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 Gamma = 6.67 filled with water (Pr = 3.27, Ra = 2.12 x 10(11)). The cavity models the integrated solar collector-storage element installed on an advanced facade. 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 degrees C, in the estimation of heat transfer, stratification, and flow configuration. (C) 2013 Elsevier Ltd. All rights reserved.