Specific Fan Power (SFP) is a parameter that quantifies the energy-efficiency of fan air movement systems. It is a measure of the electric power that is needed to drive a fan (or collection of fans), relative to the amount of air that is circulated through the fan(s). It is not constant for a given fan, but changes with both air flow rate and fan pressure rise.
SFP for a given fan system and operating point (combination of flow rate and pressure rise) is defined as:
where:
There are various sub-definitions of SFP for different specific applications, including SFPe (building energy performance calculations), SFPv (for performance verification tests), SFPi (individual fan), SFPAHU (air handling unit), SFPFCU (fan coil unit), and SFPBLDG (whole building). These are explained in and in part in. Reference 1 also describes how account for intermittently operated fans, e.g. kitchen hoods, and part-load performance in variable air volume (VAV) systems.
SFP can be expressed in the following equivalent SI units:
SFP and fan system efficiency
As you can see above, SFP can be expressed in units of pressure, since pressure is a measure of energy per m³ air. The relationship between SFP, fan pressure rise, and fan system efficiency is simply:
where:
In the case of an ideal lossless fan system (i.e.