Exploring the efficiency of indirect green façades with native plants to lower rising façade temperatures : A way to improve urban living in tropical regions

Abstract

Urbanisation has drawn more people to towns and cities, resulting in extremely high population densities and a lack of available urban green spaces in metropolitan cities such as Chennai, India. This urbanisation has led to dangerous climate conditions as more and more structures are built and green horizontal cover is removed. Rising temperatures and the urban heat island effect make cities, especially those in tropical regions such as Chennai, vulnerable to the impacts of climate change and thermal issues. The aim of this paper is to discover whether indirect green façade technology could be used to reduce surface temperature and improve indoor thermal comfort. In this study a preliminary literature analysis was carried out on the different types of vertical greening systems (VGS) and their use in urban areas. A survey was also conducted with residents in Chennai to understand how vertical greening was viewed by the local people. The literature findings concluded that VGS could be effective when used on the façades of buildings to improve thermal comfort inside and outside buildings, but there was little research on this technology in hot and humid climates. The survey demonstrated that the residents of Chennai were aware of the benefits of VGS for aesthetic purposes, but were not so aware of how they could be used to save energy; many residents lacked the technical knowledge of how VGS could be used to improve thermal conditions and were concerned by their potential structural damage. A field experiment was then conducted using two different native plant species, Indian spinach (Basella rubra) and butterfly pea (Clitoria ternatea), which were grown on a vertical trellis structure on a terrace in a residence in Chennai to determine their effects on external surface temperature, internal air temperature and indoor humidity. The field experiment aimed to demonstrate that the effectiveness of green façade technology for thermal cooling is dependent on the type of plant species and its foliage density. The two distinct native edible and herbal plant species used had different physical characteristics. The results of this research indicated that Basella rubra and Clitoria ternatea reduced the maximum surface temperature by 7°C and 4°C respectively and reduced indoor temperature by a maximum of 3.6°C and 2.4°C respectively.