There's no heating in the garage, but there is damp.
On the other hand, it does have a nice large south-facing roof, so I want to have a go a building a solar heater.
I have in mind a wooden frame, containing a long folded tube behind a double-glazing panel and backed with a reflective surface.
The tube would be a long series of aluminium drinks cans, painted matt black.
The will have ducts to the garage; one to draw cold air out of it, and the other to bring warm air from the heater back in.
A small solar-powered fan would draw air through the tube.
I've found several descriptions of such projects, and their success.
Using air rather than water seems much simpler than trying to make a system that uses water to transfer the heat, while using empty drinks cans for the tube would help keep weight down.
"D.M. Procida" wrote in message news:1kaz59f.1a03sgkic99fkN% snipped-for-privacy@apple-juice.co.uk...
I assume that, given that hot air rises, you will have a strong enough fan to drive the hot air down to floor level before exiting the ducts? I would be interesed to know which bits you use to achieve this, as I have a south facing roof on the shed and could use some 'free 'heating in the winter.
I know nothing about these things, so this may be a silly suggestion, but why not make a big double glazed window in your south-facing roof so that the sun comes in and does all the work in situ, so to speak?
With the shadecloth collector, heated air never comes in contact with the glazing. This much reduces glazing heat loss. With cans, heated air is generated on both sides of the can. The hot air outside the can meets the glazing, and heat loss occurs.
Hot surfaces radiate heat away. Black drink cans simply radiate this back out (their silver interior doesnt). Shadecloth reradiates in both directions, and the multiple layers mean that a lot of the reradiation is blocked from existing the collector.
The shade cloth collector allows free flow of air, so if mounted on a wall, no fan is needed. Parallel strings of cans arent quite as good in this respect, and a bit more fan power is needed when roof mounting.
Finally the cloth collector is far lses work to make.
I'd need some kind of fan anyway, as this thing will be mounted on the roof of the garage.
What exactly is shade cloth? I have some dark blue blackout blind material hanging round - would that do?
How does the air filter through the shade cloth? There's a version here:
that uses aluminium mesh rather than cloth.
Yes, certainly.
Many designs seen to use nothing more than corrugated PVC rather than double-glazing, which seems like an odd choice when large double-glazed panels can be had for nothing if you look in the right skip.
You can increase both output and efficiency with an external reflector. If its a single storey garage attached to a 2+ storey house, putting the collector as near to the house as possible means you can add a reflector on the house wall, and capture more light & heat in the collector.
Firstly it would depend on the volume of your garage.
{Someone throw me a mathematician and/or engineer quickly}
If your garage is at 5C and the air in your heating array is at 35C then you have a 30C temperature difference. If you want your garage to be a nice pleasant 20C then you have to replace half the volume of your garage with warmed air to achieve this - but quickly enough to compensate for the heat loss through the structure. Hmmm.....half the volume of your garage every 30 minutes to allow you to get up to temperature in 30 minutes (which does not seem an unreasonable taget)? So work the volume of your garage out in cubic feet, halve it, divide by 30 and you know how many cubic feet per minute you have to shift. This specifies your fan(s). These specify your solar panel. You would have to allow a bit more push because you are having to push warm air downwards whereas I think most extractor fans expect to be pushing air horizontally. The hotter your heat exchanger gets, the less volume you should have to exchange. e.g. get your heat exchanger to 65C and you only need to exchange 25% of the garage volume of air.
Someone who has already done this or at least the calculations should be along shortly (I hope).
It might be nice to add some thermal mass to the system so that heat collected during the day could released at night when condensation is more likely. Using water as a medium with an insulated cylinder for thermal storage might provide that for you. Circulation by convection.
OK, I think I understand this better now. As air rises through the system, it has less opportunity to lose heat by conduction with the cooler glazing at the front.
I don't think this is going to work for me though, because the only place I can mount it is on a sloping garage roof - I haven't a suitable vertical south-facing surface to mount it on.
I think something like this might work though (you have to imagine this rotated 30 degrees anti-clockwise, because it's on a sloping roof):
*Yes. But thats a costly way to do it.
*You also cant have circulation by convection when the heat source is
*on the roof.
For some values of can't - if the heat exchanger is on the lower 2/3 of the roof and the water tank is in the top 1/3 then there will be limited gravity circulation. However you are then potentially looking at a strange hot water tank - a long thin cyclinder? Not the easiest and simplest way of doing things, and you also have to worry about freezing during long periods of no sunshine. However an electric water pump driven by a solar panel could be an alternative to the electric air pump to give a pumped hot water system with all the components more or less level with each other. I think this is how some solar water heating systems work. Of course you would also need a pump to circulate the stored heat - and what is going to power that?
Just realised that I might have 90% of the components of a heating system lying around. My shed (uk.d-i-y passim) faces north, and the rear south facing wall is close to a fence. Just checked, and the top third of the wall is in sunlight at the moment, and we are quite near the winter solstice (a month?). So it looks as though I have potential sunlight throughout the winter. Now I have two sheets of corrugated plastic lying around and lots of bits of potentially useful wood. So perhaps I could construct a frame out of battens and run the two sheets of plastic horizontally along the wall. Paint the wall black, drill some holes through the wall top and bottom, and I have a heat exchanger which will heat the top of my shed under the insulation and hopefully circulate the air by drawing in colder air at shoulder height and pushing it out at head height.
First cut gives warm head and cold feet, but does increase the overall temperature of the inside of the shed. Main issue - long and thin heat exchanger so a lot of holes at bottom and top to ensure good air flow. Would fewer larger holes be better, perhaps offset to get a diagonal flow?
Main question - how deep should the wood frame be? Less volume of air should heat quicker and flow faster, I would think.
Second cut could include a deeper frame and shadecloth.
Third cut could include a solar powered fan. [I do have a lot of small panels of garden solar lights - wonder if these could be recovered?] Better to push cold air up, or pull warm air through or down?
If I wasn't overloaded with 101 things to do I might rush out and experiment :-)
Other issue - how to stop it overheating in the summer when the last thing you want is hot air circulating in your nice cool shed.
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