Not alot of welding in this, but a good and timely project.
Most of you blokes would be able to knock up one of these heaters in an afternoon. I'll make one before next winter.
It's a 'solar box heater'. Well, that's one way to search for them on google. There are lots of commercial ones around, but I find it hard to justify the price - around $4,000.
Without going into too much detail (because there are dozens of versions):
- Essentially, it's a shallow collector box - maybe 6 foot x 3 foot and one foot deep. This goes on the roof angled to the winter sun. It has solid sides and base (sheet metal would be dandy) and clear perspex face. So the sun hits the face and heats the air in the box.
- Then you have a 4 inch duct to pull the heated air from the box into the building. In the duct, you have a solar powered in-line fan so the running costs are zero.
- You need to allow air into the box. You can either just have an entry hole to draw air from outside, or a 4 inch return duct drawing air from the building. The means that the air entering the box will be pre heated.
www.sunlizard.com.au is one of the Aussie commercial versions.
www.solair.com.au sell a European sourced product.
And there are loads of others.
So there isn't much to these things - that's why I baulk at $4,000+.
The great thing about them is that the running costs are zero - when the sun shines, the heater pumps warm air into the building. We get lots of winter sun in Sydney and some of you would, too. On days with heavy cloud, it's back to conventional heating.
PV Solar cells and fans are pretty cheap - I bet less than $100 for a really good one.
You blokes could knock up one of these things for a few hundred dollars.
There are lots of little things:
1. Need to slow the air down in the collector box - baffles - so it stays there long enough to heat.
2. Painting the inside of the box black dramatically increases the heating - matt black is best.
3. The ducting needs to be as direct and as short as possible.
I reckon some of you should do the research on fan sizes, box size etc and have a go at making and testing one of these things and then I can just shamelessly copy what you've done.