Concerns about the environmental impact of fluorocarbons and hydrofluorocarbons on the environment call for expanded uses of environmentally sound refrigerants, such as water or ammonia. For commercial chiller applications in the capacity range of 15-10,000 refrigeration tons with little heating requirements, water is usually the preferred refrigerant due to its non-flammable and benign nature.
Aqueous absorption fluid cycles taking advantage of such refrigerants have been known and used for many decades. Single effect and various two-stage designs are commercially used in many countries. However, the increasing concern about the overall CO.sub.2 generation in the process of converting fossil fuels into energy used for air conditioning or refrigeration calls for higher energy conversion efficiencies than currently obtained with single stage (COP=0.6 to 0.8) or two-stage (COP=0.9 to 1.25) absorption equipment.
U.S. Pat. No. 4,732,008 teaches the use of two single stage cycles coupled to achieve three refrigeration effects. The independent loops carry different absorption fluids with the lower stage using fluids such as aqueous LiBr solutions. However, the needed upper stage fluid crystallization and vapor pressure suppression properties require the use of a different fluid. Performance estimates lead to COPs of 1.5 to 1.7 if suitable upper stage fluids are used.