"Tap" The Sun

Enlarge Image Image Gallery The integrated thermosiphoning air panel (TAP) is the perfect solar collector for metal buildings because the side of the structure can act as the unit's absorber plate.

From Mother No. 91

The easy, low-cost way to add solar heat to you mobile home or metal outbuilding.

The integrated thermosiphon air panel (TAP for short) is a fresh approach to solar air heating—one that's perfectly suited to the 10 million or so folks who live in mobile homes and to owners of the countless metal-sided storage, industrial, and commercial buildings around the world. By making use of the building itself as a part of the collector, the TAP keeps material costs down, simplifies construction, and maintains a low visual profile. And because it relies on thermosiphoning to move air past the absorber, the TAP avoids the complexity and cost of an electrically driven fan.

What It Takes

What do you need to build your own TAP? The critical element, of course, is sunlight: You need a metal-sided wall that faces within 25° of south and that isn't shaded in the crucial winter months. You'll also need some hand tools, such as a drill, metal snips, screwdrivers, a caulking gun, a 1/4" nut driver, and maybe a circular saw. Add to these items less than $100 worth of locally available materials and a weekend's work, and you'll have solar heat flowing into your home.

How Big?

A rule of thumb for solar air heaters is to allow one square foot of collector for every 10 square feet of floor area you wish to heat. (The room should first be caulked, weatherstripped, and at least moderately insulated. Always take care of such energy-conserving fundamentals before adding solar heat.) Thus, a 180-square-foot room suggests an 18-square-foot collector. This, however, is only a rough estimate. The available wall space for mounting the collector and the limitation of standard tempered glass sizes (28", 34", or 46" X 76"; 34" or 46" X 90") will determine the actual dimensions of your collector.

Because the TAP relies on passive airflow to distribute the heat collected on its absorber, you'll get the best results by sizing the collector to warm the room directly adjacent to the wall on which it's mounted. Though heat will eventually be transferred to other rooms, oversizing the TAP to try to heat more than one room will make the first room too warm.

Available Materials

The collector frame is made of 25-gauge, 4" or 6" metal track available from a drywall supplier or contractor. To insure that air moves through the collector without restriction, use the 4" material for any TAP that's less than 80" high and the 6" metal track for taller units.

Air moves into and out of the collector through metal grilles that run all the way across the top and bottom of the unit, and these too must be large enough to prevent restriction. The height of the grilles should be equal to twice the metal track size: 4" track requires 8"-high grilles. Because wall studs will be in the way, however, you'll probably have to use several grilles to cover the intake and exhaust areas. Unfortunately, when you shop for grilles, you may find that the perfect sizes simply aren't available. If you run into this problem, compromise by using the next larger size; you don't want to take a chance of restricting free movement of air through the collector.