Techniques for measuring the infrared emittance of roof surfaces in situ are not well developed. Roof surfaces are often attached to or are part of a thick layer of asphaltic material with low-thermal conductivity. Standard steady-state techniques for use of portable infrared emissometers cannot be directly applied. This paper documents experience with a portable infrared emissometer using a special transient technique. With it, correction for the non-steady conditions is theoretically possible according to the manufacturer. Calibration of the technique was attempted with four roof coatings exhibiting a range in infrared emittance from 0.39 to 0.85. Values with the transient technique were, on average, 0.052 too high. The technique was applied to 24 coated and 4 uncoated surfaces on thick roof membranes. Results are also presented for infrared emittance of these 28 surfaces estimated from images recorded by an infrared camera. Independently measured surface temperatures were matched by adjusting the emittance of the surface in the camera's post-imaging analysis software. The infrared camera and the portable emissometer results agreed within the ±0.05 uncertainty of either technique if the latter's accuracy correction was ignored.

Authors: Phillip W. Childs; Thomas W. Petrie, Ph.D.; Jerald A. Atchley

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001