Indoor air quality in buildings must be guaranteed for the health and comfort of the occupants. In order to assess the ventilation strategy of a considered room, the parameter of the air change efficiency ( εa ) can be used. The objective of this work is to provide designers with a graphical tool for a reliable estimate of the value of εa of a room. The temperature gradient between the outdoor air supply and the indoor air is so low that the ventilation flow can be assumed as isothermal when high-efficiency heat recovery systems are used. By means of charts, the optimal location of the openings for a better εa can be determined during the design process, in order to subsequently apply them. It is concluded that it is very important to consider the εa in the case of openings located in facing walls given that its range varies between 40% and 65%. In contrast, its use can be obviated in the case of openings located in non-facing walls, as the value of εa obtained is close to 50%; this means a perfect mixing air flow pattern, which is the reference value for the estimation of the indoor air quality (IAQ) in the different national regulations.
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