Field study comparisons of constant concentration and PFT infiltration measurements.

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 field studies include side-by-side measurements of multi-zone air infiltration rates using the CCTG and PFT methods. The results are reported from two tests in an unoccupied singlefamily house and eight tests in an occupied house. Test periods varied from one to three weeks. The measurements from the unoccupied house showed that there were no major discrepancies between the two methods. The PFT measurements in the occupied house were consistantly lower than those by the CCTG method. Warm weather periods with substantial, periodic airing resulted in the PFT method producing underprediction errors greater than 30%. During the cold weather periods when the fluctuation in the infiltration rate was due to weather changes and a small amount of airing, the underprediction error ranged from 5 to 29%.