Re: GBlist: Re: Dust Mites
Hal Levin (hlevin@cruzio.com)
Sun, 02 Mar 1997 13:49:47 -0800
At 12:30 PM 3/1/97 -0400, you wrote:
>Gregory Thomas wrote:
>>
>>(snip) Two
>> buildings could have the same blower door equivalent leakage areas, but
>> different actual leakage rates due to the driving forces of the HVAC
>> equipment, if the ducts leak and/or there are pressure imbalances. Forced
>> air systems don't dry air except through leakage.
>>
>> Greg Thomas
>
>One effect from forced air systems is under-emphasized, and sometimes
>mistaken for air dryness. Unless you have a very good filtering system,
>such as the HEPA type or an electrostatic precipitator that is
>maintained regularly, using the air that you breathe as your heat
>transfer medium is prone to distribute dust and keep fine dust in
>suspension. The smaller the dust particles, the harder they are to
>filter out, and the longer they will remain in suspension. Dust
>particles can cause throat and lung irritation, and this sensation can
>be (and probably often is) mistakenly assumed to be "dry air". For
>example, when you wake up in the morning in the winter and your throat
>is "dry" - a sensation that most of us have experienced in some of the
>houses we have lived in.
>
>We've had some discussion on this list in the past, and people have
>described their personal experiences, including how humidification has
>solved the dry air problem in their house. I'm sure that many of these
>observations are accurate. It would be useful, though, to figure out how
>to differentiate between the two different causes (dust and low R.H.) of
>a similar effect, namely the sensation of dryness. This will be
>complicated by the fact that two different individuals might have
>different levels of sensitivity to both dust and dryness. A further
>complication is that remedial measures for dryness can also be effective
>against dust, since dust particles have shorter settling times with
>higher R.H. In other words, you may think you have a dryness problem and
>that you have fixed it with a humidifier when actually you have a fine
>dust problem that you have, in fact, fixed with the humidifier.
>
>A good test case might be a sensitive individual who lives in a house
>with both a radiant heating system and a forced air heating system run
>with, and without, a HEPA filter.
>
Others (including Jan Sundell of Sweden, in a thesis on sick building
syndrome) have hypothesized the confusion between the sensations of dryness
and the sensations of upper respiratory irritation. I think a good test case
is hard to find. The preferred way might not be an individual but large
groups under as controlled conditions as possible, and, if not well
controlled, at least well-characterized so that the statistical analysis can
be done. I would also hope that very good characterization of the particles
themselves would be done including size distribution and, if possible,
something about their chemical or even biological composition.
Hal
Hal Levin <hlevin@cruzio.com>
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