27 March 1984 Using High-Resolution Hand-Held Radiometers To Measure In-Situ Thermal Resistance
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Abstract
A field study was carried out to investigate the accuracy of using high-resolution radiometers to determine the in situ thermal resistance of building components having conventional residential construction. Two different types of radiometers were used to determine the thermal resistances of the walls of six test buildings located at the National Bureau of Standards. These radiometer thermal resistance measurements were compared to reference thermal resistance values determined from steady-state series resistance predictions, time-averaged heat-flow-sensor measurements, and guarded-hot-box measurements. When measurements were carried out 5 hours after sunset when the outdoor temperature was relatively steady and the heating plant was operated in a typical cyclic fashion, the following results were obtained: for lightweight wood-frame cavity walls, the radiometer procedures were found to distinguish wall thermal resistance 4.4 h.ft2- °F/Btu (0.77 m2•K/W) systematically higher than corresponding reference values. Such a discrimination will per-mit insulated and uninsulated walls to be distinguished. However, in the case of walls having large heat capacity (e.g., masonry and log), thermal storage effects produced large time lags between the outdoor diurnal temperature variation and the heat-flow response at the inside surface. This phenomenon caused radiometer thermal resistances to deviate substantially from corresponding reference values. This study recommends that the ANSI/ASHRAE Standard 101-1981 be modified requiring the heating plant to be operated in a typical cyclic fashion instead of being turned off prior to and during radiometer measurements.
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Douglas M Burch, Douglas M Burch, Donald F Krintz, Donald F Krintz, "Using High-Resolution Hand-Held Radiometers To Measure In-Situ Thermal Resistance", Proc. SPIE 0446, Thermosense VI: Thermal Infrared Sensing for Diagnostics and Control, (27 March 1984); doi: 10.1117/12.939139; https://doi.org/10.1117/12.939139
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