Natural draft air heater

I'm going to slap this together over the weekend and see if it
will give off any heat. Any opinions about this? Think it will work?
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Guv Bob
Reply to
Guv Bob
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give off any heat. Any opinions about this? Think it will work?
A shield to prevent wind losses would probably be essential. Perhaps a small solar fan to push the air along.
Rather than a reflective system, what about using a 50m roll of 1/2" poly reticulation pipe as the collector. Very cheap & larger collection area (though not focused energy gathering).
Reply to
Dennis
Not a lot of quantitative engineering specs there to make a judgment, and I am not really an expert, but here are some observations:
If you want warm air to enter the house you have to remove (hopefully colder) air through another opening or let it escape. Hot air heating systems circulate air within the house. The type of reflector you illustrate has to be tilted throughout the day, but it will probably be ok for a couple of hours around midday with no movement depending on the diameter of the pipe and design of reflector. A hot air system requires large diameters to transfer heat efficiently. A small pipe will not allow much heat transfer with air especially just relying on convection. If you use large aluminum air ducts, that might be OK as long as the input is fed from a cool part of the interior, not the exterior. Of course then your reflector has to be very large.
Water has much better heat capacity, and convection of water in a pipe can transfer much more heat than convection of air in the same size pipe. I would fill the pipe with water, have it convect to a radiator inside, and then the return will go back to the low end of the reflector. Also, make the reflector a CPC design (compound parabolic concentrator, see for example:
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) so it does not have to be tilted throughout the day.
Reply to
anorton
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This is interesting. Anybody built one and evaluated it? While it looks rational, I wonder about stuff that's been around for decades, looks vastly superior, but is not in general use. How come it's not standard construction?
Reply to
mike
My understanding, is that there is not a lot of power with solar. Watts per yard, or BTU per square yard, or whatever the measurement. Not a lot of power. Some design factor or other, will make or break the output.
You'd by very wise to do some internet research, and see if you can find actual plans of a collector someone else built. Others have gone through the test stages, and done the leg work for you.
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I'm going to slap this together over the weekend and see if it will give off any heat. Any opinions about this? Think it will work?
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Guv Bob
Reply to
Stormin Mormon
there is a ton of info out there on "passive solar heaters" (not water) -- I'm doing one this spring out of sliding patio door I took out. you build a frame, room air goes in the bottom and hits a series of baffles (black ins ide) and outlets at the top (with small thermostatically controlled fan -- heat rises). if you have good southern exposure and design it well, these p ut out a LOT of heat.
i just thought of using my patio door last week -- no need to scrap it now.
Reply to
mkr5000
Actually the CPC design is becomming very common in solar concentrators for hot water. You can see see lots of collectors like this for sale on the web.
Like any other engineering choice, there are trade-offs. A simle parabolic cross-section reflector is a little cheaper and can also concentrate the light onto a smaller tube yielding higher tempertures and better efficiency on clear days. However, it needs a tracking motor and mount to follow the sun. In a large solar farm with long banks of reflectors, the cost of the motor and maintenance of moving parts is probably more than offset by better efficiency from higher temps and the lower cost reflector itself. In a smaller installation, it is probably the other way around. Also, the CPC design is more efficient at concentrating energy on hazy or slightly cloudy days, so it might be the better choice if you are not in the dessert.
The other choice is a flat panel collector, or array of tubes, but that yields lower temperature water. This is still the most common for a small installation.
Reply to
anorton
I'm going to slap this together over the weekend and see if it will give off any heat. Any opinions about this? Think it will work?
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Guv Bob
I might work, but very poorly. The small pipe will have significant resistance to air flow and a concentrating collector will reradiate much of the heat out of the collector. Google "solar flat plate air collector". Art
Reply to
Artemus
off any heat. Any opinions about this? Think it will work?
You'll get SOME heat.
Reply to
clare
will give off any heat. Any opinions about this? Think it will work?
Hey, I already get plenty of heat from the knuckleheads at work!! LOL! The only way to find out is to put something together so I'll give it a try this weekend.
Reply to
Guv Bob

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