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Appendix B - Standard Flow Rate vs.
Volumetric Flow rate
Since thermal flow sensors are sensitive to changes in air density and
air velocity, all thermal flowmeters indicate flow rates with reference to
a set of standard conditions. For TSI instruments, standard conditions
are defined as 21.1°C (70°F) and 101.3 kPa (14.7 psia). Other
manufacturers may use different values.
Standard flow rate is the flow rate the air would be moving if the
temperature and pressure were at standard conditions. It is usually
the most useful measure of airflow because it defines the heat-
carrying capacity of the air.
Volumetric flow rate is the true volume flow of the gas exiting the
flowmeter.
In some instances, volumetric flow rate rather than standard flow rate
may be of interest. To output the volumetric flow rate, the instrument
will multiply the standard flow measurement by the following density
correction factor:
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