Experimental study of the solar photovoltaic contribution for the domestic hot water production with heat pumps in dwellings

Abstract

The present paper describes experimental work, carried out during an entire year on a heat pump used for domestic hot water (DHW) production, which is powered from photovoltaic panels and the grid simultaneously. The system was designed and controlled to give priority to the renewable source to reach the maximum solar contribution. The aim of the study was to analyze the real possibilities of using photovoltaic energy to produce DHW with heat pumps in dwellings. The system developed (heat pump + PV) works without batteries and therefore the energy storage is carried out by the hot water accumulated in the tank. The design of the system was carried out in order to optimize the solar contribution. Some key aspects of the design are: the heat pumps’ power, the water storage volume, the control strategy and a device to derive the excess of PV electricity to a secondary heater. The system was tested for typical DHW production of a typical family of 4 residence: 130 liters at 55°C, about 6.2 kWh a day. Tests were carried out in the university laboratory located in Alicante (Spain). The results during a year of study demonstrates that the annual average efficiency of the heat pump (SPFHP) could be close to 3.5 and the annual average efficiency of the whole system would be near 9, while the solar contribution would be higher than 60%.