AMCA InMotion - September 2019 - 4
1.5
1.25
in. wg
Static pressure
kPa
2.0
8
0.68
2.7
0.0
100%
system curve reaches zero flow rate is the
nominal static-pressure set point. Often,
70%
2
1.2
0
IES 90.1 and the International Energy
Conservation Code (IECC). Where the
5.0
4
0.3
System curve
6
1.0
0.5
with recent versions of ANSI/ASHRAE/
this is about 0.75 in. wg (187 Pa). Both
ANSI/ASHRAE/IES 90.1 and the IECC
40%
0
0.0
3
1.5
6
7.2
3.0 3.4
9
12
12.6
4.5
6.0
15
7.5
18.0
21
24
cfm x 1,000
10.5
8.5
Airflow
12.0
m3/s
require it to reset based on VAV-box
position, so it effectively is much lower
in properly operating systems.
In a VAV air-conditioning system,
the peak flow rate is needed on only
FIGURE 1. Operating points in a typical VAV system.
the hottest days ("100%" in Figure 1).
On average days, with the building
Selecting the Correct FEI for a VAV System
requiring less cooling and less flow, we can slow the
FEI is a solid indicator of the ability of a fan to serve a duty
rotational speed of the fan using a variable-frequency
point efficiently. However, it is based on a single point of
drive, allowing the fan speed to track the changing cooling
operation; in a VAV system, there are many points of opera-
needs of the building. For our discussion, let's say the
tion. Figure 1 shows the system curve of a VAV air handler
average flow rate is 70 percent and the minimum flow rate
that might serve one floor of a multistory high-rise. The
is 40 percent, as illustrated in Figure 1.
curve is offset upward from the origin because the controls
In this case, the FEI rating should be determined at
are set to provide a minimum static pressure in older systems
the peak flow rate. Determining it at the average flow rate
and a minimum pressure reset downward from an initial
would be problematic for two reasons: the first related to
set point based on VAV-box position in systems complying
compliance, the second to structural integrity.
Impeller diameter,
in. (mm)
Fan-impeller type
(all double-width)
FEI at
40% flow1
FEI at
70% flow2
FEI at
100% flow3
18 (464)
Airfoil
1.07
0.97
0.89
20 (508)
Airfoil
1.21
1.14
1.01
22 (565)
Airfoil
1.23
1.20
1.13
24 (622)
Airfoil
1.27
1.29
1.25
16 (406)
Backward-inclined
1.01
0.89
OVERSPEED
18 (464)
Backward-inclined
1.02
0.90
0.82
20 (508)
Backward-inclined
1.10
1.01
0.93
22 (565)
Backward-inclined
1.21
1.12
1.04
24 (622)
Backward-inclined
1.24
1.23
1.16
Backward-inclined
1.22
1.23
1.18
27 (686)
m3/s,
1. 7,200 cfm, 1.2 in. wg (3.40
304 Pa)
2. 12,600 cfm, 2.7 in. wg (5.95 m3/s, 674 Pa)
3. 18,000 cfm, 5.0 in. wg (8.49 m3/s, 1,245 Pa)
TABLE 1. FEI ratings at various duty points for a range of fan sizes.
4
20 19 A M CA i n m o t i o n
w w w. a m c a .o r g
http://www.amca.org
AMCA InMotion - September 2019
Table of Contents for the Digital Edition of AMCA InMotion - September 2019
Contents
AMCA InMotion - September 2019 - BB1
AMCA InMotion - September 2019 - BB2
AMCA InMotion - September 2019 - Cover1
AMCA InMotion - September 2019 - Cover2
AMCA InMotion - September 2019 - Contents
AMCA InMotion - September 2019 - 2
AMCA InMotion - September 2019 - 3
AMCA InMotion - September 2019 - 4
AMCA InMotion - September 2019 - 5
AMCA InMotion - September 2019 - 6
AMCA InMotion - September 2019 - 7
AMCA InMotion - September 2019 - 8
AMCA InMotion - September 2019 - 9
AMCA InMotion - September 2019 - 10
AMCA InMotion - September 2019 - 11
AMCA InMotion - September 2019 - 12
AMCA InMotion - September 2019 - 13
AMCA InMotion - September 2019 - 14
AMCA InMotion - September 2019 - 15
AMCA InMotion - September 2019 - 16
AMCA InMotion - September 2019 - 17
AMCA InMotion - September 2019 - 18
AMCA InMotion - September 2019 - 19
AMCA InMotion - September 2019 - 20
AMCA InMotion - September 2019 - 21
AMCA InMotion - September 2019 - 22
AMCA InMotion - September 2019 - 23
AMCA InMotion - September 2019 - 24
AMCA InMotion - September 2019 - 25
AMCA InMotion - September 2019 - 26
AMCA InMotion - September 2019 - 27
AMCA InMotion - September 2019 - 28
AMCA InMotion - September 2019 - 29
AMCA InMotion - September 2019 - 30
AMCA InMotion - September 2019 - 31
AMCA InMotion - September 2019 - 32
AMCA InMotion - September 2019 - 33
AMCA InMotion - September 2019 - 34
AMCA InMotion - September 2019 - 35
AMCA InMotion - September 2019 - 36
AMCA InMotion - September 2019 - 37
AMCA InMotion - September 2019 - 38
AMCA InMotion - September 2019 - 39
AMCA InMotion - September 2019 - 40
AMCA InMotion - September 2019 - 41
AMCA InMotion - September 2019 - 42
AMCA InMotion - September 2019 - 43
AMCA InMotion - September 2019 - 44
AMCA InMotion - September 2019 - Cover3
AMCA InMotion - September 2019 - Cover4
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