Analysis of Capture and Containment Efficiency of a Ventilated Ceiling

The efficiency of an exhaust system is especially important in a kitchen environment in which the exhaust is located at ceiling level. The capture efficiency of the total system must be guaranteed so that the spread of impurities throughout the kitchen is prevented. A capture efficiency model is derived and it is used to estimate the efficiency of a ventilated ceiling. This paper demonstrates that a simple equation that includes the average contaminant level in the occupied zone and the exhaust concentration could be a suitable platform for capture efficiency analysis in both measurements and simulations. With a ceiling height of 2.3 m, the capture and containment efficiency can be as high as 85 - 90 %; with a 2.6 m ceiling height it is 80 - 85 %. These values are quite reasonable compared with the capture efficiency of a default hood in the German code of practice (VDI, 1984).