English

The reintroduction of toxic gases emitted from roof stacks can significantly affect the quality of the air inside a building. The determination of a safe distance between the sources of pollution and the fresh air intakes is based on a complex exercise that must take into account several wind, physical and topographical factors. Estimates of maximum concentrations as a function of downwind distance from a stack can be obtained using empirical models provided by the American Society of Heating, Refrigerating and Air Conditioning Engineers [ASHRAE, 1997](1).

The control of emissions from open surface tanks is usually perfomed using simple exhaust systems or combined with push (1). In the first case the exhaust entries generate omnidirectional speed fields within the tank, which rapidly reduce efficiency as the distance increased and are recommended for tanks of less them 1 metre in length. In the push-pull systems, a curtain of air sweeps over the surface of the tank and drags emission towards the exhaust causing a jet wall which (2), when well formed, permits high capture efficiency (3).

Large premises, such as airport tenninals or international conference centers, have high ceilings and large floor area. Most of passengers who use these facilities do not stay for a long time as they do in office blocks or residential housings, but occupy the buildings en masse for short periods of times.

In 1998, a program was initiated to develop an innovative backshelf hood system that could achieve a much lower capture and containment (C&C) exhaust rate than traditional backshelf hoods. As part of this effort, an evaluation of the state-of-the-art tools in use in commercial kitchen ventilation in the United States was undertaken. This paper presents the new hood concept KVL, a description of the latest techniques available for determining C&C performance, and comparisons of the KVL new hood concept to other hoods.

A pulse pressurization technique to measure the airtightness of the building envelope is developed. The governing equations are introduced and the procedure for deriving airtightness parameters from the pressure decay curve is shown. Pulse pressurization is supplied using a high-pressure air tank. The pressure decay after pulse pressurization is measured provides the air leakage equation for a test house.

When a person works facing a local exhaust ventilation (LEV) hood, it may be possible to obtain higher concentrations of aerosols in the breathing zone (BZ) than without the hood because recirculating eddies form downstream of the body. These eddies shed periodically in an alternating pattern called vortex shedding, which is thought to be a primary determinant of contaminant transport in and out of the breathing zone (1, 2, 3). Previous computational fluid dynamics (CFD) studies have explored the effect of timedependent airflow on occupational exposure to gaseous contaminants (2, 3).

A great deal of the literature on general ventilation expresses the adequacy of the volumetric flow rate of air in terms of the number of room air changes per hour. Although the concept of air change rate has very little relevance to the control of contaminants as it relates to the size of the room and not to the scale of the problem, the overall amount of air entering and leaving a workplace is of fundamental importance in assessing the quality of the working environment.