Finite-volume thermal analysis of building roofs under two-dimensional periodic conditions

A finite-volume implicit procedure is presented for the determination of the thermal performance of two-dimensional composite building roof elements. The elements are subjected to steady periodic change in ambient temperature, solar radiation and non-linear radiation exchange on the outside surface and to a constant indoor-air-temperature on the inside surface. The solar radiation is calculated by the ASHRAE clear-sky model. TEACH-C computer program is utilized to solve the finite-volume equations. The validity and accuracy of the numerical model are checked by comparing results with exact analytical solutions for simpler problems. The model versatility is demonstrated by an application to a “Hordi-type” (rib-slab) structure used in roofs in Saudi Arabia. The climatic data of Riyadh for a representative day for July are employed. The Hordi units used are made of an insulation material to further increase the overall thermal resistance (R-value) of the roof. Sample results show that the ribs of the reinforced concrete slab act as thermal bridges which degrade the roof R-value appreciably.