Fan Curves
13
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Transcript of Fan Curves
How to Read a Fan Curve
Fan Curves
Three main components• CFM
• Static Pressure
• Brake Horsepower
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
Pre
ssur
e
Fan Curve (Pressure to CFM relationship)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
0
0.05
0.1
0.15
0.2
0.25
0.3
Bra
ke H
orse
Pow
er
Brake Horsepower Curve (CFM to BHP relationship)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
Pre
ssur
e
0
0.05
0.1
0.15
0.2
0.25
0.3
Bra
ke H
orse
Pow
er
Typical Fan Performance Curve
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12 14 16 18 20
CFM x 100
Pre
ssur
eConstant Horsepower Curve
Typical System Resistance Curve
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
Pre
ssur
e
System Resistance Curve
Sum of all system components:• Ductwork• Elbows• Transitions• Filters• Coils• Dampers• Louvers• Building pressure
Ps = k * CFM2
Pressure Increases with the Square of CFM!
Varying System Resistance Curve
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14 16 18
CFM x 100
Sta
tic P
ress
ure
Going from curve A to curve B is an example of a system that a damper closes or filters get dirty.
Curve B
Curve A
Increasing Resistance to flow
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
Pre
ssur
e
0
0.05
0.1
0.15
0.2
0.25
0.3
Bra
ke H
orse
Pow
er
Operating PointFan Performance Curve
Brake Horsepower Curve
System Resistance Curve
Operating Point
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18
CFM x 100
Pre
ssur
e
0
0.05
0.1
0.15
0.2
0.25
0.3
Bra
ke H
orse
Pow
er
Fan Performance Curve
Brake Horsepower Curve
System Resistance Curve
Operating Point
Reading BHp Curve
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30 35 40 45
CFM x 100
Pre
ssur
e
700 RPM
350 RPM
Operating Pointat 700 RPM
Operating Pointat 350 RPM
Varying Operating Points
Large change in Ps
Small change in CFM
Small change in Ps
Large change in CFM
CFM
Ps
Selecting Point of Operation
Ps
Operating Point
Optimum Range
Unstable
CFM
Selecting Point of Operation
