Building a Cost-Effective Solar Air Heater

Building a Cost-Effective Solar Air Heater BUILDINGS New Techniques If you have a south wall you can utilize it as a source of free solar heat Solar air heaters are most cost-effective when incorporated into new construction but can be simple to add to existing buildings This passive heating system known as thermosiphon utilizes natural convection to circulate fluid without a mechanical pump Instead it relies on the buoyance of heated air to create circulation through a collector These collector systems are simple and virtually foolproof You don’t have the cost maintenance or power requirements of other heating systems’ fans sensors or controllers There’s little that can go wrong once they’re up and running You’ll also get an excellent economic return by minimizing other fuel and it’s possible to adjust the temperature if things heat up more than expected On the negative side solar collectors require the sun to work If you live in a cloudy region backup heat may be necessary Likewise the building might require more thermal mass and insulation to prevent heat loss at night Gary Reysa writing for Mother Earth News about his homemade thermosiphon setup reported that it could produce the heat equivalent of $2 of propane in 2006 dollars on sunny days in Bozeman Montana His thermosiphon collector consists of clear corrugated polycarbonate panels fastened to 2-in by 6-in studs The panels let in sunlight and an absorber suspended inside warms expands and rises in response which creates a convection current The top and bottom vents allow air circulation so cool air enters through the lower vents gets heated by the absorber until it rises to the upper vents and returns to the interior similar to a lava lamp This process continues for as long as the sun heats the collector Nighttime temperatures reverse this airflow as the collector cools to outside temperatures However simple flapper valves on the top vents can stop the circulation from reversing and keep the heat inside Reysa reports that the collector raises indoor temperatures to between 60 and 75 F on sunny winter days 25 to 35 degrees above outside temperatures However it barely nudges the temperature up on cloudy days You can also expect it to take at least 3 hrs to heat the interior temperature from freezing to over 60 F Note that this heating system only works well in spaces with adequate insulation Solar collectors fall short of heating drafty spaces The complete project took Reysa 3 working days He minimized costs by integrating the collector within the building structure and using materials on hand bringing the overall cost down to about $350 From a heating efficiency standpoint the larger the collector the better Costs don’t differ much between using a small portion of a wall or most of it A larger size also helps counteract heat loss on cloudy days and upper vents can be adjusted to prevent overheating

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