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Replacing refrigerant R22

by Brian Ware
NBS Technical Author

Because of the adverse impact of CFCs, HCFCs and halons on the environment (ozone depletion, global warming) we should avoid specifying these gases as refrigerants. Here, we bring you up to date on alternatives to one commonly-used HCFC refrigerant, R22.

Regulatory requirements

The choice of refrigerants for air conditioning systems has changed since they first appeared on the market. After many years of widespread use, R22 is being replaced in line with EC Regulation 2037/2000. This can be summarized as follows:-

From 1st July 2002 cooling-only air conditioning equipment that uses R22 has not been permitted to be manufactured.
From 1st January 2004 no more heat pump equipment can be manufactured that uses R22.
After 1st January 2010 no more virgin R22 can be used in existing systems.
After 2015 no more recycled R22 can be used in existing systems.

Alternatives to R22

Many alternatives to CFCs, HCFCs and halons are based on hydrofluorocarbons (HFCs). Although HFCs do not contain chlorine and so cannot cause ozone depletion (ozone depletion potential = 0), they are potent greenhouse gases. Concern about their contribution to global warming has led to their inclusion in the Kyoto Protocol on reducing emissions of greenhouse gases.

There are three main HFC alternatives to R22 at present: R407C, R134a and R410A.

R407C is a blend comprising 23% R32, 25% R125 and 52% R134a. It is the most similar to R22 in terms of pressure and performance but has a temperature glide of 5 K (i.e. its operational temperature spans a 5 K range).

R134a is a single HFC compound. It has a lower pressure than R22 and gives good performance as an air conditioning refrigerant. A larger displacement compressor is required, and the system has to accommodate larger volume flows. Because of its low pressure R134a is suitable for applications where high condensing temperatures are required.

R410A is a blend comprising 50% R32 and 50% R125. It operates at a significantly higher pressure than R22 and special systems have to be designed for this reason. It has superior heat transfer properties, lower pressure drops and minimal temperature glide. Because of its higher heat transfer properties the evaporator and condenser can be smaller.

Environmental issues

Global warming potential (GWP) is a measure of how much effect a chemical will have on global warming, measured over 100 years. Carbon dioxide is the datum reference, so has a GWP of 1.0. The lower the GWP, the better.

Refrigerant	GWP	Atmospheric lifetime (years)
R407C	1610	36
R134a	1300	14
R410A	1900	36

GWP of refrigerants is only relevant when the gas is released into the atmosphere. Accordingly, in terms of global warming, it is important to also consider energy consumption during plant operation.

The energy efficiency of systems can be assessed by comparing the kW electrical input against the kW cooling capacity. The ratio of cooling capacity to input power is known as the coefficient of performance (COP). This should be as high as possible.

Refrigerant leakage is another factor having a direct impact on the environment, but also results in a reduction of efficiency. Research by the Building Research Establishment showed that in critically charged systems (systems without additional refrigerant charge stored in system liquid receivers) a 15% loss of refrigerant caused a 45% reduction in COP.

The TEWI (total equivalent warming impact) incorporates the effects of ‘direct’ refrigerant emissions, caused by leaks or losses during servicing or decommissioning of systems, and ‘indirect’ emissions of CO₂ from the fossil fuel consumed to generate energy to operate the system, over its operational life.

Minimising the environmental impact of cooling systems is linked to life cycle costs. Systems with the lowest whole life cost are generally those with the lowest energy consumption, and these also have the lowest impact on global warming.

Environmental impact depends not only on the choice of refrigerant but also on a range of interrelated factors. As well as the factors outlined above, designers should avoid unnecessary plant operation and minimize refrigerant charge.

Specification

For new works, do not specify CFCs and HCFCs. Do specify refrigerants with the lowest possible GWP and atmospheric lifetime. For some existing installations it is possible to convert CFC equipment to operate with HFC refrigerants, but in many cases this is impractical or uneconomical. In such cases the optimum solution is either premature system replacement or taking extreme care to minimize refrigerant losses.

Finally, whenever a new system is installed or when an existing system is extended, modified or converted to a different refrigerant, follow the requirements of BS EN 378:2000 Specification for refrigerating systems and heat pumps. Safety and environmental requirements.

Updated August 2007