Passive integral collector storage (ICS) solar water heaters can potentially heat water at lower costs then active systems with freeze protection. However, ICS panels can freeze in cold weather. This study developed a model relating the freeze behavior to climate conditions, validated the model experimentally and then ran the model with long term U.S. weather data to delineate regions safe for the passive solar heaters. Both, a single- and a double-glazed tubular ICS panels were modeled and tested. It was found that freezing begins when the water in the supply/return lines freezes and initiates a pressure build up in the collector which can eventually burst the large collector tubes when the water inside freezes and expands. It was found that freezing can be delayed by installing heat tape over the supply/return lines. Using a model of the collector and TMY2 weather data, correlation maps were developed to show in which regions of the U.S. ICS panels with and without heat tapes can be installed safely.

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