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ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

International Heat Transfer Conference 13
August, 13-18, 2006, Sydney, Australia

EXPERIMENTAL MEASUREMENTS OF BUOYANCY-DRIVEN CONVECTIVE HEAT TRANSFER INDUCED BY SUN PATCHES WITHIN A PASSIVE SOLAR TEST CELL

Get access (open in a dialog) DOI: 10.1615/IHTC13.p6.350
12 pages

Abstract

Experimental measurements are presented of the convective heat transfer within a full-sized, passive solar test cell obtained using so-called ‘Mayer ladders’. Buoyancy-driven air movement was induced by the ingress of solar radiation through the south-facing, glazed facade of the thermally light-weight test cell subject to external climatic variations typical of those experienced on dry, sunny days in the northern European winter. The incoming daylight created a sun patch, or ‘spot’, that migrated across the floor, back wall and sides of the test cell. Earlier, companion studies found (using both computations and flowfield measurements) that the resulting, complex room flow contained vortices of various sizes, and near-wall shear layers. The induced buoyant plume impinged on the ceiling, where it spread out, before descending back to the floor. In the present study, point measurements obtained via Mayer ladders are shown to yield convective heat transfer data to acceptable levels of uncertainty. This data was compared with the extended correlating equations for buoyancy-driven convection over isolated surfaces across the range of laminar, transitional and turbulent flow. Good agreement was found for the sun patch projected onto the test cell floor, in contrast to the assumption that convection occurs over the whole floor - as is typically presumed for modern building energy simulation programs. Ignoring the effect of buoyancy-driven convection from the sun patch is likely to have significant implications on building thermal models. Not only is the heat transfer coefficient higher than for the surrounding surfaces, but the convective heat flux is also greater due to the larger surface to air temperatures. The results therefore provide insights into the convective heat exchange within, and the thermal design requirements for, passive solar buildings.