This PWI (for European Technical specification) applies to the natural and hybrid ventilation system design, dimensioning, energy performance assessment and implementation of these systems in relation to indoor air quality. This technical specification is applicable to non-residential. The specification is applicable to natural and hybrid ventilation -systems and strategies, encompassing only the natural part of hybrid ventilation systems. For information on mechanical ventilation and the mechanical part of hybrid ventilation systems in nonresidential buildings see EN 16798-3:2017. For performance of ventilation systems in residential buildings see EN 15665:2009 and CEN/TR 14788:2005. Ventilative cooling (cooling of indoor spaces using natural or mechanical ventilation strategies) and ventilation aspects of combined systems (ventilation with heating and/or cooling) are not covered by this Technical specification. For ventilative cooling see the Technical specification on “ventilative cooling systems”.