Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 33

Up to this point, all the kinds of collectors we have talked about have used a liquid as the heat transfer medium. Air can also be used as the heat transfer mechanism in a solar collector. Air collectors are flat plate collectors and share all the same characteristics of liquid-type flat plate collectors in size and construction. Instead of an absorber plate made of copper piping and copper fins, the absorber plate in an air collector is typically made of a solid sheet of aluminum. The aluminum absorber plate is coated with a selective surface or black paint and is usually dimpled to increase efficiency. When the sun shines on the absorber plate, it gets hot. Air is drawn from the building and is blown across the back of the absorber plate and heated. The hot air is then delivered to the building through ductwork. A blower circulates the air through the system.

Figure 3.11: Air collector

Air collectors can come in standard sizes that are very similar to flat plate collectors and they can also be site built to fit a particular building. We personally manufactured site-built air collector solar space heating systems in the early and mid-1980s and had great success. These collectors should be less expensive than liquid-type solar thermal collectors because the absorber plates in them are much simpler and are typically made of aluminum, which is less expensive than copper. These collectors can produce the same Btus per square foot as any other collector, so they can have very attractive returns on investment.

Another kind of air collector is a transpired collector. This collector is an unglazed flat plate collector. It draws fresh air through tiny holes that are punched in the absorber plate. This fresh air is heated as it passes through the collector and is delivered into the building. This kind of collector is used for heating makeup air in buildings that require many air changes per day. As these collectors are even simpler, with no glazing and very simple frames, their cost is very attractive, and these systems have very good returns on investment.