Air change effectiveness measurements in two modern office buildings

Local age of air and air change effectiveness were determined in two office buildings using tracer gas techniques to study the air applicability of the associated measurement procedures in mechanically ventilated office buildings. Measurement issues examined include the establishment of a uniform tracer gas concentration at the start of the test and the relationship of ventilation system configuration and system operation to the test procedure. Air change effectiveness was determined at locations in the occupied space based on the local age of air at that location and the age of air in the corresponding ventilation system return duct. Values of the air change effectiveness in the occupied space were generally close to one, which is consistent with good mixing of the ventilation air within the occupied space. Deviations from 1.0, on the order of 10%, did occur, but given the limited experience with these measurement procedures in the field it is not clear whether these deviatio11S are significant. These tests provide data on air change effectiveness to supplement the limited database on mechanically ventilated office buildings in the U.S. In addition, the experience obtained with the measurement procedures will assist in the development of a standardized approach to measuring air change effectiveness in the  field.