Fan Intake Sizing
Fan Intake Sizing
(OP)
I recently was involved in the installation of a radiator/fan unit. The unit, with a 42" fan (19,500cfm), was installed in place of an older unit, with a 36" fan (12,400 cfm). The new radiator/fan unit is also taller than the older unit. The fan shroud of the new unit is less than 8" from the roof of the enclosure that it is installed in (the lovred intake is on the side of the enclosure). The motor for the new fan is also drawing close to 15 Amps, when its spec'd FLA is 13 Amps.
I was wondering what the appropriate methods for calculating the minimum clearance for a unit such as this were. Also, would it be better to just install an intake on the roof, and if so, what is the best method for sizing that intake.
Im an electrical engineer, and have never delt with HVAC type engineering before. I'd appreciate any help you can give.
THANKS
I was wondering what the appropriate methods for calculating the minimum clearance for a unit such as this were. Also, would it be better to just install an intake on the roof, and if so, what is the best method for sizing that intake.
Im an electrical engineer, and have never delt with HVAC type engineering before. I'd appreciate any help you can give.
THANKS





RE: Fan Intake Sizing
TOK
RE: Fan Intake Sizing
RE: Fan Intake Sizing
you went from 12400 to 19500 in the same enclosure.
Your intake and/or exhaust surface area are probably to small for that much flow.
Please provide more details on sizes of those areas and if there is loovers and/or dampers.
Will be easier to help evaluate/estimate static preasure.
RE: Fan Intake Sizing
With loovers you should consider them like 50 % of free area
so you would need 2*39 sq ft.
at exhaust is the same but you can target 1000ft/min.
these are ball park figures. You can increase those speeds to reduce surface area needed, but then you increase static preasure and amp draw on motor.
It also depends on noise level (faster = noisy)
And if rain can be sucked in at intake (if enclosure is outdoor)
if this is not clear let me know
RE: Fan Intake Sizing
I’m not sure what you mean by “fan shroud” but if your fan inlet is now positioned such that the incoming air is unevenly loading the blades and it’s a propeller bladed fan, (rather than a centrif.) you might have problems down the road. Whatever type of fan, if the air is entering at an oblique angle you’ll not be getting the performance you require due to system effect. The minimum distance you need is one fan diameter.
Sounds like you need an additional intake (on the roof?). As ddace said, you need about 40 square feet of free area.
Cheers.