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

摘要

This paper describes improvements that can be introduced at both a structural and control level in order to improve the overall efficiency of solar kits 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 surrounds the entire storage tank. One major structural improvement has been designed. It consists of the replacement of one single electrical element as an auxiliary heater by three smaller ones with different lengths. This configuration requires the manipulation of two additional actuators. An advanced control strategy has been developed to handle the resulting complexity and to achieve higher performances. The actuators are the pump driving the fluid in the collector loop and the three electrical elements. A predictive control strategy has been proposed and validated. It requires solving of an optimization problem and implementation of a state estimator. Weather forecasts as well as prediction of the users' needs in terms of tapped water are required to implement this predictive control strategy. The weather forecasts are provided on-line by the Swiss Meteorological Institute (SMI). The prediction of the users' needs is updated every day using an extended Kalman filter. Segmentation of the auxiliary heater coupled with a suitable advanced control strategy have led to significant improvements in terms of comfort and energy consumption.