A comprehensive study on the effect of hot water demand and PCM integration on the performance of SDHW system

Abstract

In this study, a commercial SDHW for Tehran meteorological data is modeled numerically in order to investigate the effect of three main influential sets of parameters, including the solar system characteristics, the water demand profile, and the PCM integration. First, a sensitivity analysis of intrinsic parameters is conducted. Then, the system performance is analyzed under the thermal stratification effects. After recognition of the system, the effect of hot water demand and several time-profile is investigated. Finally, in order to determine the whole range of operating conditions, both fully-mixed (single-node) and fully-stratified (multi-node) tanks are considered for applying phase change material (PCM) as a storage medium. Genetic Algorithm (GA) is used to achieve the best PCM parameters including the melting temperature, and the total volume and its distribution in the storage tank. Sensitivity of the optimized PCM−embedded system to the melting temperature is conducted in order to propose some practical PCMs for use in such systems.According to the results, in the non-uniform high daily water consumption the thermal stratification is more beneficial which can lead to 9% increase in the ASF. Also, it is found out that a solar water heater system performance is very demand dependent so that it induces up to 8% ASF variation in different demand conditions. Therefore, integration of the PCM in SDHW systems, which can increase the ASF by 4%, is very case dependent with respect to the results of optimization and sensitivity analysis.