Influence of sampling positions on accuracy of tracer gas measurements in ventilated spaces

Since natural ventilation is a more energy friendly approach to provide effective ventilation, this technique is gaining more interest. The major problem of natural ventilation is lack of an accurate, continuous and online measuring and controlling technique for air change rates, which is crucial for monitoring emissions from buildings and for control of indoor air conditions. A literature review defined available techniques to measure the ventilation rate. The ventilation rate measured with the tracer gas method is compared with an accurate measurement of the ventilation rate in a laboratory test installation. Due to non-perfect mixing, large variations in ventilation rates are present depending on the sampling positions. In a mechanically ventilated test installation with accurate reference method, tracer gas experiments were performed to demonstrate the apparent difficulties. This research outlines the problems which are still apparent with the tracer gas technique. The errors in the ventilation rate for measurements inside the ventilated airspace can rise to 86% of the actual ventilation rate.