[Strawbale] Forced air systems and particle resuspension

[David Neeley]

Greetings!

I did some work with a lady a while back who is a "canary." That is, her
environmental sensitivities are so severe that she is among the very first
to respond to a wide range of contaminants in the atmosphere.

As a result of that work, I learned a fair amount about it *then*, but I'll
have to dig through a somewhat sketchy memory for some of this.

First, although it is true that in a general sense there is more pollution
of various kinds inside most houses than outside, there are regional sources
of environmental contaminants in most regions of the earth. I saw a map of
the U.S., for example, that was actually a book of maps, each with a
different pollutant mapped. Interestingly enough, at that time it appeared
that one of the most environmentally benign areas of the  U.S. was in the
hill country to the West and North of Austin, Texas.

Next, remember the problems we have in sealing houses against infiltration
of outside air--to keep them warm in winter and cool in summer. The same
penetrations allow pressure differentials to exist, especially considering
the action of winds on the outside of the home. The pressure is higher on
the side meeting the prevailing wind, lower in the lee of that wind. This
pressure differential can cause air movement into and out of the house,
which also can affect the infiltration of outside contaminants and dirt. Add
to that the operation of forced air systems, breezes from doors opening, and
even the small breeze from occupants moving around and you can and do have
dust spread around.

Household dust is to a surprisingly large extent composed of dead skin cells
we are constantly shedding in the course of our lives. In addition, house
dust mites that feed on those dead skin cells are also extremely common.
(See http://en.wikipedia.org/wiki/House_dust_mite)

For anyone with asthma or allergies especially, carpets should be completely
absent. Hard surface floors simply cannot catch, hold, and release so much
dust--and they are far easier to keep truly clean.

In addition, bed coverings and mattress pads that have been introduced that
are impervious to dust mites can help. Recently, an interesting study found
that dust mite proliferation was slowed by the simple practice of not making
the bed immediately upon arising. The additional airing and drying that came
from the jumbled bedclothes made a climate much less inviting for dust mite
survival--they like it to be slightly damp and very dark, conditions
increased by the immediate bed making of the serious homemaker! (Gee, why
didn't this study come out when I was a kid?).

Various kinds of air filters are helpful where there is an adverse reaction
to dust or contaminants. Probably best would be a two-stage filtration
regime, starting with a good electrostatic filter and followed up with a
HEPA filter. The electrostatic would remove the bulk of the particulates,
allowing the HEPA to be more efficient and for its filters to last much
longer. If, for example, you do have or plan on installing a forced air
system, an electrostatic filter might be an option in that system. These do,
unfortunately, consume a fair bit of power.

One device that might be very helpful in a mechanically heated and cooled
house would be an energy recovery ventilator--which should in these cases be
strongly considered, especially if your house is actually well sealed from
the outside. Optimally, air should be changed with the outside on a regular
basis, and such a ventilator will substantially reduce heating and cooling
costs in a super-insulated and well sealed house.

In a typical forced air system, however, with air recirculated within the
house envelope, an electrostatic filter will do much to reduce the dust and
other particulate contaminants inside.

David

On Jan 7, 2008 10:16 AM, Speireag Alden <speireag at gmail.com> wrote:

>
>
>
>     I'll bet that vacuuming puts it off the scale, unless it's a
> central system which exhausts to the exterior.
>
> > One of the houses in this study showed high particle counts
> > whenever the kid rolled over in bed. His duvet was rarely cleaned
> > and it
> > gave off huge numbers of particles everytime he moved.
>
>     Wow.  That suggests to me that generalization is very difficult
> in this situation.  However, it also suggests that the problem is
> very amenable to point-source solutions.