solar

[hotwired]

Building 4 x8 ft heat panel what should the distance from glass to back of panel be.

[mikey ny]

I am also working on a solar panel and never even considered that thought. Mine has about 2 to 3 inches of air space between the glass and heat exchanger. I am not done yet but it does make real hot water. 180 f plus. My uneducated guess (key word UN)is that the less space the better, the air may absorb or even reflect some of the heat you are trying to keep. Just a guess.

[dudevato]

Here is a site that covers alot of the 'rules of thumb'  

http://www.mobilehomerepair.com/solarrules.htm

[dudevato]

Here's another I have in my 'favorites' http://www.homepower.com/files/hotairhp72.pdf

[GaryGary]

Hi,

If its a solar air collector, you might want to take a look at these two designs:

http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

This is a simple thermosyphon air panel that I built for my shop.  Its going to be in the HomePower Oct/Nov issue.

http://www.builditsolar.com/Projects/SpaceHeating/SolAirHtSysBook/SolAirHtingBk.htm

This is a book that you can download from my site for free (courtesy of the authors) that has a LOT of design and construction detail on air panels.

You might also just scan down this page, and see if anything looks good:

http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

To specifically answer the question about spacing of the absorber plate from the glass.

I don't think its too critical.  The radiation losses from the absorber plate out the glass are probably not effected much by spacing.  The conduction losses from the hot air out the glass will go down some if you can space the absorber further from the glass and try to circulate air in such a way as to keep cooler air toward the glass.  For example, in a thermosyphon panel you want the cool air to enter at the bottom of the collector, and on the glass side of the absorber -- it then heats as it goes through the absorber -- this keeps the cool air near the glass and the hot air behind the absorber, and reduces conduction losses.

Gary

[Kevin L]

I was getting all fired up to build a air flow solar panel this fall, and wouldn't you know it, my house is facing perfectly South West.  Maybe next house.  Not willing to give up 35% of the energy just cause I can't oreint the panels in the correct direction.  We've been talking about building another house in the next 4-5 years, here is another excuse.

[GaryGary]

Hi,

Have you thought about a low thermal mass sunspace with heat ducted to your house?

You might be able to orient it more south and still get the heat to your house?

These can be very cost effective for heating if you go with the greenhouse style construction rather than the Better Homes and Gardens style.

Gary