A secondary refrigerant distributes the MT cooling around the supermarket. The LT arrangements are identical to the cascade system.
Heat from the chill cabinets is transferred to the MT evaporator/heat-exchanger by circulating glycol as a secondary heat transfer fluid. Heat exchangers can be located close to the compressors and when assembled with an air cooled condenser this package can be delivered as a factory assembled unit similar to an air conditioning chiller. This results in a significantly reduced MT refrigerant charge and potential refrigerant leakage is reduced due to the factory manufacturing.
Secondary refrigerant systems require a pump to circulate the coolant around the supermarket and there is an extra heat exchanger temperature drop. The heat exchanger requires a temperature difference to drive the heat transfer and so the MT evaporating temperature must be lower than the secondary refrigerant temperature, leading to an increase in compressor energy consumption. The secondary refrigerant temperatures and temperature differences used in this model are explained in the Energy section.
Secondary Glycol systems require less refrigeration service effort than DX solutions.