Energetic and economic analysis of a PV-assisted air-to-water heat pump system for renovated residential buildings with high-temperature heat emission system

Air-to-water heat pumps are attractive as a replacement of inefficient fossil fuel-based heating systems in thermally renovated buildings. If existing radiator heating systems are not replaced during renovation, high flow temperatures limit the efficiency of the heat pump. For such systems we analysed the possibility to reduce grid electricity consumption by combining the heat pump with a photovoltaic system, a thermal storage (water tank) and an intelligent rule-based control system that enables targeted heat pump operation with on-site PV electricity. Detailed TRNSYS simulations were carried out for space heating and domestic hot water preparation in a single-family house in Zurich in two renovation scenarios. Different strategies for improved control were analysed and combined to an integrated control approach. To perform an economic analysis, the payback time of the PV system was analysed for different PV and storage sizes. Assuming typical Austrian electricity prizes and feed-in tariffs, the shortest payback time of 17.1 years can be achieved with 5 kWp of PV, combined with a storage volume of 1 m ³. If operated with this optimum size and the advanced control, the system saves 2400 kWh/a (a reduction of –29%) of grid electricity, and the net cost of electricity is lowered by 585 €/a (–35%) as compared to the same system without PV. A sensitivity analysis was performed to consider the situation in different countries, using different electricity prizes and feed-in tariffs. The results show how these influence the payback time and the optimum size of the PV system.