Performance Evaluation of a Demonstration System with PCM for Seasonal Heat Storage: Charge with Evacuated Tubular Collectors

A seasonal heat storage with phase change material (PCM) for a solar space heating and domestic hot water combisystem was tested in automated operation during charge with solar collectors. A water tank was operating as buffer heat storage. Based on measurements during a representative day with sunshine, the storage system performance was evaluated regarding charge with solar heat. It shows the system behavior during typical operation resulting from the control strategy. Heat transfer rates from the solar collector array (22.4 m² aperture area) to the heat stores reached a peak of 19 kW, when PCM was melted. 30 kWh of heat was transferred to the 750 l water volume as it heated up. Afterwards 46 kWh of heat was transferred to the segmented PCM storage. In total 56 % of the total irradiation on the tilted collector plane was utilized to heat the storage units. During PCM charge heat transfer fluid temperatures were increasing with the state of charge. This is in contrast to maximization of solar yield. However, the energy conversion efficiency (65 %) of the collector array was satisfying. By considering pump electricity consumption, an overall performance ratio of 30.8 was obtained.