Retrotec Blower Door - Manual (Page 49)

Page 49 of 87
©Retrotec Inc. 2015
5.8 Wind effects on enclosure pressure measurement
Induced enclosure pressures are the difference between outdoors and inside the measured zone. The outdoor pressure
pickup point(s) will be affected by wind. Steady winds create pressure that can be subtracted from readings but wind in
never steady at it’s the fluctuations that cause problems. Generally, on the windward side of the building impacts the
ends of pressure tubes creating a positive pressure due to the wind velocity being stopped by the tube. Positive
pressures will also result from the overall air movement being stopped by the windward side of the building creating a
positive pressure field that can extend 5 to 20 feet from the building. To overcome these effects, it is best to use pickup
point(s) away from the direct impact of wind.
The impact of the wind can be best measured by the effect on the gauge. First, extend the exterior pressure pickup point
of the tube away from the fan’s airstream and about 5 feet from the building. Monitor the gauge for a few minutes. If
the gauge reading is above 2 Pa, insert a T in the tube end and cover the tube end with a flat sheet. If still above 2 Pa, T
the tube and add two equal length tubes sufficient to be placed in two wind free locations on opposite sides of the
building. It may be necessary to T these tubes once more to create 4 pressure pickup points, again with equal length
tubes.
Ensure the tube ends are not in contact with water since that will seal them off.
Red tubes are always run through the Door Panel and connected to the Red port on the gauge. If testing from inside the
building, red tubes will be run outdoors. If testing from outside the building, a red tube runs through the panel but Blue
tubes are used to pick up the outdoor pressure. This is done to ensure, the gauge always reads the pressure in the
building with the correct sign, namely, if the building is being depressurized, the gauges will read negative. If
pressurized, the gauges will read positive. This works whether the tester and gauges are indoors or outdoors.