Fan Law 2 - Calculated Industries Sheet Metal/HVAC Pro Calc User Manual

Fan Law 2

The formula for Fan Law 2 (built into this calculator) is:
S
S
Fan laws use the temporary storage registers a, b, a-new, and b-new.
Fan Law 2 calculates using the entry of the three known variables
and Ç r to calculate the unknown fourth value.
Example 1:
A fan is producing 15,300 CFM at 3.2" SP. If the fan is adjusted to
14,000 CFM, what will the new SP be?
KEYSTROKE
1. Enter current CFM into "a" old:
o o
1 5 3 0 0 Ç 4
2. Enter new CFM into "a-new":
1 4 0 0 0 Ç 7
3. Enter current SP into "b" old:
3 • 2 Ç 5
4. Calculate new SP or "b-new":
Ç r
Example 2:
After doing a traverse, you find that the duct has 1850 CFM and a
SP of 1.2". You adjust the zone dampers and take a new SP that is
0.83. What is the new CFM?
KEYSTROKE
1. Enter current CFM into "a" old:
o o
1 8 5 0 Ç 4
2. Enter current SP into "b" old:
1 • 2 Ç 5
3. Enter new SP into "b-new":
• 8 3 Ç 8
4. Calculate "a-new" or new CFM:
Ç r
76 — S M
HEET ETAL
where,
SP = Static Pressure
CFM = Feet
/HVAC P
RO
C
ALC
per Minute
3
A
STORED
A
n
STORED
B
SP FAN LAW2 2.679311
n
A
B
B
n
CFM FAN LAW2 1538.58
n
DISPLAY
0.
15300.
14000.
3.2
STORED
DISPLAY
0.
1850.
STORED
1.2
STORED
0.83
STORED