Retrotec Blower Door - Manual (Page 48)

Page 48 of 87
©Retrotec Inc. 2015
It has been noted that test fans can read 5 to 20% high when being struck by
wind. Experiment with your fan on a wind free day by testing an enclosure,
holding fan speed constant and taking a reading. Then, blow air at your fan at
different angles and velocities and note any effects.
When this was demonstrated in the classroom this apparatus was used to
demonstrate this effect but an enclosure actually works better. In this case the
fan blowing into the flex was set to the same approximate flow rate as the fan
at the end with a 50 Pa pressure in the duct. The flow rates were compared. The
fan at the end was out of the airstream and could be relied upon to create the
same flow rate as long as the pressure in the flex was about the same. Then, the
fan at the front had air blown at it at about 15 mph using another test fan to
determine if there was an effect. Three different fans were mounted at the inlet
of the flex. Two had their flow reading increase by 5% while another increased
by 20% with the fan at the end of the duct recording the same flow rate as
before. This meant that the air blowing at the fans were causing them to read
high.