What is Static Pressure?

The Static Pressure is the combined pressure drop through your entire mechanical ventilation system. It's one of the main drivers for fan energy that can be affected by design. The more corners, the smaller the ducts and the tighter the diffusers, the higher the static pressure. Most HVAC engineers should be able to tell you what the static pressure is assumed to be fairly early in a project.

Its units are Pa in metric and Inches of Water in IP units.

What is Peak Specific Fan Power?

Peak Specific Fan Power describes the about of power needed per unit of air flow when the air flow is at the design flow rate. It's often used to describe the efficiency of the fan in a ventilation or air conditioning system.

Its units are W/l/s (metric) or W/cfm (IP). 

The formula below provide a rough guide for converting static pressure to peak specific fan power. These assume motor efficiency of 0.9 and Fan Efficiency of 0.5.

SI

Peak Specific Fan Power (W/l/s) = Static Pressure (Pa) / 501 

IP
Peak Specific Fan Power (W/cfm) = Static Pressure (In H2O) * 4.25