Continuous Measurements of Air Change Rates in an Occupied House for 1 Year: The Effect of Temperature, Wind, Fans and Windows.
Continuous Measurements of Air Change Rates in an
Occupied House for 1 Year: The Effect of Temperature,
Wind, Fans and Windows.
(757 K)
Wallace, L. A.; Emmerich, S. J.; Howard-Reed, C.
Journal of Exposure Analysis and Environmental
Epidemiology, Vol. 12, No. 4, 296-306, July 2002.
Keywords:
residential buildings; indoor air quality; temperature
effects; wind effects; fans; windows; infiltration;
tracer gas; ventilation; air change rates; quality
control; meteorology; statistics; wind direction; wind
velocity; regression rate; floors
Abstract:
A year-long investigation of air change rates in an
occupied house was undertaken to establish the effects
of temperature, wind velocity, use of exhaust fans, and
window-opening behavior. Air change rates were
calculated by periodically injecting a tracer gas (SF6)
into the return air duct and measuring the concentration
in 10 indoor locations sequentially every minute by a
gas chromatograph equipped with an electron capture
detector. Temperatures were also measured outdoors and
in the 10 indoor locations. Relative humidity (RH) was
measured outdoors and in five indoor locations every 5
min. Wind speed and direction in the horizontal plane
were measured using a portable meteorological station
mounted on the rooftop. Use of the thermostat-controlled
attic fan was recorded automatically. Indoor
temperatures increased from 21DGC in winter to 27DGC in
summer. Indoor RH increased from 20% to 70% in the same
time period. Windows were open only a few percent of the
time in winter but more than half the time in summer.
About 4600 hour-long average air change rates were
calculated from the measured tracer gas decay rates. The
mean (SD) rate was 0.65 (0.56) h-1. Tracer gas decay
rates in different rooms were very similar, ranging only
from 0.62 to 0.67 h-1, suggesting that conditions were
well mixed throughout the year. The strongest influence
on air change rates was opening windows, which could
increase the rate to as much as 2 h-1 for extended
periods, and up to 3 h-1 for short periods of a few
hours. The use of the attic fan also increased air
change rates by amounts up to 1 h-1. Use of the furnace
fan had no effect on air change rates. Although a clear
effect of indoor-outdoor temperature difference could be
discerned, its magnitude was relatively small, with a
very large temperature difference of 30DGC (54DGF)
accounting for an increase in the air change rate of
about 0.6 h-1. Wind speed and direction were found to
have very little influence on air change rates at this
house.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899