Solar hot air collectors are mounted on south-facing vertical walls or roofs. Solar radiation reaching the collector heats the absorber plate. Air passing through the collector picks up heat from the absorber plate.
Freezing, overheating and leaks are less troublesome for solar air collectors than for liquid collectors. But since liquid is a better heat conductor, solar collectors using water or a heat transfer fluid are more suited to hot water heating for the home. A solar hot air collector is most often used for space heating. There are two types of air collectors: glazed and unglazed.
Photo Credit: U.S. Department of Energy
Glazed Air Collectors
Glazed air collectors heat air through circulation. A fan moves cold air from the home to the collector. After passing through the collector, the heated air is ducted back to the home. There are multiple system designs:
through-pass air passes through from one side of the absorber to the other. This system has the most surface area, making it an efficient way to transfer heat. Lower pressure, though, can require more fan power. Deterioration of select types of absorber materials after years of exposure to solar radiation can worsen air quality and performance.
back, front and combination passage in these cases, air is directed to either the back, front or both sides of the absorber. This system is more prone to dust accumulation, which eventually lowers the absorber efficiency. In cold weather, the air passing by the glazing is also prone to heat loss.
Unglazed Air Collectors
An unglazed solar air collector is relatively inexpensive. These collectors are best for areas with high ventilation needs and fewer space heating needs. Therefore these collectors are most commonly used in commercial applications, and are less suitable for residential use.