Proposal for a Simplified CFD Procedure for Obtaining Patterns of the Age of Air in Outdoor Spaces for the Natural Ventilation of Buildings

Built urban environments modify the air quality of the natural ventilation processes in buildings. The experimental assessment of outdoor air change (OACH) processes is complex due to the air volumes involved. The quality of the OACH can be analysed through the ventilation efficiency concept, which has been extensively studied in order to characterize the ventilation of indoor spaces. Ventilation efficiency through the age-of-the-air concept assesses the air-change capacity of a certain space. A procedure formulation for obtaining an adequate control domain (CD) to evaluate outdoor air change efficiency (OACE) is proposed. A methodology in two phases is presented: first, an evaluation stage, in which the outdoor air behaviour patterns are studied; then, a second phase where an ideal control domain (ICD) is obtained in order to comparatively assess several cases in similar urban environments. The outcomes determine a proposed ICD for evaluating the design of efficiently ventilated buildings in open urban built environments. The methodology of validation proposed simplifies the assessment of the building shape and its impact on the quality of the OACH by the OACE. The suggested ICD has dimensions of L = 5H; D = 3H; and T = 2H. ICD enables the representation of the air behaviour and fulfils the imposed requirements to evaluate efficiency with a mean accuracy lower than 0.6%