Refrigeration apparatus

Abstract

A refrigeration apparatus uses supercritical range refrigerant, and includes a multi-stage compression mechanism, a heat source-side heat exchanger, a usage-side heat exchanger, a switching mechanism switchable between cooling and heating operation states, and a second-stage injection tube. The second-stage injection tube branches off refrigerant, which has radiated heat in the heat source-side heat exchanger or the usage-side heat exchanger, and returns the refrigerant to the second-stage compression element. Refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube at least during a beginning of a reverse cycle defrosting operation, which is performed to defrost the heat source-side heat exchanger by switching the switching mechanism to the cooling operation state.

Description

TECHNICAL FIELD[0001]The present invention relates to a refrigeration apparatus, and particularly relates to a refrigeration apparatus which has a refrigerant circuit configured to be capable of switching between a cooling operation and a heating operation and which performs a multistage compression refrigeration cycle by using a refrigerant that operates in a supercritical range.BACKGROUND ART[0002]As one conventional example of a refrigeration apparatus which has a refrigerant circuit configured to be capable of switching between a cooling operation and a heating operation and which performs a multistage compression refrigeration cycle by using a refrigerant that operates in a supercritical range, Patent Document 1 discloses an air-conditioning apparatus which has a refrigerant circuit configured to be capable of switching between an air-cooling operation and an air-warming operation and which performs a two-stage compression refrigeration cycle by using carbon dioxide as a refrig...

AI Technical Summary

Benefits of technology

[0005]A refrigeration apparatus according to a first aspect of the present invention comprises a compression mechanism, a heat source-side heat exchanger which functions as a radiator or evaporator of refrigerant, a usage-side heat exchanger which functions as an evaporator or radiator of refrigerant, a switching mechanism, and a second-stage injection tube. The compression mechanism has a plurality of compression elements and is configured so that the refrigerant discharged from the first-stage compression element, which is one of a plurality of compression elements, is sequentially compressed by the second-stage compression element. As used herein, the term “compression mechanism” refers to a compressor in which a plurality of compression elements are integrally incorporated, or a configuration that includes a compression mechanism in which a single compression element is incorporated and / or a plurality of compression mechanisms in which a plurality of compression elements have been incorporated are connected together. The phrase “the refrigerant discharged from a first-stage compression element, which is one of the plurality of compression elements, is sequentially compressed by a second-stage compression element” does not mean merely that two compression elements connected in series are included, namely, the “first-stage compression element” and the “second-stage compression element;” but means that a plurality of compression elements are connected in series and the relationship between the compression elements is the same as the relationship between the aforementioned “first-stage compression element” and “second-stage compression element.” The switching mechanism is a mechanism for switching between a cooling operation state, in which the refrigerant is circulated through the compression mechanism, the heat source-side heat exchanger, and the usage-side heat exchanger in a stated order; and a heating operation state, in which the refrigerant is circulated through the compression mechanism, the usage-side heat exchanger, and the heat source-side heat exchanger in a stated order. The heat source-side heat exchanger is a heat exchanger having air as a heat source. The second-stage injection tube is a refrigerant tube for branching off the refrigerant whose heat has been radiated in the heat source-side heat exchanger or the usage-side heat exchanger and returning the refrigerant to the second-stage compression element. In this refrigeration apparatus, refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube, at least during the beginning of a reverse cycle defrosting operation for defrosting the heat source-side heat exchanger by switching the switching mechanism to the cooling operation state.

[0008]In view of this, in the refrigeration apparatus according to a first aspect of the present invention, refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube, at least at the beginning of the reverse cycle defrosting operation. Thereby, in the refrigerant circuit in this refrigeration apparatus, circulation is performed whereby the refrigerant discharged from the compression mechanism is actively drawn into the compression mechanism through the usage-side heat exchanger. At this time, sufficient use is made of the heat stored in the refrigerant tube or the like between the usage-side heat exchanger and the switching mechanism due to the heating operation performed until immediately before the reverse cycle defrosting operation was performed, the temperature of the low-pressure refrigerant in the refrigeration cycle drawn into the compression mechanism increases, and the refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube, thereby minimizing the decrease in the temperature of the intermediate-pressure refrigerant in the refrigeration cycle drawn into the second-stage compression element. Therefore, the temperature of the high-pressure refrigerant in the refrigeration cycle discharged from the compression mechanism can be greatly increased, and the defrosting capacity per unit flow rate of the refrigerant when the reverse cycle defrosting operation is performed can be improved. Moreover, it is at least in the beginning of the reverse cycle defrosting operation that a state is created in which refrigerant does not return to the second-stage compression element through the second-stage injection tube, and circulation for drawing refrigerant into the compression mechanism through the usage-side heat exchanger is not continued excessively in the refrigerant circuit after the amount of heat stored in the refrigerant tube or the like between the usage-side heat exchanger and the switching mechanism has decreased and the effect of improving the defrosting capacity can no longer be sufficiently achieved; therefore, the temperature decrease on the usage side can be minimized.

[0009]Thus, in this refrigeration apparatus, when the reverse cycle defrosting operation is performed, defrosting capacity can be improved while the temperature decrease on the usage side is minimized.

Problems solved by technology

In cases in which a reverse cycle defrosting operation is used as the defrosting operation, wherein the outdoor heat exchanger is made to function as a radiator of refrigerant by switching the switching mechanism from an air-warming operation state to an air-cooling operation state, the indoor heat exchanger is made to function as an evaporator of refrigerant regardless of the intention being to cause the indoor heat exchanger to function as a radiator of refrigerant, and a problem is encountered in that the temperature decreases on the indoor side.

However, when the second-stage injection tube is used to reduce the flow rate of the refrigerant flowing through the indoor heat exchanger as described above, the refrigerant tube or the like between the indoor heat exchanger and the four-way switching valve is heated and made to store heat by the high-temperature refrigerant discharged from the compressor through the air-warming operation which had been performed until immediately before the reverse cycle defrosting operation, and the defrosting capacity cannot be improved because this stored heat is not sufficiently utilized when the reverse cycle defrosting operation is performed.

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