A propane water-to-water heat pump booster for sanitary hot water production: Seasonal performance analysis of a new solution optimizing COP

Electrical heat pumps for sanitary hot water production achieve a high performance with a good matching of water and refrigerant temperature profiles during the heat rejection stage, as it happens in CO2 systems. This work considers the thermodynamic possibility to adapt the condenser pressure of a propane heat pump to maximize the COP, while producing sanitary hot water up to 60 C from a heat sink equal to 15 or 25 °C. The performance of the heat pump is calculated through specific models which, in combination with a TRNSYS model of the whole system, allowed to assess its seasonal performance for a hotel in Strasbourg, also varying the control logic and the size of the storage tank. Results obtained led to the conclusion that, for achieving a high seasonal performance, the control logic of the tank has the largest influence.