Drop-in Performance of Low GWP Refrigerants in a Heat Pump System for Residential Applications

摘要

R410A is one of the main refrigerants used for air conditioning and heat pump systems in residential applications. It has zero ozone depletion potential but its global warming potential is about 2,000. In China and Japan, refrigerant R32 (GWP = 675, zero ODP) has been proposed, as possible replacement for R410A but this refrigerant is slightly flammable. HFO-1234yf is a refrigerant with low GWP (GWP = 4, zero ODP) that is currently being used in European car market as a possible replacement for R134a. The direct impact on the environment of these two refrigerants might be gauged based on their low GWP but a measure of their indirect contributions on greenhouse gasses effects is still an open question. Having a low GWP might not be sufficient to reduce the overall environmental impact if the energy performance of the heat pump system is significantly penalized. In addition, considerable amount of engineering and manufacturing work might be necessary for developing new components that are fit to work with these low GWP refrigerants. This paper focuses on an experimental comparison of the drop-in energy performance and capacities of refrigerants R32 and R1234yf in a R410A heat pump split system for ducted HVAC in residential applications. The experiments were conducted in a large scale psychrometric chamber at Oklahoma State University and on a 5 ton heat pump unit that was commercially available. The experiments were conducted for cooling and heating modes of the unit and the outdoor temperature was varied from 17F (-8C) to 115F (46C). Cooling tests at AHRI standard rating conditions were performed and the refrigerant charge was optimized. Two additional conditions were considered with high outdoor temperatures of 110F (43C) and 115F (46C) to analyze the condenser pressure and discharge temperature of the refrigerant when the unit run at extreme high ambient off-design conditions. The paper highlights some challenges related to R32 and R1234yf and discusses an optimization of the thermal expansion valve when these refrigerants are directly retrofitted in the unit. It was observed that the COP was higher for both R32 and R1234yf as compared to R410A with some peculiar behavior at very high temperatures, for which R32 COP was lower than that for R410A. The capacity for refrigerant R1234yf was 40 to 50% lower and the management of the charge as well as the adjustments of the TXV was problematic without any additional modification to the system.