56 Electronic Balancing Tool EBT720/EBT721 and ProHood PH720/PH721
Thus, to convert from Actual Velocity to Standard Velocity, use the following equation:
STDACT
air
air
VV
STD
ACT
=×
ρ
Eq. (5)
Substituting known values into Eq. (5), we get:
STDACT
ACT
ACT
VV
92.29
46070
460T
=×
+
×
+
or,
STD
ACT
ACT
ACT
V714.17
460T
V =×
+
×
Eq (6)
where: P
ACT
is the local atmospheric pressure, as measured by the EBT/PH, for example, in units
of (in. Hg)
T
ACT
is the local temperature of the air flow being measured, in units of (°F)
V
ACT
is Actual Air Velocity, in units of (AFPM)
V
STD
is Standard Air Velocity, in units of (SFPM)
Similarly, to convert from Standard to Actual Air Velocity, use the following equation:
ACT
ACT
ACT
STD
V05645.0
P
V =×
×
Eq (7)
For Volumetric Flow measurements, the analysis is exactly the same.
Thus:
STD
ACT
ACT
ACT
Flow714.17
460T
Flow =×
+
×
Eq (8)
ACT
ACT
ACT
STD
Flow05645.0
P
Flow =×
×
Eq (9)
where: Flow
ACT
is Actual Air Flow, in units of (ACFM)
Flow
STD
is Standard Air Flow, in units of (SCFM)
Note: The Models EBT720/EBT721 and Models PH720/PH721 perform these calculations
automatically. You can choose to view velocity or flow measurements in either “Actual” or
“Standard” units of measure.
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