424 Energy Project Financing: Resources and Strategies for Success
quality. Outside air intakes should not be located near strong sources
of pollutants such as combustion stacks, exhausts from fume hoods,
sanitary vents, busy streets, loading docks, parking garages, standing
water, cooling towers, and vegetation. The outside air intake must be
separated sufficiently from locations where ventilation air is exhausted
to prevent significant re-entrainment of the exhaust air.
Incoming air should be filtered to remove particles. The recom-
mended minimum particle filtration efficiencies vary among IAQ and
ventilation standards and guidelines; however, use of filters that exceed
minimum requirements is an option to improve IAQ, often with a
small or negligible incremental cost. If unacceptable concentrations of
gaseous pollutants are present in outside air, gaseous air cleaning may
be required.
5.1.3 Maintain Minimum Ventilation Rates
The minimum ventilation rates specified in the applicable code
requirements should be maintained or exceeded. The HVAC system
should be designed so that rates of outside air intake can be measured
using practical measurement techniques. In buildings with variable air
volume (VAV) ventilation systems, special controls may be needed to
ensure the minimum outside air intake into the air handling unit is
maintained during all operating conditions (Cohen 1994, Drees and
Wenger 1992, Solberg et al. 1990).
In addition to maintaining the minimum rate of outside air intake
into the building, the ventilation system must be designed and balanced
to assure the proper air delivery to each major room or section of the
building. In VAV systems, VAV control units must have a minimum
open position^1 to ensure the required outside air supply to specific
regions of the building.
When the air supply and return air registers are placed in or near
the ceiling and the supply air is warmer than room air, the supply air
may short circuit to the return registers resulting in poor ventilation
at breathing level; i.e., a poor air change effectiveness (e.g., Fisk et al.
1997b, ASHRAE 1998). The ventilation system should be designed to
assure a high air change effectiveness or the rate of outside air supply
should be increased to correct for poor air change effectiveness.
- When internal cooling loads are low, the supply air temperatures may need
to be increased to prevent overcooling of the conditioned space.