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Paraffin wax is applied to a solar water heater (SWH) as a thermal energy storage material due to its high energy density. Several previous studies have shown that integrating water and paraffin wax in the SWH tank can increase the thermal energy storage capacity. However, the thermal stratification of thermosyphon-type SWHs with horizontal tanks has not been explicitly disclosed. This paper investigates the thermal stratification of water inside the SWH tank containing paraffin wax. Paraffin wax was filled into a cylindrical capsule. The capsules were then put into the SWH tank and arranged parallel to the axis of the tank. The experiment was conducted for the duration of the charging process. The solar radiation intensity, the water, and the paraffin wax temperature were recorded. The resulting data was accustomed to graph the evolution of water and paraffin wax temperature. Based on the graph, thermal stratification was formed visually inside the tank. Stratification analysis was conjointly performed with the Richardson number calculation. The calculation shows that the value of Richardson's number is more than one. These results explain that thermal stratification occurs in the SWH tank. The addition of capsules containing paraffin wax can maintain thermal stratification. [ABSTRACT FROM AUTHOR]

Water use as a heat storage material in solar water heaters (SWH) has disadvantages, including its low energy density, which requires a large volume of thermal energy storage. Phase-change material (PCM) is a latent type of heat storage material that has the advantage of being a high energy density. Therefore, PCM is quite interesting to be applied to SWH systems. In the operation of SWH, it is necessary to know the characteristics of hot water usage. This paper aimed to determine the characteristics of a continuous and gradual discharging method on SWH that applies PCM. This study used a thermosyphon type of SWH. The tank was placed horizontally on the top side of the collector with a volume of 60 liters. Twenty-four cylindrical capsules containing paraffin wax were inserted into the tank. Thermocouples were installed on the waterside and the PCM side. Continuous and gradual methods were carried out in the discharging experiment. Experiments using a continuous discharging method given information that water temperature decrease continuously in the tank. Experiments with a gradual discharging method showed PCM's contribution, which can transfer thermal energy to the water. The gradual discharging method explained that the SWH system produced hot water that can be used for bathing as many as five people every day with water temperatures of 45 °C at an average solar radiation intensity of 514.89 W/m2. The use of PCM makes a positive contribution to the thermal energy storage in the tank. [ABSTRACT FROM AUTHOR]