I'm not sure I totally understand the question, but here's something that might help?
That's the method we occasionally use to determine airflow across, (for instance) electric duct heaters in variable volume systems. It might be used if there's a particular reason why we can't do a duct traverse, or use a flow hood, or aren't particularly interested in being as accurate as possible for our airflow readings. This method has good potential for error in the field.
It's simple. With the system stabilized, measure the volts and amps of the electric duct heater. Ohms law states that volts times amps equals watts.
One watt is equivalent to 3.41 btu's. Multiply your watts times 3.41 which gives you your sensible capacity.
Take the temperature of the air before it passes through the electric heating element, and take the temperature of the air downstream of the heater.
Subtract the air temp entering from the air temp leaving for your delta T.
Plug your readings into the formula and the result is cubic feet of air per minute. We normally don't worry about the density of the air, or the power factor of the power supply.
This method normally works well enough for resistive loads like electric duct heaters, but there are much better methods for determining airflows. Basically, in my world, it's an extra trick in the trick bag.