U
SER
’
S
G
UIDE
— 75
FAN LAW EXAMPLES
Fan Law 1
The formula for Fan Law 1 (built into this calculator) is:
Fan laws use the temporary storage registers a, b, a-new, and b-new.
Fan Law 1 calculates using the entry of the three known variables
and
Ç R
to calculate the unknown fourth value.
Example 1:
A 1,250 CFM fan is running at 750 RPM, but it needs to supply
1,400 CFM. What is the RPM required?
KEYSTROKE
DISPLAY
1. Enter current CFM into “a” old:
o o
0.
1 2 5 0 Ç 4
A
1250.
2. Enter new CFM into “a-new”:
1 4 0 0 Ç 7
A
n
1400.
3. Enter current RPM into “b” old:
7 5 0 Ç 5
B
750.
4. Calculate new RPM or “b-new”:
Ç R
RPM
n
FAN LAW1 840.
Example
2:
You
set
up
a
fan
with
a
VFD
for
14,000
CFM
running
at
855
RPM.
You
change
the
RPM
to
1050.
What
is
the
new
CFM?
KEYSTROKE
DISPLAY
1. Enter current CFM into “a” old:
o o
0.
1 4 0 0 0 Ç 4
A
14000.
2. Enter current RPM into “b” old:
8 5 5 Ç 5
B
855.
3. Enter new RPM into “b-new”:
1 0 5 0 Ç 8
B
n
1050.
4. Calculate new CFM or “a-new”:
Ç R
CFM
n
FAN LAW1 17192.98
STORED
STORED
STORED
STORED
STORED
STORED
where,
CFM = Feet
3
per Minute
RPM = Revolutions per Minute