FKS 1DP- PBM-E User Manual - Copyright © 2018 FlowKinetics
LLC, All Rights Reserved
22
oscillating significantly, then another measuring point should be
considered, as the results may not be representative.
5.
When stabilized, record the desired reading(s) (either using the
inbuilt traverse routine, or log the reading to memory).
6.
Move the Pitot Static probe to the next traversing point and repeat 5
and 7 until the traverse is complete.
7.
Repeat for the other traverse locations.
Once the traverse has been completed, the volumetric flow rate through the duct
can be calculated as follows. Find the average speed and then multiplied it by the
cross sectional area of the duct to find Q:
Volumetric flow rate (Q)
:
n
i
i
duct
V
n
A
Q
1
1
where: A
duct
is the duct cross sectional area.
n is the number of points (total number of points surveyed).
V
i
is the indicated speed at each measurement point.
Using a
Centroids of Equal Areas
or
Log-Tchebycheff
point distribution allows
the speed measurements to simply be summed and averaged.
NOTE:
Assuming fully developed turbulent flow with low air swirl (rotation), i.e.
after a long section of duct, the average duct speed may be estimated using a
single Pitot reading at the center of the duct. The average speed is then
approximately 0.9 of this reading with an accuracy of
5%.
Guidelines suggest that for a speed distribution to be acceptable, 75% or
more of the speed pressure measurements must be greater than 10% of the
maximum measured speed pressure of the survey (
For specifics regarding
validation of surveys, etc, the following references are suggested: (1) ASHRAE.
1988.
Practices for measurement, testing, adjusting and balancing of building
heating, ventilation, air-conditioning and refrigeration systems
. Standard 111-1988,
Atlanta, GA and (2) AABC. 1989.
National standards, 5
th
ed., volume
measurements
. Washington, D.C.
).
