Study of Unsteady State Thermal Characteristics of Homogeneous and Composite Walls of Building and Insulating Materials for Passive Cooling

摘要

Passive cooling is one of the methods to keep the building cool and to reduce the load on air conditioner. Passive cooling demands the study of the thermal characteristics like admittance, transmittance, decrement factor, time lag, surface factor and surface factor time lags. These characteristics were determined for both homogeneous and composite walls. In this study, five building materials like Laterite stone, Burnt brick, Mud brick, Reinforced brick and Fly ash bricks were selected as homogeneous building materials. Five local Insulating materials such as Saw dust, Rice husk, Coir board, Jute felt and Jute fiber were selected to form the composite wall along with building materials. The composite walls were framed using the combination of building and insulation materials. Total hundred combinations of composite walls, without insulation and with insulation material located at inner side, at mid plane and at outer side of the composite walls were studied. To study the thermal characteristics of such configurations of composite wall, one dimensional heat flow diffusion equation was solved using matrix algebra under periodic boundary conditions. The penetration length, phase velocity of the heat waves in the wall and optimum fabric thickness of the selected building and insulating materials were calculated. From this study it is found that the decrement factors of the fly ash brick (0.4) and jute felt (0.4) are the least and the time lags of the fly ash bricks (8.15h) and jute felt (8.75h) are the highest among all the studied homogeneous building and insulating materials. Hence these two homogeneous materials are more effective building and insulating materials at suppressing temperature swings. From the study ultimately it is concluded to recommend fly ash brick composite walls with jute felt and coir board insulation located at the mid center plane and outside of the wall respectively.