Convective heat transfer coefficients in cavities: a review of correlations for modelling double skin facades

Convection is an essential mechanism for heat transfer in double skin façades, which are building envelope systems characterised by a (naturally or mechanically) ventilated cavity. The study of this mechanism in the built environment is already challenging when convection is analysed at the room level, where each surface can be analysed independently. The application of the same approach to the study of the convective heat transfer in the double-skin façade cavity, however, is questionable given the potentially different range of dimensionless numbers characteristic for DSF performance. These differences are often due to dimensional aspects (cavities of small enclosed space), asymmetrical boundary conditions, a varying range of velocities, etc., which must be taken into account when choosing the proper correlation for the surfaces facing the ventilated gap of a double skin façade, i.e. glazing and shading system.

This paper gathers and analyses the correlations available in the literature, with a particular focus on studies related to the asymmetrically-heated channels, for different typologies and flow regimes. The set of correlations presented can be applied to the airflow under different regimes (natural convection, mixed ventilation and forced convection), different cavity dimensions (narrow or wide cavity), and that takes into account the presence (or the absence) of the shading device inside of the cavity.