Building a solar air heater is an easy and rewarding project for both beginner or experienced DIYers and there are all kinds of different designs and plans floating around — just ask Mr. The most popular and flexible DIY solar heater projects seems to be the self-contained unit which can be attached to a wall or roof for supplementary heat. All of these units share common features and can be built with basic power and hand tools.
All else being equal, the solar absorber material and airflow within the "box" is where the designs below differ. This can have a big impact on the efficiency and effectiveness of the unit as a whole.
Finding the right combination of heat gain and air throughput may require a bit of experimentation. A solar heater that can move a lot of F air is more effective than F air moving too slowly.
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High interior temperatures lead to much more heat loss through the glazing. Fan speed and duct size will affect the air flow.
Renewable Energy: Solar Air Heater
The designs described below do not show the fan, which is usually located on the outlet end to pull air through the unit. A layer of lightweight plastic works well to seal the opening if the outlet has some hardware cloth over it.
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Although these units are shown tilted to face the sun, they can be installed vertically in northern latitudes as well. The back-pass collector has been around for a long time and there are a few variations in designs. The basic idea is that the air is heated as it moves upwards behind the heated solar absorber.
Alternating baffles may be added to slow or disrupt the airflow to increase the heat transfer.
Some window-mounted back-pass systems allow cool interior air to enter through an isolated chamber at the back. The air gains heat as it rises, travelling behind the solar absorber. The absorber may also be situated to allow air to travel on both sides for more surface contact.
Comparing Solar Air Heater Designs & Performance
The heated air exits from the top of the unit. The black mesh screen provides lots of contact surface for transferring heat to the moving air, while adding very little resistance to the air flow. In most instances, the screen is tilted within the box so the screen is closer to the glazing at the top of the unit.
A layer of black window screen can be stapled to each side of a wooden frame and mounted within the box.
In the tests that Gary and Scott ran there seemed to be no appreciable difference in performance between metal and fibreglass window screen material. As with all solar heaters, try to keep as much air as possible away from the glazing to reduce heat loss. The Aluminum soffit absorber is essentially a variation on the screen absorber and functions on the same principle.
The solar absorber is made from panels of commercially available perforated soffit material. The absorber panel is constructed by mounting perimeter cleats on the inside of the box with the bottom cleat against the back of the unit and the top one close to the glazing.
The side cleats run diagonally to provide a continuous mounting surface for the perforated soffit. The rising air picks up heat as it scrubs the heated surface, passing through the perforations to exit through the top vent.
The materials cost are higher for this type compared to the screen absorber. The "pop can" solar heater has gained popularity in recent years and a close cousin, using aluminum downspouts has entered the field. The solar absorber in these units is essentially a series of metal tubes that the air travels through, picking up heat along the way.
The unique feature on the tube type collectors is that they use sealed plenums at the top and bottom in order to direct the air through the tubes. The air enters the bottom plenum, usually near the center of the unit.
Some builders add deflectors to help spread the airflow more evenly across all the tubes. Since the plenum is sealed and isolated from the glazing, the only way the air can travel is up through the tubes, picking up heat from the surface as it moves. The heated air exits the tubes into the upper plenum where a fan pulls it out into the room. The main differences that I can see between using pop cans and downspouts is the materials cost vs.
The pop cans are cheap and easy to collect, but it takes a lot of work to clean, cut out the tops and bottoms, stick together with silicone and then paint a couple of hundred of them. The downspouts would be very fast and easy to cut, paint and install in the unit, but cost more. Comparing the efficiency of DIY solar heater designs is a pretty sketchy area at best. Every builder uses their own methods of measuring temperature, airflow and efficiency so the short answer is — no one REALLY knows for sure.
7 DIY Pop Can Solar Heaters
On the plus side, in the winter of solar enthusiasts Gary Reysa and Scott Davis put in the time and effort to run some side by side comparison tests on a few of the designs described above. Even though Gary and Scott live in different parts of the US, they used the same materials and designs for their tests and came up with similar results.
You can check out their comprehensive comparison test which includes methodology, graphs, thermal pictures and other details at BuildItSolar. Best performance overall as well as the cheapest and easiest to build. Both Gary and Scott were surprised and used this design for reference when testing the others. Performance essentially tied with the reference screen type — but a bit more complicated and expensive to build.
High pressure drop bad. Improvement possible though redesign. See thermal image above. Future tests will likely show improved performance.
Images: BuildItSolar. Tagged as: climate change , conservation , DIY , energy saving , passive , pop can heater , solar , solar panels.
Please add a timestamp on your article so we know how recent it is. Any updates on your comparison results? Eric, this post was written in January of As indicated in the article, the comparison tests for solar panels conducted by Gary Reysa and Scott Davis were done in They will likely post any new data on their sites when they have it.
I think that for the Back-pass type, the alternating baffles should have a diagonal baffle addition under each of them. This would prevent the hot air to get stuck and those places. I am in Islamabad, Pakistan. We have a short winter. We have overhead water tank. For the water heater I intend to use zig zagged rubber pipe sandwiched between blackened aluminium sheets in an insulated wooden enclosure with polycarbonate sheet on top.
For space heating I intend to use blackened aluminium sheet with back pass air. My problem is we have teasing months only.
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The rest of the 8 months are hot with summer temperatures soaring up to above 40C. How will it effect the rubber piping in the water heater? Any suggestions? Thank you.
I suggest you ask Gary at BuilditSolar. Hello Rick, I am working on a project for portable solar wall for existing buildings with large solar walls in Michigan, i would love to discuss with you about your findings if that is possible. Thanks Ayush email:achutani mtu. There is a problem with the screen collectors: that they get dirty, which is to say lighter in color and less absorptive.
To say that backpass collectors have high resistance to airflow is unwarrantedly broad.
It depends on how you make them. Previous post: Solar Heat: Free for the Taking.
Next post: Woodworking: Pick a Pocket Joint. Good Luck. Thanks for sharing your thoughts about solar air collector. Stonehaven original design project plans and other products are protected by copyright and are made available for your personal, non-commercial use only.