Local exhaust ventilation systems are normally the most cost efficient method for controlling air pollutants and excessive heat. For many manual operations, capturing pollutants at or near their source is the only way to insure compliance with threshold limit values in the workers breathing zone. Local exhaust ventilation optimize ventilation airflow thus optimizing system costs especially where recirculation is not used.
ANSI/ASHRAE 110-1995, Method of Testing Performance of Laboratory Fume Hoods (ASHRAE 1995) yields quantitative data about fume hood containment and can be used in a classical total quality management (TQM) approach to process improvement. This involves measuring process indicators, analyzing probable causes of poor performance, implementing changes to the process, and again measuring the indicators to determine the efficacy of the changes implemented.
Computer programs for the calculation of non-isothermal air flow in rooms have been developed in the last years as reasonable precise and effective tools for non-conventional and difficult tasks in air conditioning technology. This paper shows possibilities based on the additional numerical calculation of the convective mass transfer. Several simple examples describe the influence of the hood and the room air flow on the convective heat and mass transfer. Based on this knowledge the optimal arrangement of the hoods, the air outlets and the air inlets can be determined.
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