Evaluating the impact of thermal mass on periodic thermal response of building envelopes

Indoor thermal comfort in naturally ventilated buildings is regulated by the periodic thermal response of building envelopes. The performance of building envelopes is predominantly appraised through time-domain analysis in terms of thermal lag and damping. This study presents the performance appraisal of building envelopes using both time- and frequency-domain analysis. For this, naturally ventilated buildings of three different envelope types – Low-Mass Concrete Block Masonry (LCBM), Conventional Brick Masonry (CBM) and Traditional High-Mass Brick Masonry (THBM) – were evaluated through real-time field measurements. Outdoor and indoor air temperatures, surface temperatures and heat fluxes were recorded during summer and winter seasons. Fast Fourier Transformation (FFT) was applied to identify the dominant periodic component and quantify cyclic heat transfer dynamics. The results indicate that LCBM provides the greatest attenuation of thermal fluctuations owing to its insulating characteristics, whereas THBM exhibits greater phase delay, demonstrating the beneficial effect of thermal mass in delaying heat transfer. In contrast, CBM exhibits stronger coupling with outdoor thermal excitation. A new frequency-based thermal indicator, Dynamic Thermal Inertia Index (DTII), has been developed and validated. The study highlights the importance of integrating both temporal and spectral analysis for comprehensive assessment of dynamic thermal behaviour.