Transport refrigeration system with thermal storage sink

In a transport refrigeration unit of the type adapted to provide cooling and to be defrosted, a refrigeration system including:

• a three-way valve having an inlet, and first and second outlets in accordance with first and second positions, respectively;
• a refrigerant compressor having a discharge line connected to supply said three-way valve, and a suction line;
• a refrigerant condenser;
• a refrigerant evaporator;
• a first thermal expansion device at the inlet to said evaporator;
• a thermal storage sink having a storage medium;
• a defrost heat exchanger in heat exchange relation with said evaporator;
• first refrigerant line means connecting the first outlet of said three-way valve to said condenser for operation of the system in a cooling mode with said three-way valve in said first position;
• second refrigerant line means extending from said condenser through said thermal storage sink to said first thermal expansion device
• hot gas refrigerant line means connecting the second outlet of said three-way valve to the inlet of said defrost heat exchanger, the outlet of said defrost heat exchanger being connected to a second thermal expansion device in a third refrigerant line and upstream of said third refrigerant line passing through said thermal storage sink and to the suction side of said compressor;
• whereby in a cooling mode with said three-way valve in said first position the refrigerant passing through said thermal storage sink is sub-cooled and transfers heat to said storage medium, and in a defrost mode with said three-way valve in said second position refrigerant passing through said thermal storage sink is evaporated and picks up heat from said storage medium so as to hasten the defrosting process.