Alternative Technology Assn Forums

1. 

   scott drew
   Member

   Dear All,

   Seeking suggestions for a solar air heater.

   Problem: a small room in the house is used by my wife as an office. It is 6m x 6m and 2.4m high. It has masonry walls. It does not get any direct sun. It happens to be the coldest room in the house which is unfortunate in winter because it is the room where my wife spends most of the day. In summer it is the best room to be in!

   Solution suggestion: The other week I bought a polycarbonate green house for seedlings. That got me thinking. There is a possibility I could build a 1m x 1m x 30cm deep box that attaches to a sunny window inside the house. It is only about 2m away from the cold office. I am thinking I can get some polycarbonate sheets and knock up a box, attach it to the window to make a solar heater. Then pipe the warmer air to the cold office. I would circulate the air from the box to the office using a small solar panel to run a computer cooling fan inside some 50mm plastic pipe. Thus the air circulates when the sun hits the panel, pumping warm air into the office.

   So the questions are...

   How big do I make the box? I need a box big enough that will warm the air in it prior to it being pumped out. The size of the window is fixed, but I can vary the depth of the box.

   Should I use an open space inside the box or baffle it in such a way that the air comes in at the bottom and zig zags its way to the top where it will be pumped out?

   What materials do I use? I need to have a clear section to let the light into the box. I was thinking of getting (or painting) the back and sides black. But what do I use for the box. The pipe/air duct is easy as I'll use plastic water pipe. Fan and small solar panel I can get from Jaycar probably.

   Any suggestions and please point out any faults you can see!

   Posted Sunday 27 May 2012 @ 12:34:14 am from IP #
2. 

   Lance
   Key Master

   There were solar box heater articles in issues 60 and 68 of ReNew and there have been more recent house features with similar systems. You don't need a deep box as such, most solar box heaters are more like flat panels, usually about 100mm deep. Inside you have corrugated iron painted black to collect heat and provide a large surface area for air heating. Cover it in clear polycarb and make sure the box has no leaks and is reasonably well insulated. Many designs draw air in at the top, pass it down the back of the iron then back up the front.

   Remember that in winter even on a sunny day you are lucky to get 500 watts per square metre, and realistically it will be less for most of the day, so I would say at least 4 square metres for your unit, but the bigger, the better. Just remember though that once the air is already warm it won't collect any more heat, so if you make it too tall, the air will be warm halfway up the panel and the top half of the panel will be less effective. But, this also depends on the rate of airflow through the panel, so if you have a variable speed fan you can adjust airflow for best efficiency.

   Or, rig up a little microcontroller or even a simpler temp sensing circuit that varies the fan speed to keep the air at the outlet in a set temp range...

   Posted Sunday 27 May 2012 @ 1:10:44 am from IP #
3. 

   ghostgum
   Member

   On cold overcast days, our gas heating system provides heat to all the house. On cold sunny days, the northern windows heat the main living room enough for the central heating to turn off. Our southern study remained cold on these days.
   We have a Solarventi SV14 (1.4 square metres) on a north wall, providing heat to the south facing study 4.5 metres away. On a sunny day, it keeps the southern room at a similar temperature to the rest of the house. I would have preferred a larger collector, but the next size up was too large to fit on that north wall.

   Your room is bigger than ours, and I agree with Lance's suggestion of 4 square metres.

   Have a look at http://www.builditsolar.com/ for some ideas.
   If you are using an existing window as a collector, then you are removing the heat from that room and will make it colder. I would suggest looking at the aluminium fly wire collector method on Build-it-solar. You could make a collector that collects half the light and energy with the fly wire, and lets the remainder pass through a polycarbonate collector back and into the room.

   Posted Monday 28 May 2012 @ 1:26:18 am from IP #
4. 

   darrynm
   Member

   For a larger system you could try http://www.sola-mate.com/ or http://www.ecoheat.com.au/

   Posted Monday 28 May 2012 @ 5:13:05 am from IP #
5. 

   scott drew
   Member

   Lance,

   Thanks for the suggestions and calculations for size they are very helpful. Have dug out my back issue cd and looked at renew 60 and 68. They are very helpful and full of great ideas for my project.

   Thanks heaps.

   Darrynm I think those systems are quite expensive for what they are, especially when no one is going to see my one and I can probably knock up something similar (not quite as professionally finished) myself. Cheers for the suggestion though.

   Posted Tuesday 29 May 2012 @ 12:19:21 am from IP #

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