Retrotec Multi-Fan Blower Door - Manual (Page 19)

Page 19 of 37
©Retrotec Inc. 2015
Problem 3B: Imbalanced flow can also be caused by individual set points as shown in Figure 17. When
more than one fan are individually set to control to the same pressure, the balance of flow between the
fans can shift so that some fans speed up which can cause others to slow down or stop altogether. To
utilize the flow capacities of all fans, a different method of fan control must then be used to ensure the
flow rates between the fans are balanced. In this scenario all 6 fans are going different speeds.
Figure 17: Problem3B: Unbalanced flow caused by Individual set point control of multiple fans per zone
In Figure 17, Fans 1, 2, 4 and 5 were close to running at 100% speed, but Fans 3 and 6 are running at 5%
speed because air is flowing backwards through them. As a result, the target pressure of 75 Pa could not
be reached since the full output of Fan 3 and 6 are not utilized. Imbalanced flow is often a problem for
multi-point tests.
60 Pa 60 Pa
Target pressure: 75 Pa