whereSFPis a specific fan power [W/(l/s) or kW/(m3/s)], which are numerically the same;Peis electrical input power of all fans, without VSD drives and control equipment within the system (W or kW);Pedis electrical input power of all fans, with VSD drives and control equipment within the system (W or kW);qvis the air volume flow rate of the system [(l/s) or (m3/s)].SFP is explained further in EN 137793).