Sepideh Jafarian; Elham Sarkardehee; Danial Monsefi Parapari; Mohammad Reza Mojahedi
Abstract
Extended AbstractBackground and Objectives: Given the significance of human presence in open spaces and the influence of climate on urban activities and behaviors, this study addresses ...
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Extended AbstractBackground and Objectives: Given the significance of human presence in open spaces and the influence of climate on urban activities and behaviors, this study addresses the crucial aspect of outdoor thermal comfort. Urban open spaces, especially in hot climates, make users experience high thermal loads leading to thermal discomfort. Outdoor thermal comfort can be improved by controlling radiation and shading to mitigate stresses induced by surface overheating and environmental factors. This research underscores the importance of shading and radiation reduction to promote human presence, create a micro-climate, and improve comfort conditions in urban open spaces. Recognizing shade-producing factors, such as canopies, can contribute to creating desirable outdoor environments. In this context, fabric membrane structures are suitable solutions for hot climates, offering shade and natural ventilation. In hot and arid climates like Semnan, outdoor thermal comfort is not met due to factors such as intense heat, clear skies, strong sunlight, limited vegetation, and a lack of shade. Consequently, outdoor spaces are usable for only limited hours and only for specific seasons. However, by controlling the temperatures and introducing shading, a key factor in cooling the environment and reducing air temperatures during hot periods, thermal comfort conditions can be provided to some extent. Membrane canopies, with their unique properties, are suitable for outdoor spaces, particularly in hot and arid climates, offering users enhanced thermal comfort.Methods: This study investigates the effect of lightweight membrane canopies on outdoor thermal comfort in Semnan, characterized by a hot and dry climate, through a combination of bibliographic research and simulations using ENVI-met and ANSYS software. The bibliographic research is conducted through scrutinizing the sources and documents and analyzing Persian and non-Persian materials related to outdoor thermal comfort and lightweight membrane structures, employing both descriptive and analytical information analysis methods. Simulations are run using ENVI-met to assess the influence of shade on the environment and ANSYS software to simulate various common shade models, assessing their effects on thermal comfort. The simulation analysis follows a comparative research data analysis and review approach.Findings: The findings indicate that installing a membrane canopy during summer results in a temperature reduction of up to 4.7 °C, substantially improving thermal comfort conditions. Lightweight membrane canopies effectively cool the space beneath them and prevent ground overheating. According to previous researches and considering that there are two factors of high temperature and low humidity in the hot and dry climate of Semnan, the combined use of shade to reduce temperature and vegetation to increase humidity has a significant effect on thermal comfort in the hot and dry climate of the Semnan. This discrepancy is attributed to real-world conditions where wind, surrounding objects, and natural elements around the canopies disperse heat, and the flat plate strongly absorbs heat; however, in real conditions there are other objects around the canopies that reduce the intensity of heat. Although shade does not cool the ground, it effectively mitigates excessive heating. In the current simulations, the ground surrounding the canopy heats up to 70-80 °C, but temperatures are cooler under the canopy. If the lowest temperature under the canopy is the criterion, the saddle canopy is more suitable, and if the cooling capacity of the shade is important, the saddle canopy has performed better.Conclusion: Lightweight membrane canopies cause temperature differences in hot and dry climates. The Ansys simulation results with the aim of investigating the effect of the membrane shade and determining the suitable form for the light membrane shade confirm that the membrane canopy cool the space under and prevent excessive ground overheating. Out of the four membrane canopy models available, namely the Simple, Conical, Umbrella, and Saddle designs, the Saddle canopy stands out with an effectiveness rate of 43.15% in the environment, demonstrating strong performance in creating a cooler space beneath it and can be considered the most suitable choice among the canopy models.
