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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 ($49) differential temperature controller for DIY Solar Heating Projects:
http://www.mydtcstore.com

The materials used for the pop can solar project are:


1.  Used aluminum storm windows for the glazing
2.  A 4x8 sheet of OSB
3.  A 4x8 sheet of RMAX insulation

4.  Three 2x6 boards
5.  208 aluminum cans collected at work from friends over a couple of weeks
6.  A couple of old PC fans salvaged

7.  One tube of silicon caulk
8.  One tube of latex/silicon caulk
9.  One can of hi-temp spray paint

I spent about $33 on it ($5 OSB, $9 RMAX Insulation, $5 Silicon, $6 on 2x6s,
$4 on spray paint, another $4 on more caulk, fan controller was built with
spare parts, cans, windows and salvaged fans free)


The entire p
roject (except collecting the cans) took about 12 hours.
    6 Hours to build 12 tubes
    1 Hour to construct box

    1.5 Hours to build and install manifolds
    0.5 Hours to paint cans
    1 Hours to install and wire fans and put in fan controller
    1 Hour to build fan controller
    1 Hour to install windows and seal plenums and caulk


Size: 8ft x 35 inches x 6 inches deep    Glazing Area: 2.75ft x 7.25ft
= 19.9 sq ft

Here are some pictures of the collector being constructed.

Here are the free storm windows (thanks Paul) and the insulation
for the collector
                                 
             

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





















Here is my helper Alec finding cans that are the same and taking the pop
tops off.


Here's the drill and bit used to put a hole in the bottom of each can. 
You should wear some gloves if your doing it by hand like I did (don'thave
a nice drill press. After a bit of practice I can drill a hole in the back of the
can in about 10 seconds.  I started off with a hole saw but it quickly
mutilated about 10 cans before I gave up on it.



Here's some cans that have been drilled and a ring of silicon applied for making
a tube.  Each tube has 18 cans in my collector.


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 of
the tubes to force the air to blow thru the tubes.  I struggled trying to figure
out how to do it and eventually decided to try to use the RMAX.  I would
not 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:


solar pop can collector performance



All in all I am very happy with the performance of the collector.  Next I need to figure out how to install on the house and keep the wife happy
which could be somewhat of a challenge.....

If you have any questions you can add a comment or email me at:

smith100griggs@gmail.com

Brian Smith


Update:  I have started a new project this year to build a solar hot water system based on the
$1000 builditsolar.com website design.

Here is a link to the website for info on my project:
  http://sites.google.com/site/brianssolarwaterheater/

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 temperature logging for the home experimenter.

Copyright 2010 by Brian Smith

The material on this website authored by me, Brian Smith, is copyrighted.

You must have permission from me to use any of the text or pictures on these pages.


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Brian Smith,
Jan 31, 2009, 8:31 PM
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