ASHRAE Journal Supplement - AMCA In Motion - Fall 2016 - 16
9
Fan total pressure (inches WG)
8
7
6
Test block
5
4
10
9
9
8
8
7
6
5
4
Normal (maximum effciency)
3
3
2
2
1
0
0
100
200
300
400
500 600
CFM
700
800
Centrifugal fan with variable inlet vanes
FTP - 0% VIV closure
FTP - 25% VIV closure
FTP - 50% VIV closure
FTP - 75% VIV closure
HP - 0% VIV closure
HP - 25% VIV closure
HP - 50% VIV closure
HP - 75% VIV closure
7
6
Test block (maximum efficiency)
5
4
9
8
7
6
5
4
Normal
3
10
3
2
2
1
1
1
0
900 1000
0
0
100
200
300
400
Horsepower
FTP - 0% blade closure
FTP - 25% blade closure
FTP - 50% blade closure
FTP - 75% blade closure
HP - 0% blade closure
HP - 25% blade closure
HP - 50% blade closure
HP - 75% blade closure
10
Fan total pressure (inches WG)
Axial fan with blade pitch
Horsepower
10
500 600
CFM
700
800
0
900 1000
Figure 6. Difference in peak efficiency location-blade pitch control axial vs spin control centrifugal fan. Image courtesy of Howden.
Fan total pressure (inches WG)
HP - 1180 rpm
FTP - 880 rpm
HP - 880 rpm
8
9
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
0
100
200
300
400
500
CFM
600
700
800
Fan total pressure (inches WG)
FTP - 1180 rpm
9
0
10
10
Two-speed with variable inlet vanes
1180 rpm:
FTP - 0% VIV closure
FTP - 25% VIV closure
FTP - 50% VIV closure
FTP - 75% VIV closure
HP - 0% VIV closure
HP - 25% VIV closure
HP - 50% VIV closure
HP - 75% VIV closure
7
6
880 rpm:
10
FTP - 0% VIV closure
FTP - 25% VIV closure
FTP - 50% VIV closure
FTP - 75% VIV closure
HP - 0% VIV closure
HP - 25% VIV closure
HP - 50% VIV closure
HP - 75% VIV closure
9
8
7
6
5
5
4
4
3
3
2
2
1
1
1
0
900 1000
0
0
100
200
300
400
500 600
CFM
700
800
Horsepower
Variable speed
Horsepower
10
0
900 1000
Figure 7. Effect of speed control on centrifugal fan
performance. Image courtesy of Howden.
Figure 8. Effect of two speed operation on centrifugal fan
performance. Image courtesy of Howden.
each motor speed or a single set of windings that operates at
two different speeds using pole amplitude modulation. Depending on the application, switching from one discrete speed to
another may provide a sufficient level of speed control.
Although they are more expensive than single-speed motors,
two-speed motors provide a wide range of fan output within
a single unit, avoiding the need for a more costly ASD. This
type of control normally is associated with another method
of flow control for adjustments necessary between the discreet
speeds of the two-speed motor, such as inlet vanes or parallel
bladed inlet box dampers.
requirements, its budget or any other real-world circumstances,
engineers can use this article to assist them in selecting the
best control option.
CONCLUSION
Conditions may require that flow change, and these are the
four main ways engineers can approach the demand for
control. Based on project's functional and performance
16
Summer 2016
AMCA
RELATED ARTICLES
1. AMCA Industrial Process/Power Generation Market Group.
"What to Know About Field Testing Industrial Fans."
AMCA inmotion (Summer 2015): 16-20.
2. AMCA Industrial Process/Power Generation Market Group.
"Construction of Fans for Industrial Process and Power
Generation Applications." AMCA inmotion (Summer
2014): 16-20.
3. AMCA Industrial Process/Power Generation Market Group.
"Selection of Fans for Industrial Process and Power Generation Applications." AMCA inmotion (Fall 2013): 6-12.
inmotion
W W W. A M C A . O R G
http://WWW.AMCA.ORG
Table of Contents for the Digital Edition of ASHRAE Journal Supplement - AMCA In Motion - Fall 2016