Sensitivity Analysis of the Uncertainty of the Heat-Flux Method for In-Situ Thermal Conductance Assessment in Glazed Façades

The discrepancy between design-stage predictions and actual building energy performance, known as the “performance gap,” poses a barrier to achieving energy efficiency goals, especially in modern buildings with high-performance envelopes and complex façades. Characterization of façade elements, both on site and in laboratory facilities, can help ensure envelope quality and mitigate this gap. Although glazed envelopes are increasingly used in contemporary architecture, current regulations lack standardized procedures for experimental heat transfer assessment in buildings. This paper explores how existing standards for heat flux measurements in opaque envelopes could be adapted to transparent façades. A detailed uncertainty analysis is provided to define measurement conditions that ensure accurate conductance results. A sensitivity analysis—based on both analytical error propagation and Monte Carlo simulations—identifies minimum sensor precision, temperature gradients, and test durations needed for reliable in situ assessments. Results show that uncertainty is mainly driven by small temperature gradients and systematic sensor errors. Measurements taken over six hours with a minimum 5 K gradient yield acceptable uncertainty. The proposed framework supports the development of rigorous experimental protocols for assessing the conductance of transparent façade elements, accounting for real-world conditions and measurement limitations.