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12.4.2.
Set pressure in front of return register to zero method or using
your Blower Door as a powered flow hood
Another possibly more convenient way to eliminate the insertion effect of the Device, would be to
measure the pressure at the flange or box that connects the flex to the wall register, then Set Pressure
on the gauge to 0 so the fan will speed up until there is no resistance to flow caused by the Device. You
can then measure the flow rate caused by the air handler through that register. Since the flow rate into
the return will cause turbulence and the presence of the attachment will change the air flow lines into
the register, this method may not be as accurate as the previous method.
If there are multiple registers, the flow through each register could be measure separately, then the sum
of all register could be used to determine total air handler flow.
Typically, once installed the pressure tap on the flange will yield a negative pressure that will be
displayed on Channel A. You would then Set Pressure to zero which would cause the fan to speed up and
return the pressure at the flange to zero which closely approximates the condition prior to the flange
being installed over the return register.
This method will NOT work when the Device is mounted to the airhandler cabinet since the pre-existing
pressure will already be a large negative value and setting this to zero would eliminate all the resistance
of the return ductwork and give a much larger flow rate than was actually present under normal
operating conditions.
Optional
Sierra Building
Science device
for measuring
air handler
flow using a
blower door
connected with
flex to a
return.
Summary of Contents for DucTester 300
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