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Solar Air Collector from Maine Solar Primer

This is a simple, wall mounted thermosyphon solar air heater.

It is from the Maine Solar Primer, 2nd Edition.

By Richard Komp with drawing by Caleb Crawford.

Note that the "value of oil" and "value of electricity" are way out of date -- current values would be 3 or 4 times the amounts given.

Some additional notes:

Design Guidelines for Thermosyphon Collectors

The buoyancy forces that drive the air flow through a Thermosyphon collector are weak.
The collector must be designed to minimize flow resistance. High flow resistance will
result in higher collector temperatures, higher losses, and lower efficiency. For low flow
resistance, flow passages must be large, and the absorber must transfer heat to the air
efficiently and with little flow resistance.

The depth of the collector should be about 1/15th of the height (more is better).
The top vent and bottom vent areas should each be at least 50% of the collector cross
sectional area (more is better).
Streamlining the entrance and exit vent areas may also help reduce airflow resistance
and increase collector efficiency.
Changes that improve collector flow path will normally result in a decrease collector
output temperature along with a more than compensating increase in flow rate. For best
efficiency you want a lot of air flow with a modest temperature rise.

An alternative to the solid absorber shown in this plan is the flow through absorber. A flow through absorber uses expanded metal lath or window screen for the absorber, and arranges the flow path such that the air must flow through the absorber in traveling from the inlet vent to the exit vent. Many people think that this is somewhat more efficient than the solid absorber. Here is one example of a collector that uses the flow through absorber: http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm