Energy Savings from a Compact and a Large Multi-Family Solar Water Heaters
Abstract
Two hot water solar heaters (HWSH) are modeled using the simulation software Trnsys, the case study corresponds to the domestic hot water (DHW) needs of a 40 dwelling building in Paris, France. System designs are built in agreement to all physical and thermal restrains, and the objective is to obtain high energy savings with respect to a hot water electric heater. The compact HWSH uses a hybrid electric-solar tank to store the harvested solar energy in order to limit the occupied space in the cellar and to achieve a night thermal treatment of solar hot water avoiding bacteria formation. The large HWSH has a supplementary tank for the solar energy storage to optimize the energy savings. Both systems use a part of the useful solar energy via a heat exchanger to balance the heat loss of the circulation loop. If solar energy at high temperature is not available an auxiliary heater maintains the circulation loop at set-up temperature. The results show that by exploiting the solar energy, the designed compact and large HWSH could save electricity up to 21.7 MWh/y and 22.8 MWh/y, respectively, for the same DHW load. These savings represent respectively 20.5% and 21.6% of the total annual electric consumption of the standard system. The financial savings strongly depend on the energy price. In this paper, based on the relatively low price of electricity in France in 2009, the compact HWSH could save 1421 €/y and the large HWSH could save 1518 €/y.