Environmental Engineering Reference
In-Depth Information
ple (1 olf/individual), smoking (6 olfs/individual smoker), and building
materials and furnishings are added together. The source strength is deter-
mined by adding the square meters of source materials present. Olf values
are not available for many materials typically found in building spaces. As
a consequence, olf values are estimated for different types of spaces such as
offices, schools, assembly halls, etc.
In the PAQ procedure, a desired air quality is identified, perceived air
quality is estimated to determine the olf load, and ventilation rates required
to handle the total olf load are calculated.
In the PAQ Procedure, ventilation rates of 4, 7, and 16 L/s/person (8.4,
14.7, and 33.6 CFM/person) would be required to achieve minimum, stan-
dard, and high levels of PAQ. This would be equivalent to 30, 20, and 10%
occupant dissatisfaction and 2.5, 1.4, and 0.6 decipols, respectively.
The PAQ Procedure differs from the IAQ Procedure in that it is designed
to provide sufficient outdoor air to maintain human comfort. It does not
address health concerns directly. It also differs from the IAQ Procedure in
its level of development and evaluation (much more developed) and its
relative simplicity. The PAQ Procedure, however, would be difficult for
building designers to use because, in addition to being based on people, it
is based on a variety of other sources whose contribution to PAQ cannot be
known with certainty
, that is, before the building is constructed.
Information generated in the development of the PAQ Procedure is
interesting in a number of ways. In
Figure 11.13
,
the percentage of dissatisfied
occupants decreases rapidly with increasing ventilation rates. The greatest
improvement in occupant satisfaction is observed as ventilation increases
up to 10 L/s/olf, with limited improvement in satisfaction scores as venti-
lation rates increase further. It appears that in the case of PAQ the optimum
ventilation rate is approximately 10 L/s/olf, which is nearly equivalent to
the 20 CFM/person ventilation rate specified in ASHRAE's 1989 standard.
Figure 11.13
appears to confirm the wisdom of ASHRAE's recommendations
on ventilation requirements for mechanically ventilated office buildings.
a priori
Conventional ventilation systems can be
operated to speed up the decay rate of initially high material-, finishes-, and
furnishings-based VOC concentrations in new or remodeled buildings and
thereby improve indoor air quality. Such reductions can be achieved by what
is described as “flush-out” ventilation. In flush-out ventilation, AHUs in a
building, wing, or floor are operated to provide a continuous supply of 100%
outdoor air for 3 to 6 months. Flush-out ventilation may begin during con-
struction or when the building is available for occupancy.
“Flush-out” ventilation is based on laboratory and field studies that have
demonstrated that VOC and HCHO levels decrease with time and that
emission rates increase with increasing ventilation rates, resulting in an
acceleration of their normal decay with time. “Flush-out” ventilation has
been used for new building occupancy in Scandinavian countries and been
recommended for use in Washington and California.
c.
Flush-out ventilation.
