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Re: A wall warmer with a fan



Dan Settles <settl001@mc.duke.edu> wrote:
>nick@vu-vlsi.ee.vill.edu (Nick Pine) wrote:
>><daniel@daystar.laser.net> wrote:

>Why did you use glazing on the roof? 

Mainly, I wanted to blow down some warm air into the rest of the house from
this 32' long (E-W) x 14' high attic during the winter. But it also seems
to have made it a much more interesting space. I'm not sure what's next. 

>I suppose this might be nice in the winter on a sunny day, but doesn't
>this turn your attic space into an oven in the summer?  

That's what the two 1' turbine vents near the ridge are for, combined
with the 4 2' x 3' attic windows near the floor. But you are right, it
still gets up to 120 F or so when the sun is shining in the summer, altho
it's reasonably cool at night. I had planned on 2 4' x 4' skylights for
ventilation originally, but when those seemed expensive and not great 
ventilators, since they only opened a few inches, I switched to turbine vents,
3 as planned, 2 as installed, after the contractor started complaining and
re-interpreting the specs. I shoulda stuck to my guns. The summer venting
and shading up there can still be improved, tho.

>I was wondering how you plan to actually build this with the sloping shade
>cloth.  In the original plan the vertical shade cloth could be easily
>attached between the glazing and the side of the house.  How will you now
>attach the glazing to this sloped surface.  I know this is not impossible,
>but I'm wondering what you may have thought of that I haven't considered
>as yet.

Perhaps it was not clear from my last posting, but the vertical sleepers
in this case would not be continuous, they would be only say, 1' long, with
3' vertical gaps between them, still on 4' centers. The center of each sleeper
would be located at horizontal seams in the glazing panels. 

The one at the bottom would be a solid 2 x 4 on edge, with the shadecloth
underneath, stapled to the original wall, and the glazing 4" away from
the original wall. The next one, 4' up, would be a 2 x 4 ripped into a
1' piece and a 3" piece (nominally) with the 1" piece attached to the wall,
then the shadecloth, then the 3" piece, then the glazing on top of that
sandwich. The next one up would be 2 2 x 2's with the shadecloth in the
middle. Etc. So the glazing would attach to a plumb vertical surface, a
constant 4" away from the wall, even tho the shadecloth is sloped.
 
At some point (soon I hope) I'll have another big detailed drawing
from my architect. Perhaps this time he will include the lap fasteners
along the horizontal glazing seams, every foot or so.

>I was also wondering if you plan to cut out the shade cloth in front of
>the 2' X 2' vents as I saw in a previous post?  Is this just so you can
>reach the exterior vents through this area?
 
It seems like a good idea to have no shadecloth in front of either vent,
so the airflow resistance would be smaller in that particular area, which
is the bottleneck. That was the idea, at least. In this redesign, there is
no need to operate the (upper) exterior vent manually. It uses a couple of
$10 automatic foundation vents instead. 

>> >Another thought, if you reversed flow to make the warm air enter the room
>> >from floor level, it would have to travel past furniture and people on
>> >it's way up, possibly increasing the effective performance.
>
>Yes, warm air rises, but since this is no longer a passive system maybe
>there could be some benefit from reversing the air flow with the fan if
>you'd rather have the warm air on the bottom floor.

Maybe. It isn't hard to make warm air flow downhill with a fan, but
why do that? I'd still like this thing to be able to operate by natural
convection without a fan, at low solar intensities. And it seems to me
that either way, the air will be pretty well mixed up in the room, a
fairly uniform temperature, when the sun is shining.

>An alternative would be to just attach the outflow to new or present air
>ducts and distribute the heat through the whole house.

Well, yes. Or add an oil burner, and put new vinyl siding back on :-)
This particular house has a fairly open plan, and a hot air heating system,
so it should work pretty well without extra ducting.

>> >> Who will be the first to build one of these?
>
>Maybe me.

Wonderful! :-)

>> I wouldn't mind being the second... :-)

Nick


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