tracer gas

Over the years there has been significant advance in the development of experimental methods and analysis for the use of tracer gases in the evaluation of ventilation systems. As a rule, these advances have been in the direction of greater complexity and more sophisticated data analysis methods. Most of these advances are difficult for buildings researchers to understand, not to mention the confusion they have created for practitioners.

A small test room has been built which is five times smaller than the so called Annex-20-room. Different kinds of tracers have been used for visualizing of flow patterns. Velocities, concentrations and mass transfer coefficients have been measured. The measuring instrumentation is based on thermal anemometry (hot wire probes) and a special ammonia-mass transfer method, respectively, in order to estimate the heat flux coefficient at the walls.

This investigation is concerned with the determination of velocity pressure loss-factors for HVAC system components using tracer-gas techniques. Experimental work was carried out using an HVAC system and k-factors for various components such as bends, branches, contractions, expansions and orifice were determined. Results were compared with measurements made using a pitot tube and values given in the CIBSE Guide and ASHRAE Handbook. The performance of different types of filters used in HVAC systems was also examined.

Building air flow is directly related to the building energy consumption and indoor air quality. As buildings become increasingly air tight, air flow through building background cracks becomes more important, and can account for up to half of the total building air infiltration. However, background leakage is not well understood, due to the lack of appropriate measurement methods. The multi-fan guarding zone or deduction technique provides a means for testing background leakage distributions, an important parameter for characterising the background leakage.

This paper describes a method for measuring tbe dispersal of airborne contaminants by light-sheet illumination of aerosol tracen and digital image processing techniques. The goals of the research were twofold: to use field-portable and safe equipment to make near-instantaneous measurements of tracer aerosol concentrations over arbitrarily positioned two-dimensional planes of near-mom dimensions; and to carefully define similarity conditions under which aerosol dispersal can be considered an accurate surrogate for passive molecular dispersal.