Solar hot air assist design needed.

[barry]

Try alt.energy.homepower for such a NG. J

[Bob]

If this is to go into a window, why do you need a collector? Just let the sun come in the window.

Bob

[m Ransley]

Alt.energy.homepower might help

[SQLit]

A friend of mine sold these in the 70's in Iowa. Took one winter for him to bail on the idea. The reason you do not still see them is that they did not work all that well. His worked well in the day time and turned into a radiator exhausting the heat from his house at night.

[C & M]

I'm wanting to install a simple solar collector for heating air into my shop, just as an assist - not full-out heating. Apologies in advance if this isn't the right forum but couldn't find a NG that seems to fit. I know that I saw a slew of these back in the 70's but I'll be hanged if I can come up with one now. I was thinking of a flat, baffled collector which would convect air from inside the shop, to the bottom chamber of the panel while the top chamber heated up and convected the warm air into the shop. It would seem logical that the baffle plate should be sheetmetal for quicker heat-up. The window is only 20" wide so I guess the width of the collector is predetermined (or maybe I can make it wider and neck it down to fit the window - other funtional issues come to mind with that). The installation was to angle the collector to match your latitude (+/-) and fit the top with an extension appropriately angle to bring it into the shop, with diverters to prevent the heated air from re-entering the collector. So, what's the consensus of opinion? No fair asking the wife.

[MattMika]

Try

and click on projects. They have a few different plans...

[nicksanspam]

Good idea.

Sounds overly complex. All you need is some glazing over a dark south wall with an air gap behind it and a hole at the bottom for shop air to enter the gap and a hole at the top for solar-warmed air to move back up into the shop during the day and a lightweight one-way plastic film damper over the hole at the top (and/or bottom) to prevent reverse airflow at night.

The glazing could be a layer of 4-year greenhouse polyethylene film (5 cents/ft^2) or 20-year polycarbonate (about $1/ft^2) eg corrugated Sun Tuf from Home Depot. The damper could be a dry cleaner bag, hinged at the top, opening into the shop, with some hardware cloth over the hole to keep it from flopping back outside through the hole at night. The glazing might be

6" from the south wall, or it might be a useful sunspace, eg an 8' radius x 16' long quarter-cylinder with 5 $5 bows on 4' centers made from 2 12' 1x3s bent to an 8' radius with 1x3 spacer blocks on 2' centers screwed between the 1x3s.

Sure. The vent opening area might be 2-5% of the sunspace glazing area.

Vertical glazing works better for winter heating.

Nonsense. They work fine. NREL says 480 Btu/ft^2 of sun falls on the ground and 900 falls on a south wall on an average December day in Boston, with an average 36 F daytime temp, so a $50 8'x16' sunspace like the one above with 250 ft^2 of R1 glazing with 90% solar transmission might collect

0.9x8x16x(480+900) = 159K Btu of sun and lose 6h(70-36)250ft^2/R1 = 51K Btu, for a net gain of 108K Btu, roughly the heat equivalent of a gallon of oil or a therm of natural gas.

The solar subsidies of the 70s brought forth a lot of incompetent vendors. Sounds like he forgot the one-way plastic film dampers, aka "the 7 cent solution" :-)

Nick

[redbelly98]

One idea, not terribly complex, is here:

Mark

[C & M]

That's the one I remember. I'll have to sort thru all of the other ideas too. Thanks to all!! C of C&M

[DA]

Pick up the last issue of Home Power magazine. It has *exactly* what you need: an article on building auxiliary assist solar air heater for a barn/shop. With bill of materials and improvements list. I think you'll get some ideas from it.

Cheers! D.

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[C & M]

WoooHoo thanks!

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[mmcconoughey]