| 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 measured 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 was measured outdoors and in five indoor locations every 5 min. Wind speed and direction in the horizontal plane was measured using a portable meteorological station mounted on the rooftop. Use of the thermostat-controlled attic fan was recorded automatically.Indoor temperatures increased from 21 degrees C in winter to 27 degrees C in summer. Indoor relative humidities 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 4,600 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 h-1 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 30 degrees C (54 degrees F) 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 effect on air change rates at this house.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 measured 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 was measured outdoors and in five indoor locations every 5 min. Wind speed and direction in the horizontal plane was measured using a portable meteorological station mounted on the rooftop. Use of the thermostat-controlled attic fan was recorded automatically.Indoor temperatures increased from 21 degrees C in winter to 27 degrees C in summer. Indoor relative humidities 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 4,600 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 h-1 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 30 degrees C (54 degrees F) accountin |
