Numerical model for evaluating thermal performance of residential building roof integrated with inclined phase change material (PCM) layer

Abstract

Phase change materials are gaining popularity as an effective passive cooling technique for the design of energy efficient buildings. In this regard, a concise and easier numerical model is essential for building designers to evaluate the impact of PCMs for heat transfer, cooling load reduction and thermal comfort. A full-scale 3D numerical model is developed considering incompressible laminar flow of molten PCM. Model equations are solved in ANSYS Fluent using PISO algorithm (Pressure Implicit Split Operator) for pressure velocity coupling. In order to adopt combined radiative and convective boundaries of the roof, a User Defined Function (UDF) is written in C++ programming language. Developed numerical model is validated against the experimental results available in the literature. Numerical model predictions show that for the climatic conditions of Chennai, PCM integrated roof maintains the ceiling temperature within a narrow range of optimum value and reduces peak heat loads. Further thermal performance evaluation is established for different inclined PCM layer. Three inclination angles of PCM layer 0°, 2° and 4° are considered for the performance evaluation. It is found that a significant reduction in daily heat gain can be achieved by providing the inclination to the PCM layer in the roofing. PCM layer inclined at an angle of 2° has demonstrated the best performance by offering improvement in time, reduction in decrement factor, improved melting and solidification cycle and daily heat gain savings for the given roof structure.