Thermodynamic assessment of ultra-low-global warming potential refrigerants for space and water heaters

Abstract

[EN] The current paper studies the most suitable ultra-low-global warming potential (GWP) (GWP < 30) candidates in the market, considering also its grade of flammability and toxicity, for heat pumps employed for different space heating and domestic hot water (DHW) applications. A pre-design thermodynamic model has been developed to evaluate the performance and size limits for any subcritical or transcritical heat pump under certain working conditions. This generic model is based on the pinch point approach, so it does not depend on a certain type of heat exchangers, it only depends on the external working conditions. The results showed that all subcritical ultra-low-GWP, nonflammable, and nontoxic refrigerants considered have either lower coefficient of performance (COP) or volumetric heating capacity (VHC) compared with the reference high-GWP refrigerants R-410A and R-134a. Additionally, the only refrigerants with higher COP, such as R-717 (ammonia) or R-290 (propane), are either extremely flammable or toxic. For the applications need of high water-side temperature lift, the transcritical refrigerants R-744 (CO2) and R-170 (ethane) showed the best performance, regarding both COP and VHC values, of all the refrigerants studied. The refrigerants R-161, R-1270 (propylene), and R-1234yf presented a balanced performance in both space heating and DHW applications. This makes them potential candidates to be employed in subcritical multi-temperature levels heat pumps.