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USER’S GUIDE — 77
Fan Law 3
The formula for Fan Law 3 (built into this calculator) is:
Fan laws use the temporary storage registers a, b, a-new, and b-new.
Fan Law 3 calculates using the entry of the three known variables
and Ç d to calculate the unknown fourth value.
Example 1:
A fan is running at 15,800 CFM using 6.3 BHP. If the CFM is
increased to 20,000 CFM, what is the new BHP?
KEYSTROKE DISPLAY
1. Enter current CFM into “a” old:
o o 0.
1 5 8 0 0 Ç 4 A 15800.
2. Enter new CFM into “a-new”:
2 0 0 0 0 Ç 7 An 20000.
3. Enter current BHP into “b” old:
6 • 3 Ç 5 B 6.3
4. Calculate new BHP or “b-new”:
Ç d BHPn FAN LAW 3 12.77789
Example 1 (a):
For the fan above, what is the maximum CFM if a ten HP motor is
used?
KEYSTROKE DISPLAY
1. Clear entered CFM in “a-new”:
0 Ç 7 An 0.
2. Enter new BHP into “b-new”:
1 0 Ç 8 Bn 10.
3. Calculate new maximum CFM or “a-new”:
Ç d CFMn FAN LAW 3 18430.77
STORED
STORED
STORED
STORED
STORED
where,
BHP = Brake Horsepower
CFM = Feet
3
per Minute
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