Building Science - Pressurization
"Building scientists
have learned that buildings work as a system of interrelated
elements."
—EPA,
Montana State University, USDA
Building Sciences is the study of how buildings
function under various environmental conditions. Some of the
key elements are moisture movement, relative
humidity, pressurization, air
leakage, temperature and
the building envelope itself.
Pressurization
Maintaining buildings under positive pressure
relative to outdoors can help to maintain indoor air quality
by limiting the infiltration of outdoor air that may adversely
affect thermal comfort and may contain moisture and pollutants.
Allowing air to move freely and unimpaired from room to room
in the conditioned areas of a home is essential. Balanced pressure
helps maintain consistent temperatures without placing abnormal
stress on the envelope.
Many normal household items can work against
your ventilation system. Some of these include the stove vent,
clothes dryer, and bathroom fan. The function of each these is
to remove air from the home and push it to the outside. This
can create a negative pressure in the home. If the proper amount
of make up air is not supplied by the design, the negative pressure
in the home will draw the air from uncontrolled areas. The uncontrolled
make-up air can be from a crawlspace, cracks in the foundation,
leaky window seals, the water heater flue and the chimney. When
air is pulled in through the water heater flue, chimney or furnace
flue, carbon monoxide is also being pulled into the home. This
is called "back-drafting". Uncontrolled air from the crawlspace
or foundation cracks can contain radon, moisture, and other contaminants.
The proper system design will take into account
household items that could create a back-drafting situation.
Ultimately, structure, ventilation and filtration
all influence the performance of the entire system. Indoor air
quality can be greatly improved by using the proper design strategy
and good building materials. Mechanical systems should be designed
and installed by trained experts aimed toward protecting the
health, quality of life and productivity of the building occupants.
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