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BEAM P
LUS FOR
N
EW
B
UILDINGS
I
NDOOR
E
NVIRONMENTAL
Q
UALITY
(I
EQ
)
V
ERSION
1.2
Copyright © 2012 BEAM Society Limited. All rights reserved.
Page 138
6.3 I
NDOOR
A
IR
Q
UALITY
I
EQ
5 C
ONSTRUCTION
IAQ M
ANAGEMENT
I
EQ
6 O
UTDOOR
S
OURCES OF
A
IR POLLUTION
I
EQ
7 I
NDOOR
S
OURCES OF
A
IR POLLUTION
I
EQ
8 IAQ
IN
C
AR
P
ARKS
B
ACKGROUND
Indoor air quality (IAQ) is defined by a list of the constituents, in both
solid and gaseous states, in air. Subjectively, IAQ is the human
perceived response to nasal irritants in the air. ASHRAE [5] defines
‘Acceptable Indoor Air Quality’ as “air in which there are no known
contaminants at harmful concentrations as determined by cognizant
authorities and with which a substantial majority (80% or more) of the
people exposed do not express dissatisfaction.”
A key factor in determining appropriate standards for IAQ is the duration
of exposure. Exposure to indoor pollutants for a matter of minutes (e.g.
car parks), hours (e.g. entertainment establishments), or over a working
day (e.g. offices, classrooms, etc) will be different for most parameters
depending on dose and response. For example, limits of the exposure
considered acceptable for the general public, include the young and
infirm, are different from exposures considered acceptable for the
sedentary workplace, and certainly, the industrial workplace.
Sources of indoor pollutants include outdoor pollutants, building fabric
materials, interior finishes, building systems and equipment, appliances,
consumer products, and the occupants and their activities. The selection
of building materials is important, as pollutants can be emitted for weeks,
months or even years after installation. The design of the building
envelope should consider moisture and vapour penetration, and
infiltration. Air intakes should be sited away from pollutant sources and
avoid short-circuiting with exhausts. Ventilation system design should not
introduce pollutants, and filtering should be effective in removing outdoor
pollutants.
6.4 V
ENTILATION
I
EQ
9 I
NCREASED
V
ENTILATION
I
EQ
10 B
ACKGROUND
V
ENTILATION
I
EQ
11 L
OCALISED
V
ENTILATION
I
EQ
12 V
ENTILATION IN
C
OMMON
A
REAS
B
ACKGROUND
The outside air ventilation to a centrally air-conditioned building should
be adequate for the intended levels of occupancy. The criteria often used
to indicate satisfactory provision of ventilation in occupied premises is
the level of carbon dioxide (CO
2
) at design occupancy. In Hong Kong, it
is usual that the minimum values for ventilation rate for various spaces
will be specified in accordance with an appropriate version of ASHRAE
62 [5], or an equivalent design standard. However, the amount of
ventilation supply reaching the breathing zone of occupants is critical to
the adequacy of the ventilation. Inadequate distribution within zones or
within rooms can result in dissatisfaction at a local level, even if the total
ventilation supplied to a space meets specification. It is not possible to
use CO
2
as a measure of satisfactory performance in unoccupied
premises, but it is possible to determine if ventilation will be satisfactory
through measurement of ventilation rate and ventilation effectiveness.
There are three basic requirements for ventilation of occupied rooms and
rooms used for habitation [6,7]; background ventilation, local exhaust,
5
American Society of Heating, Refrigeration and Air-conditioning Engineers. ASHRAE 62.1-2007: Ventilation for Acceptable
Indoor Air Quality. Atlanta 2007.
6
ASHRAE Standard 62.2. Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. Atlanta 2007.
7
UK Department of the Environment and Welsh Office. The Building Regulations Part F Ventilation.