Using an automated gas chromatograph with electron capture detector
(GC-ECD) detection system, the decay of the tracer gas concentration
at seven locations within the house was monitored sequentially
each minute. The air change rates were calculated as the best fit
slope of the natural logarithm of the SF6 concentration vs. time. The
mean and standard deviation of the air change rates for the seven
monitoring locations were calculated to check the air mixing inside
the house. The relative standard deviations (RSD) for the SF6 concentrations
at the seven monitoring stations were typically smaller than
10%. The averaged air change rates observed during the tests ranged
from 0.15 h−1 to 0.54 h−1 for the hood-off periods and from
0.46 h−1 to 1.65 h−1 for the hood-on periods. The measurement errors
ranged from 8% to 15%, based on combining two independent
measurement uncertainties in quadrature. These two uncertainties
include the uncertainty due to incomplete air mixing plus precision
(4.3% to 6.5%) and calibration drift of the instrument (5%).