Multiple cell air movement measurements.

The multiple tracer gas technique developed at UMIST has been applied to the measurement of roof-space ventilation rates and house to roof-space air movement, for various types and combinations of roof-space ventilation. It has been shown that ridge tile ventilators, whilst increasing roofspace ventilation rates at low wind speeds, also significantly increase house to roof-space airflows over the whole range of wind speeds. This has implications not only in terms of energy wastage, but, more significantly , in terms of increased moisture rates to the roof-space. Methods of reducing air leakage to the roof-space are briefly discussed. The use of a kitchen extract fan is shown to reduce airflow from downstairs to upstairs to between 10 and 30 m 3/ hr. It is pointed out that in order to be able to gain a better understanding of air movement within the building envelope, it will be necessary to make use of three and four tracer gas measurements.