Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants

•COP dependence on subcooling as a function of condenser size is shown.•Comparison between two different subcritical prototypes for the production of SHW.•Subcritical systems have a COP improvement between 5% and 20%.•Subcritical system able to produce water at 90 °C with higher efficiency (11%).

Heat pumps that work with a high degree of subcooling in subcritical systems have shown a significant margin of improvement when working with sanitary hot water applications. Recently, two different approaches to overcome the high degree of subcooling have been presented in the literature: with a subcooler (separate from the condenser) and by making all the subcooling in the condenser. In this paper, a comparative evaluation between both alternatives is presented, and the obtained results are compared with a representative solution already available on the market using natural refrigerants for this application. The results of this analysis have shown that in a system with subcooling in the condenser, it is possible to obtain a COP comparable to that of transcritical CO2 heat pump water heaters. Furthermore, the system with subcooling has been demonstrated experimentally as being capable of producing water up to 90 °C and has shown a COP up to 20% higher than some CO2 commercial products (catalogue data reference).