Fan Static Pressure Calc 1

[questionguy]

I'm in a position of having to evaluate the HVAC designs submitted by contractors. My question is, what does the "Static Pressure" spec given for a fan mean? I understand what static pressure is, and any google search of this topic just brings up a million educational resources explaining what static pressure is. But what I'm wondering is what does the "static pressure" spec quoted by a fan manufacturer actually mean?

Is that the static pressure that will be set up across the fan? Is that the maximum downstream static pressure that the fan can reliably push air into?

Thanks a lot for any feedback on this.

 

[miningman]

well others may have a differing definition but I would say that the SP provided by the manufacturer is the pressure that the fan generates to move a known quantity of air thru a system of known or calculated resistance. Change either of these and the SP changes as wel

 

[Compositepro]

Static pressure is what you will measure in the duct just after the fan using a port flush with the wall. If you measure with a tube that is facing the airflow, that is the dynamic pressure. Static pressure varies with the flow rate. The maximum static pressure of the fan is when the outlet is closed-off and flow rate is zero.
The static pressure that has been quoted to you is most likely at the flow rate that you told them you needed to operate at. The "fan curve" graphically plots the static pressure versus flow rate for the fan, and is what is used to select the right fan.

 

[GT-EGR]

There are a lot of pressure values in a submittal, but two of them are the most important.

External static pressure, is the static pressure available after you exit the unit, so it is the pressure available to push through all the ductwork. If you are just looking at a fan and not an air handler, than this is the same thing as total static pressure.

Total static pressure, is the total static pressure the fan will create. It includes the external static pressure, but also includes the static pressure required to push the air through the internal components (coils, filters, whatever else). This is th true number that the fan is selected for, although the external static pressure is an important part of that.