contaminant

Sandberg and Skaret differentiate between the terms air change efficiency and ventilation effectiveness. Air change efficiency is a measure of how effectively the air present in a room is replaced by fresh air from the ventilation system whereas ventilation effectiveness is a measure of how quickly an air-borne contaminant is removed from the room. The AIVC guide covers ventilation effectiveness and related concepts. It shows the origins of the concepts used, provides proofs of essential formulae, and suggests standard symbols and definitions.

The computer programs published so far have enabled the calculation of airflows at constant temperatures or of air temperatures at constant airflows. The first version of a new microcomputer program has now been developed in which the airflows and temperatures are calculated simultaneously. The time dependency of temperatures, airflows and contaminant concentrations is considered in the calculation method. The source strength of contaminants, outdoor air temperature, wind velocity and direction, convection and radiation loads can all be freely scheduled.

Results of 3-D computational fluid dynamic simulations of the air flows, temperature distribution and contaminant remove efficiencies for typical workstation configurations which include the option for localized supply of outdoor air will be presented. A typical office configuration including desks, partitions, localized heat and contaminant sources will be modelled. The results will be compared to similar simulations the same workstation environment using ceiling supply and return plenum configurations.

A passive tracer gas technique has been used in an experimental study of the distribution of contaminants in a room with displacement ventilation. Humans are simulated by heated metallic bodies and the tracer concentration in the breathing zone (exposure) is shown to be greatly influenced by both the position of the tracer source and the air convection current around the bodies. It is shown that pollutants emitted close to a body are completely and directly transported to the upper mixed zone and not mixed into the lower zone.

The work in this paper contributes to the work in the IEA - Annex 20 "Air Flow Patterns within Buildings" and presents a series of full-scale measurements of the concentration distribution in a room with isothermal mixing ventilation. Vertical profiles of the concentration in the middle of the room have been measured under different conditions. With the contamination source in the middle of the room the vertical profiles were changed radically with an increase of the air change rate from n= 1.5h^-1 to n=6h^-1 due to a change in the flow structure in the room.