Improving thermal resistance of lightweight concrete hollow bricks: A numerical optimisation research for a typical masonry unit

Heat loss/gain through the walls accounts for about 30% of the total building energy losses. Bricks are indispensable parts of buildings as a very common masonry wall unit; hence the present work aims at optimising thermal resistance of lightweight concrete hollow bricks through a CFD based numerical research. The optimisation is conducted over a certain number of independent variables such as hollow geometry and design, number of hollow rows across the heat transfer path and hollow depth for natural convection aspects within the hollow enclosure. A reliable CFD software ANSYS FLUENT 18.1 is utilised in the research. The accuracy of the CFD results is justified first through the reference model brick (RMB). Overall heat transfer coefficient (U-value) of RMB is determined to be 0.916 W/m2. K, which is in good accordance with the manufacturer’s data report (0.9 W/m2.K). Following this, parametric research is carried out for various scenarios to optimise the U-value as a function of brick mass. Based on the findings, the maximum improvement is found to be about 53% (U-value 0.43 W/m2. K) through the case of B48 which has an h-ratio of 1 (continuous hollow from top to bottom). Moreover, depending on the increase in h-ratio, it is achieved that the thermal performance of the bricks proportionally increases. The minimum weight of the brick design (B45) is found to be 7.645 kg and the corresponding U-value is obtained as 0.44 W/m2. K.