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[Audio] EN 13779: 2007 (E) 8 NOTE 2 Further information on ventilation effectiveness is given in Annex E and CR 1752. NOTE 3 Another term frequently used for the same concept is " contaminant removal effectiveness". 3.5 specific fan power for the building or the whole system ( SFP) is the combined amount of electric power consumed by all the fans in the air distribution system divided by the total airflow rate through the building under design load conditions, in W.m- 3.s. Specific power of each fan is defined as tot v SFP η p q P P ∆ = = (2) where: PSFP is the specific fan power in W.m-3.s P is the input power of the motor for the fan in W qv is the design airflow through the fan in m3.s-1 ∆p is the total pressure difference across the fan in Pa ηtot is the overall efficiency of the fan NOTE 1 The coefficient is valid for the design airflow with clean filter conditions, all components dry and any bypasses closed. It is related to an air density of 1,2 kg. m-3. It should be taken into account that the design performance is not usually the rated maximum performance of the ventilation components, but typically between 40 and 60 % of the maximum performance. NOTE 2 Further guidance for the applications, calculation and validation of the specific fan power is presented in Annex D. 3.6 demand controlled ventilation ventilation system where the ventilation rate is controlled by air quality, moisture, occupancy or some other indicator for the need of ventilation 3.7 ventilation system combination of appliances designed to supply interior spaces with outdoor air and to extract polluted indoor air NOTE The system can consist of mechanical components (e.g. combination of air handling unit, ducts and terminal units). Ventilation system can also refer to natural ventilation systems making use of temperature differences and wind with facade grills in combination with mechanical exhaust ( e.g. in corridors, toilets etc.). Both mechanical and natural ventilation can be combined with operable windows. A combination of mechanical and non-mechanical components is possible (hybrid systems)..