Behaviour of ventilated hollow core slabs for improving the energy efficiency of office buildings

Abstract

Ventilated hollow core slabs (VHCSs) have shown to reduce energy requirements in building heating and cooling applications, as they enhance the use of building thermal mass by increasing the contact between the ventilation air and the structure. This thesis aims to contribute towards the accurate modelling of VHCSs for evaluating their thermal performance for building cooling applications under hot climatic conditions. For this purpose, a numerical procedure is developed for the prediction of the thermal performance of VHCS units. A turbulence model suitable for this purpose is identified first by assessing the ability of five different turbulence models to predict the dimensionless velocity and temperature profiles as well as the Nusselt numbers in a horizontal pipe subjected to turbulent mixed convection conditions typical of VHCSs. The Standard k-ε model showed the best performance, and as such, it is adopted to model the thermal performance of a VHCS geometry for which experimental thermal responses are reported in the literature. The numerical predictions of local temperatures within the VHCS agreed well with the experimental measurements, and hence the Standard k-ε model is adopted here for the modelling of VHCSs. The validated numerical approach is firstly applied to evaluate the impact integrating various types of micro-encapsulated phase change materials in VHCSs on their daily thermal performance in terms of the slab’s cooling potential when ventilated at night using naturally cold air under two ideal room temperature conditions. Analysis is also carried out towards quantifying how the ‘inter-interconnections’ of the hollow cores contribute to the thermal behaviour of VHCSs. The geometry is then simplified to represent a segment of a standard VHCS to evaluate the ability of the slab’s geometric parameters and the inclusion of thin metal sheeting on its hollow core and bottom surfaces to improve the slab’s cooling potential in office building applications.