Air change in flats with natural ventilation: measurements and calculations.

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. A comparison has been made between measured air change rates and calculated air change rates using the JK-CIRCUS computer program. The results show that airtightness of wall and windows in older flats is equivalent to an average n50-value of 1.5 air changes/h. n,, is the air change rate at a differential pressure of 50 Pa between interior and exterior. The building regulations specify an n50 air change rate of less than 1.0 air changes/h in new blocks of flats. Calculations using the JK-CIRCUS program show that, for a flat having a natural ventilation system, improving the airtightness of the windows will result in a maximum reduction in air change rate of 0.1 air changes/h for an external wind speed range of 2-8 m/s.