Ventilation effectiveness comparison between extract ventilation and balanced ventilation in a scale model

The differences between extract ventilation and balanced ventilation are subject of many discussions in sales markets where both solutions have their share. Often, the differences are marked in terms of energy, because balanced ventilation is normally accompanied by heat recovery. But there is another difference in terms of the ventilation effectiveness of the system.This document reports experiments in a scale model of a house showing the difference between extract ventilation and balanced ventilation in ventilation effectiveness, and therefore in achievable indoor air quality. The ventilation effectiveness is measured in terms of the cleaning time, i.e. the time it takes for smoke to be completely extracted from individual rooms.The results indicate that for an undisturbed (design) system the cleaning time for individual rooms is independent on the ventilation system. But in disturbed situations like an open window or wind pressure on the building, the cleaning time is different for various individual rooms, and dependent on the ventilation system.The conclusion is that for balanced ventilation, the ventilation effectiveness is not reduced by occupant behavior or wind conditions. On the other hand, for extract ventilation the ventilation effectiveness is lower in particular individual rooms as a result of these disturbances.