The impact of two-stage discharging on the exergoeconomic performance of a storage-type domestic water-heater

The present study is concerned with the exergoeconomic performance analysis of a storage-type electrical water heater, being subjected to two volumes of hot water removals at 5 L/min; the first one immediately after the heating of water in the tank, and the second, after some time has been waited since the completion of the first discharge. This two-stage discharging regime is designed and experimented in such a way to represent the two shower taking periods after the hot water preparation in the tank is accomplished. From the experimental results, correlations between exergy destruction and the standing time between the two discharging periods, for different initial volume extractions are developed. Using these correlations it is deduced that in order to minimize the cost of exergy destruction in a two stage discharging regime, the initial withdrawal of hot water volume must be maximized, while the standing period between the two discharges is minimized. For long standing periods, the economic feasibility of thicker thermal insulation must be assessed.