Preliminary ventilation effectiveness measurements by a pulse tracer method.

Workers in 'white collar' jobs continue to complain about air-quality' problems. Although there is a growing commercial interest in the measurement of gaseous and solid pollutants, there is no information on the effectiveness of New Zealand office ventilation systems. A set of baseline data is necessary to develop an understanding of the effectiveness with which air is provided in office spaces. This paper describes the results of preliminary ventilation effectiveness measurements made in mechanically ventilated spaces using a pulse tracer gas method. Electron-capture tracer-detection equipment was modified to release a single pulse of sulphur hexafluoride (SFg) into the fresh air supply duct and to monitor the concentration increase and decay in a matrix of breathing zone locations. A pulse approach was chosen on the basis of equipment suitability but it was found to have some drawbacks in terms of dependence on calibrations and long data-recording times. The local mean age-of-air was determined at a matrix of locations in the largely un-partitioned zones of two unoccupied spaces of each of two large office buildings. A numerical approach was developed to allow the data acquisition to be truncated at a practical time and the remainder of the integration to infinity to be determined by extrapolation. The paper discusses the practicalities of this approach to measuring air change efficiency and, in the course of discussing the results, makes recommendations for further work.