Performance Modeling Comparison of a Solar Combisystem and Solar Water Heater

As homes move toward zero energy performance, some designers are drawn toward the solar combisystem due to its ability to increase the energy savings as compared to solar water heater (SWH) systems. However, it is not trivial as to the extent of incremental savings these systems will yield as compared to SWH systems, since the savings are highly dependent on system size and the domestic hot water (DHW) and space heating loads of the residential building. In this paper, the performance of a small combisystem and SWH, as a function of location, size, and load, is investigated using annual simulations. For benchmark thermal loads, the percent increased savings from a combisystem relative to a SWH can be as high as 8% for a 6 m2 system and 27% for a 9 m2 system in locations with a relatively high solar availability during the heating load season. These incremental savings increase significantly in scenarios with higher space heating loads and low DHW loads.