414 Energy Project Financing: Resources and Strategies for Success
indoor spaces. Maintaining buildings under positive pressure relative to
outdoors can help to maintain IEQ by limiting the infiltration of outdoor
air that may adversely affect thermal comfort and that may contain
moisture and pollutants. Maintaining pressure differences between dif-
ferent indoor spaces can limit the rate of pollutant transport between
these spaces. For example, smoking rooms, bathrooms, and laboratories
are often depressurized so that pollutants generated within these rooms
do not leak into the surrounding rooms.
4.5.4 Air Cleaning
Gaseous or particulate air cleaning (ASHRAE 1996, Chapters 24
and 25) may be used to remove air pollutants from recirculated indoor
air or from incoming outdoor air. Most commercial buildings use par-
ticle filters in the HVAC system. Commonly, these filters have a low
particle removal efficiency for particles smaller than approximately one
micrometer in diameter (Hanley et al. 1994). However, particle filters
with a wide range of efficiencies for submicron-size particles are readily
available for use in commercial buildings and indoor particle concentra-
tions may be lowered substantially by the use of higher efficiency air
filters. To maintain the efficiency of filter systems, the filter installation
method must prevent significant air leakage between or around the fil-
ters. In contrast to particle filters, gaseous air cleaners, such as beds of
activated carbon, are used in only a small minority of buildings because
of their higher costs and uncertain performance; however, considerable
effort is being devoted to the development of new technologies for
gaseous air cleaning.
Air cleaning systems require regular maintenance. For example, air
filters must be periodically replaced to prevent reductions in air flow
and to limit odor emissions and microbiological growth from soiled
filters.
4.5.5 Natural Pollutant Removal Processes
For some pollutants there are other natural removal processes.
Examples are loss of ozone due to its reaction with indoor surfaces and
the deposition of particles on surfaces. These removal processes can
substantially influence the indoor concentrations of these pollutants.
4.5.6 Air Recirculation and Air Flow Patterns
The indoor air flow pattern also influences IEQ. Mechanical re-