CHILLERS REFRIGERANTS
NATURAL N
Chillers have been developed that don’t need to use hydrofl uorocarbon refrigerants, thereby escaping EU restrictions. Nicholas Cox explains
GAS
atural hydrocarbon (HC) refrigerant chillers are often regarded as just an easy way to clock up additional BREEAM
points, but they now need to be taken much more seriously, particularly in light of current legislation. The EU has passed regulations to impose restrictions on the use of hydrofl uorcarbon (HFC) refrigerants in air conditioning systems1. With this change in mind, larger air-cooled chillers that use HC refrigerant have been developed in recent years. HC chillers had been available in the UK as far back as 1995, but their capacities were limited to about 200 kW. HC chillers with outputs of up to 1,367kW are now on the market. Energy savings of more than 20% have
been achieved with HC chillers relative to comparable HFC chillers, with roughly half of this attributable to refrigerant selection and the balance as a result of improved engineering design2. The good performance of HC refrigerants can be attributed to a lower compression ratio due to higher suction pressures and lower discharge pressures at specifi c operating temperatures; to improved heat transfer in heat exchangers as a result of more favourable fl uid thermal and transport properties; and to reduced system pressure losses arising from lower refrigerant density and viscosity. For example, in the Earthcare Hydrocarbon Series (EHS) chiller, the HC refrigerant R-290 is used as a replacement for R-22, resulting in an extremely low
42 CIBSE Journal June 2012
The EU has passed regulations to impose restrictions on the use of hydrofl uorocarbon refrigerants in air conditioning systems
global warming potential of only three times higher than CO2, compared with 2,090 for HFC-410A. Energy effi ciency can be maximised through a combination of factors, including: the favourable thermodynamic characteristics of HC; the use of sub- cooling circuits that improve coeffi cient of performance (CoP); and fl oating head pressure control that allows the condensing temperature to fl oat as low as 20C if ambient conditions allow, instead of the normal 40C. This is particularly benefi cial for chillers that operate all year round or
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