Mechanical subcooling has been used for approximately 25 years in large, low temperature refrigeration systems in the grocery and supermarket industry. Typically, these employ watercooled condensers, utilizing excess air-conditioning or medium temperature refrigeration capacity to subcool the refrigerant upon exiting the low temperature system condenser to increase the refrigerating capacity. The possibility exists of incorporating mechanical subcooling on smaller capacity air-cooled freezing systems, with a subcooling system designed solely for subcooling purposes. A computer model is developed to predict design and offdesign performance of such a system operating under high ambient air temperature conditions with several different main and sub-cooling system refrigerant combinations. The development of the model is presented along with results at design conditions that show improvement over a conventional system of 6 to 80 percent in COP and 20 to 170 percent in capacity. The results are consistent with manufacturer’s observed information and initial expectations on performance and size of the subcooling compressor.

Units: I-P