The impact of outdoor shading strategies on student thermal comfort in open spaces between education building

Highlights

• To investigate the performance of outdoor spaces between the buildings (shaded with trees and man made shading device).

• To improve thermal comfort for students and usage of this space using simulation ENVI-met model.

• High air temperature is observed in most outdoor open spaces.

• Using shade structure made from steel strongly affect surrounding air temperature as its temperature exceeds 43 °C.

• Significant effect is achieved through providing shading and increasing the density of trees.

Abstract

The aim of this study is to evaluate and improve student thermal sensation in the open spaces of the Faculty of Engineering, Assiut University, Egypt using different shading strategies. Firstly, the thermal conditions of outdoor spaces were evaluated based on field measurements in different locations of shaded outdoor spaces between educational buildings within the Faculty of Engineering. Then, the microclimate model ENVI-met was applied to evaluate the impact of different shading scenarios on improving student thermal comfort. Also, the Thermal Sensation Vote (TSV) of the was studied by a questionnaire survey using the 118 effective questionnaire responses of the student sitting in the spaces between buildings. Hence, the results concluded that high air temperature is found in most outdoor open spaces, especially in the sitting area with low trees density and high Sky View Factor (SVF). Similar results were obtained by the TSV analysis. In addition, a significant reduction in the Predicted Mean Vote (PMV) values resulted from the ENVI-met simulation model with an average temperature difference of 0.7 °C due to increasing tree density for the main open space. Thus, it is recommended to increase greenery and tree density, to reduce heat stress and create student thermal comfort in outdoor.

Introduction

Outdoor thermal environment factors affect people who use outdoor spaces; especially in the university campuses. However, in hot and dry climate zones, the thermal stress due to solar radiation affects students' thermal sensation based on the design of built environment (Lin, 2007-3] e.g., ground surface covering, evaporation and evapotranspiration of plants, and shading by trees and man-made objects (Lin, Ho, & Huang, 2007, Robitu, Musy, Inard, & Groleau, 2006). The quality of outdoor spaces increases the time spent for recreational activities in outdoor environments. The sites and land cover materials affect thermal comfort in open spaces (Johansson & Emmanuel, 2006). Also, thermally comfortable outdoor environments affect strongly indoor environments and lead to decreasing energy demand for space cooling.

Many field studies on outdoor thermal comfort have been conducted to provide information on the effect of different outdoor spaces on people’s thermal sensation. Makaremi, Salleh, Zaky, Jaafar, and Hosein (2012) studied the thermal comfort conditions of outdoor spaces and human comfort levels in university campuses of Malaysia using field measurements and questionnaire survey. The findings showed that the thermal comfort index (PET) in the shaded spaces is beyond than the comfort range in tropical regions (Makaremi et al., 2012). Al Sabbagh, Yannas, and Cadima (2016) studied improving the thermal sensations of walking subjects at different times of the year for the pedestrians in Dubai. The results showed that the presence of wind and shade helped improve thermal sensation and comfort and increase walkability (Al Sabbagh et al., 2016). Lin, Matzarakis, and Hwang (2010) analyzed outdoor thermal conditions inside a university campus in central Taiwan, and used RayMan model for predicting long-term thermal comfort. Analytical results indicate that the sky view factor (SVF), significantly affects outdoor thermal environments. Analytical results indicate that a high SVF (barely shaded) causes discomfort in summer and a low SVF (highly shaded) causes discomfort in winter. The median shading levels contributed to the longest thermal comfort period (Lin et al., 2010).Yang, Hien, Wong, and Jusuf (2013) studied thermal comfort in outdoor urban spaces in Singapore in 13 different locations using measurements and a questionnaire survey. The findings show that the sun sensation/ solar radiation have the most influence on human thermal sensation in outdoor spaces (Yang et al., 2013). Hwang, Lin, and Matzarakis (2011) analyzed the outdoor thermal conditions in six locations on urban streets in Huawei Township on central Taiwan. The results indicate that slightly shaded locations typically have high-frequency hot conditions in summer, especially at noon. However, highly shaded locations tend to have a relatively lower PET in winter. And since the thermal comfort condition varies in different seasons, the study may have some significant applications. For example, some shading devices on urban streets may be added in summer and removed in winter (Hwang et al., 2011). Ali-Toudert and Mayer (2006) concluded that thermal comfort is very difficult to reach passively in extremely hot and dry climate regions, but an improvement is possible (Ali-Toudert & Mayer, 2006). Shashua-Bar, Pearlmutter, and Erell (2011)) concluded that the vegetative treatment achieves the highest cooling efficiency in shade trees alone due to the water usage of irrigated grass that needs high water demand (Shashua-Bar et al., 2011). Huang, Cheng, Gou, and Zhang (2019) conducted field measurement and questionnaire survey in a university campus in Mianyang, China located in the hot summer and cold winter climate zone. The measurements were conducted over six days and the survey collected 523 responses. The results concluded that shading might significantly affect the TSV of respondents in winter and summer. From the economic side, Yang et al. (2019) investigated the benefits provided by different vegetation species on summer outdoor thermal comfort in area between a multistory building and its associated expenses. ENVI-met was used to simulate the improvements induced by different vegetation species on outdoor thermal comfort in a simplified area between typical building. Although shrubs and ground-cover plants can improve the outdoor thermal comfort. Hence, an economical greening layout is the most economical method to improve the outdoor thermal comfort.

On other hand, many studies have used dynamics simulations software ENVI-met to study the effect of different outdoor strategies (using trees, man-made shading device, water pools and different albedo) inside university campus or others on outdoor thermal comfort. For example Taleghani, Sailor, and Tenpierik (2014) addressed air temperature and mean radiant temperature as key factors affecting outdoor thermal comfort at Portland State University, Oregon, USA. Thus, field measurement and simulation have been conducted by ENVI-met for 7 location in the university to study three different strategies: vegetation, water pools and surface albedo. The result indicated that, vegetation and water pools are the most influence strategies. Also, Srivanit and Hokao (2013) focuses on the importance of greening as a potential strategy for reducing ambient air temperatures in the institutional campus of Saga University, Japan. Two strategies have been proposed to improve campus environments by adding trees to current green areas and growing a grass layer on the rooftop of educational buildings. Numerical simulation model that uses ENVI-met and on-site measurement have been conducted. Accordingly, combining both modification strategies led to reduction of air temperature with an average 0.24 °C. Tobi Eniolu Morakinyo and Kalani (2016) have integrated micro-scale model (ENVI-met) and building energy simulation program (EnergyPlus) as a new approach to study the thermal condition of two similar buildings in the Federal University of Technology, Akure, Nigeria. One of the buildings is with tree-shaded, while the other is not. It was found that integrated greenery is an effective approach. Taleghani (2018) reviewed the impact of high-albedo materials on outdoor thermal comfort at the campus of Delft University of Technology. Firstly, the thermal conditions of an area around the courtyard building was explored through measurement and simulation. Then thermal comfort within the courtyard was investigated. The results showed that outdoor thermal comfort depends on mean radiant temperature, and high-albedo materials increase the radiation from the ground to the sky, so it made the open space of the courtyard uncomfortable. Also, Ghaffarianhoseini, Berardi, Ghaffarianhoseini, and Al-Obaidi (2019) presented field measurements and parametric simulations to evaluate the microclimatic characteristics in a university campus in the tropical climate of Kuala Lumpur, Malaysia. Simulations in Envi-met and IES-VE are used to investigate the current outdoor thermal conditions, using thermal metric indices. The study concluded that effective redesign of outdoor spaces, through adequate attention to the significant impacts of shading and vegetation, can result in improving comfort level. Also, investigation of the influence ratio between Height/Width for spaces between buildings on outdoor open spaces was studied towards the development of a comfortable microclimate at open spaces level for pedestrians by using the three-dimensional numerical model ENVI-met on a summer day (Ali-Toudert & Mayer, 2006; Hwang et al., 2011; Johansson & Emmanuel, 2006; Lin et al., 2010).

Therefore, the creation of outdoor thermal comfort for people in urban environments, especially in the university campus, is an important issue for encouraging students' outdoor activities such as open day social activities, reading, eating under trees and interactions. Also, several studies indicate that there is a lack of research on students' thermal assessment of open space environments in hot dry climate that strongly affect the usage of urban spaces. According to previous studies, vegetation and shaded strategies are the most influence factors on outdoor thermal comfort. So, the aim of this study is to investigate the impact of different shading strategies (shaded with trees and man-made shading device) on student thermal comfort between the buildings of the Faculty of Engineering based on outdoor monitoring and evaluation.