Negative is
Really "Negative" - By Doug Long, ASCS
I was having
lunch with one of the HVAC contractors that we often work with a
couple of weeks ago at one of my favorite cafeterias. I'm not going
to mention the establishment, but there is probably one very close
to you and the strawberry pie is irresistible.
As a force of
habit, I was looking up to see the condition of the diffusers. I
typically try to do this after I have eaten. The condition was not
good and we noticed something else.
All of the
drop-in tiles were bowed downward. With the amount of exhaust
ventilation required for an establishment like this, it was obvious
that the facility was under negative pressure and the relative
humidity was too high.
The negative
condition of the facility was pulling in fungus, dirt and mold
spores into the room. The tiles were absorbing moisture from the
humid air. Visible signs of fungal growth were apparent on many of
the tiles. Roof leaks could have contributed to some of these
conditions, but the negative pressure of the building was adding to
the amount of moisture pulled from the common area above the grid.
Not a pretty sight.
Another
noticeable problem was the amount of outside air flooding the
facility every time the doors opened. Undesirable dirty and humid
Houston air entering the building added to the indoor air quality
issues. The condition of the return air grills was a good
indication of the amount of particulate matter being "sucked" into
the structure.
With all of the
unfiltered and unconditioned air entering the building under these
negative pressure conditions the air quality was definitely being
impacted, to the NEGATIVE!
The steps to
positively pressurize a building and positively impact indoor air
quality are the subject for another article. For now, identifying
these problems for your customer is the first step on the path to
better indoor air quality for your clients.
