Ventilation effectiveness measurements in selected NZ office buildings.

Office workers continue to complain about air quality problems, and a significant industry has developed to measure pollutants and environmental conditions such as temperatures and humidity. The effectiveness of the ventilation system is often ignored because it is a difficult measurement to carry out and interpret. The results contained in this paper make a start towards understanding the performance of mechanical ventilation in New Zealand office buildings. A common ventilation approach in New Zealand office buildings involves supplying nonrecirculated fresh air to the vicinity of unit air handlers in the plenum. This fresh air is mixed with exhaust air, and directed through ceiling registers to work stations below. Exhaust air returns through ceiling grills directly into the plenum and thence eventually to an in-plenum extract. In these cases some fresh air may be lost directly to the exhaust and the air change effectiveness of the system may fall short of the dilution ventilation description. In this project the local mean age of the air was determined at a matrix of locations in four buildings in both open plan and partitioned working areas and in the plenums. Measurements were made using a pulse tracer approach with sulphur hexafluoride (SFg) and a gas chromatograph with an electron capture detector. The importance of planning the ventilation system around the floor layout has been illustrated by local mean age-of-air results. Air change effective results have shown that within a diverse range of air handling systems, most can be described by the dilution ventilation model.