Appendix A
16
In some instances, actual air velocity rather than
standard velocity may be of interest. To obtain the
value for actual velocity, multiply your standard
velocity readings (as indicated by the
V
ELOCI
C
HECK
) by the following density correction
factor:
Act Vel
Std Vel
.
.
.
.
T
P
=
+
+
460
460 70
14 7
.
Where
T = Ambient temperature in °F
P = Ambient pressure in psia
If you use metric units, the equation becomes:
Act Vel
Std Vel
.
.
.
.
T
P
m
m
=
+
+
273
273 211
1014
.
.
Where
T
m
= Ambient temperature in °C
P
m
= Ambient pressure in kPa
Example No. 1
You want to measure the actual velocity in a duct.
The air temperature in the duct is 55°F and the
