CO2 refrigeration system with integrated propan subcooler for supermarkets in warm climate.

A CO2 refrigeration system with a secondary propane cycle was developed for operation at a higher ambient air temperature. The system has a CO2 gas cooler with integrated propane condenser and a propane sub-cooler. This allows sub-critical operation of CO2 at all ambient temperatures. A prototype unit was instrumented and tested. The optimal points for start of propane cycle was found at the ambient temperature of 23.5°C (field tests) and 19.4 °C (simulation). COP of the system was calculated for different European capitals. COP can be increased (up to 15.0 %) by increasing of air-velocity through the heat exchanger. An effective design of CO2-propane condenser was suggested. New design increases COP from 8.84 % to 6.91 % at 18.7 °C and 40.0 °C ambient temperature respectively.