ABSTRACT
Computer simulation techniques have become reasonably reliable in evaluating the thermal performance of building envelope components such as fenestration systems. However, the simplified constant surface film coefficients normally yield discrepancies in the prediction of surface temperatures when compared to measured results, especially at edge-of-glass area. Within the context of a comprehensive study on the overall thermal performance of metal curtain walls, an experimental study was carried out to determine the local convection film coefficients. A customized large-scale computer-controlled 3-dimensional traverse system was built to measure the air velocity and air temperature within the boundary layer of a curtain wall specimen. The local convection film coefficients were determined from the linear approximation of air temperatures measured within the inner region of the boundary layer. The air velocity increases and the convection heat transfer coefficients decreases when the cold air flows down the glass surface. The measured results indicated that natural convection prevails along the interior glazing surface of the test specimen. When the airflow approaches the frame, the convection coefficient drops significantly from 2.04 to about 0.17 W/m2 · Kat 12.7 mm from the bottom sightline. When the outdoor temperature is lowered, the greater temperature difference between glass surface and room air induces stronger natural convection and results in higher convection film coefficients. The experimentally determined local convection film coefficients are applied in 2-D FRAME simulations to evaluate the reliability of simulation programs in predicting the condensation potentials for curtain walls.
