Perhaps the most explosive new area of the sheet metal
industry is that of Indoor Air Quality (IAQ). The Testing,
Adjusting and Balancing Bureau is striving to discover
new IAQ improvement strategies.
Even though every IAQ investigation is unique and the
solutions are always tailored to solve the specific
problem, there are only three basic strategies to improve
indoor air quality:
- Control pollutants at the source
- Dilution (i.e., improve ventilation)
- Treatment (e.g., filtration)
Strategy #1: Control pollutants at the source
Preventing pollutants from reaching the general air
stream is the job of the engineering group. Keeping
track of what enters the building constitutes good planning
and is often a cost-effective solution. Where the pollutant
origin is very specific, there are several methods for
controlling it at the source.
- Local, dedicated exhaust systems remove concentrated
pollutants before they can spread.
- Remove and replace the offending product or material,
if possible.
- Replace equipment or processes, if possible.
- Limit the locations of certain activities to specific
areas.
- Improve accessibility of HVAC ductwork and equipment
for maintenance and cleaning.
Strategy #2: Improve Ventilation (Dilution/Removal)
Dilution/removal is a common ventilation principal.
In older homes, the combustion furnace or boiler uses
oxygen and exhausts flue gases up the chimney - ventilation
happens through loose-fitting doors, windows, and cracks
in the building structure. Newer, tighter, weatherized
homes and buildings may not provide this air exchange.
Most local building codes refer to the ASHRAE standards
for design ventilation rates. Defined in "cfm per
occupant" for most spaces and "per square
foot" for others, these rates describe the amount
of outside air that should keep the occupants safe.
The standards cover the overall building ventilation
rate. Keep in mind that ventilation air must reach to
and be distributed in the space where it is needed.
Internal pressure zones and relative location pf supplies
and returns can affect IAQ. Drafts and stagnant areas
can indicate poor local air distribution.
A building's use and its system design play important
roles in solving an IAQ problem. For example, restaurant
kitchens generally have large exhaust systems, but slightly
lower and make-up air systems. The seating area's air-handling
system brings in some outside air, which by pressure
differential, migrates toward the kitchen's exhaust.
Strategy #3: Treat the Air
This third general strategy involves treating the air
stream to remove offensive impurities. To some degree,
most buildings already treat air to improve its quality
to our comfort: heating coils warm air, humidifiers
add moisture, cooling coils remove hear and humidity,
and filters remove particles.
Technology exists to achieve nearly any desired air
quality level. Equipment can remove particles of all
sizes, even molecular-size impurities, mists, smokes,
and odor-causing vapors. Even the simplest HVAC systems
remove larger particles with fiber or cloth filters.
Electronic filters, which remove smaller particulates,
are becoming increasingly common.
No single method or piece of equipment can solve all
IAQ problems. The fiber-mesh filters in most HVAC systems
can only remove large particles. They are ineffective
for fine particles, such as smoke, spores, fine dusts
and tin y fibers like asbestos. Particulate filters,
in general, are ineffective at removing gaseous pollutants.
Activated charcoal and other materials can filter some
gaseous pollutants and particulates.
Air-cleaning devices, which require additional energy
for HVAC equipment fan motors because of the added resistance
to the airflow, are highly effective in eliminating
particles, but most of them do not remove gases or vapors.
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