Performance of an air-to-water heat pump system in a low energy residential building: modelling and experimental results

A modulating air-to-water heat pump system, installed in a Belgian low-energy residential building, has been monitored from December 2006 to December 2007. This paper presents the system performance derived from the monitored data and the development of a heat pump model. The heat pump is connected to a floor heating system and to a domestic hot water (DHW) tank. For the monitored heating seasons, with average outdoor temperatures of respectively 5.7°C, the average COP of the heat pump in building heating mode was 4.1 and in DHW production mode 2.4. The seasonal performance factor (SPF) of the whole system during the heating season (including building heating mode, DHW mode and transmission losses of the DHW tank) amounted to 3.3. The building and heating system are modeled in TRNsys. A new heat pump model is developed to take the capacity modulation into account. A second order polynomial, with outdoor temperature, condenser outlet water temperature and instantaneous building heating demand as independent variables, is found to give the best fit.status: publishe