Carbon dioxide (CO2) is a colorless gas at ordinary temperatures. It has a slight odor and an acid taste. Carbon dioxide is nonexplosive and nonflammable. It has a boiling point of 5°F (?15°C). Apressure of over 300 psi is required to keep it from evaporation. To liquefy the gas, a condenser temperature of 80°F (26.6°C) and a pressure of approximately 1000 psi are needed. Its critical temperature is 87.8°F (31°C). It is harmless to breathe except in extremely large concentrations. The lack of oxygen can cause suffocation under certain conditions of carbon dioxide concentration.
Carbon dioxide is used aboard ships and in industrial installations. It is not used in household applications. The main advantage of using carbon dioxide for a refrigerant is that a small compressor can be used. The compressor is very small since a high pressure is required for the refrigerant. Carbon dioxide is, however, very inefficient, compared to other refrigerants. Thus, it is not used in household units.