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Posted by doofy@uh_huh.com on September 23, 2007, 4:02 pm
> We moved into a ~3500 sq.ft split level rambler in the spring.
>
> The 30 year old construction is MUCH better than average, with
> polyethylene vapor barriers in all the walls and ceilings, good windows,
> etc...
>
> Problem, is it is almost TOO tight. Stale air...
>
> Luckily, it is an All Electric house with a fairly recent and efficient
> Heatpump.
>
> The question is How much outside air to bring in?
>
> I was considering putting in a 6" duct with a motorized damper from the
> return to the outside. The Run would be about 25' when I get done snaking
> it where it can go.
>
> Will a 6" duct provide sufficient Air passively or do I need something
> like an in-line Fantek ?
>
> I will be controlling the damper with a home automation system than
> monitors the outside temp & humidity along with the inside and trying not
> to waste too much energy. I was also thinking about putting a pressure
> differential switch in so that when the Kitchen fan, dryer and/or the bath
> fans generate a negative pressure in the house the damper would also
> open...
>
> Eventually the duct would feed a whole house dehumidifier so I could get
> rid of the consoles in the furnace room... they keep the house comfortable
> at higher temperatures than using the AC to remove the humidity and use
> less energy to do so.
>
> I am in Central Maryland, just north of Washington DC... so we get all
> kinds of weather and humidity...
>
> POLITE thoughts please ?
>
>
> Bob
---------------------------------
You can be simple and use a 10 to 20 percent OA which is kind of a general rule
of thumb.
To do this you would need to know how much CFM is circulating thru your return
duct and
then calculate how big an damper is needed to provide the necessary amount of OA
CFM. If
you are going to use EMS controls then you can put in a good size damper and
regulate it.
If you don't want to calculate CFM flows then you can put a temp sensor to
monitor the SA
and adjust the OA damper based on RA and OA temps. Do it on a cold day and
adjust the SA to
be a few degrees lower then the RAT. This is a quick and dirty way but effective
if all
else fails. You can be more complicated and use a CO2 monitor and control the
outside air
based on that as long as you use EMS controls.
Les
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