A constant concentration tracer gas (CCTG) measuring system needs a control algorithm to calculate, at each sampling time, the required tracer gas injection rate to keep the gas concentration at a target level. A new control algorithm is presented here in full detail. Practical considerations concerning modifications to take into account the physical limitations of the CCTG system and the computing of the optimal control parameters are also presented.
The technique of tracer gas measurement has during recent years tended towards increasingly complicated measuring methods. The new measuring techniques are essential in order to procure more information about the circulation of air through buildings, or in order to perform more accurate measurements in large and complex buildings. The measuring method by means of "constant concentration of tracer-gas", which has been applied at Technological Institute for about 7 years, has proved to be a very accurate measuring method for both small and very large buildings.
The accuracy of tracer gas measurements of building air infiltration rates has been a widely discussed topic. One question that has often come up at past AIVC conferences is the ability of passive methods, such as the Perfluorocarbon Tracer (PFT) method, to accurately measure fluctuation air flow rates. A series of field studies is being conducted to compare the air infiltration measurements of the constant concentration tracer gas (CCTG) and PFT methods and provide recommendations for their proper implementation in the field.
The constant concentration tracer gas (CCTG) technique is typically used to measure air infiltration rates in mulitzone buildings. The measurements are performed by injecting metered amounts of a tracer gas into each zone so as to keep all the zones at a target concentration. One drawback to this method is that no information is gained about the level of interzone flow rates in the building. Modified constant concentration techiques are described which allow selected infiltration and interzone air flow rates to be estimated.
A constant concentration tracer gas system was designed and constructed to continuously measure the air infiltration rate in as many as ten zones of a building. The portable, microcomputer controlled system injects a metered amount of tracer
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