Vapor Compression Systems

Vapor compression refrigeration is the primary method used to provide mechanical cooling. All vapor compression systems consist of four basic components (plus the interconnecting piping): evaporator, compressor, condenser, and an expansion device. The evaporator and condenser are heat exchangers that evaporate and condense the refrigerant while absorbing and rejecting heat. The compressor takes the refrigerant vapors from the evaporator and raises the pressure sufficiently for the vapor to condense in the condenser. The expansion device controls the flow of condensed refrigerant at this higher pressure back into the evaporator.

Historically, the common refrigerants were R-11, R-12, R-22, and compounds in the R-500 series. With the CFC phaseout, new refrigerants have been developed to replace R-11 and R-12 in new equipment. These new refrigerants can also be used to retrofit existing equipment in many cases. However, these retrofits are not "drop-ins" and should be done by trained technicians.

Food processors often use ammonia (R-717). While potentially hazardous, ammonia is inexpensive and environmentally benign. Experts anticipate wider use of ammonia due to concerns over CFC phase-out. Interestingly, R-22 was developed as a safe alternative for cooling systems that would perform best at ammonia refrigerant characteristics.

The manufacturer selects the specific refrigerant used in any equipment to best match the cooling system design and size. The availability and cost of these refrigerants and the consequences of refrigerant leaks and disposal have become very serious concerns for today's building owners and the design community. Each of these issues is addressed in other areas of this interactive knowledge program.

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