Hi everyone,

I'm curious how people model fan power when the only information provided
is rated motor HP.

I often see a mechanical schedule that lists the same motor HP for
different units (i.e. have varying airflows); this often applies to smaller
fan coils that have fractional motor HP ratings. I've tended to model these
systems based on a Watts per cfm (W/cfm) basis (using estimated total
static pressure and efficiency) rather than the rated motor HP, so that a
fan with half the airflow would draw half the fan power.

I've also noticed that a calculation of power using amps x volts (say for a
single phase) often will indicate a higher total Watts than the rated motor
HP.

Does anyone have any insight into the relationship between actual fan power
draw and rated motor HP in real life applications (is there a correlation
or is it uttery dependent on parameters such as static pressure, impeller
efficiency, motor efficiency, etc.)? Is there a preferred way to model fan
power where only rated HP is provided?

Thanks,
Chris