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Heat transfer characteristics of building elements must be known to evaluate energy losses through a building envelope. Laboratory tests of walls under dynamic temperature conditions provide data that can be used to determine thermal properties. Dynamic testing is particularly important for massive envelope components that store as well as transmit heat.
A block-brick cavity wall was tested in the calibrated hot box facility at the Construction Technology Laboratories, a division of the Portland Cement Association. The wall consisted of 100-mm (4-in.) clay brick on the exterior face, a 70-mm (24-in.) cavity, 150-mm (6-in.) concrete block, and 3 mm (⅛ in.) of plaster on the interior face. Metal rectangular ties were used for tying brick and block wythes.
Laboratory tests were performed on the wall with and without expanded perlite fill in the cavity. The wall was subjected to steady-state, transient, and periodically varying temperature conditions. Steady-state results are used to define heat transmission coefficients, such as U and R values. Data obtained during transient and periodic temperature variations are used to define dynamic thermal response of the wall. Dynamic response includes heat storage capacity as well as heat transmission characteristics of the wall assembly. Test data are also used to determine the effects of perlite insulation in the cavity.
The cavity wall construction is similar to that of a test building monitored by the National Bureau of Standards (NBS) in Gaithersburg, Maryland. Two of the dynamic temperature cycles applied to the wall during laboratory tests were derived from actual wall surface temperatures at the NBS test building. Heat flow meter data from the test building are compared with calibrated hot box test results.
Laboratory test results provide a data base for evaluation of building envelope performance where cavity walls are used. The results also provide information on the effectiveness of expanded perlite as a cavity-fill material.
buildings, calibrated hot box, cavity walls, concrete, energy, heat transmission, masonry, thermal resistance, thermal inertia, thermal insulation
Van Geem, MG
Senior research engineer, Construction Technology Laboratories, Portland Cement Association, Skokie, IL