On-demand dynamic performance of a thermal battery in tankless domestic solar water heating in the tropical region

This paper reports an experimental investigation of a new design of solar water heater (SWH) employing evacuated tube heat pipe solar collectors (HPSCs) and latent heat storage (LHS) as a thermal battery. In this design, the solar energy incident on the HPSC is collected and stored in the LHS tank via a heat pipe with fins attached to the condenser ends. The stored solar heat is then transferred to the domestic hot water supply via another set of finned-tube heat exchangers located inside the LHS tank. The experimental results of the on-demand performance of the latent heat thermal storage were reported under three different modes, which are weather condition, the daily volume of hot water production, and draw-off starting situation. Results indicated that this design of the thermal battery is able to provide the demanded hot water for households in any weather condition in a tropical climatic region like Malaysia. For a domestic application with solar collector size of about 2 m(2), this design can provide at least 112-170 L per day in the worst weather condition. In a fully/partially sunny day, the thermal battery is able to provide much more hot water for domestic demands. It was also found that low thermal conductivity of the Paraffin is useful here, by preventing heat loss of the tank to ambient for long-term heat storage. Therefore, the system is able to provide hot water for the next morning normal usage.