CO2 Refrigerator

1. Outline

Carbon dioxide (CO2) is a nonflammable, harmless, and odorless refrigerant. It has an ozone depletion potential (ODP) of 0 and a global warming potential (GWP) of 1, and is environmentally friendly like ammonia.

In recent years, carbon dioxide is being studied in and outside Japan as a refrigerant for car coolers and hot water heat pumps. We developed and commercialized, a supercritical CO2 ice heat storage system (photo) using an oil injection type screw compressor.

2. Features

Because a CO2 refrigerating cycle contains a supercritical area, engineering problems different from conventional refrigerating systems occur in compressors and heat exchangers. In order to achieve an efficient CO2 refrigerating cycle, a compressor capable of compressing at pressures 7.5 MPa or higher is required. This system adopts an oil injection type screw compressor which has a good track record in various types of gas compressors uses newly developed screw rotors to compress CO2 from 2.3 to 9.0 MPa. To assure pressure resistance, a shell and tube type heat exchanger was adopted for the condenser and evaporator. Brine cooled in the evaporator is used to generate ice in the storage tank. The refrigerating capacity is 141 kW, and the heat storage capacity is 2430 MJ.