Study of Airflow around Occupants Seated in Desks Equipped with Upper and Lower Air Terminal Devices for Slightly Warm Environments

Abstract

This paper will discuss the study of turbulent and mean airflow exiting air terminal devices and surrounding occupants seated in classroom desks for slightly warm environments equipped with personalized ventilation systems with upper and lower air terminal devices. In the turbulent airflow analysis the air root mean square, the air turbulence intensity, and the air velocity fluctuations frequencies are calculated, while in the mean airflow analysis the mean air velocity and temperature, the human body skin temperature, and the thermal comfort indexes are evaluated using a multi-node thermal regulation model for two different airflow rates. In the experimental tests made in a wood chamber a manikin, a ventilated desk, and two interior climate analyzers are used. The fluctuations of air velocity and temperature are measured in the air terminal devices and in 15 human body sections around the manikin, while the mean value of air relative humidity and mean radiant temperature are evaluated inside the experimental chamber. The mean air temperature in the air terminal devices is around 28°C (82.4°F), while the mean radiant temperature in the occupation area, the mean air temperature far from the occupation area, and the internal mean air relative humidity in the occupation area are around 28°C (82.4°F), 28°C (82.4°F), and 50%, respectively. The airflow rate in tests I and II are 25.75 m3/h (15.16 ft3/min) and 48.04 m3/h (28.27 ft3/min), respectively. The mean air velocity, root mean square, and turbulence intensity for test I are 0.59 m/s (1.94 ft/s), 0.13 m/s (0.43 ft/s), and 22.4%, in the upper air terminal device, and 0.9 m/s (2.96 ft/s), 0.15 m/s (0.49 ft/s), and 16.7%, in the lower air terminal device; while, for test II they are 1.72 m/s (5.64 ft/s), 0.16 m/s (0.52 ft/s), and 9.4%, in the upper air terminal device, and 1.06 m/s (3.48 ft/s), 0.16 m/s (0.52 ft/s), and 14.9%, in the lower air terminal device. In test I the mean air velocity and the airflow rate are higher in the lower exit air terminal device than in the upper exit air terminal device; while in test II, the opposite is true. It is also true that the skin temperature is slightly lower in test II than in test I, mainly in human body sections near the air terminal devices, such as the chest, arms, and legs. The occupant in test I conditions is thermally uncomfortable; however, in test II conditions, the obtained results are near the comfort recommendations.