Vapor Compression Refrigeration

Last Updated on Thursday, 05 November 2009 01:57 Written by Richard Wednesday, 21 January 2009 20:16

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Air Conditioners Heat Pumps and Vapor Compression Refrigeration

Refrigeration Cycle

Modern air conditioners and heat pumps use vapor compression refrigeration as the primary method for moving heat to where it is either not wanted or it is wanted in the case of a heat pump in heating mode. Vapor compression refrigeration uses chemical refrigerants to absorb heat and move the heat to another place. While water is considered a refrigerant it is not used in vapor compression refrigeration. Instead, chemical refrigerants are used to absorb heat in air conditioners and heat pump systems to move the heat in the desired direction. Vapor compression refrigeration uses these refrigerants along with a compressor and other refrigeration components such as an evaporator and a condenser make it possible to provide heating and cooling in modern air conditioners and heat pump systems.

Vapor Compression Refrigeration, Compressors and System Capacity

The type of compressor used in vapor compression refrigeration depends on the system capacity in many, but not all cases. Larger capacity systems used in commercial air conditioning such as chilled water systems typically utilize centrifugal and screw compressors while lower capacity systems use reciprocating, rotary, and scroll compressors in the vapor refrigeration cycle to provide heating and cooling in air conditioner and heat pump systems. Residential systems use primarily scroll and reciprocating compressors for the vapor compression refrigeration cycle where trends indicate scroll compressors becoming more and more typical in residential air conditioners and heat pumps in the vapor compression refrigeration cycle. Rotary compressors are commonly used in windows unit, mini-splits, and other small capacity systems.

How the Vapor Compression Refrigeration Cycle Works

Vapor Commpression Refrigeration

Liquid refrigerant is channeled into an evaporator where the liquid changes state to a vapor by absorbing heat. The liquid refrigerant evaporates into a vapor and is then pumped to a compressor. This low temperature low pressure vapor is loaded with heat as it makes its way to the compressor. In the compressor the low temperature and low pressure vapor is compressed and it leaves the compressor at a high temperature and high pressure vapor and makes its way to the condenser. In the condenser the heat contained in the high pressure and high temperature refrigerant is released to another medium depending on whether the system is chilled water or an air source air conditioner or heat pump system. The condenser removes a large amount of heat from this high temperature and high pressure refrigerant vapor. The pressure and the temperature of the refrigerant drops enough to change the vapor from a vapor to a liquid. The same amount of heat absorbed in the evaporator is rejected in the condenser allowing a change of state to occur and the refrigerant vapor changes to a liquid or the vapor condenses to a liquid. The pressure and the temperature are still high relatively compared to the pressure and temperature of the evaporator refrigerant temperature and pressures. The same refrigerant that went through the evaporator (at a low temperature and low pressure), went through the compressor, and went through the condenser is now channeled to a metering device. The purpose of the metering device is to drop the temperature and drop the pressure of the refrigerant so it can then be used in the evaporator to absorb more heat and return to the compressor for the vapor compression cycle to begin again.

Common Refrigerants in Vapor Compression Refrigeration

In residential air conditioning and heat pump systems there is a trend moving away from R-22 and changing refrigerants to R-410A. This is a direct result of the Montreal Protocol and laws mandating that CFC's and HCFC's be discontinued because the chlorine contained in these refrigerants is dangerous to the ozone layer and environment. CFC's and HCFC's both contain chlorine and other gases that have been deemed harmful to our atmosphere. Both CFC's and HCFC's are considered by the Montreal Protocol to have ozone depleting potential and global warming potential. As R-22 in residential systems is slowly being replaced by R-410A the prices for R-22 are rising and the prices for R-410A is in decline because production of R-410A is increasing. Larger chilled water systems and commercial air conditioning systems are using R-410A, R-134A and other refrigerant blends. Industrial refrigeration uses ammonia and propane for refrigerants among some other exotic refrigerants used in industrial HVACR systems. Research for new refrigerants such as CO2 is underway to find refrigerants that least impact the environment and is more efficient than conventional chemical blend refrigerants.

Vapor Refrigeration Cycle, HVAC refrigeration, Refrigeration systems