A method has been developed to measure real-time airflow in multifamily buildings. This method uses a multi-tracer measurement system (MTMS) and simultaneous measurements of pressure, temperature, and environmental conditions. These measurements are evaluated along with the results of blower door and flowhood fan tests to develop a complete picture of the airflow patterns in multifamily buildings due to temperature differences, wind, and mechanical ventilation.
Six units in an unoccupied three-story multifamily building in Portland, Oregon were tested for a period of eight days during February and March 1992 using this method. The apartments were equipped with timer-controlled ventilation fans that were set to come on at regular two-hour intervals throughout the test period, enabling a thorough evaluation of the effect of various fan conditions on the flow of air from the outside as well as between units.
The average ventilation rate from natural driving forces alone (wind and stack effects) was about 40 m3/h per unit, or 0.22 air changes per hour (ACH). The average ventilation rate during the periods with all ventilation fans running was 75 m3/h (0.41 ACH). There was also a significant amount of inter-apartment airflow, which was dominated by flow from lower units to the unit directly above from temperature-driven stack effects. Operating all exhaust fans together had little effect on the interzone flows; however, operation of a single exhaust fan significantly increased the interzone flow to that apartment from all adjacent units. The percentage of total airflow that was outdoor air was found to be lower for higher units than for lower units.