E.3 Specific fan power (SFP)Specific fan power is not a measure for a fan, but for the combined fan and system. Specific fan power (SFP) is a term that defines the energy consumption of a system and is the sum of the energy consumed by all fans, drives and controls in an air movement system divided by the volume flow of that system, either the total supply volume or the total extract volume whichever is the greater. It is a useful term to use for a system as it encourages the reduction of the resistance losses within the system. As the resistance losses are reduced, the necessary fan power to overcome those losses is reduced and therefore the energy consumed to provide that fan power is reduced. Some caution should be applied as there are other effective means of reducing energy consumption by recovering energy. For example, heat exchangers that improve the energy use of a heating/cooling system but increase the system losses and hence the SFP value; however, these can deliver more energy savings than what is consumed by the increased energy consumption. The overall carbon emissions of a system should be considered.