Research Article Building Thermal, Lighting, and Acoustics Modeling E-mail: juanangel@smart.mit.edu Thermal impact of the orientation and height of vertical greenery on pedestrians in a tropical area Juan A. Acero 1 (), Elliot J. Y. Koh 1 , XianXiang Li 1 , Lea A. Ruefenacht 2 , Gloria Pignatta 1,4 , Leslie K. Norford 3 1. CENSAM, Singapore-MIT Aliance for Reasearch and Tecnology (SMART), 1 Create Way, #09-03, Singapore 138602 2. Singapore-ETH Centre (SEC), 1 Create Way, CREATE Tower, #06-01, Singapore 138602 3. Department of Architecture, Massachusetts Institute of Tecnology (MIT), 265 Massachusetts Ave, MA 02139, USA 4. Faculty of Built Environment, UNSW Sydney, NSW 2052, Australia Abstract At the beginning of the 21st century, increasing amount of greenery in urban areas has been a priority for many urban planners following a social and environmental demand of the population. Many sustainability benefits can be attributed to urban green infrastructures. In this study we focus on analyzing the impact of vertical green systems (VGSs) on outdoor climate variables and thermal comfort by means of modelling techniques (ENVI-met v.4.3). The study is carried out in a courtyard surrounded by high-rise buildings in the hot and humid tropical climate of Singapore. Results show that weather conditions have a significant influence on the outdoor thermal performance of VGSs. Thermal comfort perception can be reduced by one category (e.g. from hot to warm) close to the façade depending on the geographic orientation of the VGS. Finally, this study shows that thermal benefits for pedestrians are provided mainly by the lowest meters of the VGS. Green elements above 6 meters in the facade reduce significantly the impact at pedestrian level. Results provide an insight to the implementation and dimensions of VGSs as urban infrastructure to improve the outdoor thermal environment, particularly in the tropical urban environment. Keywords outdoor thermal comfort, vertical greenery, modelling, facade orientation, weather conditions Article History Received: 4 October 2018 Revised: 19 February 2019 Accepted: 12 March 2019 © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019 1 Introduction Greenery has been extensively used to improve livability in cities (Fuller and Gaston 2009; Newman 1999; Wolch et al. 2014). One of its major impacts is reducing the accumulated heat in the urban fabric by increasing the latent heat flux through evapotranspiration (Oke 1987). As a result higher vegetated urban areas can be cooler than areas with lower presence of vegetation. Thus, urban vegetation can minimize the well-known Urban Heat Island (UHI) phenomenon. During the 21st century vertical greening systems (VGSs) have become popular because they aim to reduce building outdoor surface temperature by shielding the walls from external radiation. This has a significant impact on the building’s energy performance, but also it improves the urban thermal environment. Controlling these effects (energy consumption and urban temperature) is relevant in the context of climate change where temperatures are expected to rise. In this sense, many governments have committed to reduce carbon emissions and energy use in buildings, as well as provide a better thermal comfort (outdoor and indoor) to the population. Additionally, VGSs and other types of urban greenery have a relevant psychological impact on urban dwellers through their aesthetic appearance (Jungels et al. 2013; Klemm et al. 2015; Köhler 2008; Li et al. 2016; Wong et al. 2010b) and have economic benefits (Joye et al. 2010; Safikhani et al. 2014; Zhu and Zhang 2008). The VGSs have special relevance in high density developments where the building surface area is much greater than the roof and ground surface. In this case, tree-planting is limited (Morakinyo et al. 2017b) but a large amount of vertical surfaces can be greened to avoid the absorption of solar radiation and consequently reduce the UHI effect. Different studies have evaluated the effects of VGSs on ambient temperature, surface temperature and thermal BUILD SIMUL https://doi.org/10.1007/s12273-019-0537-1