Measurement methods based upon multiple tracer gas techniques have become an established branch of the study of air infiltration and interzonal air movements. Three general groups of techniques have emerged, namely constant concentration, constant emission, and decay. Of the decay type group of techniques, several methods of deriving airflows from measured concentration/time curves have been suggested.
Displacement flow systems are becoming popular, especially in Scandinavia, for comfort ventilation. In these systems air is supplied near the floor at low velocity; the temperature of the supply air is a few degrees below that of the air in the room. The supply air is heated by persons and/or machinery in the room. Turbulent plumes are formed above these heat sources.
The air change rate in existing, older blocks of flats having natural ventilation has been measured by the tracer gas method. Measurements were made in the buildings in as-found condition. The average air infiltration rate was 0.26 air changes/h (with the ventilation ducs closed), with an overall ventilation rate of 0.47 air changes/h. The average overall ventilation rate is very close to that recommended on the basis of health requirements, although values both above and below this are encountered in many flats.
Login