An efficient model development and experimental study for the heat transfer in naturally ventilated inclined roofs

Abstract

Roof ventilation is an efficient way to reduce the heat transmission into building interior in summer. In this work, a theoretical model is developed to predict the heat flux transferred through the naturally ventilated inclined roof in a fast and accurate manner. In particular, the thermal resistance due to the coupled radiation and convection in roof cavity is modeled using the circuit transformation theory. Moreover, based on the computational fluid dynamics (CFD) analysis, correlations are proposed for the convective resistances in the naturally ventilated inclined cavity. Laboratory experiments are further carried out to validate the CFD model, and a satisfactory agreement is found between the experimentally measured and numerically simulated airflow velocity and temperature in the cavity. In order to evaluate the accuracy of developed model, the heat flux transferred into building interior is predicted by both the developed model and a full CFD model. A good agreement is achieved between the predictions of the two models. Based on the developed model, parametric studies are conducted to investigate the influences of key roof parameters on the heat flux transferred into building interior. Ranked in order of significance, the influential parameters are the solar reflectance of exterior roof surface, infrared emittance of cavity surface, thermal resistance of lower roof slab, thermal resistance of upper roof slab, roof inclination and cavity spacing.