Passive Solar heat idea

[Zaga]

I saw this quite some time ago, I don't remember where or what it was called, but this is just the forum that will appreciate this sort of idea!

It's a mostly passive (requires one small fan) solar heating window that will work on sunny days in the winter, could be a good fit for an unheated garage or workshop.  The basic idea is a black box a few inches thick on the south (if you're in the northern hemisphere) facing wall with dividers to essentially make a long tube.  Here, I drew a picture because explaining is not working right now.  It's covered with an old window that is snug to the dividers.  Each end has a hole that can be closed off from the inside and one end has a fan to be turned on when using the shop.

Hope that helps someone!

[Zaga]

Adding - here's a few posts with practical details.

http://loveandtrash.com/2011/09/how-and-how-not-to-make-a-diy-solar-heater/

http://www.mobilehomerepair.com/article17solar.html

[igthebold]

I've seen this technique used to implement a basic solar dehydrator. I think it seems sound, if a little eyesoreish. The one I saw was made with soda cans painted black.

[Two9A]

Interesting. The concept of a solar water heater operates on the same general principle: a black box (on the roof) with a circuitous pipe instead of an airflow. When I was holidaying in Turkey, I saw them everywhere.

I see no reason why this wouldn't work, though it may be worth mounting the panel to the roof to catch more sun, and perhaps running a pipe from the lower "inlet" to floor level so it can suck up cold air.

[igthebold]

Is there a theoretical way to measure the heat output of something like that? The guy measured the temps at 145F, and described it as a "draft." How would one convert "a 145F draft" to something like BTUs?

[Zaga]

I don't know, but that's a very good question.  I suppose if you're already using south facing windows to catch heat in the winter that the BTU's from that are also very hard to calculate.  Free or nearly free to run is good though.

[strider3700]

www.builditsolar.com and the yahoo group simply solar has everything you ever need to know about building solar air heaters. They compare different styles, construction methods, materials, sizes, shapes,... everything trying to find the best/easiest/most cost effective design.

It's all about DIY and it's 100% free none of this buy the plans on ebay crap that is out there.

[carolinakaren]

This idea is a little different, but you guys might like it too.  A friend of mine made a heater for his workshop using a small fan and the same passive concept...only he ran his tubing through the middle of his compost piles, which heated the air in the tubing.  I've heard that this is more common in Europe than in the U.S., but it worked very well for him.

[TomTX]

This idea is a little different, but you guys might like it too.  A friend of mine made a heater for his workshop using a small fan and the same passive concept...only he ran his tubing through the middle of his compost piles, which heated the air in the tubing.  I've heard that this is more common in Europe than in the U.S., but it worked very well for him.

That technique has been documented in use in Europe since the Roman Empire, composting manure to heat a greenhouse.

[Zaga]

That's pretty cool!  I've heard of using compost to heat a seed bed for early spring starts in a coldframe, similar concept.

[Gerard]

wrt the original post, if I understand solar heatin' science right, this contraption won't actually give you any more heat than you already get just by opening your curtains. The energy enters your house through the window, is reflected by light surfaces, absorbed by dark surfaces, and stored by heavy stuff. So this thing will give you the same amount of heat as you already get when sunlight hits your floor, bounces around the room, and gets soaked up by the drywall etc. It's just more concentrated, which can be useful sometimes (e.g., heating water).
You'd be better off spending your building time making your home interior heavier, so it'll store that energy for you.

[TomTX]

Well, if you put it outside (not blocking the window) it captures heat you would not otherwise get.

[AlexK]

Is there a theoretical way to measure the heat output of something like that?

Yes. Sunlight is about 1000 Watts per square meter so that is the maximum amount of heating you can theoretically get. In reality there will be heat losses to the environment. From my intuition I am guessing the biggest loss would be convection cooling of the glass surface, which would cool the air passing through. Double glazing would help there. If you orient the inlet well below the outlet, natural convection will circulate the room air through the heater when the heater air is hotter than the room air, no fan needed.

A window in the room would capture the same amount of heat from the sun and provide light at the same time. But your design requires less modifications to the structure, and you could close the vents at night to keep the heat in the room.

[Darrell]

Zaga .... as soon as I seen your diagram, and than the second link you provided in the second post, I thought "Mark Bower". Wow, that brings back memories. Mark has an amazingly great, and early blog / forum, on the art of mobile home maintenance. As I think back, I definitely would qualify him for the status of "mustachian" ... he is a family man, business owner, likes to help others, thinks positively, is curious, and is full of common-sense. Thanks for the link ... I'm off to see how his site has evolved.

[Matte]

Would work, I dont think you would be too impressed with the gains though.  Especially if you were putting it inside a modern window, they block many of the sun rays to keep unwanted heat out in the summer.  Look at solar vacuum tubes if you want some passive solar heat.  There pretty cool.

[reverend]

Instead of the alumin(i)um flashing, it might be a lot easier if you have access to refrigerator coils to spray them black and mount them inside to heat the air. It would be a lot less work and sliced up hands. :)

It wouldn't block/guide the air as well, but it might provide more surface area, and wouldn't it be possible to allow the case to heat up more if the outlet is a bit smaller or the inlet is? It would limit the speed of the air rushing through the box (convection), or am I just making things up?

[Darrell]

Here's a DIY plan:

http://solar.freeonplate.com/diy-how-to/DIY-solar-panels.htm

... or you can buy them from a manufacturer such as:

http://www.cansolair.com/