In-situ measurement of thermal transmittance on facade components and its implications on building cooling loads in hot-humid climate

Defining accurate thermal properties for building components is crucial in predicting energy consumption in new designs and retrofit strategies. This study presents an in-situ investigation of the thermal transmittance (U-value) of building façade components and evaluates their implications for cooling energy demand in a hot-humid climate. Addressing the gap in tropical building studies that often rely on theoretical U-values, the research added focuses on aluminium-framed window assemblies, with specific measurements taken on the bottom sill and meeting stile. The field measurement was done using the Heat Flow Meter (HFM) method in accordance with ISO 9869-1:2014. Field measurements were conducted on an air-conditioned building façade in Depok, Indonesia, under a temperature gradient exceeding 10 °C. The in-situ U-values revealed significantly higher heat transfer in aluminium frames (up to 10.48 W/m²·K) compared to the wall (3.76 W/m²·K). The measured U-Value is still in accordance with the building database, however, significantly lower compared to the Indonesian National Standard. Cooling energy usage predictions were done by comparing two simulation scenarios of U-value from the in-situ measurement and three scenarios from theoretical U-values. The results showed that by using theoretical U-values for single and double glazing could overestimate the annual cooling loads by up to 45.9 %. Overestimating cooling loads due to inaccurate U-values can lead to inefficient material use and higher construction costs. These findings underscore the importance of integrating localised, in-situ data into simulation models to ensure more accurate energy performance predictions.