GB2535051A

GB2535051A - Refrigeration cycle device

Info

Publication number: GB2535051A
Application number: GB1605957.8A
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: 2016-08-10
Anticipated expiration: 2033-10-28
Also published as: JPWO2015063837A1; GB2535051B; WO2015063837A1; CN105705882A

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 high-pressure-side heat exchanger. 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 principal depressurization device depressurizes the coolant in a manner such that the coolant inside the first connecting tube enters a gas-liquid two-phase state. 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. When such a related-art refrigerating machine Ls 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).

[0003] The increase in the length of the communication pipe causes an increase in a charged refrigerant amount of the refrigerating machine. As a result, in the related-art refrigerating machine, a refrigerant cost increases, and a product cost of the refrigerating machine increases. Further, when the charged refrigerant amount increases, a liquid return to the compressor is liable to occur when the refrigerating machine starts up or when load changes, which degrades reliability of the related-art refrigerating machine. In addition, in some cases, a fluorocarbon refrigerant such as hydrofluorocarbon (HFC) is used for the refrigerating machine, but in recent years, use of a fluorocarbon refrigerant having a high global warming potential has become a problem from a viewpoint of global environmental protection.

[0004] Hitherto, in order to achieve reduction in cost, improvement in reliability, and reduction in global environmental load, there is proposed a refrigerating machine in which the charged refrigerant amount is reduced by arranging a main pressure reducing mechanism in the heat source unit and lowering a pressure inside the communication pipe by the main pressure reducing mechanism to thereby bring the refrigerant inside the communication pipe to a two-phase gas-liquid state (see, for example, PTL 1).

Citation List Patent Literature [0005] [PTL 1] JP 2012-112622 A

Summary of Invention Technical Problem

[0006] However, in a related-art refrigerating machine described in PTL 1, a pressure loss of refrigerant inside the communication pipe increases when refrigerant in a two-phase gas-liquid state flows through a communication pipe. 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 reducing a charged refrigerant amount 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; a high-pressure-side heat exchanger configured to cool 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 main pressure reducing device is configured to reduce the pressure of the refrigerant so as to bring the refrigerant inside the first communication pipe to a two-phase gas-liquid state; and 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 refrigerant in the first communication pipe is brought to a two-phase gas-liquid state by the pressure reduction of the refrigerant conducted by the main pressure reducing device, and hence an effect of reducing the charged refrigerant amount within the refrigeration cycle apparatus can be ensured. Further, the pressure loss of the refrigerant inside the first communication pipe is suppressed to a range that prevents the saturation temperature of the refrigerant at the evaporator from falling below the in-use evaporating temperature, and hence reduction in proper operation range of the refrigeration cycle apparatus can be avoided.

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 a refrigeration cycle apparatus for comparison.

FIG. 3 is a graph for showing a relationship between an inner diameter of a first communication pipe illustrated in FIG. 1 and a length of the first communication pipe that are exhibited when a pressure reduction amount of refrigerant passing in a two-phase gas-liquid state through the first communication pipe becomes a maximum pressure reduction amount.

FIG. 4 is a graph for comparing a change of a refrigerant amount with respect to the length of the first communication pipe illustrated in FIG. 1 between the refrigerant in the two-phase gas-liquid state and refrigerant in a single-phase liquid state.

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 graph for showing a relationship between the inner diameter of the first communication pipe illustrated in FIG. 7 and the length of the first communication pipe that are exhibited when the pressure reduction amount of the refrigerant passing in the two-phase gas-liquid state through the first communication pipe becomes the maximum pressure reduction amount.

FIG. 9 is a graph for comparing a change of the refrigerant amount with respect to the length of the first communication pipe illustrated in FIG. 7 between the refrigerant in the two-phase gas-liquid state and the refrigerant in the single-phase liquid state.

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, an R404A refrigerant being a fluorocarbon refrigerant is used as the refrigerant of the refrigeration cycle apparatus.

[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. 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 orwater) . 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. Further, the main pressure reducing device 13 reduces the pressure of the refrigerant so that the refrigerant at an inlet of the first communication pipe 3 is brought to a two-phase gas-liquid state. 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. The refrigerant is guided inside the first communication pipe 3 while maintaining the two-phase gas-liquid state over an entire segment of the first communication pipe 3.

[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 forcooling) 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 a refrigeration cycle.

[0021] For example, in a refrigeration cycle apparatus for comparison that uses an R404A 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 refrigeration cycle apparatus for comparison, the first communication pipe 3 is provided on a high-pressure side within the refrigeration cycle. Therefore, in the refrigeration cycle apparatus for comparison, the refrigerant passing through the first communication pipe 3 is brought to a single-phase liquid state, which increases a charged refrigerant amount.

[0022] In contrast, in the refrigeration cycle apparatus according to this embodiment, the refrigerant inside the first communication pipe 3 is brought to a two-phase gas-liquid state due to the pressure reduction of the refrigerant conducted by the main pressure reducing device 13. This reduces the refrigerant amount inside the first communication pipe 3, and reduces the charged refrigerant amount within the refrigeration cycle apparatus. Further, in the refrigeration cycle apparatus according to this embodiment, compared with the refrigeration cycle apparatus for comparison, a design pressure of the first communication pipe 3 is lower due to the pressure reduction of the refrigerant conducted by the main pressure reducing device 13, and a material thickness of the first communication pipe 3 is reduced.

[0023] When the refrigerant 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. Further, the pressure loss of the refrigerant inside the first communication pipe 3 becomes larger when the refrigerant is in the two-phase gas-liquid state than in the single-phase liquid state. 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) . [0024] For example, when the refrigeration cycle apparatus installed in the shop such as a supermarket is assumec, a maximum length of the first communication pipe 3 is approximately 100 m. In the refrigeration cycle apparatus for comparison, the inner diameter of the first communication pipe 3 is designed so that the refrigerant maintains the single-phase liquid state at an outlet of the first communication pipe 3 even when a large pressure loss for the maximum length (approximately 100 m) of the first communication pipe 3 occurs. Further, the inner diameter of the first communication pipe 3 is not changed depending on the length of the first communication pipe 3.

[0025] In contrast, in the refrigeration cycle apparatus according to this embodiment, the refrigerant inside the first communication pipe 3 is brought to a two-phase gas-liquid state. In the refrigeration cycle apparatus according to this embodiment, in order to ensure a proper operation of the refrigerating cycle apparatus, 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] FIG. 3 is a graph for showing a relationship between the inner diameter of the first communication pipe 3 illustrated in FIG. 1 and the length of the first communication pipe 3 that are exhibited when the pressure reduction amount of the refrigerant passing in a two-phase gas-liquid state through the first communication pipe 3 becomes a maximum pressure reduction amount. In this case, the maximum pressure reduction amount represents a pressure difference between a maximum pressure (upper limit) that allows the refrigerant to maintain the two-phase gas-liquid state and a pressure (lower limit) for the evaporating temperature used by the user (in-use evaporating temperature of the evaporator 14). Therefore, in FIG. 3, a maximum difference between an inlet pressure and an outlet pressure of the first communication pipe 3 exhibited when the refrigerant inside the first communication pipe 3 maintains the two-phase gas-liquid state is shown. Note that, in FIG. 3, the relationship is shown between the inner diameter of the first communication pipe 3 and the length of the first communication pipe 3 exhibited when a refrigeration capacity of the refrigeration cycle apparatus is 8.5 kW with the in-use evaporating temperature of the evaporator 14 being -4000.

[0027] It is understood as shown in FIG. 3 that the inner diameter of the first communication pipe 3 exhibited when the pressure reduction amount of the refrigerant inside the first communication pipe 3 becomes the maximum pressure reduction amount becomes larger as the length of the first communicationpipe 3 increases. Therefore, the inner diameter of the first communication pipe 3 that maintains the maximum pressure reduction amount increases as the length of the first communication pipe 3 increases, and the refrigerant amount inside the first communication pipe 3 increases with the increase in the inner diameter of the first communication pipe 3.

[0028] In regard to the inner diameter of the first communication pipe 3 according to this embodiment, the inner diameter of the first communication pipe 3 is set based on the length of the first communication pipe 3 so that the pressure reduction amount (pressure loss) of the refrigerant inside the first communication pipe 3 becomes the maximum pressure reduction amount (fixed value) . [0029] FIG. 4 is a graph for comparing a change of the refrigerant amount with respect to the length of the first communication pipe 3 illustrated in FIG. 1 between the refrigerant in the two-phase gas-liquid state and the refrigerant in the single-phase liquid state. In regard to the refrigerant amount inside the first communication pipe 3, it is understood as shown in FIG. 4 that the refrigerant in the single-phase liquid state is larger in amount than the refrigerant in the two-phase gas-liquid state when the length of the first communication pipe 3 is equal to or smaller than 186 m, while the refrigerant in the two-phase gas-liquid state is larger in amount than the refrigerant in the single-phase liquid state when the length of the first communication pipe 3 is longer than 186 m. That is, it is understood that an effect of reducing the refrigerant amount by bringing the refrigerant to a two-phase gas-liquid state inside the first communication pipe 3 is lost when the length of the first communication pipe 3 is longer than 186 m. Therefore, in this example, the length of the first communication pipe 3 is set to be equal to or smaller than 186 m.

[0030] For example, even v,,Then the refrigeration cycle apparatus according to this embodiment installed in the shop such as a supermarket is assumed, the length of the first communication pipe 3 is at most approximately 100 m, which is equal to or smaller than 186 m, and hence a proper operation of the refrigerating cycle apparatus can be conducted by ensuring that the outlet pressure of the first communication pipe 3 is kept equal to or larger than the pressure for the in-use evaporating temperature of the evaporator 14 while obtaining the effect of reducing the refrigerant amount by bringing the refrigerant to a two-phase gas-liquid state inside the first communication pipe 3.

[0031] Further, as a quality of the refrigerant in the two-phase gas-liquid state increases, a gas amount increases, and hence the effect of reducing the refrigerant amount increases. Therefore, the refrigerant amount inside the first communication pipe 3 can be further reduced by lowering a degree of subcooling at an outlet of the condenser 12 to increase the quality of the refrigerant. Further, the quality of the refrigerant inside the first communication pipe 3 increases as the pressure of the refrigerant inside the first communication pipe 3 decreases, and hence the refrigerant amount inside the first communication pipe 3 can also be reduced by lowering the inlet pressure of the first communication pipe 3.

[0032] However, when the degree of subcooling at the outlet of the condenser 12 is lowered (for example, when the refrigerant that is still in a two-phase gas-liquid state exits from the outlet of the condenser 12), the refrigerant is not sufficiently condensed by the condenser 12, and hence the condenser 12 cannot be used effectively, which raises a fear that an operation efficiency of the refrigeration cycle apparatus may be lowered. Therefore, by bringing the outlet of the condenser 12 to a saturated state (that is, by setting the degree of subcooling of the refrigerant at the outlet of the condenser 12 to 0), the effect of reducing the refrigerant amount can be obtained without lowering the operation efficiency of the refrigeration cycle apparatus. Based on the above description, in this embodiment, the condenser 12 is designed so that the degree of subcooling of the refrigerant becomes 0 at the outlet of the condenser 12.

[0033] In such a refrigeration cycle apparatus, the refrigerant inside the first communication pipe 3 is brought to a two-phase gas-liquid state due to the pressure reduction of the refrigerant conducted by the main pressure reducing device 13, and hence the refrigerant amount inside the first communication pipe 3 can be reduced, which allows reduction:n the charged refrigerant amount within the refrigeration cycle apparatus to be achieved. This allows reduction in cost and reduction in global environmental load to be achieved. Further, an occurrence of a phenomenon (liquid return) that the liquid refrigerant returns to the compressor 11 can be prevented, and a failure or the like of the compressor 11 due to the liquid return can be prevented. Therefore, improvement in reliability of the refrigeration cycle apparatus can be achieved. In addition, the pressure of the refrigerant inside the first communication pipe 3 can be lowered, and hence pressure resistance performance of the first communication pipe 3 can be lowered, and the material thickness of the first communication pipe 3 can be reduced. This facilitates bending, connection work, or the like for the first communication pipe 3, and can alleviate time and labor for on-site instal lation work for the refrigeration cycle apparatus. Therefore, reduction in construction time and construction cost of the refrigeration cycle apparatus can be achieved.

[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 reduction in the charged refrigerant amount and the avoidance of the reduction in the proper operation range can be satisfied at the same tine.

[0036] Further, the inner diameter of the first communication pipe 3 is set based on the length of the first communication pipe 3 so that the pressure loss of the refrigerant inside the first communication pipe 3 becomes the maximum pressure reduction amount (fixed value), and the length of the first communication pipe 3 is set to be equal to or smaller than 18 6 m, which allows the refrigerant amount inside the first communication pipe 3 to be reduced more positively than in a case where the refrigerant inside the first communication pipe 3 is brought to a single-phase liquid state.

[0037] 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.

[0038] 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. The flow rate control unit 21 reduces the pressure of the refrigerant in the two-phase gas-liquid state which has passed through the first communication pipe 3. 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.

[0039] 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. Further, in this example, an adjustment width of the pressure reduction of the refrigerant used by the flow rate control unit 21 of the cooling unit 2 is set to approximately 0.3 MPa. Therefore, the outlet pressure of the first communication pipe 3 is higher than an evaporating pressure by 0.3 MPa.

[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 and the refrigerant in the two-phase gas-liquid state passes through 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 the evaporating temperature at the evaporator 14 can be controlled more positively by the flow rate control unit 21. This allows the refrigerant to be evaporated sufficiently at the evaporator 14, 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 liquid return can be avoided more positively.

[0042] 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 as to bring the refrigerant inside the first communication pipe 3 to a two-phase gas-liquid state. 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 evaporated sufficiently at the respective cooling units 2 while reducing the refrigerant amount inside the first communication pipe 3 more positively, which allows improvement in cooling performance at each cooling unit to be achieved.

[0043] 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 a liquid receiver 31. The liquid receiver 31 pools the liquid refrigerant that has exited from the condenser 12. With this configuration, the refrigerant at an outlet of the liquid receiver 31 is brought to a saturated liquid state. The liquid refrigerant pooled in the liquid receiver 31 is sent to the main pressure reducing device 13. The other configuration is the same as that of the second embodiment.

[0044] In such a refrigeration cycle apparatus, the liquid refrigerant that has exited from the condenser 12 is pooled in the liquid receiver 31, and the liquid refrigerant pooled in the liquid receiver 31 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.

[0045] 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 31 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 third embodiment, the liquid refrigerant that has exited from the condenser 12 is pooled in the liquid receiver 31, which can avoid the lack of the refrigerant at the condenser 12, and can avoid the lowering of the operation efficiency of the refrigeration cycle apparatus.

[0046] Fourth Embodiment FIG. 7 is a block diagram for illustrating a refrigeration cycle apparatus according to a fourth embodiment of the present invention. The refrigeration cycle apparatus according to the fourth embodiment is a binary refrigeration cycle apparatus including a high-temperature refrigeration cycle section 41 in addition to a low-temperature refrigeration cycle section having the same configuration as that of the refrigeration cycle apparatus according to the first embodiment. A low-temperature refrigerant is used in the low-temperature refrigeration cycle section, while a high-temperature refrigerant is used in the high-temperature refrigeration cycle section 41. In this example, CO2 being a high-pressure refrigerant is set as the low-temperature refrigerant, and the pressure on the high-pressure side of the low-temperature refrigeration cycle section is set to be equal to or smaller than a supercritical pressure.

[0047] The heat source unit 1 further includes the high-temperature refrigeration cycle section 41 in addition to the compressor 11, the condenser 12, and the main pressure reducing device 13. The high-temperature refrigeration cycle section 41 includes a high-temperature compressor 42, a high-temperature condenser 43, and a high-temperature pressure reducing device (expansion valve) 44. The heat source unit 1 includes a plurality of connection pipes for connecting the high-temperature compressor 42,thehigh-temperaturecondenser43,thehigh-temperaturepressure reducing device 44, and the condenser 12 in order. With this configuration, in the high-temperature refrigeration cycle section, when the high-temperature compressor 42 is driven, the high-temperature refrigerant is sent from the high-temperature compressor 42 to the high-temperature condenser 43, the high-temperature pressure reducing device 44, and the condenser 12 in the stated order, and returns to the high-temperature compressor 42.

[0048] The high-temperature compressor 42 compresses a gaseous high-temperature refrigerant. The high-temperature refrigerant compressed by the compressor 11 is sent to the high-temperature condenser 43.

[0049] The high-temperature condenser 43 condenses the gaseous high-temperature refrigerant sent from the high-temperature compressor 42 to make a liquid high-temperature refrigerant. The high-temperature condenser 43 cools and condenses the high-temperature refrigerant by emitting heat from the gaseous high-temperature refrigerant to coolant (for example, air or water) . The refrigerant condensed by the high-temperature condenser 43 is sent to the high-temperature pressure reducing device 44.

[0050] The high-temperature pressure reducing device 44 expands the liquid high-temperature refrigerant sent from the high-temperature condenser 43 to reduce a pressure thereof. The high-temperature refrigerant having been reduced in pressure by the high-temperature pressure reducing device 44 is sent to the condenser 12.

[0051] The condenser 12 is a cascading heat exchanger configured to exchange heat between the low-temperature refrigerant sent from the compressor 11 and the high-temperature refrigerant sent from the high-temperature pressure reducing device 44. In the condenser 12, the low-temperature refrigerant is cooled and the high-temperature refrigerant is heated by transfer of heat from the low-temperature refrigerant to the high-temperature refrigerant.

The high-temperature refrigerant is heated to be evaporated, and is then sent from the condenser 12 to the high-temperature compressor 42.

[0052] The pressure on the high-pressure side of the low-temperature refrigeration cycle section is set to be equal to or smaller than the supercritical pressure of the low-temperature refrigerant. With this configuration, the low-temperature refrigerant is cooled to be condensed by the condenser 12, and is then sent from the condenser 12 to the main pressure reducing device 13 in a single-phase liquid state.

[0053] In the same manner as in the first embodiment, the inner diameter of the first communication pipe 3 is set based on the length of the first communication pipe 3 so that the pressure reduction amount of the low-temperature refrigerant inside the first communication pipe 3 becomes the maximum pressure reduction amount. In this example, the effect of reducing the refrigerant amount to be obtained by bringing the low-temperature refrigerant to a two-phase gas-liquid state inside the first communication pipe 3 can be obtained by, as shown in FIG. 8 and FIG. 9, setting the length of the first communication pipe 3 to be equal to or smaller than 95 m. The other configuration is the same as that of the first embodiment.

[0054] In this manner, evenwhen CO2 is set as the low-temperature refrigerant to be used for the low-temperature refrigeration cycle section of the binary refrigeration cycle apparatus, the reduction in the charged refrigerant amount within the refrigeration cycle apparatus can be achieved by bringing the low-temperature refrigerant inside the first communication pipe 3 to a two-phase gas-liquid state. Further, the reduction in the proper operation range of the refrigeration cycle apparatus can be avoided by suppressing a pressure loss of the low-temperature refrigerant inside the first communication pipe 3 within a range that prevents the saturation temperature of the low-temperature refrigerant at the evaporator 14 from falling below the in-use evaporating temperature of the evaporator 14.

[0055] Note that, in the fourth embodiment, the low-temperature refrigeration cycle section has the same configuration as the configuration of the refrigeration cycle apparatus according to the first embodiment, but the low-temperature refrigeration cycle section may have the same configuration as the configuration of the refrigeration cycle apparatus according to the second embodiment.

[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.

[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 and the third embodiment, a second detector (pressure sensor or temperature sensor) configured to detect the temperature or the pressure of the refrigerant maybe 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 at the outlet of the refrigerant at 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 first embodiment, the second embodiment, and the third embodiment, an R404A refrigerant is used as the refrigerant of the refrigeration cycle apparatus, and in the fourth embodiment, CO2 is used as the refrigerant of the refrigeration cycle apparatus. However, the refrigeration cycle may be operated in a supercritical region on the high-pressure side by using such a refrigerant (for example, natural refrigerant such as CO2, fluorocarbon refrigerant such as 332, mixed refrigerant containing any one of CO2 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 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.