The measurement of the temperature of window glass exposed to direct solar radiation was studied experimentally under clear sky conditions. Thermocouples of different constructions were mounted on the surface of a 3.18 mm (i/8-inch) window glass panel and their outputs were monitored simultaneously under both direct solar radiation and shaded conditions. The thermocouples used for the experiment were a pair of thin foil type with butt-bonded bare metal junction, a pair of thin foil type encased in thin polymer/glass laminates, and a 40 gauge wire, beaded junction. For the foil types, one from each pair was coated with a highly reflective white paint. Shading was applied after stable output was established, and responses from the step change in irradiation level were recorded. It was found that there can be a 0.2°C to 0.7°C difference in the measured temperature for the glass surface between a bare metal junction and a junction coated with a high reflectivity (in the shortwave spectrum) paint. The difference in indicated temperature between an unpainted laminated junction and a painted junction can be as high as 1.0°C. The radiative properties of the junction’s surface, both in the solar and the infrared spectrum, are shown to have equal effect on the surface temperature measurement.

Units: SI