Due to varying air-ducting methods, collectors are commonly classified as one of three types: through-pass collectors, front-pass, back pass and combination front and back pass collectors.
Through-pass air collector – In the through-pass configuration, air ducted onto one side of the absorber passes through a perforated or fibrous type material and is heated from the conductive properties of the material and the convective properties of the moving air. Through-pass absorbers have the most surface area which enables relatively high conductive heat transfer rates, but significant pressure drop can require greater fan power, and deterioration of certain absorber material after many years of solar radiation exposure can additionally create problems with air quality and performance.
Back, front, and combination passage air collector – In back-pass, front-pass, and combination type configurations the air is directed on either the back, the front, or on both sides of the absorber to be heated from the return to the supply ducting headers. Although passing the air on both sides of the absorber will provide a greater surface area for conductive heat transfer, issues with dust (fouling) can arise from passing air on the front side of the absorber which reduces absorber efficiency by limiting the amount of sunlight received. In cold climates, air passing next to the glazing will additionally cause greater heat loss, resulting in lower overall performance of the collector.
Materials
There are two common methods used to create a solar air heater. The first is a pop can design and the other directs the air through a channel in a “snake” pattern. Both methods use similar materials and tools with only a few exceptions.
To build a “snake” design, a piece of sheet metal for the base would help increase thermal mass and improve heat transfer to the passing air. Also, sand paper may be required.
Alternatively, building the pop can design requires a large number of pop cans and either a mortar or glue to connect the cans.
