Analysis of coupled natural convection-conduction effects on the heat transport through hollow building blocks

In the present study, the coupled convective and conduction heat transport mode in a common hollow building brick is studied. Heat transfer rate through building bricks is examined in order to asses the suitable brick insulation configuration. Three different configurations for building bricks are considered. The first is a typical brick of three identical hollow cells (air cavities), the second is obtained by filling these cells with ordinary polystyrene bars and the third is obtained by using hollow polystyrene bars. The geometry of the first and third configurations considered in this study is simply a solid closed frame surrounding square cavities filled with air. The second configuration is a solid composite slab. Solving Navier-Stocks equations assuming Boussinesq approximation, using the commercial Fluent software, showed that the cellular air motion inside blocks' cavities contributes significantly to the heat loads. Insertion of polystyrene bars reduced the heat rate by a maximum of 36%. Using a hollow polystyrene bars reduces the heat rate by 6% only due to the air motion inside cells. In order to estimate the heat rate during a day, the air temperature and solar insolation data of a typical summer day for the city of Jeddah, Saudi Arab, are used. A quazi-steady state approach is implemented to estimate an equivalent facade surface temperature, which is then used as boundary for solving the simulation model. Such an approach showed that the effective overall daily heat rate reduction using polystyrene filled bricks to be 25%. (c) 2005 Elsevier B.V. All rights reserved.