Analysis of airflow in a full-scale room with non-isothermal jet ventilation using PTV techniques

ASHRAE Transactions, Jan, 2007 by Lingying Zhao, Yuanhui Zhang, Xinlei Wang, Gerald L. Riskowski

Study of non-isothermal ventilation was limited because of the complexity of the problem and the lack of proper measurement technologies. Most research used a hot-wire anemometer to measure airflow. Traditional airflow measurement technology, thermal based anemometers, had inherent difficulty in measuring low-speed and non-isothermal airflow. High temperature sensing heads of thermal anemometers cause significant amounts of free convection and need accurate temperature compensation. For the non-isothermal indoor airflow case studies, both low-speed airflow and temperature fluctuation in the flow field causes measurement difficulties. Zhang et al. (1992) concluded a 25% uncertainty for air velocity measurement using a hot-wire anemometer. Furthermore, thermal anemometers can only measure limited locations with no direct airflow direction measurement.

Particle tracking velocimetry (PTV) technologies use particle streak tracking to measure air velocities of an entire flow field simultaneously. This technology is not limited by low-speed airflow and is not significantly affected by the air temperature. Airflow characteristics of non-isothermal ventilation can be measured more accurately using PTV techniques.

Therefore, the objectives of this study were

* to quantify airflow patterns and air velocity distribution in animal buildings under non-isothermal ventilation conditions using PTV technologies for evaluation of numerical models,

* to characterize airflow of non-isothermal ventilation under typical mild weather and winter weather conditions, and

* to analyze strategies for improvement of airflow distribution under winter ventilation conditions.

EXPERIMENTAL DESIGN AND MEASUREMENT

Test Facility

A room ventilation simulator (RVS) (Wu et al. 1990) was used to simulate the ambient environmental conditions. The RVS consists of a 9.1 x 12.2 x 3.6 m (30 x 40 x 12 ft) outer room, which can simulate weather conditions from -25[degrees]C (-13[degrees]F) to 40[degrees]C (104[degrees]F) any time during the year. Humidity in the outer room can be controlled by a humidifier and dehumidifier within a range of 20% to 90%. A full-scale, adjustable testing room having dimensions of 5.5 x 3.7 x 2.4 m (18 x 12 x 8 ft) and equipped with two ventilation plenums with dimensions of 1.1 x 3.7 x 2.4 m (3.6 x 12 x 8 ft) and 0.7 x 3.7 x 2.4 m (2.3 x 12 x 8 ft), respectively, was constructed within the RVS. This served to simulate typical mild weather and winter non-isothermal ventilation under two typical ventilation schemes, crossflow and return flow ventilation (Figure 1). Air inlet and outlet were simulated on two sidewalls. In this study, air inlet refers to room air diffusers where fresh air enters the room and air outlet refers to room exhaust where mixed air was exhausted from the room. One long side wall of the test room is made of glass to permit convenient optical access. The other two side walls contain two glass slits to transmit light. The other walls, floor, and ceiling surfaces are painted with black and nonreflective paint to form a good optical background. The configuration and top view of the testing room was presented in Zhao et al. (1999).