The effect of using a desuperheater in an air-to-water heat pump system supplying a multi-family building

Abstract

Heat pumps are increasingly used for thermal energy supply in multi-family buildings. However, especially in case of central domestic hot water preparation systems, high temperatures of at least 60 °C are required because of the risk of legionella growth. This leads to lower efficiency and, due to the operational limits of air-source heat pumps, often also to increased operation of the electrical backup heater. In this study, we analyse the effect of a desuperheater integrated in a heat pump, enabling high water temperatures to be provided at comparatively low condensation pressures. Using a heat pump model that was validated with measurements, we performed system simulations of an air-to-water heat pump with and without desuperheater in a multi-family building. We consider two different temperature levels for the domestic hot water distribution, as well as three different climates for different load conditions for space heating and cooling. The results show electricity savings due to the desuperheater of 3.3–5.2%, depending on the climate and system configuration. These savings are partly due to using a stratifier tube for charging the storage tank with the desuperheater, which increases the electricity savings by 1–4% points in the system considered. The payback times of the desuperheater integration are 7.4–17 years for all variants.