Need advice on sealing glass to a homemade Solar Collector Box

[ilbebauck]

Im making my first Hot Water Solar Collector to go on the roof and will be using a 60' roll of 1/2" i.d. Copper Tubing in a 2x6" wooden box , with a Thermopane Window that comes in a vinyl enclosure frame to sit on top of the box. Im going to paint the wooden box , copper tubing roll , and window enclosure frame a flat black using special high temp. paint intended for Solar Collectors . I suspect the temperature of the window enclosure frame is going to get very very hot in the summer , so, im wondering what sort of adhesive or weatherstripping I should use to seal the window enclosure frame to the wooden box that will hold up very well in extremely hot temps and moisture ? Thanks.

[DD_BobK]

Since your box is made of 2x6's...water is going to get in. Consider in oyur design & fab allowance for liquid water to escape AND water vapor as well...otherwise you're going to get condensation on the bottom side of the glass which will interfere with the solar collection.

cheers Bob

[hrhofmann]

Do you want to use a thermopane glass? Won't that keep some of the sunlight out, or is the heat net loss enough less to cover the extra sunlight loss?

[DD_BobK]

Bob-

Good catch on the thermopane glass.....I totally missed that.

OP- I would suggest sizing your collector box such that "free" ancient (as in no special sunlight transmission inhibiting glass) sliding glass door panels could used. If the frames are aluminum (check with a magnet) you can use wood working tools (saws, drills, etc) to modify the frame.

cheers Bob

[ilbebauck]

The window is going to be special ordered with regular glass...not low 'e' or tinted . I want thermopane glass so heat is kept in the box more instead of escaping. I plan on sealing the vinyl window frame to the wooden box real well , but I will put in a couple drain holes in the box in case moisture condenses in it (which I doubt will occur) .

[hrhofmann]

Use a j-shaped drain. That way water will hold in the drain to keep air flow out, but will still drain if water builds up. But, watch out for condensation building up inside the unit; You may want to have the whole thing airtight.

[ransley]

Wood absorbes moisture, dry in your home its around 5-11%, outside maybe 15% dry, on a roof it might be higher and transmit in and condense, even oil paint is rated for moisture permeability, Sherwin Williams will get you the info specs on their stuff, I used to have their spec book, maybe its online. Sheet metal is best, but if wood is used paint the whole box. SW has good products and will help at the tech level so you can seal the wood completely, Ive seen collectors all fogged up. Get glass with a warranty on the seal and fogging, my local does it. alt.energy.homepower might have panel makers, Read the "Born On" date on the silicone sealant you buy, it degrades to sometimes worthless in 6 months, if its an issue finding new contact manufacturers like Dow, use what they recomend to clean before caulking. The high heat and humidity will stress everything. One consideration you may not have though of I can think is wood expands, and you will get it real hot, that might ruin the glass seal fast as the frames expands and contracts daily, there again Metal is best, and sheet metal is cheap. On metal paint should last much longer, it will be what 160f in the box? think of the wood expanding- contracting every day. Ive seen doors move 1/16th" a day, every day, painted black and they wont get as hot nor were they Flat Black which absorbes more energy. But maybe im wrong im just thinking

[DD_BobK]

When you state "thermopane"...do you mean two layers of glass with a space between?

Depending on the operational temperature of the water in the collector tubes (pool heater? domestic water? living space?) ....double pane may actually reduce heat gain

Please post photos of unit after a few days of sun after the rain stops. My money is on water vapor condensing on the innermost surface of the glass. BTDT

cheers Bob

[ilbebauck]

Thanks everyone for the tips and considerations. Ill take precautions on the box being airtight and will coat the wood with a moisture barrier coating of some sort. Once i get this built and in operation, ill be posting some results .

[blueman]

I think you are being penny-wise and dollar-foolish in trying to make this a DIY project. Solar collectors are hi-tech engineering and even small "errors" can result in huge losses in efficiency or even ruined collectors -- it doesn't take much leakage to cause condensation which in turn will destroy efficiency.

It has taken *many* years for big companies and experienced engineers to get the engineering right so that the conversion is not only efficient but stays that way for years. Even with the best of companies, they have to offer long warranties because people doubt the ability of the collectors to maintain their efficiency over the years of abuse from hot, cold, sun, rain, snow, acid rain, grime, etc.

Remember that even making a lasting doubl-pane picture window was not an easy feat and early failure was (and maybe still is) a common problem until better engineering came up with more lasting solutions. Yet you are designing something that will go in an even more harsh environment where it will literally bake all day in the sun and then cool at night -- repeatedly.

I can't imagine that a DIY solution would even begin to compete with the know-how, experience, high-tech materials & seals, fabrication tools, etc. that are available to an experienced manufacturer.

Seems to me like an exercise in frustration in the making...