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USER’S GUIDE — 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 An 1400.
3. Enter current RPM into “b” old:
7 5 0 Ç 5 B 750.
4. Calculate new RPM or “b-new”:
Ç R RPMn 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 Bn 1050.
4. Calculate new CFM or “a-new”:
Ç R CFMn FAN LAW1 17192.98
STORED
STORED
STORED
STORED
STORED
STORED
where,
CFM = Feet
3
per Minute
RPM = Revolutions per Minute
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