Problem statement:The thermal performance modeling of hybrid water heater with evacuated glass tube solar collector and flue gas of rice husk combustion was developed. The solar global radiation and ambient air temperature data used in the system modeling belongs Phitsanulok province from 7 am-5 pm in the summer season. Approach: The system can be divided into two parts, i.e., evacuated glass tube thermosyphon solar collector and thermosyphon heat exchanger with flue gas of rice husk combustion. The evacuated glass tube was a coaxial double-layer tube made of Borosilicate. Its outer tube diameter and inner tube diameter were 58 and 47 mm respectively. The inside cavity of evacuated glass tube holed thermosyphon which was made of copper tube and filled with R134a at the filling ratio of 70% of evaporator volume. For latter, the temperature and flow rate of flue gas that was released from the cyclone furnace and used as a heat source of heat exchanger were constant at 150°C and 50 m 3 min −1 . The heat exchanger was consisted of array of thermosyphon which was made of stainless steel tube and filled with distilled water at 50% filling ratio of evaporator volume. Results: The effects of various parameters on the system performance were computational analyzed. The hybrid water heater system with optimum design of both thermal performance and economic can be obtained and produce the hot water at the temperature exceeding 70°C and the flow rate of 1 m 3 day −1 . Conclusion: The thermal performance of this optimum hybrid water heater system was investigated along the time of the day in summer.

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In this study, the evacuated tube solar water heater system using thermosyphon has been investigated experimentally as well as theoretically. Solar radiation and ambient temperature data from Chiang Mai province were used for the modelling system by explicit finite difference method. The effects of thermosyphon diameters and number of evacuated tubes on the net saving of solar water heater system were analyzed. The mathematical results showed that the optimal number of evacuated tubes and thermosyphon diameter occurs at eight evacuated tubes, which are 15.88 mm of evaporator diameter and 22.22 mm of condenser diameter under personal hygiene conditions. The solar water heater system at optimal parameters was constructed and tested for the system prototype. The theoretical results were validated by the experimental results. It was found that the theoretical results can be used to predict temperature, heat transfer rate, and thermal efficiency to show good agreement with the experimental results as well as previous research. The experimental and theoretical results showed that the maximum temperature for hot water was 65.25 °C and 71.66 °C, respectively. Moreover, the thermal efficiency of the system based on the theoretical result was 60.11%, with relative error being about 3.04% of the experimental result.