Abstract
Housing is one of the three major sources responsible for the global greenhouse gas emissions, mainly due to the consumption of large amounts of fossil fuels during daily use. Although central-heating system is not used in Taiwan, summer air-conditioning demand is still the main reason of high carbon dioxide emissions. In order to reduce daily carbon dioxide emissions, phase change materials used in the buildings envelope can regulate indoor temperature for human comfort. In this study, we use computational fluid dynamic software, ANSYS Inc. Fluent, to simulate the building performance and construct a real size 3D model to emulate the phase change process and temperature regulation. In the 3D building envelope model, three different kinds of materials are incorporated, they are concrete, expanded polystyrene and n-octadecane respectively. Concrete is the traditional wall material and it reduces 0.25 K from outside temperature. Expanded polystyrene is heat insulator, and it reduces 1.26 K. We chose n-octadecane as the phase change material and it reduces 2.29 K. Results show that phase change material can stabilize indoor temperature and its thermal performance is the best. In the second part, we used simplified 2D model to study the relationship between thermal conductivity of n-octadecane and its thermal performance. We concluded that n-octadecane with higher thermal conductivity is more efficient to use. Finally, hollow wall can reduce 2.43 K but there will cause a rise in indoor air temperature. As a result, n-octadecane is an effective energy saving material used in a building envelope in subtropical climate.