Abstract
The local ventilation efficiency of a mechanical ventilation system may in general terms be defined as ‘providing air in those parts of a room where it is required’. In this paper different definitions of the local efficiency and methods for measuring it are discussed. Finally, results from measurements of the ventilation efficiency are presented. These indicate that, in some cases, only a minor proportion of the ventilation air flow is utilised in the occupied zone. Furthermore it is demonstrated that it is normally not advisable to use the slope of the tracer gas curves in a linear logarithmic plot as a measure of the ‘local ventilation rate’. The slopes will normally, after a certain period of time has elapsed, become equal. Then they reflect only the overall ventilation rate and not local differences.
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