Environmental Engineering Reference
In-Depth Information
Supply air
Exterior
wall
Blower
Cooling or
heating
element
Return air
from room
Filter
Outside air
Dampers
Floor
Unit ventilator
Figure 11.11
Unit ventilation (univent) system. (From Spengler, J.D.,
Environ. Health
Perspect.,
107, Suppl. 2, 313, 1999.)
systems with sufficient capacity to provide outdoor ventilation rates to attain
and maintain acceptable air quality.
In North America, ventilation standards have, over the years, been devel-
oped by a consensus process by professional or standards-setting organiza-
tions. The American Society of Heating, Refrigerating, and Air-Conditioning
Engineers (ASHRAE) has been the lead organization in the development of
ventilation guidelines. ASHRAE guidelines are given further authoritative
status by their acceptance and publication by the American National Stan-
dards Institute (ANSI).
i. Ventilation Rate Procedure. The primary approach to setting ven-
tilation standards is to specify ventilation rates. Ventilation rates are
expressed as volumetric air flows needed per building occupant, commonly
cubic feet per minute (CFM) per person or liters per second (L/s) per person.
The Ventilation Rate Procedure is based on the pioneering experimental
work of Yaglou in the 1930s, who determined the amount of outdoor air
needed to maintain relatively human odor-free environments in buildings.
As a consequence of Yaglou's work, a ventilation guideline of 10 CFM
(4.76 L/s)/person was used by building designers in the period 1936-1973.
In 1973, ASHRAE, taking energy conservation concerns into account,
reduced its consensus standards to 5 CFM (2.34 L/s)/person for nonsmok-
ing office and institutional environments. Higher ventilation rates were
recommended for other environments such as hotel rooms, taverns, audi-
toriums, residential living areas, industrial environments, and where build-
ing occupants smoked. This standard was widely used until 1989, when it
was revised.
