Mitigating the Urban Heat Island effect through building envelope modifications

Mitigation techniques aiming to counterbalance the Urban Heat Island (UHI) phenomenon deal with the intensive usage of green spaces, application of highly reflective materials, materials having high thermal resistivity, decrease of the anthropogenic heat, solar control of open spaces, use of environmental heat sinks and increase of the wind flow in the canopy layer. Though materials having high thermal resistivity do not directly mitigate the UHI effect however upon using them as constructional materials, the buildings become naturally cool which reduces the anthropogenic (waste) heat from the buildings thereby mitigating the UHI effect. In addition to this, the reduction in the power demand would eventually lead to the reduction in the burning of coal in the thermal power plants and consequently reduces the release of CO2 (a green house gas). Moreover, if naturally grown materials (like bamboo in the present case) are used for construction applications, it would pave way for 'profitable greening' which would significantly reduce the UHI effect in two ways (1) by increasing the latent heat flux through evotranspiration (2) by sequestering CO2. The embodied energy of local materials having high thermal resistivity like Rammed Earth is significantly less than that of the popularly used Cement and Bricks which makes it a greener option having relatively low carbon footprint. Cumulating these facts it can be stated that usage of 'natural materials' having adequate strength and high thermal resistance offers high potential for mitigating the UHI effect. With this background, the present study of investigating the thermal performance (in terms of energy consumption for space cooling) of composite materials like Bamcrete (bamboo -concrete composite) and natural materials like Rammed Earth along with energy intensive materials like bricks and cement was undertaken. In addition to this, the thermal performance of building envelope modifications like (i) increasing the thickness of wall, (ii) construction of a cavity wall was also attempted. Of the 6 scenarios simulated, the use of 6" bamcrete in walls depicts the highest cooling potential (around 7.5%) when compared to the popularly used 5" brick thick wall. The present study is first of its kind to quantitatively report the performance of 'bamboo'-a wonder grass of India, in reducing the cooling load of a building. The results should definitely help the green building community to take suitable actions at their ends for designing buildings having low carbon footprint and effectively mitigate the UHI effect. (C) 2018 Elsevier B.V. All rights reserved.