192 Energy Project Financing: Resources and Strategies for Success
dust and asbestos; gases like carbon monoxide, ozone, carbon dioxide,
volatile organic compounds, anhydrous ammonia, radon, outgassing
from urea-formaldehyde insulation, low oxygen levels; and biologicals
like mold, mildew, fungus, bacteria, and viruses.
POLLUTANT CONTROL MEASURES
Particulates
Particulates are controlled with adequate filtration near the source
and in the air handling system. Mechanical filters are frequently used in
return air streams, and baghouses are used for particulate capture. The
coarse filters used in most residential air conditioners typically have fil-
tration efficiencies below twenty percent. Mechanical filters called high
efficiency particulate apparatus (HEPA) are capable of filtering particles
as small as 0.3 microns at up to 99% efficiency. Electrostatic precipitators
remove particulates by placing a positive charge on the walls of col-
lection plates and allowing negatively charged particulates to attach to
the surface. Periodic cleaning of the plates is necessary to maintain high
filtration efficiency. Loose or friable asbestos fibers should be removed
from the building or permanently encapsulated to prevent entry into
the respirable airstream. While conducting an audit, it is important to
determine exactly what type of insulation is in use before disturbing an
area to make temperature measurements.
Problem Gases
Problem gases are typically removed by ventilating with outside
air. Dilution with outside air is effective, but tempering the temperature
and relative humidity of the outdoor air mass can be expensive in ex-
treme conditions. Heat exchangers such as heat wheels, heat pipes, or
other devices can accomplish this task with reduced energy use. Many
gases can be removed from the airstream by using absorbent/adsorbent
media such as activated carbon or zeolite. This strategy works well
for spaces with limited ventilation or where contaminants are present
in low concentrations. The media must be checked and periodically
replaced to maintain effectiveness.
Radon gas—Ra 222—cannot be effectively filtered due to its short
half life and the tendency for its Polonium daughters to plate out on
surfaces. Low oxygen levels are a sign of inadequate outside ventila-