrigeration cycle apparatus.

[0056] The specific embodiments of the present invention have been described above, but the present invention is not limited to the respective embodiments described above, and can be carried out with various changes within the scope of the present invention. For example, the design pressure of the first communication pipe 3 isnot limited to 4. 15 MPa, and a des ign pressure on the high-pressure side of the refrigeration cycle apparatus using an R4 04A refrigerant (that is, 2.94 MPa) may be set as the design pressure of the first communication pipe 3. In this case, as shown in FIG. 9 and FIG. 10, the inner diameter of the first communication pipe 3 is set to be equal to or smaller than 11.0 mm, or the length of the first communication pipe 3 is set to be equal to or smaller than 275 m, to thereby set the magnitude of the pressure loss of the refrigerant inside the first communication pipe 3 within the range that prevents the saturation temperature of the refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14.

[0057] Further, in the respective embodiments described above, a first detector configured to detect the temperature or the pressure of the refrigerant may be provided to the first communication pipe 3 or the evaporator 14, and the main pressure reducing device 13 may be controlled by a control unit based on the pressure of the refrigerant inside the first communication pipe 3 which has been obtained from a detection result obtained by the first detector. In this case, for example, a pressure sensor (first detector) configured to detect the pressure of the refrigerant can be provided to the first communication pipe 3 to obtain the pressure of the refrigerant inside the first communication pipe 3 from information obtained by the pressure sensor, and a temperature sensor (first detector) configured to detect the temperature of the refrigerant can be provided to the evaporator 14 to obtain the pressure of the refrigerant inside the first communication pipe 3 from temperature information on the evaporator 14 obtained by the temperature sensor. Further, for example, the temperature sensor (first detector) configured to detect the temperature of the refrigerant can be provided to the first communication pipe 3 to obtain the pressure of the refrigerant inside the first communication pipe 3 from the temperature information on the first communication pipe 3 obtained by the temperature sensor. With this configuration, the pressure of the refrigerant inside the first communication pipe 3 can be adjusted with more accuracy.

[0058] Further, in the second embodiment to the fifth embodiment, a second detector (pressure sensor or temperature sensor) configured to detect the temperature or the pressure of the refrigerant may be provided to the evaporator 14, and the flow rate control unit 21 may be controlled by a control unit based on the pressure of the refrigerant at the outlet of the evaporator 14 which has been obtained from a detection result obtained by the second detector. With this configuration, the degree of superheat of the refrigerant at the outlet of the evaporator 14 can be adjusted with more accuracy. [0059] Further, in the respective embodiments described above, the number of cooling units 2 is not limited to one, and a plurality of cooling units 2 may be provided. In addition, a plurality of heat source units 1 maybe provided. When a plurality of heat source units 1 are provided, the refrigerant sent from each of the main pressure reducing devices 13 of the respective heat source units 1 is guided through the common first communication pipe 3 to be sent to the cooling unit 2.

[0060] Further, in the respective embodiments described above, CO2 is used as the refrigerant of the refrigeration cycle apparatus, but such a refrigerant other than CO2 (for example, fluorocarbon refrigerant such as R32, mixed refrigerant containing any one of 002 and R32, ethylene, ethane, or nitrogen oxide) as to allow the refrigeration cycle to be operated in a supercritical region on the high-pressure side may be used as the refrigerant of the refrigeration cycle apparatus.

[0061] Further, the refrigeration cycle apparatus according to the respective embodiments described above can be applied not only to the showcase for cooling installed in the shop but also to various cooling devices, refrigerating apparatus, and the like.