Deviation of draught rate in a simplified office environment with diffuse ceiling ventilation

Deviation of draught rate was investigated in an occupied zone of double office room with 1-hour measurement period at 10 Hz sampling rate. The objective of the study was to examine a reliability of 3-min measurement period while determining local thermal discomfort due to draught as specified in the standard ISO 7726. Therefore, the draught rate model defined by the standard ISO 7730 was investigated. The airflow measurement was carried out in a test chamber of 5.5 m length, 3.8 m width and 3.2 m height by using the omnidirectional low velocity thermal anemometers. The target indoor air temperature was 26°C. The studied heat load strength levels were 40, 57 and 80 W/floor-m2. The desired cooling power was provided by introducing the supply airflow rates of 3.6, 5.2 and 7.3 l/s,floor-m2 through a diffuse ceiling panels, respectively. The supplied air temperature was 17°C. Two opposite workstations were located near the heated windows at a perimeter area. The other side of the room was an open area. Both workstations had a heated sedentary test dummy, a laptop and a monitor. The results indicate that a measuring period of dataset records should be extended in order to improve a measured sample while assessing local draught rate conditions. This is because buoyancy flows and air distribution flows have a considerable effect on the measured draught rate level, although the boundary conditions of room are controlled and stable. The importance of work lies in showing a temporal and spatial deviation and how long measurement periods are recommended to diminish the deviations to insignificant level. The study suggests 10-min measurement period for the local assessment of probable percentage of dissatisfied on draught.