Google it and you'll find quite a few stories of people implementing their particular ideas.
Originally, my own idea was to collect the heat from the roof cavity and then, either pump it down through an inner wall to circulate under the floor, or pump it through holes in the ceiling into rooms where heat was required.
The advantages are:
- It can be turned on and of with the flick of a switch
- There is only a small investment in materials
- It's hidden from sight
- It can be reversed in summer to extract heat from inside the house
- You need to be able to crawl through roof cavities.
First Serve
My first experiment was on the North facing door of my garage.
The idea was to heat up the garage and in doing so, the floor of the room above the garage would be warmer, and so heat up that room as well.
And if I screwed up, I'd just put in a new door.
I cut a rectangle out of the outer wall of the door, creating a cavity in the door itself.
I then braced the edges of the rectangle and extended them beyond the thickness of the door to increase the depth of the cavity.
Klik on the pictures for a larger view
I then painted a piece of corrugated iron mat black and suspended it in the door cavity in such a way that air could flow all around it.
50mm holes were drilled, one below and one above the metal.
Plexiglass was used to make an airtight cover, which would let sunlight in, and as little as possible out.
On the inside of the door, I attached a small 12 Volt, ½ Amp computer fan to the bottom hole to blow cool air into the chamber.
Hot air then gets expelled through the top hole.
The fan is powered by a 12V, ½Amp solar panel.
It is probably better to have the fan blow cool air into the chamber, than to have it suck hot air out, to prevent overheating the fan.
The expelled hot air can reach temperatures up to 60° C when the sun is shining.
Even on cool winter days!
Advantages:
- Very efficient. No tubing to transport air, so no heat loss
- Easy to construct
- Low cost
- Closed circuit air flow. No need to screen out insects
- The inside of the door gets a bit hotter.
Second helping
The second solar air heater I built is a little different.
It is a complete chamber which stands a little away from the wall.
Because of this the back and sides have to be reasonably insulating or else too much heat will be lost in winter, and too much heat passed through to the house wall during summer.
The air in- and outlet are built into the side of the chamber.
This allows it to be placed closer to the house wall and makes installation easier.
As with the door model, I used matt black corrugated roof sheeting as a heat collector and plexiglass as a cover.
It is not a closed circuit as the inlet is open to outside air. And so it needs a little screen to keep insects out.
It is placed at such a hight on the wall, that it is in full shade for the 4 hottest months of the year and in full sun in the 4 coldest months of the year.
If it gets too hot inside anyway, the yellow cap can be removed to allow the hot air to continue through to the outside.
A cap on the hole inside stops any hot air coming through.
The above foto shows the temperature of the air coming out of the solar heater on a sunny August day when the outside air temperature was about 16° to 17° C
I removed the thermometre before it reached the maximum of 60°, because it didn't look like it was going to stop there.
The little computer fan pushing this air through, is capable of moving 25 to 30 cubic foot p/min (about ¾ m³ p/min).
That's a lot of free hot air.
Advantages:
- Easier placement. Location, angle, etc.
- Can be installed as close or as far from the wall as required
- Always fresh air inside without the need for an open window.
- More materials required and so more costly.
- Need to open the outside port and close the inside one to effectively turn off the heating function.
It is now the warmest in winter when turned on.
Final Tastings
Plexiglass is expensive.
And so is real glass.
So I was glad that I had picked up an old glass door, some years ago, that someone had put out for garbage collection.
It had been sitting in my shed for so long, I was itching to put it to some use.
It probably was the catalyst to this project.
Because it's lighter, you can use less expensive materials, such as brackets, bolts screws etc.
Plexiglass does expand a lot more, so I had to leave at least a 4mm gap all round for expansion.
As a filler between the plexigass and the frame, I used the spongy material which is used between concrete slabs. This allows the plexiglass to expand and contract while maintaining an airtight barrier.
I used these solarpanels: Powertech Monocrystalline Solar Panel - 5W prices currently, 29-11-2010 range from $37 (at Jaycar) to $150. Shopping around is imperative.
