Solar Air Heater - Part I, Construction

For this heater, it was decided to go with air as the circulating fluid because it's easy to work with, very simple and would work well in our situation.

An excellent site with lots of project ideas is Built it Solar

The air from inside the space (garage in our case) will be run through the air heater and exhausted back inside.

The first step is to build the largest box possible. For us, an 8 ft by 4 ft box is nice because it's fairly big, and sheets of plywood come in that size, which makes it more easy to put together.

Below are the materials. Since these will be outdoor, get pressure treated wood.

• 8ft by 4ft treated plywood - $15
• 2 of 2in x 10in treated lumber - $27
• 2.5in galvanized outdoor screws - $7
• 3 black aluminum foil sheets - $100
• Regular aluminum foil - $20
• High temp insulation - $45
• 8ft by 4ft polycarbonate sheeting - $111
• Two 8ft 1in x 1in aluminum L channel - $38
• 25ft of foam rubber - $11
• 2x Silicon glue - $11
• 1x Silicon sealant - $11
• DC duct fan - $43
• Approximate Total = $440

Cut the 12ft long 2in x 10in pieces of lumber. Better yet, get them cut at Home Depot. The first 5 cuts or so are free.

There are two 8ft long pieces and two 44in long pieces (4ft - 4in). The shorter pieces need to compensate for the thickness of the two longer pieces, otherwise you will get a box that is 8ft long by 4ft and 4 inches wide. Here they are arranged in the box form.

The 6in duct connector being placed on top of one of the 44in pieces of lumber, to draw a hole eventually to be cut out.

Drilling holes on the edge of the circle so a jigsaw can fit and cut the line.

This part took a long time as the thickness of the wood made the cuts very slow, even with brand new blades.

And the other side as well.

Next step is to make the box. One way to do this is to split the rectagle in two parts, build both L shaped assemblies and then put them together at the end.

Before putting the pieces together, some silicon sealant was used to keep out moisture at the seams where the wood pieces meet.

Then using a 90 degree clamp to hold two pieces together. Drilled 4 holes and screwed them together.

An L bracked was used for extra strength.

Here are the two separate pieces.

Combining both pieces together.

Completed rectangle.

Adding the plywood back of the box. Also sealing where the plywood touches the wood on all the edges.

Extra sealant on the parts of the plywood which looked like moisture could seep in.

The next step was to add the 6in duct fittings to the two holes.

Sealing it.

Applying the first layer of the insulation and using the silicon glue to keep it in place.

On the two long sides.

There's no picture of the entire box being insulated, but it was added to the short edges as well.

Fiberglass is not good to inhale, so it is vital that the entire insulation be covered in another material to separate it form the airflow. Regular aluminum foil is cheap and good to use. It also reflect heat back so very little of it gets transfered to the insulation.

However, before that, two pieces of 8ft aluminum channel will be placed along the top of the box to create a path for the air to go back and forth inside the box, thus giving it more time to heat up.

Lined it up with the box and cut a piece of the channel.

Cut and filed down the edges.

It will line up something like this.

Then bent the end.

Now it fits nicely on the inside of the box and will not interfere with the piece of polycarbonate sheet on the top. Drilled a hole and screwed it in. Also applied some glue for extra strength.

Started to line the insulation with aluminum foil and used the silicon glue to glue it to the insulation and to itself.

Next was time to add the dividing lines of the box so the air flow goes around the whole of the box.

And the other side.

Both dividers done. These were difficult to do as it was hard on the back, having to bend down to work inside, without stepping in and ripping the aluminum foil.

Here you can also see one of the two handles added on each side for ease of moving the box. It turned out to be fairly heavy due to the thick wood.

Next it was time for the black aluminum foil.

Used the same high temperature silicon glue as before.

Holding it in place to glue it to the sides. This aluminum foil is thicker than the household aluminum and thus easier to work with. The edges also give some really nice deep cuts, so in retrospect, gloves are highly recommended.

The rubber adhesive seal was put around the perimeter of the top of the box, and the polycarbonate sheeting was screwed on top.

Then it was taken outside and put on two pillars.

Intake.

Exhaust.

Airflow.

There will be a follow up with an active Arduino-based fan control system post.

Would I recommend this method to build a solar air heater? I would not. This box was difficult and expensive to build. While the box is, I am assuming, fairly efficient from the insulation and light absorbing and heat distribution properties, there are numerous other ways to make it cheaper and easier to build while having a respectable efficiency.

For example, instead of spending $100 on black aluminum foil, regular foil or some other material could be painted black with some spray paint, which may cost considerably less.

Data measurement and efficiency calculations will be done once we get the 24V to 12V switching regulator printed and soldered (to run the 12V fan off the 24V system we have) and the Arduino based controls and measurements side of it complete.