Environmental Engineering Reference
In-Depth Information
liner materials in air-handling units (AHU) and supply and return air ducts;
(6) microbial growth in condensate drip pans, wet duct liner, and AHU filters;
(7) steam humidification with toxic corrosion-inhibitor additives; (8) inade-
quate dust control; (9) inadequate control of temperature, relative humidity,
and air velocity; and (10) inadequate ventilation air flows into building
spaces due to system imbalances.
Inadequate outdoor air flows to maintain bioeffluents at acceptable levels
may be associated with a variety of factors. These include: (1) provision of
outdoor air for ventilation not included in building design and construction;
(2) HVAC systems not designed/selected to provide adequate outdoor air
flows, i.e., they were underdesigned for occupant/building needs; (3) build-
ing or space occupant capacity increased beyond the original building design;
(4) malfunction, obstruction, or deliberate disabling of outdoor air system
dampers; (5) system-operating practices that minimize the provision of out-
door air to conserve energy and reduce costs; and (6) reduced air flows due
to poor maintenance of filters, fans, and other HVAC system components.
It is important that the problems described above be evaluated when
conducting problem building investigations. Checklists for evaluating
HVAC system operation and performance are included in both USEPA's
Building Air Quality Manual
kit. Because of their extensive
nature, they are not reproduced here. Readers should consult one or both of
these documents for their personal use of these checklists.
The investigator should obtain information about the nature, operation,
and maintenance of the HVAC system from building facilities personnel
familiar with it. Subsequently, a walk-through inspection should be con-
ducted to locate HVAC system components and determine pathways of air
flow. The inspection should include all AHUs, heating/cooling elements,
fans, filters, supply air ducts and diffusers, return air plenums and ducts,
and outside air intakes. The inspection should include an assessment of
potential problems. These include clogged condensate drip pans and growth
of microbial slime, and system design and malfunction problems such as
overloaded/collapsed filters, nonfunctioning dampers, etc.
In comprehensive HVAC system assessments, outdoor air ventilation
rates are measured using flow hoods (preferable with small intakes), pitot
tubes, or other airflow measuring devices. Carbon dioxide levels are measured
in building interiors to determine whether they conform with guideline val-
ues, particularly when direct measurement of ventilation airflows is not pos-
sible or practical. Other factors evaluated may include occupancy and space
use patterns, differences in air flow in problem and nonproblem areas (using
a flow hood), and the potential for air stratification and poor air distribution.
Assuming that there is little or no infiltration due to pressure imbalances,
ventilation rates can be determined by the use of instruments that measure
airflow through outside air intakes. The preferred instrument for this task
is a flow hood. Unfortunately, many outside air intakes are too large for the
practical use of flow hoods for such measurements. As a consequence, out-
door airflows must be determined by means of pitot tubes or other velocity
and
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