Appendix C 425
5.1.4 Recirculation of Indoor Air
Recirculation of indoor air is standard practice in some countries,
such as the U.S., and discouraged in other countries such as those of
Scandinavia. When air is recirculated, it should be filtered to remove
particles. However, filters are often used only to prevent soiling and
fouling of the HVAC equipment. These filters have a very low efficiency
for respirable-size particles (smaller than 2.5 micrometers). Use of filters
that exceed minimum requirements is an option to improve IAQ, often
with a small or negligible incremental cost.
5.1.5 Maintenance of the HVAC System
Regular preventive maintenance of the HVAC system is necessary
to assure proper delivery of outside air throughout the building and to
limit growth of microorganisms in the system. A written plan for peri-
odic maintenance should be developed and followed and maintenance
activities should be documented. Elements of periodic maintenance that
are important for maintaining good IEQ include changing of filters^1 ,
cleaning of drain pans and cooling coils, checking fan operation, and
checking dampers that influence air flow rates. Testing and balancing
of an HVAC system may be necessary in the following circumstances:
(a) after significant changes in the building, HVAC system, occupancy;
or activity within the building (b) when control settings have been re-
adjusted by maintenance personnel; and c) when accurate records are
not available.
5.1.6 Integrated Approach to IEQ
It is widely recognized that an integrated or whole-building ap-
proach is the most effective means of saving energy in buildings because
the energy performance of the building depends on the interactions of
building systems and their control and operation. The IEQ performance
of a building also depends on the interactions among building design,
building materials, and building operation, control, and maintenance.
Therefore, an integrated or whole building approach is recommended
to maximize IEQ. Such an integrated approach may include the inte-
grated consideration of the following: a) IEQ targets or objectives, b)
occupancy and indoor pollutant sources and pollutant sinks and their
- Filters become sources of odors. Also, microorganisms may colonize fil-