11
11
APPENDIX A
Correction Factors for Standard Flow Rate to Actual Flow Rate
The LoFlo Balometer
®
Capture Hood measures
standard volumetric flow rate. Standard flow is
defined as the flow rate at standard conditions,
70°F (21.1°C) and 14.7 psia (29.92 inHg, 760
mmHg). Actual flow rate is the true volumetric rate
of air at the local temperature and barometric
pressure. If you desire standard flow rate, use the
displayed reading. However, if the actual flow rate
is desired, use the information below.
To correct the standard flow rate to actual flow
rate use the equation below.
Vact = Vstd x CF
Vact = Actual flow rate
Vstd = Standard flow rate (this is displayed
by the instrument)
Tact = Actual Temperature
act = Actual barometric pressure
std = Standard density 0.075 lb/ft
3
(at 70°F and 14.7 psia)
a = Actual density in lb/ft
3
CF =
std
/
a
(Correction Factor)
Using the equations or chart below, you can
bypass the full density calculation.
Calculations in imperial units
CF = (14.7/
act)*(460+ Tact)/530
Where
act is in psia and Tact is in °F
Calculations in imperial units
CF = (29.92/
act)*(460+ Tact)/530
Where
act is in inHg and Tact is in °F
Calculations in metric units
CF = (760/
act)*(273.15+ Tact)/294.25
Where
act is in mmHg and Tact is in °C
For your convenience, we have made a chart for
determining the correction factor given
temperature and pressure.
NOTE
: The atmospheric pressure as reported
by the National Weather Service is corrected to
sea level and cannot be used if measurements
are not at sea level.
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