Energy, exergy and economic viability of a heat storage system used for domestic hot water supply in urban and isolated households

The endeavor of the paper is the study the feasibility of using a locally made daily solar storage system, SSS, for domestic hot water supply especially in urban and isolated households. In order to evaluate the system efficiency during the charging and discharging periods an experimental and a numeric investigation were simultaneously achieved. Results showed that the daily energy efficiency of the energy stored in the HSU ranged from 30 to 49.5% whereas the daily exergy efficiency ranged from 19 to 27%. The results show also that for wet sand the quantity of daily destocked energy varies in the array of 1.75-0.8 kW h. The results showed that 75% of the total DHW requirements can be achieved from the heat storage system during the night. The results of the economic analysis shows that the SSS, the annual energy kept (YES) and the payback period (PBP) were about 1317 kW h/year and 4 years based on electric water heater and about 460 m3 gas saving and 3.5 years based on gas water heater, respectively.