John Poole of Refrigerant Solutions offers an application-based approach to replacing R22.
AS EVERYONE will be aware, in less than 12 months time it will be unlawful to top up systems with virgin R22 (even if purchased before the end of 2009), which also means that stocks of R22 also cannot be used to keep equipment running beyond the end of this year. Only recovered R22 will be permitted for sale and use after this date.
What to do, then, to replace R22 in such a short time frame? The scale of the problem is little short of daunting with many thousands of systems currently operating on R22. This unique refrigerant remains the most widely used gas in the acr industry today, with over an estimated 100,000 tonnes in use in Europe.
During the transition away from CFCs to HFCs, retrofitting directly from a CFC (eg R502) to a HFC (eg R404A) was found to be both costly and in many cases technically unsatisfactory.
The oil in the system needed to be replaced by a synthetic lubricant, which in some cases was not practical, and there were many cases of a deleterious effect on the seals.
This is the reason why interim refrigerants were introduced to replace CFCs without the requirement to change the oil or change any of the hardware. These transitional substances contained at least one HCFC component in the blend which facilitated oil return and enabled plant and equipment to be time expired.
Clearly, any replacement for R22 must be non ozone depleting which rules out this type of compound.
HFCs, such as R407C, are not soluble in mineral and alkyl benzene lubricants and new synthetic oils have been developed. These new lubricants pick up moisture rapidly which can cause severe problems if not properly controlled and are considerably more expensive than the traditional oils.
Having learnt from the experiences with replacing CFCs and the problems incurred with retrofitting directly to HFCs, Refrigerant Solutions (RSL) started work on replacements for R22 which could be used with the existing lubricant in the system, provide a similar performance to R22 and of ,course, have a zero ODP.
In finding the best match for R22, RSL, based on its knowledge of existing R22 applications, selected condenser pressure, energy efficiency and compressor volumetric capacity as the major thermo-physical design criteria.
Early in the development it was recognised that these criteria could reasonably be matched with those of R22 using potentially acceptable blends, but that no single blend or fluid could be formulated to mirror the performance of R22 across the range of applications at both medium to high and low temperatures where R22 is commonly found.
After considerable research work, RSL decided to develop three products to match R22 in its main applications.
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RS-44 (R424A)
RS-44 is a direct drop-in replacement for R22 in ac applications in systems with a capillary as well as an expansion device. There is no need to change the lubricant since, as with all the RS series of refrigerants, RS-44 is compatible with mineral, alkyl benzene and POE oils. RS-44 has been designated an ASHRAE number of R424A with an A1 classification.
A testing programme showed that, compared to R22, RS-44 had a higher COP, lower head pressures, lower discharge temperatures and pressures, a similar performance and good oil return with all types of oils including both traditional and the new synthetic lubricants.The lower discharge temperatures experienced with using RS-44 provides significant operating benefits.
Trials with RS-44 have shown energy savings from 10 to 20% compared to R22 when RS-44 is retrofitted into the same system while achieving similar capacity.
RS-45 (R434A)
RS-45 is a potential option for OEMs and can also be used to replace R22 across the range of applications and temperatures including ac and low temperature refrigeration.
RS-45 is a capacity match for R22 but should not be used in systems with a capillary. RS-45 replaces R22 at both higher temperatures and lower temperature applications where an expansion device is present.
RS-45 is a near azeotropic blend with a glide of 1.5°C, one third that of R407C, which facilitates its use across a wide temperature range and provides significant benefits in the case of flooded systems. RS-45 has a COP which matches R22, similar discharge pressure to R22, identical compression ratio, is non flammable (ASHRAE safety classification of A1) and a considerably lower discharge temperature than R22 which provides significant operating benefits including a much lower risk of oil degradation.
RS-52 (R428A)
RS-52 is similar to R507 in its performance with high capacity at low temperatures. RS-52 has been designed as a replacement for R502 and the interim ozone depleting blends (eg R402A, R403B, R408A and R411B), but is also an excellent replacement for R22 at low temperatures where the system is designed to withstand R502 pressures.
The high capacity of RS-52 at low temperatures is a prominent feature of this new refrigerant. RS-52 has a temperature glide of less than 1°C, and is also suitable for use in flooded systems.
Refrigerant Solutions Ltd
0161 926 9876