Cheap solar hot air collector.

[Dan 04617]

I've got a UMaine handout with a design for a solar collector designed to be used as a grain dryer heat source. It's essentially a 20x96 greenhouse without a frame. Turn off the fans and it mostly collapses except for the tapered 4' tall endwalls. The floor is black poly. Turn on the intake fan and the collector inflates, with intake air coming through 24" poly tube greenhouse vent duct, which runs the length of the collector. A piece of black 25-50% shade cloth covers this duct, supported by a wire. So the air comes in the intake, is warmed by the black poly on the ground, is warmed as it rises through the shade cloth, and then exits into your area to be heated.  All the plastic is held to the ground by an anchored 2x frame and wiggle-wire greenhouse plastic fasteners around the perimeter.

Has anyone here used anything like this for supplemental heat in a house? Would the high air flow rate make it a problem to hook up to a house?

[hydrosun]

Years ago I made a simple solar air heater using black poly as the heat collector and it smelled like a new car for quite awhile. Not sure what chemicals were being outgassed into  the house. It may be fine for drying grain but I wouldn't want it in the house. I've used dark window screen as the heat collector for years without it degrading. It is mounted at an angle between the air inlet and outlet, forcing the air to go through the screen and transferring the heat more efficiently than a black surface at the bottom of the solar heater.

Chris

[ConsiderThis]

Wow, this is pretty interesting.

I wonder if it's the heat that makes the poly smell...

Have you seen those SolarSheat things? Costly.

[GaryGary]

Hi,

There are a lot of somewhat similar, low thermal mass, poly sunspace/greenhouse designs around and in use.  They can be quite effective as solar heaters -- lots of collection area for not much money.  So, I don't see why that scheme would not work.

Some people find that some form of insulating material (e.g. garden bark) under the black poly on the floor keeps the heat from going into the floor.

The replacement thermal controls that HD and like sell for controlling attic fans make pretty good controllers for this type of heater.  Its just a thermal snap switch with an adjustable turn on temp of about 85F to 120F -- just set it to turn the blower on at the temp you want.

Can you provide a link or source that shows the design in more detail?

One potential problem might be snow accumulation on the deflated bag?

Or, how it behaves in the wind (but some inflatables do quite well).

While the idea of the inflatable/collapsible structure is clever, I'm not sure that one of the inexpensive pipe frame greenhouse plans might not be better in the long run?

Lots of them here:

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#Greenhouse%20Plans

The main thing if you want it for house heating is to keep the thermal mass in the GH itself very low -- this way it heats fast and is ready to transfer heat to the house very quickly after the sun gets on it.

Gary

[powersource4U]

A Cheap solar hot air collector CAN consists of Aluminum Cans (Soda- Beer) with holes in the bottom and top fastened together, painted black, mounted in a frame with sealed Tempered glass facing South. You will have to have a blower of some sort and connetect the cans and the hot air collector using flex vent dryer tube, seal the back of the frame with aluminum or galvanzed sheet. Make sure you you put insulation in this from heat and outside air. This is almost the same manner CanSolair builds theirs.