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©Retrotec 2017
Adjust the
[Set Speed]
until Channel A reads a pressure of 0 Pa. Record the flow in CFM. To have the
DucTester automatically acquire and maintain a 0 pressure, press
[Set Pressure]
[0]
[Set]
and the gauge
will cause the DucTester to increase in speed to eliminate whatever pressure it sees at the time that the
keys are pressed.
Ensure the pressure that is to be set to 0 actually exists before the keys are pressed because it uses the
direction of the pressure to set the direction of control. This means that the will fan speed up to
eliminate the pressure it first sees regardless of sign. Make sure the “@ Pressure” feature i
s turned off,
otherwise erroneous results will occur due to the result being divided by whatever tiny pressure occurs
above or below zero.
12.4
Measure air handler flow using a blower door
A blower door can be the ideal tool to
measure air handler flow because it has more
flow capacity than any residential airhandler.
A Duct Tester can also be used but will not
measure the largest residential air handler
flows. In California for example, 350 CFM is
required per Ton; so a 5 Ton system would
need 1750 CFM of airhandler flow. Above
the capacity of most duct testers.
Using this measurement method may be the
lowest cost alternative since either a Blower
Door and/or Duct Tester may already be on
site when the system airflow must be
measured, all you must do is to connect
them to the duct work with the flexduct.
Both methods will typically have errors of less than 7% or 5 CFM whichever is greater.
Since flow will be measured in real time, airhandler flow rate can be displayed on a Smart Device while
adjustments are made to the system; such as opening register control dampers, opening and closing
interior doors that will all affect total airhandler flow rate.
Both methods duplicate the inlet conditions to those that would be in effect at the register prior to
measurement. In the plenum matching method, the flow is going to be the same so the pressure at the
register will effectively be zero while in the second method this value is measured directly.
12.4.1.
Supply plenum pressure matching method
Run the airhandler with a clean filter in place. Measure the static pressure in the supply plenum with a
Blue tube going to Channel A. Insert a static pressure probe in an area where the pressure signal is
stable meaning it does not fluctuate more than 3% on 5 second averaging. Record this pressure.
The Flow Device with the flex duct must then be connected to a return or air handler cabinet using a
flange or box attached to the flex duct. To ensure the Device measures the exact flow that was there
before the Device was connected, the test fan must be run at a speed that will recreate that same flow
rate. Set Pressure to the previously measured supply plenum pressure and the Device will adjust its
speed automatically to recreate the original plenum pressure and yield an accurate flow measurement
through the return register. Use the “@” feature which will extrapolate your readings to the exact
pressure previously recorded in the supply plenum.
Figure 41 Flex attached to Blower Door
