Low Cost Solar Air Heater

Here is a solar air heating collector project I built in a week in my basement

Quick Links 11/15/10:

1. Solar Hot Water Heating Test Project: http://sites.google.com/site/brianssolarwaterheater/

2. Low Cost ($54) differential temperature controller for DIY Solar Heating Projects: http://www.mydtcstore.com

The materials used for the pop can solar project are:

Here are some of the cans getting rinsed before assembly into collector tubes

Here's a close up of the box edge I put a little rabbet in with the table saw

to seat the windows on. You can also see the silicon sealing the joints of a

tube that's drying. I build two tubes a night, one along each edge of the box

each night, letting them dry for a day before moving them.

It takes about 20 minutes to drill, silicon, and join together a tube with 18 cans

after a bit of practice.....

Here's whats done so far. I've put the insulation in the back of the box. I used OSB

plywood for the back but you might consider using a more expensive plywood

sheeting since the OSB is really heavy......

By this weekend I will have the tubes done and will build up the plenums

for the ends, paint the cans black, and wire up some fans and an old thermostat I have. Then I'll install the windows and wait for some sun...Well two days later all the tubes are done.Now I decided to build the manifolds that seal off the tops and bottoms ofthe tubes to force the air to blow thru the tubes. I struggled trying to figureout how to do it and eventually decided to try to use the RMAX. I wouldnot use RMAX if your not going to use forced air as I suspect it could get too hot without good airflow.One of the problems was that some of the tubes were slightly different lengths which made sealing them off more difficult. I decides to made smaller holes for the bottom manifold and just seal them from outside. Notice the holes are smaller than the can diameter. For the top I ended up making them bigger so some cans could rise

thru the opening since some tubes were longer. For the holes, I just pushed this

hole saw thru from the front, then again from the bottom.

Here's a picture of one of them getting installed and sealed with more silicon.

You can see one of the fans I'm using (12V, 2.4W, 67CFM) and a wire that

connects up to the top fan controller. One fan pulls air into the box at the

bottom, one fan blows air out at the top. I had to cut a hole in the back

of the box before installing the fan.

This is of the top plenum and shows the fan controller and another fan.

Update: Here is a link to the website for info on my

differential temp controller kit: http://www.mydtcstore.com

It could be used for controlling the fans, and it has upto 8

temperature sensors and does temperature logging for the

home experimenter.

I designed and built the simple fan thermostat to control the fans. The circuit

turns the fans on when its around 110F inside the box, turns them off

when the temperature goes below 70F. Here a picture of the board and

a schematic from an LT SPICE simulation that shows the circuit.

You can download LT SPICE for free off the web and design little circuits like

this. The file I used for this is attached at the bottom for those with electronics

interests. You can build one for about $2 worth of parts from Digikey. If

several people were to ask for a kit, I might make a PCB with a few more features

available.

Once the manifolds were in, time to paint the tubes. Here is the paint I

used for the cans.

Here's a picture of all the tubes painted. It took the whole can to paint

208 cans.

Finally comes putting in my storm windows for glazing and sealing up with

more caulk. I ended up just putting a RMAX insulation lid on the two plenums

on the ends in case I need to get back inside an work on it. Here are two

pictures showing the windows being added. There was some problem with

this install a one window ended up being about 1/2 less wide than the others.

Well now I need to get it outside and see what kind of BTUs I can get out

of it on a sunny day.

Well today is February 1, 2009 in Madison, Alabama.

Started testing in the mid-morning at around 55F and sunny. Once the sun

full on the collector the temperature really started to climb, but the fans

didn't turn on. Turns out one of the power cables pulled out of the terminal

block while the power cord was hanging in back.

Here's the collector leaning up against the top. I used a thermostat I had to

measure the temperature in the top plenum where the fan controller.

Here's the temperature inside before I opened it up and got the fans running.

Once the fan controller was reconnected to power, the fans kicked on and

stayed on all afternoon. It ran steady state with fans on at 132 for a couple

hours before it started cooling off as the sun started going down.

I took down some readings during the day and tried to calculate how much

power the unit was generating. I found the formula for this on the web and

cannot vouch for its accuracy, although the values that were calculated

seem reasonable considering there is about 2kW of solar exposure in the

glazing and cans at full sun. What the winter sun is currently providing is

considerably less. See spreadsheet below: