Fan Sizing

[D Himber]

Hi
I am having this discussion with other employees of our HVAV firm and need to clairify that when sizing a fan for a specific static pressure loss, is it correct to (in the case of an AHU with only a supply fan) calculate the internal PD in the AHU and add the external static which is where the disagreement is. I was instructed to calculate the supply and return ductwork friction loss and add this the the internal AHU PD, or do you just calculate the supply ductwork PD only?
Thanks:)

[Gib's Son]

The fan must be sized to overcome TSP (total static pressure) which is the sum of all loss', including the equipment.

The manufacturer should know what the loss through their equipment is so you need to provide them with ESP (external static pressure), which is supply and return duct loss.

[D Himber]

Thanks for the help

[Eng_Zero]

internal St. Pressure is Manfucture task.
don't consider it in your desgien requriement.

[tnhikr44]

internal St. Pressure is Manfucture task.
don't consider it in your desgien requriement.

Not a fan manufacturers task... a units manufacturers for sure, but a fan is just a fan. All static losses must be taken into account. Reducing airflow from a fan is always much much easier than increasing it, so, if I had to make a choice, I would always 'bump' the static calculation.