Evaluation Of The Thermal Performance Of Walls Using Time Lag And Decrement Factor

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ABSTRACT This study dealt with the evaluation of the thermal performance of walls in the climatic area of Kumasi using the parameters time lag and decrement factor. A numerical model was developed using the finite volume method with implicit formulation for four different wall configurations used in building constructions in Kumasi. The wall configurations had the same thickness and consisted of the mass concrete block wall, hollow concrete wall, mud brick wall and sandrete block wall. The simulation was carried in the month of March and August which respectively have the highest and lowest global solar radiation and dry bulb air temperature using mathcad software tool. The results showed that the heat gain by the walls through irradiation and ambient temperature in the area had some impact on the time lag and the decrement factor of the wall. The time lag values for the hollow concrete wall, mud wall and sandcrete had high values in March when the level of global solar radiation and outside dry bub temperature was high and reduced by an hour in August when the levels were low. The highest time lag was achieved by the mud brick wall which had five hours in the month of March. This was followed by the mass concrete wall which had time lag value of four hours for both months. The lowest decrement factor value was also given by the mud brick wall in the month of March whiles the lowest decrement factor in the month of August was given by the sandcrete block wall which also followed the mud brick wall closely in March. The numerical model was verified with analytical solution. The study is important in determining heat storage capabilities and temperature fluctuation reduction in wall configurations used in the West African tropical savannah climatic area.
A Thesis Submitted to the Department of Mechanical Engineering Kwame Nkrumah University of Science and Technology, Kumasi, Ghana In partial fulfillment of the requirements for the Degree of MASTER OF PHILOSOPHY IN MECHANICAL ENGINEERING