Effect of PCM application inside an evacuated tube collector on the thermal performance of a domestic hot water system

The article presents an analysis of the effect of PCM application inside an evacuated tube collector on the characteristic operating parameters of a solar water heating system. The temperature of hot water inside the tank and the solar fraction in a domestic hot water system were determined for a typical meteorological year in the Polish city of Czestochowa. A methodology for determining the thermal performance of the evacuated tube collector/storage unit was proposed. The charging efficiency of the evacuated tube collector/storage in a range from 33 to 66% was obtained depending on the solar radiation intensity and the temperature of PCM. An application of latent heat storage (technical grade paraffin) inside the evacuated tube collector allowed the delayed release of heat in the evening, when the intensity of solar radiation was insufficient. As a result, an increase in the temperature of hot water inside the tank was observed during the hot water peak loads in every characteristic period of a typical meteorological year. Furthermore, an evacuated tube collector/storage improved the annual solar fraction in a domestic hot water system by 20.5% compared with the reference evacuated tube collector without storage.