DIYbanter - View Single Post

Bud--

wrote:
On Dec 9, 9:45 pm, Vic Smith wrote:
On Thu, 09 Dec 2010 21:03:33 -0500, Home Guy wrote:

And I still say that having the ability to draw return air totally from
a dedicated outside duct in the summer and force the normal return air
out of the house through another duct is more energy-efficient at
cooling your house vs using an AC during those times when the outside
air temp is lower than the current inside air temp, which frequently
happens in the late afternoon and evening in the spring and late summer.
I totally agee with that.
Probably isn't done because of issues with ducting to the outside.
For my basement furnace it wold take a up window, not counting the
ductwork and diverters.
So we open the windows when it's cooler outside than in.
But if there's no breeze you really need fans in the windows to make
that work well.

--Vic

I'd say it depends on how much cooler the outside air is. And even
then, you have
the issue of humidity which is a major concern in many climates.
Pulling humid
air from outside that happens to be 5 deg cooler than the house inside
wouldn't
seem to make a lot of sense to me. And here in the NYC area, the few
days of the
year you would do that, ie some Spring and early Fall days, it just
isn't worth it comared
to the addional ducting. Besides, I thought Home Guy was all about
simplicity. At a
minimum such a system would require actuators, more controls, etc. To
do it right
you'd have to measure outside temp, outside humidity, inside temp,
inside humidity and
then have a mircrocontroller decide what to do. Sounds exactly like
the complexity that
HG wants to rip out of a new high efficiency furnace.

Some systems for commercial buildings do use all outside air when
economical. They need, if I remember right, 10% outside air when
occupied in any case. Makes it more practical to go to 100%. Duct
control is with "damper motors".

They don't just use outside temperature. They likely use an "enthalpy"
controller, which combines temperature and humidity. If you don't take
in air with humidity that is too high you don't have to worry about
inside humidity, and control on temperature. One I remember had a
temperature "set point" control in the supply air duct, that was a
potentiometer output, which connected to the damper motor that
controlled the amount of outside air that came in.

--
bud--