
on which the frequency, the voltage, the current and the fan motor power can
be displayed.
Examples of application
Fan efficiencies were measured on several fans of various units. Figure 5.16
represents the measured fan efficiencies versus their measured used electric
power. It shows a general improvement of the fan efficiency when fan motor
power increases. However, the dispersion is huge and large differences can
be observed for each power class. For example, efficiencies range from 30 per
cent to more than 60 per cent for 3 kW fans, and from 10 per cent to 35 per
cent for small fans. Figure 5.17 illustrates the fact mentioned above (see
‘Why check fan power and related quantities?’) that the air temperature
increases when the pressure differential is large. The dispersion results from
variations in fan efficiencies.
Energy effects of indoor air quality measures
In the 1970s, after the oil crises, measures were hastily taken in many buildings
to reduce their energy use. These measures were planned with only two
objectives: energy efficiency and return on investment, without taking care of
0%
20%
40%
60%
80%
100%
0 2,500 5,000 7,500
Measured power [W]
Efficiency
Figure 5.16 Fan efficiencies as a function of actual fan motor power
0.0
0.5
1.0
1.5
2.0
2.5
0 500 1,000 1,500
Pressure differential [Pa]
Temperature increase [K]
Figure 5.17 Air temperature increase as a function of pressure differential
across the fan
102 Ventilation and Airflow in Buildings
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