Enhancement of heat transfer in office buildings during night cooling - CFD study and reduced scale experimentation

Abstract

Abstract Most office buildings are designed to be ventilated and cooled using mechanical systems. In a temperate climate, when the outdoor temperatures are favorable, e.g. at night, passive ventilation and cooling techniques can be used to reduce energy consumption. Building’s thermal mass represents a way to accomplish that goal due to their ability to retain and dissipate heat. However, the portion of exposed elements in modern constructions is kept to a minimum. There are decorative components, like the suspended ceiling, that represent an insulation between the internal occupation zone and the thermal elements, preventing the desired thermal exchange. In this work, an innovative solution that optimizes the night cooling phenomena is presented. It is concerned with the use of the plenum formed by the space between the slab and the suspended ceiling for cooling purposes. Computational Fluid Dynamics (CFD) simulations were performed and the predictions validated by the experimental results. The tests were carried on a reduced scale model based on dimensional analysis and similitude criteria. The suspended ceilings used in the experiments allow the outside air to cool the slab, therefore promot ing an increase of the heat exchanged between the structural elements of the building and the zone that needs to be cooled. The results indicate that the increased amount of exposed slab area contributes to lower the day peak indoor temperatures.