New design approach and implementation of solar water heaters: A case study in Michigan

The potential of evacuated tube solar water heaters is evaluated for the state of Michigan, which has regions with low solar resources, for year-round usage. Simple empirical equations for the initial sizing design stage are provided for the entire state for a given system. The analysis includes experimental results obtained for a setup at Michigan State University and model-based results for 26 locations dispersed throughout the state. These are obtained using the System Advisor Model (SAM) software package from National Renewable Energy Laboratory. The results show that evacuated tube collector solar water heaters are appropriate for typical household water usage for Michigan's climate with payback periods as low as 8 years (variations are due to local weather conditions). In addition, a study on the optimum collector area for various hot water demands is performed; this led to identification of empirical equations useful for estimating the optimal area of a given system as a function of the hot water demand for locations throughout Michigan. A parametric study is carried out and it is found that the overall heat gain coefficient of an evacuated tube collector affects significantly its performance and it should be considered in order to select an appropriate system. The impact of additional parameters such as heat gain and heat loss coefficients on the performance of the system is also discussed.