Refrigeration cycle apparatus

1. A refrigeration cycle apparatus using refrigerant including HFO-1123, the refrigeration cycle apparatus comprising:

a compressor, a condenser, an expansion valve, and an evaporator connected in a loop;

a cooling unit configured to cool the refrigerant at an inlet of the expansion valve, the cooling unit cooling the refrigerant including HFO-1123 so that a temperature and a pressure of the refrigerant becomes equal to or less than a lower limit temperature or a lower limit pressure causing disproportionation reaction;

a first refrigerant pipe connected between an outlet of the condenser and the expansion valve, one end of the first refrigerant pipe being connected to the outlet of the condenser and another end of the first refrigerant pipe being connected to the expansion valve; and

a second refrigerant pipe connected between the compressor and an inlet of the condenser, one end of the second refrigerant pipe being connected to the compressor and another end of the second refrigerant pipe being connected to the inlet of the condenser;

wherein the first refrigerant pipe has a diameter that is smaller than a diameter of the second refrigerant pipe.

2. The refrigeration cycle apparatus of claim 1 , wherein the cooling unit comprises an auxiliary heat exchanger configured to exchange heat between a first stream of the refrigerant including HFO-1123 flowing out of the condenser and before being decompressed by the expansion valve and a second stream of the refrigerant including HFO-1123 to be sucked into the compressor.

3. The refrigeration cycle apparatus of claim 1 ,

wherein the cooling unit comprises an auxiliary heat exchanger configured to exchange heat between a first stream of the refrigerant including HFO-1123 at an outlet side of the condenser and a second stream of the refrigerant including HFO-1123, which is branched at the outlet side of the condenser and decompressed by an auxiliary expansion valve, and

wherein the second stream of the refrigerant including HFO-1123 decompressed by the auxiliary expansion valve and subjected to heat exchange by the auxiliary heat exchanger joins the refrigerant including HFO-1123 on a suction side of the compressor.

4. The refrigeration cycle apparatus of claim 1 ,

wherein the cooling unit comprises an accumulator provided on a suction side of the compressor, and

wherein a part of a pipe connecting an outlet side of the condenser and an inlet side of the expansion valve is inserted into the accumulator.

5. The refrigeration cycle apparatus of claim 1 , further comprising a high-pressure sensor configured to detect a pressure of the refrigerant including HFO-1123 at an outlet side of the compressor, and

a controller configured to control a rotation speed of the compressor so that the pressure detected by the high-pressure sensor becomes equal to or less than the lower limit pressure causing disproportionation reaction.

6. The refrigeration cycle apparatus of claim 1 , further comprising a discharge temperature sensor configured to detect a temperature at an outlet side of the compressor, and

a controller configured to control a rotation speed of the compressor so that the temperature detected by the discharge temperature sensor becomes equal to or less than the lower limit pressure causing disproportionation reaction.

7. The refrigeration cycle apparatus of claim 1 ,

wherein the condenser comprises a plate heat exchanger, and

wherein a heat exchange medium comprises water or brine.

8. The refrigeration cycle apparatus of claim 1 , further comprising:

wherein the expansion valve is a first expansion valve,

a second expansion valve connected in the loop,

a receiver provided between the first expansion valve and the second expansion valve; and

at least one of a temperature sensor and a pressure sensor to detect a temperature or a pressure of the refrigerant including HFO-1123 in liquid form to be accumulated in the receiver,

wherein an opening degree of the first expansion valve or the second expansion valve is controlled so that the detected temperature by the temperature sensor or the detected pressure by the pressure sensor of the liquid refrigerant including HFO-1123 becomes equal to or less than the lower limit temperature or the lower limit pressure causing disproportionation reaction.

9. The refrigeration cycle apparatus of claim 1 ,

wherein the cooling unit comprises an auxiliary heat exchanger configured to exchange heat between a first stream of the refrigerant including HFO-1123 at an outlet side of the condenser and a second stream of the refrigerant including HFO-1123, which is branched at the outlet side of the condenser and decompressed by an auxiliary expansion valve, and

wherein the second stream of the refrigerant including HFO-1123 decompressed by the auxiliary expansion valve and subjected to heat exchange by the auxiliary heat exchanger is injected into a compression chamber of the compressor.

10. The refrigeration cycle apparatus of claim 9 , further comprising an expansion valve inlet temperature sensor configured to detect a temperature of the refrigerant including HFO-1123 at an outlet side of the auxiliary heat exchanger, and

a controller configured to control an opening degree of the auxiliary expansion valve based on the temperature detected by the expansion valve inlet temperature sensor so that the temperature of the refrigerant becomes equal to or less than the lower limit temperature causing disproportionation reaction.

11. A refrigeration cycle using refrigerant including HFO-1123, the refrigeration cycle apparatus comprising:

a compressor, a condenser, an expansion valve, and an evaporator connected in a loop;

a cooling unit configured to cool the refrigerant including HFO-1123 at an inlet of the expansion valve so that the refrigerant including HFO-1123 at the inlet of the expansion valve has a temperature and pressure equal to or less than a lower limit temperature and a lower limit pressure causing disproportionation reaction,

a high-pressure sensor configured to detect a pressure of the refrigerant including HFO-1123 at an outlet side of the compressor,

an expansion valve inlet temperature sensor configured to detect a temperature of the refrigerant including HFO-1123 at an outlet side of the auxiliary heat exchanger, and

a controller configured to:

obtain a degree of subcooling of the refrigerant including HFO-1123 at the outlet side of the auxiliary heat exchanger based on the pressure detected by the high-pressure sensor and the temperature detected by the expansion valve inlet temperature sensor, and

control an opening degree of the auxiliary expansion valve so that the degree of subcooling of the refrigerant including HFO-1123 at the outlet side of the auxiliary heat exchanger becomes equal to or higher than a set value that is set in advance,

wherein the cooling unit comprises an auxiliary heat exchanger configured to exchange heat between a first stream of the refrigerant including HFO-1123 at an outlet side of the condenser and a second stream of the refrigerant including HFO-1123, which is branched at the outlet side of the condenser and decompressed by an auxiliary expansion valve, and

wherein the second stream of the refrigerant including HFO-1123 decompressed by the auxiliary expansion valve and subjected to heat exchange by the auxiliary heat exchanger is injected into a compression chamber of the compressor.