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BEAM P
LUS FOR
N
EW
B
UILDINGS
A
PPENDICES
V
ERSION
1.2
8.7 S
AMPLING
P
ROTOCOL FOR
IAQ A
SSESSMENTS
Copyright © 2012 BEAM Society Limited. All rights reserved.
A - 24
8.7 S
AMPLING
P
ROTOCOL FOR
IAQ
A
SSESSMENTS
As an alternative to the sampling protocol described in the Guidance
Notes, the sampling method can be simplified based on the following
rationale. This protocol seeks to reduce the number of sampling points
and sampling parameters without significantly reducing the
representation of IAQ.
P
RINCIPLE
1:
D
ETERMINING THE
POPULATION OF
MEASUREMENT POINTS
Before sampling is undertaken, the population of IAQ zone has to be
defined. A sampling zone is defined as a region of indoor space, whether
it is confined by partitions providing a physical barrier to another zones,
or a part of an open indoor space within which every physical location
(preferably the workstations) has the same quality of ventilating air, the
same distribution of the ventilating air and the same emission
characteristics of all significant pollutants. Within a zone, the pollutant
concentrations of a set of pollutants are expected to be unchanged within
any location in the zone, within the accuracy of the measuring
instruments used.
Air sampling zones can be defined by a suitably experienced person
during an initial walkthrough survey of all spaces. The total number of
zones forms the population of the representative air quality zones.
P
RINCIPLE
2:
D
ETERMINING THE
NUMBER OF SAMPLING
POINTS
If the zones within a building are viewed as the total population, once this
is defined, the number of sampling points can be computed using classic
statistical sampling theory. Determination of the number of sampling
points is done using two procedures. The first procedure involves in
grouping of similar zones into ‘categories’. When zones have the same
three factors as defined in Principle 1, they will be grouped together to
form ‘category’. In a given category, zones are expected to have similar
pollutant profiles. For example, zones within a building where the
activities are the same, such as typical offices with sedentary workers
and non-smoking, served with typical air conditioning systems, and with
the same pollutant inventories within the zones, can be grouped together
to form a category.
The second procedure follows the definition of all the categories. The
classic statistical sampling comes into effect the number of sampling
points can be reduced to provide a more economical and viable
monitoring schedule. Typically, the number of sampling points (N) in a
category can be computed by equation (1).
2
2 2
d
St
N
(1)
where t = number of standard deviations that account for the
confidence level
S = standard deviation for the variable to be estimated
d = the margin of error (e.g. 10% of the mean value).
P
RINCIPLE
3:
R
EDUCING THE NUMBER
OF SAMPLING
PARAMETERS IN EACH
SAMPLING POINT
Either if the pollutant comes from outdoor sources and its concentration
at the intake point is below the prescribed criteria at all times, or if the
pollutant is known to have a constant emission rate and its profile relative
to the ventilation rate is known and is under control at all times, this
pollutant can be discounted in IAQ sampling program.
P
RINCIPLE
4:
R
EDUCING THE
SAMPLING TIME FOR
EACH PARAMETER IN
EACH SAMPLING POINT
The reduction of sampling time is based on the assumption that when a
building enters into its routine operation that including the activities of the
occupancy and the operation of ventilation system, the function of the
zone or the pollutant inventory are ever changing, it is reasonable to
assume that the pollution profiles of the target pollutants would remain
similar with small changes of magnitude. When the pollutant profile is