Posted by jeff on January 3, 2010, 6:03 pm
I have a number of friends that could use some el cheapo solar heat.
They all see to have one large south facing wall.
A couple of years back, I built a pass through black "felt" solar
collector. This works even without a fan driving air through the felt.
So what I am thinking is just suspending glazing ("clear" poly) off
the south wall and opening the window. The sun heats the buildings south
wall and is trapped by the glazing, the heat drifts in the open window.
Or if you had two windows you could force some circulation.
Now, it seems to me that the air space needed not be great. Perhaps
just the width of a 2x4. Seems to me that you should be able to get
several thousand BTU/hr out of each 100SF of glazed area while the sun
Posted by Ecnerwal on January 3, 2010, 8:36 pm
Heat "drifing" in is not particularly effective. To get BTUs, you have
to move pounds of heated air.
If you are going to bother building anything, build the collectors -
it's hardly any more work, and far more effective, especially if you do
provide fans (you can power those off a solar electric panel for
simplicity and to work in power outages, but it costs more than using
grid power and a thermostat.) They will thermosiphon, but you get more
BTUs if you power air through.
This works better with polycarbonate than polyurethane. Corrugated
twin-wall greenhouse glazing is particularly good, and lasts a long
time. The air should come in bottom and next to the glazing, the air
should exit top and away from the glazing, and the felt (alternately,
black window screening, several layers, or greenhouse shadecloth) should
be angled to make the air spaces triangular and largest at the
Cats, coffee, chocolate...vices to live by
Posted by jeff on January 7, 2010, 12:08 am
I think you meant polyethelene.
I have a ~25' x 8' solar collector pushing air pretty much as you
describe. I'm running half sun tuf (polycarb) and half vinyl at the
moment. I've run all poly also. Originally I had 3 layers of black
screen, I now have a layer of black felt on this.
I'm also running tests on a "solar cabana" which is nothing more that
a poly covered cabana shape green house. With bubble wrap and poliso
RMax for insulating non south walls. Toasty inside when it is freezing
outside, while the sun shines.
It's my experience with this, and not running a fan that has lead me
to think simpler, at least for my cheapo friends. Twinwall polycarb and
everything else needed is a lot more money and trouble. Something is
often better than nothing!
Posted by zoe_lithoi on February 23, 2010, 3:40 am
The best way to get circulation, is to cut a hole in the wall so that
it opens up into the bottom of your solar collector. As the heat warms
up, it will flow out of your house, through the hole, up thru the
solar colector and into your window.
We could estimate how much solar energy you are gathering if we had
some more details, like where you live, what month of the year you are
interested in, the size of your solar collector.