New Heat Pump Working Fluids

One disadvantage of R-410A as a heat pump working fluid is its loss of cooling capacity when operating under high (>35°C) ambient temperature conditions. Therefore, BTC staff and a manufacturer initiated a CRADA to identify a new class of zeotropic mixture alternatives to R-22 which promise better heat pump efficiency under these conditions.
Room air conditioner under test with R-410A and
Q8 zeotropic mixture alternative.

Researchers identified an initial mixture composition that was calculated to have about a 17% higher COP at design cooling conditions than R-410A. After the manufacturing partner determined that this mixture was flammable, a nonflammable mixture was formulated, designated Q8, and analytically predicted to have about a 10% better cooling COP than R-410A. The partner's initial comparative tests with Q8 and R-410A in a room air-conditioner showed only a 1–2% gain with Q8. Analysis of the data and independent testing of Q8 and R-410A heat exchanger (HX) designs determined that Q8 suffers a heat transfer coefficient degradation in the system HXs that degraded its system performance. ORNL has developed new HX designs to overcome this performance penalty and had samples built by Heatcraft. The room air-conditioner is currently being retested at ORNL with the new HX designs.

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