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VENTILATION
STRATEGIES
To ensure
adequate ventilation, the American Society of Heating, Refrigerating
and Air-Conditioning Engineers, Inc. (ASHRAE) says that the living
area of a home should be ventilated at a rate of 0.35 air changes
per hour or 15 cubic feet per minute (cfm) per person, whichever
is greater.
Natural ventilation—uncontrolled air movement
into a building through cracks and small holes (infiltration)
and through vents such as windows and doors—is the traditional
method of allowing fresh outdoor air to replace indoor air. Nowadays,
because of central heating and cooling, as well as the desire
for privacy, people tend to make little use of windows for ventilation,
so infiltration has become the principal mode of natural ventilation
in homes. Unfortunately, a home’s natural infiltration rate
is unpredictable and uncontrollable because it depends on the
home’s air tightness, outdoor temperatures, wind, and other
factors. During mild weather, some homes may lack sufficient ventilation
for pollutant removal. Tightly built homes may have insufficient
ventilation at most times. Homes with high infiltration rates
may experience high energy costs. Also, infiltration may allow
contaminated air to enter from a polluted area such as a garage
or crawlspace,or may not ventilate the house uniformly.
Whole-house ventilation—use of one or more
fans and duct systems to exhaust stale airand/or supply fresh
air to the house—can better control the exchange of indoor
air without door air. Energy experts often quote the axiom, “seal
tight, ventilate right” as their recommended approach to
house ventilation. This axiom implies that houses should be tightly
sealed to reduce infiltration, and a whole-house ventilation system
installed to provide fresh air and remove pollutants when and
where needed, in a controlled manner (i.e., in amounts needed)
that does not negatively impact indoor air quality, building components,
or heating and cooling bills.
Spot ventilation—the use of localized exhaust
fans (e.g., kitchen range and bath fans) to quickly remove pollutants
at their source—is an important tool to improve air quality
whether natural or whole-house ventilation strategies are used.
Spot ventilation improves the effectiveness of ventilation systems
by removing pollutants at their source as they are generated and
should be an integral part of any whole-house ventilation design.
In addition to its whole-house ventilation requirement, ASHRAE
recommends intermittent or continuous ventilation rates for bathrooms
and kitchens as alternatives to operable windows:50 or 20 cfm
for bathrooms and 100 or 25cfmfor kitchens, respectively.
Next: WHOLE-HOUSE VENTILATION SYSTEM DESIGNS
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