On 2/12/2013 11:01 AM, Jon Danniken wrote:
On 02/11/2013 06:02 PM, wrote:
On Feb 11, 4:25 pm, dpb wrote:

Think you'll need a lot more area than that to do any good...look at one
of these...

That's what I was thinking. A passive 2" square vent
doesn't sound very big. And with a flap of some kind,
etc, the effective area is further reduced.

My thoughts on a 2"x2" opening would involve increasing the size to
4"x4" (or even 6"x6") and installing a little computer fan into a frame
to fit. It would be trivial to built a thermostat to turn the fan on
with a thermister and a small signal transistor and a couple of
resistors, or you could go the lazy route and use a prebuilt electronic
thermostat.

You would, of course, need to supply a source of low-voltage to the cold
frame if you decided to go this route, but it would have the benefit of
being automated.

Jon


Why not one of those solar powered vents you can buy fits the top part
of a car window? The things are inexpensive enough to play around with
then take apart, modify and use the parts to build whatever you like. ^_^

http://www.amazon.com/Solar-Powered-...061073-5857430

http://tinyurl.com/bc6k2go

TDD