Numerical comparison of the yearly performance of an indirect vapour compression heat pump working with R290 with R410A systems

In the last years, the environmental awareness is pushing the air-conditioning and refrigeration industry towards a massive use of low GWP refrigerants. Generally, despite being environmentally friendly, these new working fluids are mildly flammable, or even flammable, and therefore safety concerns arise. One possible way to cope with the flammability hazard is the reduction of the charge of the refrigerant inside the system. In this scenario, indirect systems, i.e. brine-to-water system with a remote air-to-brine heat exchanger, seem to be a viable solution since they may be built with low internal volume which, in turn, leads to a low refrigerant charge. However, the use of heat transfer fluid between the air and the refrigerant results in an increase in the energy consumption of the system, making this solution less attractive. In the present paper, a numerical assessment of the use of R290 in an indirect expansion vapour compression system is presented. The analysed system consists of a reversible brine-to-water heat pump able to supply space heating or space cooling depending on the season. The results are compared with those of a baseline R410A system, both in direct and indirect configurations. Although the refrigerant charge is well below the maximum value currently allowed, the indirect systems show a reduction in the energy performance by around 20% with respect to the direct one.