Passive Solar Collector Freeze Characteristics

The major challenge for solar water heaters is to provide heat at a cost comparable to or lower than conventional fuels. Since the price of integral-collector-storage solar water heaters (ICS) is about one half to two thirds of that for active systems with freeze protection, they can provide lower-cost energy. However, ICS are subject to freeze damage, as the collector generally has metal tubes carrying pressurized water that can freeze and burst. In order to delineate the geographical areas where ICS can be deployed safely it is necessary to experimentally determine the conditions under which freeze damage occurs, to develop a model relating the freeze behavior to climatic conditions, and to validate that model with the experimental data. Three types of ICS have been subjected to increasingly severe freeze conditions, until freeze damage occurs. Tested units include double and single-glazed conventional units, and an innovative ICS with immersed metallic heat exchanger carrying pressurized water in a plastic box of stagnant, unpressurized water. Existing models for ICS thermal performance were modified to incorporate the freezing process, and have been validated with the experimental data. The validated models will be used to predict regions of the country safe for installing the ICS. Simulations will be done over at least 30 years of weather. Finally maps are created to illustrate the regions of safe installation