Reskinning Solar Heat Collectors

 Replacing the fiberglass skins on 2 Solar Age heat collectors yourself, can save $1,000 in labor.

The two big aluminum boxes, oriented at 45 deg and facing south (we are in the northern hemisphere, southwestern US state of New Mexico), that are collecting winter sun heat on our roof and blowing 100 degree heat into our home a major part of every sunny day, are about 11′ long X 4′ wide and 6″ deep. They are lined with this type Owens Corning insulation.

After removing the top frame edges from the outer skin of 60 mil fiberglass, the top ‘skin’ can be peeled off in one sheet, exposing the 1″ aluminum square tube spacer frame and the inner sheet ‘skin’ of whatever material was used originally.
Cutting, slicing away of the sealing silicone, is required on both skins, taking care not to destroy any of the insulation. Dremel tool with reciprocating blade worked fast with minimal damage to insulation.
Remove the 1″ thick inner spacer, square tube aluminum frame work (possibly held in place with ‘pop rivets’), then the center divider section top bar, that makes the air travel  across the whole, insulated heated area in a U pattern.
Note the order of dissasembly and reverse the process to restore, sealing each of the layers of Sunlight sheeting. I used several applications of 3M mylar metallic tape to repair the aged insulation, reseal the spacer frame and for sealing each edge of both skins during reassembly, rather than 100% silicone caulk, as originally used.
Aluminum tape, to withstand accidental super heat conditions, would have been preferable to the metallic Mylar. Only the top skin required 100% silicone caulk to prevent water intrusion. Silicone, applied after final top frame sections were screwed into place.
The inner heat collector, a sheet of corrugated or dimpled aluminum, is usually toasted and has lost it’s flat black qualities while powdering. BBQ grill paint, (1 spray can) sprayed on evenly, after cleaning off the powder residue, withstands the internal high temperatures periodically occurring, whenever circulating fan is not running on sun days.
The collector chamber wafer snap disc switch (close 110 deg- open 90 deg) had failed, causing sustained overheat burning the wire connectors. Wafer snap disc switches are available on the internet for about $15.
Be sure to seal the collector’s external electrical box containing the snap disc switch connections. I used aluminum tape over each seam. The vacuum from the circulating fan will pull in cold outside air, causing a repetitive ‘start stop’ cycle of the snap switch. Circulation Fan (in ‘Active’ systems) failures can be avoided or prolonged by lubricating the fan bearings periodically.

 In operation, the cooler air flows into the system’s vacuum from the baseboard of our hall (and den), up through the wall space and into the attic duct specific for the collector.
Following a vacuum drawn (active systems) convection in a U route through the collector box, the heated air then feeds into a soft, large diameter, insulated flexible HVAC tube duct. It goes out through the roof insulated flange, into the lower side of the big insulated aluminum box.

After circulating across the aluminum collector plate (directed by a sealed wall center section), it exits through another flange, down into more soft insulated duct into the attic, where a squirrel cage blower (insulated) feeds the 100 deg heated air through  insulated flex duct, through the ceiling vent.

They were installed about 40 years ago by ‘Solar Age’. The original aluminum boxes were spaced internally with wood. The internal wood on the originals, burned into charcoal when the sun was shining without the fan running. Solar Age replaced the wood containing units, with all aluminum units (thousands of them), then folded and closed the factory.
To prolong the units life, I use big white plasticized fabric covers during summer months when the extra heat is no longer required.

This is the units first re ‘skinning’. I used 40 mil (inner) and 60 mil (outer) Sunlight fiberglass on both layers to resist heat and last longer. Internet sources for Sunlight fiberglass with one side UV coated, saved local fees for ordering and handling.
Rapidly cutting the fiberglass sheets to size required a diamond blade  from Harbor Freight, or similar cutoff disc mounted in a handheld grinder. My cuts for two layers on both units, totaled 60 linear feet. Hand held ‘snips’ were fatiguing, slow and impractical. I clamped the old sheets over the new sheets and supported both above the level cutting surface, to have a cut guide edge.
I tried the Dremel reciprocating tool saw and wore out the saw blade within the first 12″ of painfully slow progress. Wear a face shield or/and goggles and be sure to wear a well fitted breathing mask. The fine powder created by the power cutting,  is intensely invasive.

Two layers of fiberglass ‘skin’, 1″ apart (spacer frame), keep the cooler top (Outer) skin from contacting the heated inner skin section above the aluminum heat collecting plate. Result, an R factor sufficient to maintain the 100 degree heat flow most all of  the day.

When positioning the sheets during assembly, carefully align, adjust ‘All’ the edges before final taping and sealing. Remember to seal any diversion walls within the collector boxes, with whatever method you decide (I used 100% Silicone). Remember, the interior chamber gets very Hot.

These basically energy efficient units can be constructed of wood, or other suitable and convenient materials, ‘Only’ if the intense heat buildup is automatically dumped and vented by thermostat controls during times not required…. or they are covered. Otherwise the sun’s collected radiation super heats the units internally, which causes a dangerous burn of the components.

Enjoy the project. Passing on the mistakes, helps the next adventuresome technician. From “The United States of America, One Nation Under God”

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