Glass over collector

[FrankP]

Hello. New here, quick question. I am building a solar collector for hot water and doing it with recycled materials. I plan to use double pained construction glass out of a newer building. I was wondering if the heat can transfer through this to the collector at peak efficiency. It is clear glass and there is a 1/2" dead space between the glass panels. Also very strong tempered glass. I am sure the glass is UV blocking. I hope I can use this instead of lexan. Thanks in advance.

[russ]

Hello. New here, quick question. I am building a solar collector for hot water and doing it with recycled materials. I plan to use double pained construction glass out of a newer building. I was wondering if the heat can transfer through this to the collector at peak efficiency. It is clear glass and there is a 1/2" dead space between the glass panels. Also very strong tempered glass. I am sure the glass is UV blocking. I hope I can use this instead of lexan. Thanks in advance.

Single pane will serve far better - the double pane prevents much of the heat from getting to your water and there is no positive side to it.

[FrankP]

Thanks for the reply. Well it is free. That is a major plus. Lol. I would go to lexan before single pain since Florida gets some hail and such every now and then. I wonder what the difference will really be? If it is just a little then i'm not going to worry about it. I have plenty of sun here to make up for a little bit of loss in efficiency.

[rreinha]

I am sure the glass is UV blocking. I hope I can use this instead of lexan.

If it is an E rated Glass it will have a very very slight Green/Gray tint to it. It works really well at keeping UV rays from passing through. Probably not what you are looking for.

[FrankP]

If it is an E rated Glass it will have a very very slight Green/Gray tint to it. It works really well at keeping UV rays from passing through. Probably not what you are looking for.

Thanks. I pulled the applied tint off of it and it is clear. The tint was very light gray film.

[russ]

To get a bit of an idea look at http://windows.lbl.gov/choose_res/default.htm

[SteveC]

I am new to solar water heating, having finally gotten my set-up running this very week. I am on day 4, so my experience is limited to date. I built my own system, and the collector is a combination of free, scrap, and purchased materials. It is hard to argue with "free," so I would be very tempted, were I you, to try out the glass. I have a greenhouse built of sliding-glass door replacement glass panels, all double-paned, and for over 20 yr. it has been doing great. I believe it may be better for my plants if I had single-paned glass instead, but in my climate I need the double glass. As far as heat goes, in the greenhouse, I have to vent the place even during the harshest winter daylight hours, if it is sunny. So I do gain significant heat.

For the collector, I decided to go with twin-walled polycarbonate. I had to build the collector on the ground, then disassemble it and haul the parts up onto a second-story roof and reassemble. Very arduous, and a 4 x 8 sheet of glass would have been insane, working solo as I was. Plus, the sheet of poly was quite reasonable in cost. Single-sheet poly would have been even more reasonable, but I had to make a decision and finally chose the twin walled.

The insulation value of your glazing is not as important in a solar water heater collector, I feel, as in other applications. This is because the collector is gonna heat up a lot regardless of what you decide re: glazing. The temperature in my collector has already reached as high as 200 F. and three of my four days, so far, have been cloudy or partly cloudy. The one sunny day was the high point. Summers, with the longer daylight spells, will likely show higher temp's. I have read numerous accounts from other DIY-ers that they achiever as high or higher temps regardless of their glazing. The other thing is, once the sun goes down, you are not gonna be making hot water any more no matter how well-insulated your collector box is. So, the value of the double glazing may not be so critical. [Admittedly, I don't have any way to tell, since I only have one collector, and it is well-insulated.]

It is worth trying your free glass. You might want to assemble the collector in a manner that you could change if you decided the double glazing was a hinderance. That would be a bit of a pain, but not impossible. Make it so that you could pull off the glass and replace it with something else and, once decided, then go ahead and seal everything up properly.

I read about people using translucent glazing, clear, double and even triple-walled and paned, etc., and all of them claim to be getting good results. Your free stuff is worth a try.

[cssolar]

Single pane will serve far better - the double pane prevents much of the heat from getting to your water and there is no positive side to it.

Would it be possible to separate the double glazed unit, by carefully cutting around the seal with a knife.

Then you will have double the amount of glass ! for single glazing

Ps. wouldnt it be better to leave it double glazed, as the vacuum between the glass will help to insulate the collector plate ( bit like the vacuum in a vacuum tube ) ???

Cheers Tony

[inetdog]

Would it be possible to separate the double glazed unit, by carefully cutting around the seal with a knife.

Then you will have double the amount of glass ! for single glazing

Ps. wouldnt it be better to leave it double glazed, as the vacuum between the glass will help to insulate the collector plate ( bit like the vacuum in a vacuum tube ) ???

Cheers Tony

The biggest problem is that each side of a pane of glass will cause some reflection losses in the light going through. Unless the double pane windows incorporate an anti-reflection coating on all four surfaces (unlikely, since there is no reason for it in a window), the light loss will be roughly double that of a single pane, somewhere around 8% for light striking the glass perpendicularly, more if striking at an angle.

[Naptown]

Would it be possible to separate the double glazed unit, by carefully cutting around the seal with a knife.

Then you will have double the amount of glass ! for single glazing

Ps. wouldnt it be better to leave it double glazed, as the vacuum between the glass will help to insulate the collector plate ( bit like the vacuum in a vacuum tube ) ???

Cheers Tony

Insulated glass does not contain a vacuum. the panes would collapse on each other. At best they contain Argon gas which is a bit better insulator than just air

[russ]

Or krypton though that is not common as it is more expensive.

If there is a low e or low thermal coating on one of the surfaces that would not be so good.