Ventilation effectiveness measurements in real time using continuous uniform tracer emission.

Trouble shooting air distribution problems in mechanically ventilated offices often has to be carriedout in limited "after hours" periods. The method of applying a pulse of tracer to the fresh air supplyhas been found to be too time consuming to map the local mean age of air over complex floor plans.In response an automated gas chromatograph has been developed to make air change efficiencymeasurements in real time using the method of homogeneous emission. The equipment described heremeasure SF6 concentrations at a large number of locations while the tracer is released constantly andas uniformly as possible within the ventilated space. The entire process (including analysing theoutput from the gas chromatograph) is controlled with a purpose designed computer programme inVisual Basic.Ventilation efficiency measurements have been completed on twelve separate floors in eightmechanically ventilated buildings. The homogeneous emission method and the pulse method wereused and were shown to give the same result in one building and to indicate that the dilutionventilation model most closely describes the ability of common ventilation configurations to deal withpollutants in the breathing zones. Some spatial differences in ventilation performance were evident. Itwas possible to explain many of these in terms of the distribution of ventilation supply and extractpoints in relation to internal partitioning.