retrofitting with non-cfc substitutes

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RETROFITTING WITH NON-CFC SUBSTITUTES CENTRIFUGAL CHILLERS Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee, 1991: Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee. Nairobi: UNEP. Centrifugal chillers are designed for specific refrigerants. Direct refrigerant substitutes can only be made in cases where the properties of the substitute refrigerant are nearly the same as those of the refrigerant for which the equipment was designed. HCFC-123 retrofit for CFC-11 Benefits HCFC-123 became available in 1989 for retrofit into existing CFC-11 chillers. Problems It is a more aggressive solvent than CFC-11. Non-metallic materials may have to be replaced with materials which are more compatible with HCFC-123. Materials used in the motors of older hermetic chillers may not be compatible with HCFC-123, putting motor reliability at risk or requiring motor replacement. The dielectric strength of HCFC-123 is much lower than that of CFC-11 raising questions about viability with some high voltage motors. System capacity may be reduced by between 0 and 20% depending on the matching of the compressor to the load and heat exchanger effectiveness. Preliminary results from toxicology tests for HCFC-123 obtained in mid-1991, led to recommendations that exposure of personnel to HCFC-124 in an 8 or 12 hour workday be limited to a 10ppm (or lower) time weighed average concentration. This means that machinery rooms for HFC-123 chillers must be equipped with sensitive detectors, adequate ventilation systems, and means to alert operators in the event of a significant leak or spill. These precautions have not been taken in the past for CFC chiller. ASHRAE Standard 15R now requires similar precautions for CFCs and HCFCs as well. Changeout of the compressor to a higher-capacity model or purchase of additional chillers may be necessary. Cycle efficiency will be reduced by at least 1-2% HCFC-141b retrofit for CFC-11 HCFC-141b has more or less the same properties as HCFC-123 and could be used as a replacement candidate for CFC-11 as well. HCFC-134a retrofit for CFC-12 Benefits Available since 1991 for retrofit in centrifugal chillers. Problems 28
RETROFITTING WITH NON-CFC SUBSTITUTES Its use requires higher tip speeds than CFC-12, so impeller and/or gearbox replacementä is necessary. Typically, oils used for CFC-12 are not miscible with HFC-134a. PAG oils developed for HFC-134a are not compatible with CFC-12 residues, thus requiring thorough flushing of the systems before replacement. Ester oils seem to have overcome this problem. Some desiccants (e.g. activated alumina) commonly used in CFC-12 systems are not compatible with HFC-134a. HCFC-124 retrofit for CFC-114 This has been suggested as an alternative to CFC-114 in centrifugal chillers such as those used in naval applications. It is not readily available for use in either new or retrofit chillers. (1991) Problems HCFC-124 requires operation at higher pressure levels, higher compressor speeds, and smaller impeller diameters than CFC-114. HCFC-124 is not suitable for use in existing systems in most cases because the pressure levels will exceed design ratings and complete compressors replacement is necessary. HFC-152a/HCFC-124/HCFC-22 mixture for CFC-12 Benefits It is compatible with conventional refrigeration oils. Problems It is not readily available because HCFC-124 is not in large production. The mixture is likely to have degraded heat transfer performance in the flooded evaporators and shell side condensation normally used in centrifugal chillers. Thus there is likely to be a significant performance penalty when substituted in existing chillers. Servicing such a system brings on new difficulties because any vapour losses will change composition and performance. Measuring and changing equipment are not available to mitigate this problem. HCFC-22/HCFC-142b mixture retrofit for CFC-12 This azeotropic mixture is being used in France to retrofit systems using CFC-12. Benefits Both components of the mixture are available commercially. The mixture is not flammable to the proportions used to emulate CFC-12 (but flammable proportions can be encountered as a result of spills or losses). An updated version of this document will be available November 1994. HCFC-123 retrofit for CFC-11 29
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