The present work assesses the limits of the Oberbeck–Boussinesq (OB) approximation for the resolution of turbulent fluid flow and heat transfer inside a tall differentially heated cavity of aspect ratio G = 6.67 filled with water (Pr = 3.27, Ra = 2.12e11). The cavity models the integrated solar collector-storage element installed on an advanced façade. The implications of the Oberbeck–Boussinesq approximation is submitted to investigation by means of direct numerical simulations (DNS) carried out for a wide range of temperature differences. Non-Oberbeck–Boussinesq (NOB) effects are found to be relevant, especially beyond the temperature difference of 30 °C, in the estimation of heat transfer, stratification, and flow configuration.

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