The performance of the passive perfluorocarbon method.

The use of passive perfluorocarbon technique for air flow measurements has been developed and tested. The building and testing of the system took approximately one year. The reproducibility of the analysis was tested during the period. The results show that the relative standard deviation of the analysis for parallel samples is less than 7 % for each tracer in most of the cases. A drift of calibration was noticed, but it can be allowed for by using reference samples with known amounts of tracers. The accuracy of the method was tested in controlled laboratory conditions. The results reveal some rather high differences from the reference, though the results are distributed evenly on both sides of the zero line. With few exceptions, the inaccuracy of the PFT-method can be estimated to be approximately +- 20 %, when PMCP or PMCH are used. For PDCH the inaccuracy is somewhat higher. Improving the calibration procedure and allowing for the drift of calibration should improve the accuracy of the method. The test in a duct flow implies that the use of the method should be limited to room flow conditions until further research has been done. The mixing was tested in laboratory and field conditions. The results of the laboratory measurements show that the mixing was good, the relative standard deviation being generally below 10%. No stratification could be found. Field measurements were made in 50 typical Finnish homes. When the interior doors within the zone were kept open during the measurement, the concentration distribution was uniform. The standard deviations of concentration varied from 1% to approximately 25%. The technique is best suited for studies concentrating on the health and comfort of the people living in the house. If the energy use of ventilation is studied, the use of an integrating technique should be limited to cases with little temporal variation. The technique is applicable to large field surveys of ventilation. Anyhow, the complexity of room ventilation limits the number of potential users of the method. It is important to have enough knowledge of room ventilation in order to be able to conduct the measurements properly and to interpret the results correctly.