Refrigerants assessment, heat pump, global warming potential, energy efficiency
Energy conservation is the core reason for the increasing interest in high performance low global warming potential (LGWP) refrigerants. Several researchers pioneered new refrigerants that have zero ozone depletion potential and GWP less than 500. This paper presents a study that breaks new ground on LGWP developmental refrigerants and focuses on heat pump systems for residential applications. An R410A 17.6 kW (5 ton) heat pump split unit commercially available off-the-shelf for US ducted HVAC application, was retrofitted with two new developmental refrigerants that have GWP ranging from 300 to 500, which is significantly lower than that of R410A. The two new refrigerants are still in the R&D stage and are referred throughout this paper as DR-4 and DR-5. The experiments were conducted in a large scale psychometric chamber at Oklahoma State University and the refrigerant cycle pressures and temperatures were measured at design and off-design conditions with outdoor temperature ranging from -8C (17F) to 46C (115F). Very high outdoor temperatures of 43C (110F) and 46C (115F) were also considered in order to assess the characteristics of the new LGWP refrigerants at extreme high temperature ambient conditions. The findings for this work showed that DR-5 had up to 4% higher capacity and up to 22% higher COP, while DR-4 showed up to 16% higher COP but 30% lower capacity in comparison with R410A. The experimental results showed that the thermal expansion valve could be further optimized for the new refrigerants. Adjustments were made to maximize the COP of the unit while preserving the cooling capacity and data showed that the COP of DR-4 could be augmented by an additional 6% with respect to drop-in tests. The experimental data discussed in this paper are part of a broader campaign on LGWP refrigerants performance in heat pump systems. The data serve to provide some guidance to the industry and regulatory agencies for the need of future research and developmental work on the next generation of high performance LGWP refrigerants.