Retrotec DucTester 200 Series Residential Applications - Manual (Page 57)

Page 57 of 91
©Retrotec Inc. 2015
pressure, even though the gauge is not controlling anything. Press the [@ Pressure] key until the
supply plenum pressure appears as “CFM@”. Read the “CFM@” result on the gauge.
For example, if the pressure in the supply plenum is 70 Pa, Press [Set Pressure] , [70] , [Enter] to get the
DucTester to recreate the original pressure in the plenum. Press the [@ Pressure] key until “CFM @ 70
Pa” appears on the display. The CFM result displayed will be corrected for what the airflow will be
during normal operation (the supply pressure in the plenum measured at the start of the test).
If “TOO LOW” or “----“ appears on the display as the result, the pressure in the plenum is too high to get
an accurate reading. Remove the probe from the plenum, read the CFM on Channel B and use the table
that came with the flow grid to correct the flow to match the pressure measured in the supply.
9.6 Measure using air handler blower curves
If air handler blower curves are available, they will show system flow versus pressure across the air
handler, from supply to return. To determine the pressure across the air handler, measure the pressure
between the air handler cabinet on the return side and the supply plenum.
You may need the results in units other than Pascals, often inches WC, depending on what pressure
units are used on the air handler blower curves. Do this by changing the units on the display using
[Setup] >>”Mode Setup”>>”Pressure” and choosing the units required such as inches of Water Column
(in wc).
You could manually convert Pascal readings by dividing the pressure in Pascals by 250 for inches Water
Column.
9.7 Measure using Hole Flow on the gauge
Because flow through a known size hole depends on pressure across the hole, and air flow into an
enclosed space will cause pressure and flow through the hole, we can use a box with a hole in it to
measure the system air flow.
Cut the flaps off one side of a medium-sized cardboard box. Cut a 2" x 2" square hole in the center of
another side where the cardboard is only one layer thick. Punch a 0.25 inch diameter hole in the box
near the opening and insert a tube into this hole. Connect the other end of the tube to the yellow port
of the gauge (so Channel B is reading the pressure inside the box instead of from the fan). The gauge
should show Pressure on Channel B in Pascals.
Observe the pressure in the box. Increase the size of the hole in the box until the pressure is about 5 Pa.
Box pressure of 8 Pa or less are recommended because higher pressures mean the air handler is
increasingly blocked and the test method itself is affecting the performance.
On the Retrotec gauge, set the result display “Mode” to “Hole Flow”. Enter the area of the hole into the
gauge using the
[Area] key, ensuring that the units you use for area match what the gauge is expecting
for area. Units for area when calculating Hole Flow default to square inches. Read the CFM directly
from the gauge to get the air handler flow.
Because this method partially blocks the flow from the air handler, readings are not exact, especially if
pressures in the box are above 8 Pa.
9.8 Measure with a Blower Door attached to the return or cabinet
Measure the supply plenum pressure using the Static Pressure Probe supplied with each Blower Door.
Put the end of the blue tube with the probe into the supply plenum, connect the other end of the blue
tube to the “Input A” (blue) port and read the pressure from “PrA” on the gauge.
Attach a 24 inch Flex Duct (optional accessory to Retrotec Blower Doors) to the outlet side of the Blower
Door fan and the Flex Duct flange to a return or the air handler cabinet so it is blowing into the ducts on