Experimental studies on phase change material packaged in stainless steel balls for solar hot water system

Studies the heat storage and release performances of centralized solar hot water system of a residential building. Packages the phase change material (PCM) of paraffin with expanded graphite in stainless steel balls with a diameter of 60 mm. Compares heat storage and release and heat insulation performances of two PCMs with a phase-transition temperature of 55 ℃ and 60 ℃ under different solar radiation. Calculates the solar fraction based on the maximum day demand of users. The results show that the heat storage time of the hot water system is 2.0 to 4.5 hours. An average solar fraction is 75% and 80% for PCMs with a phase-transition temperature of 55 ℃ and 60 ℃, respectively. Phase change heat storage can enhance the solar fraction and is better than that without heat storage. PCMs with a phase-transition temperature of 60 ℃ is suitable for centralized solar hot water systems.