tracer gas

In the frame of the European PASCOOL project, several experiments regarding single sided ventilation were carried out at BBRI in the outdoor PASSYS test cel. The test room of 30 m³ has a vertical window of about 1 m². During a first measurement period, an open cold box, which allows one to control the vertical wind speed, was placed in front of this window. During a second measurement period, the window was directly exposed to "real wind". The air change rates were evaluated by using two different methods: a tracer gas technique and the heat balance approach.

The UK factory stock is predominantly naturally ventilated. Measurements performed in this class of building have indicated that air infiltration rates in factories are usually excessive in relation to occupants' requirements for health and safety, resulting in an energy penalty. As part of a project to investigate construction options for energy efficient industrial buildings, three factories of different cladding construction types were designed and then built at Aberarnan, South Wales.

lnadequate ventilation is often cited as the cause of unhealthy air quality within office buildings, whilst excessive ventilation is similarly assumed to be the cause of discomfort and energy waste. However, the reality is that very little data is available to assess the significance of these problems on any large scale. The perfuorocarbon tracer (PFT) technique offers the potential for overcoming the problems of applying conventional tracer gas techniques to large or multi-roomed buildings.

The paper describes the application of a new tracer gas technique for studying ventilation. The technique is called the homogeneous injection technique, since it relies on the continuous injection of tracer gas in all parts of a zone-divided ventilated system, with tracer injection rates, which are strictly proportional to the zone volumes. The steady state concentrations of tracer gas in the different zones are proportional to the local mean ages of air.

Some radon mitigation systems draw air with a high radon concentration from under the basement floors of houses and exhaust it outdoors. The objective of this project was to measure the reentry rates of radon released at roof level and at ground level near a house to determine whether exhaust above the roof is necessary. This was done by using a portable mockup of a radon mitigation system exhaust, with sulfur hexafluoride (SF6) as a tracer gas.

This work examines the application of the constant-injection and pulse-injection tracer gas techniques for measurement of airflow in rectangular ducts. Experiments were carried out in ducts with aspect ratios of 1,2, and 4. Tracer gas measurements were generally similar to measurements made using a pitot tube. Relationships for the friction-factor and hydrodynamic entrance length are presented for Reynolds number between 73,300 and 395,000.

The three common tracer injection strategies all proved reliable in a test chamber under complete mixing conditions. For field studies of air flow patterns in large rooms the step-up method or the pulse method is recommended to escape the initial complete mixing condition of the decay method.

Local age of air and air change effectiveness were determined in two office buildings using tracer gas techniques to study the air applicability of the associated measurement procedures in mechanically ventilated office buildings. Measurement issues examined include the establishment of a uniform tracer gas concentration at the start of the test and the relationship of ventilation system configuration and system operation to the test procedure.