ASHRAE Journal Supplement - AMCA InMotion - October 2020 - 29

Model: GI Cent.; size: 300AF; diameter: 30;
RPM: 1,366; density: 0.075; outlet area: 5.09
15.0

Flow vs. pressure

Total-pressure (11.2)
curve

12.5
(9.3)

5.0
(1,244)

10.0
(7.5)

4.0
(995)

7.5
(5.6)

3.0
(747)

Flow vs. power

2.0
(498)
1.0
(249)
0.0
(0)

0
(0.00)

Staticpressure
curve

5.0
(3.7)

2.5
(1.9)
0.0
(0.0)
10,000 12,500 15,000 17,500 20,000
(4.72) (5.90) (7.08) (8.26) (9.44)

300AF

2,500
(1.18)

5,000
(2.36)

7,500
(3.54)

System pressure loss, in. w.g. (Pa)

6.0
(1,493)

7.0
(1,742)
6.0
(1,493)

Flow vs. pressure

Flow vs.
total
efficiency

5.0
(1,244)

17.5
(13.0)
15.0
(11.2)
12.5
(9.3)

4.0
(995) Flow vs. power

10.0
(7.5)

3.0
(747)

7.5
(5.6)

2.0
(498)
1.0
(249)
0.0
(0)

0
(0.00)

5.0
(3.7)

Flow vs. static
efficiency

2.5
(1.9)
0.0
(0.0)
10,000 12,500 15,000 17,500 20,000
(4.72) (5.90) (7.08) (8.26) (9.44)

System curve
2,500
(1.18)

5,000
(2.36)

7,500
(3.54)

300AF

Power, bhp (kW) & efﬁciency % * 0.1

17.5
(13.0)

7.0
(1,742)

Power, bhp (kW)

System pressure loss, in. w.g. (Pa)

Model: GI Cent.; size: 300AF; diameter: 30;
RPM: 1,366; density: 0.075; outlet area: 5.09

Flow, cfm (m 3/s)

Flow, cfm (m 3/s)

Performance certified for installation Type D: ducted inlet/ducted outlet. Power ratings (bhp) do not include transmission losses. Performance ratings do
not include the effects of appurtenances (accessories).

FIGURE 7. Flow vs. static- and total-pressure curves.

factor from the right axis). The total efﬁciency is 86.8
percent. In this example, the fan is selected just to the
left of peak efﬁciency.

System Curve
Figure 8 also includes an orange parabola representing
system resistance at various ﬂows, the system curve.
Resistance generally varies as the square of ﬂow ratio:2

The fan will operate at the intersection of the system
curve and the fan

curve.4

FIGURE 8. Flow-vs.-static-efﬁciency and ﬂow-vs.-totalefﬁciency curves and system curve.

2) AMCA. (2002). Fans and systems. AMCA Publication 201. Arlington
Heights, IL: Air Movement and Control Association International.
3) ACGIH. (2019). Industrial ventilation: A manual of recommended
practice for design (30th ed.). Cincinnati: American Conference of
Governmental Industrial Hygienists.
4) AMCA. (2011). Air systems. AMCA Publication 200. Arlington
Heights, IL: Air Movement and Control Association International.
5) AMCA. (2018). Calculation of the fan energy index. ANSI/AMCA
Standard 208. Arlington Heights, IL: Air Movement and Control
Association International.

About the Author
William "Bill" Howarth is president of Ventilation & Fan
Consulting Service International LLC, a Lake Zurich, Ill.-

Conclusion

based ﬁrm specializing in ventilation-system design and

This article covered the fan curves most commonly

consultation, process-system-ﬂow troubleshooting, indus-

encountered. There are additional curves with multiple

trial-ventilation-system-design training, fan- and blower-

speeds, multiple blade angles, and combinations of fan-

specification assistance, fan- and system-performance

performance data. Curves with fan-energy-index (FEI)

testing, vibration analysis and balancing, and commis-

operating bubbles,5 motor-sizing limits, inlet-turning-vane

sioning. Previously, he was vice president of AMCA member

data, and other information are derived from the curves

Illinois Blower Inc. and, prior to that, sales manager for

shown here. Knowing to start at the required system ﬂow

AMCA member Hartzell Air Movement. He is a member of

and work up to the pressure, power, efﬁciency, or system

the AMCA Speakers Network, available to present on fans,

curve is the key to untangling fan curves.

fan testing, ﬁeld testing, and fan efﬁciency; AMCA certiﬁcation and FEI; system effect and ﬁeld work; ventilation-system

References

design and commissioning; and fan, blower, and system

1) AMCA. (2016). Standards handbook. ANSI/AMCA Standard
99. Arlington Heights, IL: Air Movement and Control Association
International.

troubleshooting. To request an AMCA Speakers Network

w w w. a m c a .o r g

presentation, go to https://bit.ly/AMCA_Speakers.

2020 A M CA i n m o t i o n

29
https://www.bit.ly/AMCA_Speakers http://www.amca.org
ASHRAE Journal Supplement - AMCA InMotion - October 2020

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