Refrigeration apparatus

1. A refrigeration apparatus comprising:

a multistage compression mechanism in which one low-stage compression part and a plurality of high-stage compression parts are respectively connected in series;

a heat-source-side main heat exchanger that functions as a radiator during a cooling operation, and functions as an evaporator during a heating operation;

a plurality of heat-source-side sub heat exchangers that

during the cooling operation, function as radiators that cool intermediate-pressure refrigerant in the course of compression that is taken into the high-stage compression parts, and

during the heating operation, function as evaporators;

a usage-side heat exchanger that functions as an evaporator during the cooling operation and functions as a radiator during the heating operation;

switching mechanisms that change conditions so that

during the cooling operation, the refrigerant is delivered from the heat-source-side main heat exchanger to the usage-side heat exchanger, and

during the heating operation, the refrigerant is delivered from the usage-side heat exchanger to the heat-source-side main heat exchanger and the heat-source-side sub heat exchangers;

an expansion mechanism that

during the cooling operation, depressurizes the refrigerant delivered from the heat-source-side main heat exchanger to the usage-side heat exchanger, and

during the heating operation, depressurizes the refrigerant delivered from the usage-side heat exchanger to the heat-source-side main heat exchanger and the heat-source-side sub heat exchangers; and

a refrigerant piping group connecting the multistage compression mechanism, the switching mechanisms, the heat-source-side main heat exchanger, the heat-source-side sub heat exchangers, the expansion mechanism and the usage-side heat exchanger so that during the heating operation, the refrigerant flows in series to not less than two of the heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers.

2. The refrigeration apparatus according to claim 1 , wherein

the plurality of high-stage compression parts are

a second stage compression part that takes in the refrigerant blown out from the low-stage compression part,

a third stage compression part that takes in the refrigerant blown out from the second stage compression part, and

a fourth stage compression part that takes in the refrigerant blown out from the third stage compression part and blows out the refrigerant to the radiator;

the plurality of heat-source-side sub heat exchangers are

a heat-source-side first sub heat exchanger that during the cooling operation, cools the refrigerant blown out from the low-stage compression part and taken into the second stage compression part,

a heat-source-side second sub heat exchanger that during the cooling operation, cools the refrigerant blown out from the second stage compression part and taken into the third stage compression part, and

a heat-source-side third sub heat exchanger that during the cooling operation, cools the refrigerant blown out from the third stage compression part and taken into the fourth stage compression part; and

during the heating operation the refrigerant

flows in series to the heat-source-side first sub heat exchanger and the heat-source-side second sub heat exchanger, or

flows in series to the heat-source-side first sub heat exchanger, the heat-source-side second sub heat exchanger and the heat-source-side third sub heat exchanger.

3. The refrigeration apparatus according to claim 2 , wherein

the plurality of heat-source-side sub heat exchangers in which the refrigerant flows in series during the heating operation are connected in series during the heating operation via the switching mechanisms.

4. The refrigeration apparatus according to claim 2 , wherein

during the heating operation, not less than two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers are connected in series with the heat-source-side main heat exchanger, and the refrigerant flows in series to not less than the two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers and the heat-source-side main heat exchanger.

5. The refrigeration apparatus according to claim 2 , wherein

during the heating operation, the refrigerant delivered from the usage-side heat exchanger via the expansion mechanism flows in parallel, the flow being distributed along three channels of

the heat-source-side first sub heat exchanger and the heat-source-side second sub heat exchanger connected in series,

the heat-source-side main heat exchanger, and

the heat-source-side third sub heat exchanger.

6. The refrigeration apparatus according to claim 5 , wherein

the plurality of heat-source-side sub heat exchangers in which the refrigerant flows in series during the heating operation are connected in series during the heating operation via the switching mechanisms.

7. The refrigeration apparatus according to claim 5 , wherein

during the heating operation, not less than two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers are connected in series with the heat-source-side main heat exchanger, and the refrigerant flows in series to not less than the two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers and the heat-source-side main heat exchanger.

8. The refrigeration apparatus according to claim 1 , wherein

the plurality of heat-source-side sub heat exchangers in which the refrigerant flows in series during the heating operation are connected in series during the heating operation via the switching mechanisms.

9. The refrigeration apparatus according to claim 8 , wherein

during the heating operation, not less than two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers are connected in series with the heat-source-side main heat exchanger, and the refrigerant flows in series to not less than the two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers and the heat-source-side main heat exchanger.

10. The refrigeration apparatus according to claim 1 , wherein

during the heating operation, not less than two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers are connected in series with the heat-source-side main heat exchanger, and the refrigerant flows in series to not less than the two heat-source-side sub heat exchangers of the plurality of heat-source-side sub heat exchangers and the heat-source-side main heat exchanger.

11. A refrigeration apparatus comprising:

a multistage compression mechanism in which a low-stage compression part and a high-stage compression part are connected in series;

a heat-source-side main heat exchanger that functions as a radiator during a cooling operation, and functions as an evaporator during a heating operation;

a heat-source-side sub heat exchanger that

during the cooling operation, functions as a radiator that cools intermediate-pressure refrigerant in the course of compression that is taken into the high-stage compression parts, and

during the heating operation, functions as an evaporator;

a usage-side heat exchanger that functions as an evaporator during the cooling operation and functions as a radiator during the heating operation;

a switching mechanism that changes conditions so that

during the cooling operation, the refrigerant is delivered from the heat-source-side main heat exchanger to the usage-side heat exchanger, and

during the heating operation, the refrigerant is delivered from the usage-side heat exchanger to the heat-source-side main heat exchanger and the heat-source-side sub heat exchanger;

an expansion mechanism that

during the cooling operation, depressurizes the refrigerant delivered from the heat-source-side main heat exchanger to the usage-side heat exchanger, and

during the heating operation, depressurizes the refrigerant delivered from the usage-side heat exchanger to the heat-source-side main heat exchanger and the heat-source-side sub heat exchanger; and

a refrigerant piping group connecting the multistage compression mechanism, the switching mechanism, the heat-source-side main heat exchanger, the heat-source-side sub heat exchanger, the expansion mechanism and the usage-side heat exchanger so that during the heating operation, the heat-source-side main heat exchanger and the heat-source-side sub heat exchanger are connected in series.