BA-92-10-3 -- Uncertainties in the Evaluation of Window SHGC and U-Values Measured Using an Indoor Solar Simulator Facility PDF

To determine the U-value and solar heat gain coefficient (SHGC) of window systems, the Solar Calorimetry Laboratory (SCL) has developed a unique laboratory test method based on the use of solar simulator test facility. The SCL procedure includes two distinct parts - the experimental measurement of the thermal performance, n, of window samples and the computation of their thermal characteristics, SHGC and U-value, from the performance test results. To evaluate the possible sources of error related to this test method and their magnitude, an uncertainty analysis was conducted. The uncertainties on the SHGC and U-values were computed based on estimates of the uncertainties in the experimental measurements. To assess the effects of the uncertainty in these measurements on the SHGC, a sensitivity analysis was conducted, and the dominant terms in the uncertainty equation were identified. To illustrate the range of typical uncertainties, three commercially available windows were considered - a single-glazed low-performance (LP) window, a typical double-glazed unit, and a high-performance (HP) window. Results show that, in the case of HP windows, the U-value uncertainty is approximately 8%, which corresponds to 3.5 W/m2 of heat flux under ASHRAE winter design conditions.

KEYWORDS: calculating, windows, transmittance, measuring, solar heat gain, laboratory testing, heat flow, performance, thermal properties, accuracy, double glazing, comparing