As concern for the environmental impact of refrigerants grows globally, CO2 (R-744) has become a common refrigerant in Europe and is quickly gaining ground in the United States. A nontoxic, natural refrigerant, CO2 does not deplete the ozone layer, making it useful for food processing, food storage and supermarket applications.

To accommodate the changing refrigeration landscape, one Washington State based manufacturer has tailored its systems to accommodate CO2. According to Colmac Coil, Colville, Wash., all of the company’s products that utilize an evaporator can be built for use with CO2, including its air coolers, blast freezers, hydrocoolers and bare coils for freezers and air handlers. Evaporators can be designed for pumped, direct expansion (DX) or brine operation to be compatible with all system types: transcritical, subcritical, cascade or single stage.

Systems using CO2 operate at higher pressures than other refrigerant systems. The tubing and pipe used in the evaporator is the main determinant of its pressure-bearing capability. Colmac offers construction in multiple tube materials, diameters, wall thicknesses and to fit any pressure requirement and application.

Colmac CO2 evaporators are available with defrost using water, hot gas, electric or an interlaced glycol circuit. Water is the most common method for defrosting CO2 evaporators because it defrosts quickly, maintains lower pressures than hot gas defrost and provides rinsing of the evaporator. Hot gas is an efficient defrost method but requires a sufficient quantity of gas and typically requires special construction due to the high pressure of CO2 at defrost temperatures. Electric defrost is common for smaller systems where hot gas or water are not available in sufficient quantities. Interlaced glycol circuits offer energy savings when a separate chilled glycol system is present. Warm glycol is pumped through a circuit in the evaporator, defrosting the evaporator and cooling the glycol.

 For more information, visit