Refrigeration System

Abstract

A refrigerant circuit ( 20 ) includes a low stage compressor ( 101, 102, 121, 122 ), a high stage compressor ( 41, 42, 43 ), an outdoor heat exchanger ( 44 ) and a utilization side heat exchanger ( 83, 93 ). During a defrosting operation of the refrigeration system ( 10 ), the high stage compressor ( 41, 42, 43 ) is driven. Refrigerant discharged from the high stage compressor ( 41, 42, 43 ) is pumped into the utilization side heat exchanger ( 83, 93 ) to heat frost on it from its inside. Thereafter, the refrigerant evaporates in the outdoor heat exchanger ( 44 ), is then compressed by the high stage compressor ( 41, 42, 43 ) and is sent again to the utilization side heat exchanger ( 83, 93 ).

1 . A refrigeration system including a refrigerant circuit in which a low stage compressor, a high stage compressor, a heat-source side heat exchanger and a utilization side heat exchanger are connected, the refrigeration system being operable in a two-stage compression refrigeration cycle by driving the low stage compressor and the high stage compressor during a cooling operation in which the heat-source side heat exchanger serves as a condenser and the utilization side heat exchanger serves as an evaporator, wherein
 the refrigeration system is configured to be switchable between the cooling operation and a defrosting operation for defrosting the utilization side heat exchanger and operate, during the defrosting operation, in a refrigeration cycle in which the high stage compressor is driven, the utilization side heat exchanger serves as a condenser and the heat-source side heat exchanger serves as an evaporator.   
   
   
       2 . The refrigeration system of  claim 1 , wherein the refrigeration system is configured to keep the low stage compressor off during the defrosting operation. 
   
   
       3 . The refrigeration system of  claim 2 , further including a bypass pipe that connects the suction side and the discharge side of the low stage compressor and includes a shut-off valve, the shut-off valve being open during the defrosting operation and being closed during the cooling operation. 
   
   
       4 . The refrigeration system of  claim 2  or  3 , wherein
 a drain pan is disposed below the utilization side heat exchanger,   the refrigerant circuit comprises a utilization side expansion valve connected upstream of the utilization side heat exchanger in the cooling operation and a drain pan heating pipe connected upstream of the utilization side expansion valve in the cooling operation and disposed along the drain pan, and   the refrigeration system is configured so that, during the cooling operation, refrigerant condensed in the heat-source side heat exchanger flows through the drain pan heating pipe, is then reduced in pressure by the utilization side expansion valve and is then fed into the utilization side heat exchanger.   
   
   
       5 . The refrigeration system of  claim 4 , wherein
 the refrigerant circuit includes a heat-source side expansion valve disposed upstream of the heat-source side heat exchanger in the defrosting operation, and   the refrigeration system is configured so that, during the defrosting operation, refrigerant condensed in the utilization side heat exchanger flows through the fully-open utilization side expansion valve and the drain pan heating pipe, is then reduced in pressure by the heat-source side expansion valve and is then fed into the heat-source side heat exchanger.   
   
   
       6 . The refrigeration system of  claim 1 , wherein the refrigeration system is configured, during the defrosting operation, to operate in a refrigeration cycle in which refrigerant discharged from the high stage compressor is further compressed by the low stage compressor, the utilization side heat exchanger serves as a condenser and the heat-source side heat exchanger serves as an evaporator. 
   
   
       7 . The refrigeration system of  claim 6 , wherein the refrigeration system is configured so that, during the defrosting operation, part of refrigerant discharged from the high stage compressor is further compressed by the low stage compressor and then returned to the discharge side of the high stage compressor. 
   
   
       8 . The refrigeration system of  claim 7 , wherein the refrigeration system is configured to return, during the defrosting operation, part of refrigerant condensed in the utilization side heat exchanger to the suction side of the low stage compressor. 
   
   
       9 . The refrigeration system of  claim 1 , further including a liquid return pipe connecting the suction side and the discharge side of the low stage compressor, the refrigeration system being configured, after the completion of the defrosting operation, to perform a refrigerant recovery action by driving only the high stage compressor to allow the high stage compressor to suck refrigerant built up in the utilization side heat exchanger through the liquid return pipe. 
   
   
       10 . The refrigeration system of  claim 9 , further including:
 an oil separator disposed to the discharge side of the low stage compressor; and   an oil return pipe for sending refrigerating machine oil recovered by the oil separator to the suction side of the low stage compressor, the oil return pipe serving also as the liquid return pipe during the refrigerant recovery action.   
   
   
       11 . The refrigeration system of  claim 10 , wherein the oil separator is configured, during the refrigerant recovery action, to separate gas refrigerant from refrigerant flowing thereinto from the liquid return pipe and send the gas refrigerant to the suction side of the high stage compressor.