Environmental Engineering Reference
In-Depth Information
theory, DV is approximately 3 times more effective in removing contami-
nants from a space than general dilution ventilation at the same air flow rate.
As indicated previously,
ventilation, including both general dilution and exhaust ventilation, is
widely used in many large, private, commercial, and institutional buildings
to maintain acceptable air quality and comfort and control odors.
The relationship between building ventilation conditions and human
bioeffluent levels determined from calculations of CO
f.
General dilution ventilation and air quality.
emission rates and
indoor measurements has been well established. It has been widely assumed
that general dilution ventilation can be used to effectively control other
contaminants as well and reduce complaints associated with “sick building
syndrome” phenomena.
The use of mechanical ventilation (as opposed to natural ventilation) has
been suggested to be a contributing factor to occupant complaints of illness
symptoms which have been reported over the past three decades. The appar-
ent relationship between “sick building” complaints and mechanical venti-
lation has been circumstantially linked to the “epidemic” of building-related
health complaints which coincided with (1) efforts of building facilities man-
agers in the late 1970s and early 1980s to reduce outdoor air ventilation flows
to conserve energy and (2) the increasing construction of new buildings
designed to be more energy efficient.
2
i. Ventilation and sick buildings. A number of cross-sectional epi-
demiological studies have been conducted to evaluate potential relationships
between illness symptoms and building ventilation systems. Several studies
have shown significantly higher complaint rates in mechanically ventilated,
as compared to naturally ventilated, buildings. In other studies, different
types of ventilation systems were compared to determine potential relation-
ships with occupant health symptoms. These studies showed higher symp-
tom prevalence rates associated with air-conditioned (with cooling) build-
ings (
Table 11.1
). The scientific evidence indicates that mechanical ventilation
per se
is not associated with increased symptom prevalence rates; rather, it
suggests that mechanical ventilation with cooling is.
ii. Ventilation conditions and symptom prevalence. A n u m ber of
cross-sectional epidemiological studies have been conducted to determine
potential relationships between ventilation rates and building occupant
symptom prevalence rates. No apparent relationships with ventilation rates
were reported in some studies, whereas others have shown limited reductions
in symptom reporting rates with increasing nominal or measured ventilation
rates. Some evidence exists to suggest that increasing ventilation rates from
minimum values results in significant reductions in symptom reporting rates
and increases in occupant satisfaction with air quality. At increasingly higher
ventilation rates, no significant improvements are observed. In general, stud-
