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This paper presents a state-of-the-art review of the thermal behaviour of the diffusive building envelope, through which slow and nearly uniform air flows. With the airflow through the envelope, it will exchange heat with solid parts, thus changing the thermal performance of the envelope. The fundamental heat exchange in the air cavities of the envelope is first investigated. Next, the study focuses on the airflow and heat transfer in the porous building materials, in order to assess airflow impact on the thermal performance of the dynamic insulation. The influence of moisture, especially possible phase change, is also discussed. The investigation shows that heat exchange in the envelope will have an impact on the energy consumption of the building. Meanwhile, much work is needed concerning engineering implementation; for example, to provide the suitable analytical methods and to avoid possible condensation.

Highly-glazed spaces are attractive in many ways (solar heating, aesthetics, etc.), however, their thermal behaviour remains difficult to predict. In such spaces, the assumptions or methods generally used in building thermal simulation tools — e.g. homogeneous air temperature in the room, simplified calculations of radiative heat transfer between walls, absence of airflow modelling within the room — do not seem appropriate. We have developed a new model (AIRGLAZE) to improve the prediction of the thermal behaviour of large highly-glazed spaces. It consists of an envelope module to calculate conductive and radiative heat transfer in the building envelope. It is coupled with a zonal airflow model to predict air motion within the room. Particular attention is paid to sun patch modelling and the internal distribution of shortwave and longwave radiation within the building; direct retransmission, reflection to the outside, and transmission to other zones of the building are taken into account. The results of AIRGLAZE are compared with measurement data from two experimental test cells: the IEA Annex 26 experimental atrium, and a test cell at ENTPE. Compared to the one-air-node approach, the zonal method significantly reduces the mean discrepancy with measurement data during stratified conditions (from 3.9°C down to 0.4°C for the Annex 26 atrium). In general, experimental and numerical results tally well in both cases.

This paper is dedicated to the numerical study of natural ventilation in a room through a large external opening using the CFD code Fluent. Bidimensional numerical simulations are performed for wind speeds up to 5.55 m·s−1 (20 km·h−1). We propose a two-step solution procedure with grid refinement. When combined with appropriate thermal boundary conditions, this technique appears very efficient at limiting local convergence problems. Through an analysis of the flow pattern in the cavity, we qualitatively explain those results and define a critical Archimedes number. Calculated air change rates are compared to values deduced from empirical correlations of the literature. Agreement is in general poor, which can be explained by the differences between the conditions of our simulations and those of the experiments that lead to those correlations. However, from our simulations, we derived very clear correlations between the air change coefficient and the Archimedes number. In the last part, our results are compared with published data from two experiments. Agreement, in terms of air change coefficient, is within 26 % on average with the Porto test cell data which is closest to our numerical conditions. One should be careful about the transposition of our results to different ventilation scenarios.