Unglazed, "transpired" air collector,
Image: United States Department of Energy,
Wikimedia CommonsAn air collector is relatively simple and provides inexpensive heat at temperatures as high as 38 degrees Celsius above ambient. The devices may be designed in a variety of ways in terms of configurations and materials used. They are grouped into two main categories: glazed and unglazed air collectors. A glazed air collector is commonly used for space heating while an unglazed air collector is often used in industrial, commercial, process, and agricultural applications.
The Unglazed Air Collector
An unglazed air collector is made of a metal absorber that is not covered by any glazing or glass, with the most common type being the transpired solar collector. An unglazed air collector is largely used in process, agricultural, institutional, industrial, and commercial applications. It is extremely common in different industrial applications where there is high ventilation needs and the buildings tend to have negative pressure and stratified ceiling heat. An unglazed air collector produces a lot of energy, with one square meter generating as much as 500 to 600 peak thermal Watts. Its high solar conversion and relatively low capital cost have made it attractive in different applications.
An unglazed air collector works by heating the external air and is usually mounted on the walls to capture the sun’s energy at a lower angle and/or off of the reflection from the snow during winter. Its external surface has a myriad of micro-perforations to capture and uniformly draw heat inside an air cavity. Heat that escapes from the building is also captured in the air cavity and re-used. An unglazed air collector can last for more than 30 years, during which they do not require any maintenance.
The Glazed Air Collector
The glazed air collector re-circulates the conditioned air within buildings by using solar thermal collectors. It absorbs thermal energy from the sun that is then used to heat air through the use of ducts. The heat is transferred to the air by conduction. Solar air collectors minimize the need for conventional sources of heat and reduce your carbon footprint. Overall, they provide a sustainable means of generating thermal energy.