Refrigerant replacement extends chiller life
Published: 22 May, 2006
TREVOR DANN discusses the issues surrounding replacing R22 in chillers to enable them to continue to be used as this refrigerant becomes increasingly unavailable.
R22 will become increasingly unavailable as a practical proposition for servicing chillers from 2009. However, effective drop-in replacements are available. Isceon (Du Pont) offers two replacements that are well suited to the needs of typical R22 chillers.
Isceon 59 (now R417A) was developed primarily to replace R22 across its range of application. In practice, it has been found less efficient on water chillers, so the blend has been tweaked to offer improved water chiller performance under the brand name Isceon 29.
Projects we have encountered include both chilled water and direct expansion.
Using the Isceon 9 series we have obviated the requirement common to HFC refrigerants to remove virtually all mineral oil from the entire system. There is no straightforward procedure for this available, and polyolester lubricants tend to render the system liable to secondary leakage due to failure of secondary seals around remote system components.
Secondary leakage became a significant drawback when the supermarkets phased out the CFCs in the mid 1990s. All HFCs are supplied at a considerable premium in comparison to R22. Not only is it a key environmental issue to keep HFCs properly contained, it is also huge financial sense.
My company is now keen to extend its knowledge and share its findings with others facing the same requirement.
Setting thermostatic expansion valves
We have noted a requirement to increase the internal orifice size of thermostatic expansion valves by at least one stage. This is omitted from the typical instructions, which merely mention that an adjustment to the valve may be required. As changing the internal cage assembly may require obscure valve parts, and probably more time at site, it is highly recommended that adequate time and material allowance is made when offering costings to allow for this.
We now include for complete valve renewal anyway, as the existing valve will be past its best on most applications.
The replacement of an Hitachi RCU240SY1 chiller on a site in the City of London site demonstrates the issues to be considered.
Four circuit water-cooled package water chillers previously used R22, with one screw compressor per circuit. The compressor style is in current production. We felt this represented a good candidate for upgrade and offered the following procedure for conversion from R22 to Isceon 29 as suggested by Rhodia/Du Pont, with additional options suggested by ourselves to take account of the chiller age and present service set up.
1. Recover refrigerant charge, weighing removed gas and comparing to plated weight. If less than 90% of expected weight is recovered, system leaks should be suspected and attention to the leak-test procedure below becomes essential.
2. Drain oil from compressor. Renew with fresh oil of the appropriate grade and renew system driers.
3. Renew any seals suspected as likely to leak. However it is not specifically necessary to renew seals. A specific requirement for Hitachi chillers is to strip down and refresh all seals on compressor terminal plate.
4. Once system works are concluded, the system should be pressure tested progressively to 12 bar with dry nitrogen. Subject to suitable isolations, the high side could be squeezed to 25 bar, but caution should be exercised that excessive pressure is not allowed to build up in the low side of older chillers or secondary (and possibly disastrous) leaks can be created.
5. Once final pressure is achieved the system should be left for 6 hours, during which time no appreciable pressure loss should occur.
6. Vent nitrogen to atmosphere. then evacuate the system.
7. Charge the system to the condenser, preferably in the liquid phase or by charging complete cylinders in the gas phase. Isceon 29 is 5% lighter per equivalent volume than R22 so reduce charge weight accordingly.
8. Set system to work, ensuring a refrigerant comparator scaled for Isceon 29 is used to verify suction superheat and liquid sub-cooling levels. This is available from the Du Pont website.
9. Carry out a final system leak check, and complete system operating log.
Changing the refrigerant for this particular chiller involves other system-specific considerations.
Renew TEV power assembly and internal orifice.
Compressor bearing overhaul.
Reseal compressor terminals.
Renew compressor contactors.
Attention to the above four items requires opening the refrigeration system. By including these operations within the scope of the conversion works, considerable savings can be achieved by reducing aspects of a project that would otherwise have repetitive system procedures. System works typically represent around half of the overall works required; the savings are obvious.
Trevor Dann is with ThermaGroup Ltd, Green Lane, Burghfield Bridge, Reading RG30 3XN.