Experimental and Theoretical Studies of Green Energy Building Using Various Building Materials and Orientation

Abstract

The cooling of buildings by using passive methods has evoked great interest. Passive cooling is one of the methods to keep the building cool and to reduce the load on the air conditioner. The most prominent building elements that ensure energy efficiency in buildings are building enclosures such as walls and roofs. Passive cooling demands the study of the thermal characteristics of walls or roofs such as admittance, transmittance, decrement factor, time lag, surface factor and surface factor time lags. For the computation of these unsteady state characteristics, one dimensional heat flow diffusion equation with convective periodic boundary conditions was solved using matrix algebra and a computer program was developed using MATLAB to compute unsteady state thermal characteristics of homogeneous and typical composite walls. Natural building materials depreciate negative ecological impact and promote environmental sustainability. Hence, it is imperative to dedicate attention to the thermal performance of natural and sustainable building materials. Laterite stone is a locally available and natural building material in South-West coastal India. The thermal properties of laterite stone exposed to various humidity and temperature levels of ambient air were measured experimentally and their impact on unsteady thermal response characteristics of the laterite walls was studied in detail. The results showed that the increase in the relative humidity from 0% RH to 98% RH decreases the decrement factor by 8.35% and increases the time lag by 2.88%, whereas, the increase in the temperature from 0oC to 60oC decreases the decrement factor by 14.5% and increases the time lag by 8.3%. The effect of thermal properties of building materials, insulation location, air space thickness and air space location on unsteady state thermal characteristics was studied. From this study, It is concluded that fly ash brick composite walls with jute felt insulation located at the mid plane of the wall give greater time lags (11.17h) and fly ash brick composite walls with coir board insulation located at the outer side of the wall give the lowest value of decrement factor (0.17) among hundred configurations of the walls studied. Optimum wall thicknesses of building and insulating materials were computed. From the results, it is concluded that mud phuska and coconut pitch are the most recommendediii homogeneous building and insulation materials, respectively, among studied building and insulating materials, from lower decrement factor and higher time lag point of view. It is also found that the insulation materials are highly responsive to short wave radiation than that of building materials. The impact of the divided air space thickness within the wall on thermal performance of the wall was also investigated. From the results, it is observed that the decrement factor decreases and time lag increases with the increase in the divided air space thickness within the composite wall for all building materials. The effect of unventilated continuous vertical air space location in the wall on unsteady state thermal response characteristics of composite walls was also studied. From this study, it is observed that Fly ash brick composite wall with air space located at the outer side and the mid center plane and fly ash brick with air space located at outer and inner sides of the composite walls are the recommended composite walls due to their highest time lag (11.28 h) and lowest decrement factor (0.166), respectively among studied building materials. The influence of the insulation location in the roof on thermal performance was investigated. The results reveal that the roof with insulation placed at the outer side and at the mid center plane of the roof is the most energy efficient from the lower decrement factor point of view and the roof with the insulation placed at the mid center plane and the inner side of the roof is the best from highest time lag point of view among seven studied configurations. The unsteady thermal response characteristics of hollow and stuffed bricks were also studied. From the results, it is observed that thermal admittance, surface factor time lag, decrement factor time lag and areal thermal heat capacity values increase with the increase in the number of air gaps in hollow bricks, whereas thermal transmittance and decrement factor reduces with the increase in the number of air gaps in the hollow bricks. The effect of wind velocity on the dynamic thermal performance of various composite walls was also reported. This research aids in designing energy efficient and environment friendly buildings for passive cooling.