In recent years, the emphasis on alternative refrigerants with no ozone depletion properties has been growing. CO2 refrigeration systems in particular have been gaining popularity. A question was asked, “Should I choose CO2 (R-744) for my refrigeration system?” and engineers at M&M Refrigeration prepared the answer with support of a comprehensive third-party study metering a cascade CO2/ammonia and two-stage ammonia system.
If a facility with processes requiring low temperatures less than -4°F or blast freezing, a cascade CO2/ammonia system might make sense. Increased system efficiency by 5.8% can be achieved, especially with very low temperature freezer storage (less than -25°F) and blast freezing operations. Improved employee safety and product quality is achieved, as no ammonia is present in food processing and storage spaces. Ammonia is contained in the compressor engine room and external condenser. Additionally, the ammonia charge required for low temperature applications is reduced compared to a traditional two-stage ammonia system. Typically, the first cost of a cascade CO2/ammonia system is lower than that of a two-stage ammonia system for several reasons, including smaller low-stage compressors, low-stage suction lines, valves, and separating vessels, and reduced insulation costs.
At part load the efficiency advantage for the CO2/ammonia system increases. Applying CO2 as a refrigerant in appropriate applications can be a cost-effective alternative with safety and product benefits. As a bonus, CO2 does not deplete the ozone layer. In the effort to reduce the energy use for low-temperature refrigeration, CO2 seems to be the solution.
The application of cascade carbon dioxide and ammonia (cascade CO2/NH3) refrigerating systems has been gaining popularity in North America for the past number of years. But to correctly answer the question, “Should I choose CO2 for my refrigeration system?”, one must first identify the objectives for the refrigeration plant.
Some of the questions to ask are: