Effect of Walling Materials’ Thermal Transmittance and Thermal Masson Indoor Thermal Comfort in Nairobi

Abstract

The control of indoor thermal environment in buildings is necessary for occupants‟ health and comfort. A study was undertaken to develop the criteria for the selection of walling materials for thermal comfort in residential buildings in Nairobi, Kenya. Indoor and outdoor temperature was monitored in three buildings with different walling materials. Natural stone, timber and expanded polystyrene (EPS) walls were considered. Using the Autodesk Ecotect 2011 thermal simulation software, different scenarios were simulated. Input data included the spatial dimensions of the buildings, climatic data (air temperature, relative humidity and solar radiation), construction materials, human activities within the buildings, clothing worn, indoor relative humidity and heat output of domestic equipment. In the simulation model, the effect of thermal transmittance and thermal mass of different walling materials on indoor thermal comfort was studied. Materials considered in the simulation included natural stones, galvanized iron sheets, concrete, fired clay, stabilized earth, timber and expanded polystyrene panels (EPS). In all cases the indoor temperature was higher than the outdoor temperature. The observed mean indoor temperature of the living room was 3.8 oC, 3.3 oC and 2.5 oC above the mean outdoor temperature for the EPS, timber and stone wall buildings, respectively. The simulation showed that thermal transmittance of walls had a more significant effect on thermal discomfort compared to thermal mass. Thermal discomfort in the buildings was found to have a direct linear relationship with thermal transmittance of the walls. To avoid thermal discomfort, thermal transmittance of walls should not exceed 0.70W/m2K. Key words: thermal comfort, thermal mass, thermal transmittance, walling materials