Advanced control strategy of a solar domestic hot water system with a segmented auxiliary heater

This paper describes improvements that can be introduced at both a structur al and control level in order to improve the overall efficiency of solar ki ts for domestic hot water supply. The plant under consideration is a solar domestic hot water system (SDHWS) manufactured in Switzerland. The heat exchanger is a mantle, which surround s the entire storage tank. One major structural improvement has been designed. It consists of the repl acement of one single electrical element as an auxiliary heater by three sm aller ones with different lengths. This configuration requires the manipula tion of two additional actuators. An advanced control strategy has been dev eloped to handle the resulting complexity and to achieve higher performance s. The actuators are the pump driving the fluid in the collector loop and t he three electrical elements. A predictive control strategy has been propos ed and validated. It requires solving of an optimization problem and implem entation of a state estimator. Weather forecasts as well as prediction of the users' needs in terms of tap ped water are required to implement this predictive control strategy. The w eather forecasts are provided on-line by the Swiss Meteorological Institute (SMI). The prediction of the users' needs is updated every day using an ex tended Kalman filter. Segmentation of the auxiliary heater coupled with a suitable advanced contr ol strategy have led to significant improvements in terms of comfort and en ergy consumption. (C) 2001 Elsevier Science B.V. All rights reserved.