How do ventilation
Controllers
communicate with
variable speed
fans?
Why do we use
Variable Speed Fans?
Example: 24 crate farrowing room
– Needs 480 cfm for minimum
– Smallest fan available is about 1000 cfm
Example: 1000 head finisher
Jay D. Harmon, Ph.D., P.E.
Professor & Extension Ag Engineer
Agricultural & Biosystems Engineering
Iowa State University
Ph: (515) 294294-0554
Email: jharmon@iastate.edu
Review
Controller Setting for VS
– Needs 7000 cfm for minimum (large pigs)
– One fan will do this, but too localized
1 Variable
Variable--Speed &
3 Single
Single--Speed Fans
Airflow rate
6
Minimum speed (%)
– motor curve
7
Stage 4
Stage 3
5
Bandwidth
8
– Temperature
T
t
difference
diff
between
b t
minimum
i i
and maximum speed (ramp length)
Stage 2
4
9
Stage 1
2
Minimum
3
10
1
Temperature
Bandwidth 1
Differential 2
Differential 3
Differential 4
Temperature
Set Point
Common Questions Associated
with Variable Speed Fans
What minimum speed do I use?
Does the percent reading on my controller
mean percent capacity of the fan?
Wh does
Why
d
my system
t
behave
b h
diff
differently
tl
after I replaced a fan motor?
What are the consequences of using
improper minimum ventilation settings?
– Too Low? Too High?
Learning Objectives
Refresh understanding of terminology
Increase knowledge of variable speed fan
p
performance
Understand how the controller read out
and fan performance are related
Improve ability to select minimum speed
and bandwidth settings
1
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
0.30
0.00
BESS Labs
Volts
Motor
Controller
RPM
Fan
CFM
%
0.15
0.20
0.25
0.30
Variable-Speed Controllers
100
80
60
Actual
Ideal
40
20
0
0
10
?
0.10
Static pressure (inches of water)
0
Why are Variable Speed Fans
Complicated?
0.05
10
0.25
80
90
0.20
60
70
0.15
50
0.10
Static pressure (inches of water)
30
40
0.05
% F u lll-sc a le a irflo w
0.00
BESS Labs
230V
200V
180V
160V
140V
120V
100V
20
230V
200V
180V
160V
140V
120V
100V
cfm
m
Why are Variable Speed Fans
Complicated?
cfm
m
Why are Variable Speed Fans
Complicated?
Controller variable-speed setting
Results from the Air Dispersion Lab, ISU
Motor Curves
Fan Delivery vs Motor Speed
CFM
M
Example At 0.05 inches static pressure
1400
1200
1000
800
600
400
200
0
Threshold
0
Motor
RPM
200
Fan
CFM
400
600
800 1000 1200 1400 1600 1800
Relationship between voltage supplied to
the motor and the resulting RPM
Varies with motor make and size.
Different motor curves exist for different
motors
Must select the right one in the controller
to make the ventilation rate increase
smoothly with temperature change
RPM
Volts
Controller
Motor
Curves
RPM
2
Volts
Prudent PS-12 Fan
with Marathon 1/6 hp motor
APP--12F
APP
2000
Volts
Motorr RPM
1500
700
RPM
1000
Volts
Motor
Curve
RPM
10 volts
500
0
0
20
40
60
80
Motor
Curve
100
120
140
Input Voltage to Motor
230
135
119
115
112
111
109
107
105
104
103
102
101
99
RPM
}
}
95 V
16 V
}
10 V
1765
1675
1575
1475
1375
1275
1175
1075
975
875
775
675
575
475
RPM
CFM w/o Cone
}
}
100 rpm
100 rpm
}
400 rpm
1432
1351
1251
1133
983
964
780
700
590
520
445
380
310
242
} 81 cfm
} 100 cfm
}
471
cfm
f
} } }
10 V
APP-12F
700 rpm
538
cfm
APP--24F
APP
2000
Volts
RPM
CFM WO/Cone
CFM W/Cone
1750
230
194
176
157
143
130
115
103
CFM or RPM
1500
1250
1000
750
Volts
RPM
Motor
Curve
500
Fan
CFM
250
0
80
100
120
140
160
180
200
220
1040
940
840
33 v 740
640
540
27 v 440
340
5798
5160
4784
200 rpm3830
2875
2072
200 rpm 823
368
} 46 v } 100 rpm
}638 cfm
}
}
}
}
}
}
1909
cfm
1704
cfm
7386
6353
5648
4688
3842
2902
1596
331
240
Volts
RPM
CFM WO/Cone
C
CFM
24-inch AP Fan MC #4
6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Volts
RPM
Motor
Curve
Fan
CFM
Which Motor Curve
in the Controller do
we pick?
Controller
Voltage
%
80
100
120
140
160
180
200
220
240
Volts
RPM
CFM WO/Cone
3
MC 1
MC 3
MC 5
MC 7
MC 9
Voltag
ge Output
120
100
Motor Curves
MC 2
MC 4
MC 6
MC 8
MC 10
Motor curve
recommendations for
various fan sizes from
Aerotech controller
80
60
40
Controller
20
Volts
RPM
Motor
Fan
CFM
%
20
40
60
% scale
80
100
Motor curve
recommendations for
various fan sizes from
Airstream controller
Controller
Volts
Motor
RPM
Generally,
minimum speed
is ~50% of
voltage
Fan
CFM
%
RPM
cfm
20 30 40
% scale
50
60
Controller
70
Volts
80
2000
1750
1500
1250
1000
750
500
250
0
90 100
Motor
RPM
Fan
CFM
140
Volts
120
RPM
100
CFM
Nearly full capacity
at 40 % Reading
80
60
40
20
% Scale
0
0
20
40
60
Controller
80
Volts
100
Motor
2000
1800
1600
1400
1200
1000
800
600
400
200
0
120
RPM
RPM / CFM
Volts
Volltage
140
120
100
80
60
40
20
0
Motor Curve 5
RPM
M/CFM
Volts
V
Motor Curve 1
Fan
CFM
4
What Changes the % Scale on the
controller?
100% Reading
– 70 F Setpoint
–2FB
Bandwidth
d idth
– 50 % minimum speed
71 F
75% Reading
120
110
100
90
80
70
60
50
40
30
20
10
0
69.8
70 F
2000
% Scale
Voltage
RPM
CFM
1800
1600
1400
1200
1000
800
600
RPM / CFM
72 F
% Scale & Voltage
Temperature!
Example:
1oF Bandwidth for MC7
400
200
0
70
70.2
70.4
70.6
70.8
71
71.2
Te mpe rature (F)
50% Reading
1oF and 2oF Bandwidths for MC1
1600
100
1400
– Curve and Motor Dependent
1200
80
1000
60
% Scale 1 deg
Volts 1 deg
40
% scale 2 deg
20
800
600
volts 2 deg
400
RPM 1 deg
200
RPM
% sca
ale, Volts
Proper Minimum Speed?
1800
120
How Can I Use this?
Avoid less than half voltage
g if book values
are unavailable
Use volt meter to measure voltage to fan
rpm 2 deg
0
69.5
0
70
70.5
71
71.5
72
72.5
Temperature
How Can I Use this?
What if my fan isn’t shown in the motor
curve recommendations or I have no
book?
Procedure:
1. Set the setpoint high so the fan will operate
at a minimum speed.
2. Set the Minimum Speed to 100%, measure
the rpm using a tachometer.
Approximately 110 V for 220 V fans
Approximately 55 to 60 V for 110 V fans
How Can I Use this?
Procedure:
3. Set the Minimum Speed to 90%, measure
the rpm using a tachometer.
4 Continue in 10% increments until the fan
4.
stops moving air.
5. Does the fan rpm steadily increase over the
range?
6. Switch motor curve number and go back to
step 2.
5
So, this is what you want from
your 1,000
1,000--cfm VS fan…
Conclusions
A total lack of understanding for everyone
involved.
The percentage readout does not correlate
to fan output or fan rpm
rpm.
A 50% minimum reading recommendation
may or may not be correct.
Motor response (rpm) over a bandwidth
may or may not be linear.
% Full-scale airflow
If you had to live with nonnon-linear VS
fan output, which situation would
be most/least acceptable?
100
80
60
40
A
B
C
Actual
Ideal
20
0
Controller variable-speed setting
cfm
1,000
800
600
400
200
0
60
70
72
80
Temp.
Quiz Yourself
What minimum speed should I use?
Does the percent reading on my controller
mean percent capacity of the fan?
Wh does
Why
d
my system
t
behave
b h
diff
differently
tl
after I replaced a fan motor?
What are the consequences of using
improper minimum ventilation settings?
– Too Low? Too High?
Thank you for your time!
What questions do you have?
6