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A recently published
report1 provides
a good start to the enormous task of understanding the issues related to
refrigerant and lubricant stability in our quest to find low global warming
potential alternatives to HCFC and HFC refrigerants. The study compared the thermal and chemical
stability of three alternative refrigerants (HFO-1234yf, HFO-1234ze and a 50/50
blend (by weight) of HFO-1234yf with R-32) with two common currently used
refrigerants (R-134a and R-410A). All
five refrigerants were tested with 3 different lubricants (a mixed acid POE, a
branched acid POE and a PVE), all of which contained BHT antioxidant. The authors have provided an excellent
summary of their results which I will not repeat here, but a few key
conclusions are:
1. The alternative
refrigerants are less stable than either R-134a, or R-410A. The levels of refrigerant decomposition
measured in the HFO alternatives in most cases were small, but no decomposition
was found with either R-134a or R-410A.
2. Contamination of
samples with air lead to higher levels of refrigerant decomposition of the HFO
alternatives.
3. The presence of
air also lead to greater decomposition of lubricants for all refrigerant and
lubricant combinations.
4. The PVE lubricant
decomposition was very low regardless of air or moisture contamination.
5. The effects of
moisture and air contamination vary significantly depending on the specific
refrigerant and lubricant and cannot be generalized.
Obviously, as mentioned above and by the authors in their
summary, this work is only a start.
Understanding material compatibility which will studied in Phase 2 is
key, as is understanding other key lubricant properties such as lubricity, solubility,
viscosity, miscibility...... The
challenge of implementing alternative refrigerants and lubricants continues to
be great but with the work that was done in the 90's as alternatives to CFC's
were developed, the process for implementing alternatives successfully is
relatively clear.
1. (AHRTI
Report No. 09004-01 - MATERIAL COMPATIBILITY & LUBRICANTS RESEARCH FOR LOW
GWP REFRIGERANTS - PHASE 1: THERMAL AND CHEMICAL STABILITY OF LOW GWP
REFRIGERANTS WITH LUBRICANTS - Final Report - March 2012)
Editor's Note: CR4 would like to thank PJ Sikorsky of GEA Consulting for contributing this blog entry.
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