I need to provide an estimation of the BHP of a fan used in a HVAC system (water-source heat-pump). I have only limited information, the fan nameplate motor is 1 HP, it will run at 750 cfm is rated at 0.5 in w.c. of ESP. I don't have any information about its efficiency (motor or total). What could be a good estimation for its BHP?
Since most motor reach their peak efficiency around 75% load I was thinking about doing 1 HP * 0.75 / eff and using 85% as its efficiency. Would this be a bad estimation?