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).
This publication is intended to provide guidance on the nature and characteristics of pollutants in the outdoor air and how this impacts on indoor air quality. In particular, the document summarises the available knowledge to provide designers with information that will help in locating their ventilation inlets to minimise cross contamination from a range of polluting sources.
Traditional air-handling unit (AHU) control systems link the position of the exhaust air damper, recirculation air damper, and outdoor air damper. Tests at the National Institute of Standards and Technology (NIST) on a variable-air-volume (VAV) AHU have shown that air can enter the AHU through the exhaust air damper. This can negatively impact indoor air quality if the exhaust air duct is located near a pollution source. This paper presents a new control system for variable air volume AHU's that use volume matching to control the return fan.