Improve Outdoor Thermal Comfort Research Articles

Numerical simulation of layout and landscape elements on the thermal environment of urban squares

Extreme urban heat poses significant challenges to the resilience and livability of cities. Urban squares are important open public spaces in cities, serving as main locations for residents' leisure and recreational activities and reflect the identity and cultural background of the cities. Improvement in thermal comfort in urban squares can improve the quality of the urban environment and help mitigate the urban heat island effect. This study developed 18 layout and landscape combination scenarios based on statistical analysis of data from 100 urban squares in regions with hot summers and cold winters. Further, the effectiveness of the proposed design solutions in improving the thermal environment was comprehensively analyzed. The results show that: 1) The block array layout with vegetation, water bodies, and permeable tiles is the most effective scenario, with a PET of 31.84 °C, approaching a comfortable level of heat stress; 2) Among the three layouts, the block array layout optimizes thermal comfort better than the main view entrance layout and main view center layout, and reduces physiological equivalent temperature by 10.51–10.77 °C compared with that of the other two layouts; 3) Scenarios incorporating water bodies provide better optimization effects than those with only trees, even when the total area covered by greenery remains unchanged; and 4) Permeable paving materials with high albedo more effectively improve the thermal comfort. Our results highlight a great potential of comprehensively using multiple landscape strategies to improve outdoor thermal comfort, and provides design basis for enhancing thermal comfort in similar sized urban squares in hot summer and cold winter areas.

Numerical Investigation of Interventions to Mitigate Heat Stress: A Case Study in Dubai

Urbanization and changes in microclimate have negative impacts on outdoor thermal comfort, making urban design more important. This study aims to improve outdoor thermal comfort in a local climate zone (LCZ) in Dubai using computational fluid dynamics (CFD) methods. This study evaluates cooling interventions, such as vegetation, architectural, and pavement material, using Reynolds-averaged Navier–Stokes (RANS) equations and the SIMPLE scheme. The results show that a combination of cooling interventions affects the average temperature between 4.44 °C and 6.14 °C. Light-colored ground material has a 5.4 °C cooling effect in the LCZ compared with dark-colored materials. The predicted mean vote (PMV) method is used to compare outdoor thermal comfort and the results show that thermal sensation in the LCZ improves from warm to slightly cool. Lastly, the most effective cooling interventions are, in order, shade structures, trees, chimneys, and bushes.

A behavioural analysis of outdoor thermal comfort in a hot, arid climate: a culture and gender equality perspective

This study investigated how gender influences subjective comfort perceptions and behavioural adaptations, to establish the limits of the thermal sensation scale for males and females in the hot, arid climate of Al Ain, in the UAE. It is the first of its kind in the Gulf Cooperation Countries. Two locations on a university campus, reflecting cultural traditions, were compared. Data collected through interviews, observations, and measurements showed that males and females have different thermal comfort ranges (22.1–33.4°C PET for males, 21.2–32.7°C for females). Factors like perceived control over exposure to discomfort influenced thermal sensation. The study suggests urban planning should consider gender equality to improve outdoor thermal comfort and encourage the use of open spaces, indicating socio-economic influences on thermal adaptation in the region.

Potential of Nature-Based Solutions to Diminish Urban Heat Island Effects and Improve Outdoor Thermal Comfort in Summer: Case Study of Matadero Madrid

Urban heat island effects and climate change are climatic phenomena responsible for periods of extreme heat in summer which severely impact citizens’ well-being and health. In this alarming context which questions the livability of our cities, Nature-Based Solutions (NBSs) are considered an unavoidable component of the complex strategy in diminishing urban temperatures. The present work aims to show the relevance of NBSs in urban temperature regulation through the estimation of their potential to improve outdoor thermal comfort of the heritage site Matadero Madrid. To this end, this article evaluates the effects of a scenario combining different solutions including NBSs and identifies which solutions are the most effective. The results show that this scenario has an impact on direct solar radiation and wind speed but does not affect air temperature and relative humidity. Furthermore, even if this scenario combining a fabric canopy, tree canopy, and green area significantly improves thermal conditions, it does not allow us to reach an optimal level of thermal comfort for visitors. To consider the implementation of more meaningful interventions, existing legal, administrative, and cultural limitations of the case study should be omitted. This would enable us to identify which restrictions could be adapted, thus unlocking the adaptation potential of Matadero Madrid.

Assessment of combined passive cooling strategies for improving outdoor thermal comfort in a school courtyard

Both artificial shading and evaporative cooling have proven to be effective strategies for improve outdoor thermal comfort. However, their combined effect on microclimates or thermal sensations has rarely been investigated, hindering our understanding of the interactions among cooling strategies. In this study, we tested the performance of sun sails with different coverage ratios, mist-spray systems with different nozzle arrangements, and a combination of these two strategies for cooling a kindergarten courtyard using validated ENVI-met models. Among the strategies, we found that the shade + mist strategy is the most effective and can reduce the physiological equivalent temperature (PET) by up to 14.43 °C and heat stress levels by 2–3 categories in originally exposed areas. This was followed by the sun sail shading strategy. The mist-spray system had a relatively weak cooling effect. The cooling effects of sun sails increased with coverage ratios and mounting heights, whereas the spatial cooling distribution of mist spraying was mainly determined by wind rather than by nozzle arrangements. In addition, we found that shading can enhance the cooling effect of mist spraying in terms of air temperature, but reducing its cooling effect in terms of the mean radiant temperature. Our results highlight a great potential of comprehensively using multiple strategies to improve outdoor thermal comfort, and provide a design basis for enhancing thermal comfort in similar school courtyards in Hunan Province in China.

An Evaluation of Different Landscape Design Scenarios to Improve Outdoor Thermal Comfort in Shenzhen

The pivotal role of urban greening in landscape design for mitigating climate change and enhancing the thermal environment is widely known. However, numerous evaluations of outdoor thermal comfort are seldom applied within the realm of landscape design scenarios. This study explores the relationship between street design and urban microclimate, aiming to propose a range of design strategies that can significantly improve thermal comfort within the street environment in Shenzhen, China. These design strategies hold immense potential for urban greening implementation and provide valuable insights to enhance the overall thermal quality of streetscapes in subtropical cities. The study employs landscape design and environmental simulation methods to evaluate the different design scenarios for the streetscape. The landscape design encompasses three scenarios with revised interventions: 1. the incorporation of building greening and enhanced pavement material albedo; 2. the introduction of trees and grass at the ground level; and 3. a combination of scenarios 1 and 2. Environmental simulations are utilized to assess the effectiveness of each design scenario. The findings reveal that increasing urban vegetation leads to a reduction in urban heat and significantly improves outdoor thermal comfort. Moreover, the incorporation of shade-providing trees proves to be more efficacious than employing vertical greening in alleviating outdoor thermal discomfort.

Outdoor thermal perception in the semi-arid climate of Constantine, Algeria: A field survey during the post-COVID-19

The purpose of the paper was to assess pedestrians' thermal perception, in the semi-arid climate of Constantine, Algeria, with particular emphasis on the protocols implemented in public spaces during the post-COVID-19. Three outdoor public spaces were selected in August 2021 to conduct a field study involving 254 respondents, randomly assigned. The adopted approach combined objective and subjective assessment, as well as numerical simulations using ENVI-met. Accordingly, microclimate monitoring and a questionnaire survey were carried out simultaneously from 7 a.m. to 7 p.m. in each study site. A strong association was found between the combined microclimate parameters (objective variables) and thermal sensation of the surveyors with (R2 = 0.74). Besides, Kruskal-Wallis H test revealed that the subjective thermal sensation was significantly influenced (p-value <0.05) by thermal history and purpose of visit (subjective variables). Most interviewees preferred ‘move to shade’ measure as a remedial behavior to reduce their thermal discomfort. Further, a neutral temperature of 22.7 °C PET was obtained by a linear regression between the Mean Thermal Sensation Votes (MTSV) and Physiological Equivalent Temperature (PET), the comfort range was estimated between 18.6 °C ≤ PET≤ 26.8 °C during summer. Regarding the COVID-19 pandemic effects, the Chi-square test suggests that the frequency of pedestrian visits was statistically independent of the imposed pandemic measures. However, the planned activities were affected by social distancing and the use of face masks increases pedestrians' thermal discomfort. Overall, the study highlights the significance of environmental and non-environmental factors to improve outdoor thermal comfort, and ensure human well-being.

Influence of greenery configuration on summer thermal environment of outdoor recreational space in elderly care centers

Greenery can improve the outdoor thermal environment in elderly care centers during heat wave in summer. However, it lacks quantitative results and rules. This study investigated the summer outdoor thermal environment of four representative elderly care centers in Tianjin to establish the thermal demand of seniors. The different thermal effects of greenery types (GTs) were revealed in elderly care centers. To improve the quality of the outdoor recreational space, this study utilized numerical simulation to quantitatively establish the influence of tree-shrub coverage rate (TSCR) on the thermal comfort of seniors. The results showed that the thermal neutral physiologically equivalent temperature (PET) of elderly people was 27.0 °C in summer, and the thermal acceptance range of PET was 23.6–36.8 °C. Shrubs overall could significantly increase the tree's ability to improve the outdoor thermal environment. Furthermore, this study proposed different TSCR strategies. TSCR of the elderly care center should be greater than 31.5% to obtain great thermal acceptance for the elderly in summer; when the TSCR of the elderly care center could not reach 31.5% due to the reality, TSCR = 10.0% was the efficient strategy to improve outdoor thermal comfort. This research provided a scientific reference for the greenery configuration plan of elderly care centers in summer.

The effect of facade materials and coatings on urban heat island mitigation and outdoor thermal comfort in hot semi-arid climate

High urban temperature is generally associated with negative effects on building energy consumption, outdoor thermal comfort, air quality, and human health. Then it is necessary to find strategies to reduce urban heat island and improve outdoor thermal comfort. This research investigates and classifies facade coatings and materials with regards to urban heat island effect in hot semi-arid climate of Shiraz. The surface temperature of 20 common and modern building facade materials during two periods for five days and their effect on outdoor air temperature is investigated through field measurement. Additionally, to study the effect of each material on urban heat island and thermal comfort index, Physiological Equivalent Temperature (PET) of a neighborhood in Shiraz was simulated with ENVI-met software on June 22. The results show that during the day under direct sunlight, the living wall has the lowest surface and air temperatures, and as the nearby air temperature increases during the night, it lowers the temperature fluctuations both during the day and night. Materials with high albedo increase the Mean Radiant Temperature and PET index despite their lower surface temperature. Materials with high thermal mass and low emissivity have lower temperature. The living wall has the lowest PET index, indoor and outdoor surface temperature during the day. It can also result in 2 °C reduction of air temperature.

Holistic Approach to Ecological Design Parameters of Building and Landscape Design on Outdoor Thermal Comfort in Hot, Humid Climate

In this study, academic staff residential buildings were studied as part of a university campus located in a hot and humid climate zone in Türkiye. Within the scope of the study, the energy efficient architectural and landscape design decisions of the buildings built in 1976 were examined. The aim was to determine the energy performance of buildings built about 50 years ago and to quantify the effect of changing landscape conditions on thermal comfort. In this aim, the outdoor thermal comfort level was determined by creating microclimate simulations for the hottest day and time of the year. Microclimatic analyses were performed with ENVI-met software and thermal comfort was evaluated with two metrics, average PMV and ASHRAE scale. The energy performance of the buildings was determined using ecological design parameters. An approach to global environmental problems is the use of ecological design principles, including architectural and landscape design principles. It is important to consider both architectural design criteria and landscape design criteria when discussing ecological design in the built environment. Architectural and landscape design decisions for hot and humid climate regions together increased energy efficiency by 51.1% to 75.5%. It was found that although the plant design improves energy performance in buildings by that range value, it improved outdoor thermal comfort by 15% to 22%. As a result, the study evaluated climate-balanced plant design with building energy performance in order to improve outdoor thermal comfort.

Assessment of Urban Heat Mitigation Strategies to Improve Outdoor Thermal Comfort Regarding Carbon Dioxide Concentration in Tehran Metropolis

Assessment of Urban Heat Mitigation Strategies to Improve Outdoor Thermal Comfort Regarding Carbon Dioxide Concentration in Tehran Metropolis

The Role of Urban Trees in Reducing Land Surface Temperature

Increasing urbanization in the world in recent years has resulted in the replacement of areas covered with plants by buildings. Because of this change, urban areas are warmer than rural areas (urban heat island). In this investigation, the urban heat island (UHI) effect, the methods of combating this effect and notably the role of urban trees are exhaustively elaborated by considering the relevant literature. In addition, suggestions were made on which species should be selected and how tree species should be positioned to reduce UHI effect. There are solid evidences that trees, urban green spaces and wider green infrastructure can bring significant reductions in urban temperatures. Urban planners and decision makers can help combat UHI and increase urban resilience to the effects of climate change, primarily by planting the urban environment with extensive shade-providing species and harnessing the most of the opportunities afforded by restoration activities. Trees and other vegetation can cool the surrounding air by evapotranspiration thanks to both transpiration from plant leaves and evaporation of water from irrigated soil. The tree canopy can considerably improve outdoor thermal comfort by preventing a pedestrian from being exposed to solar radiation, and also by protecting floors and building coverings from UHI effect. Furthermore, if a roadside afforestation is to be established to combat UHI effect, a proper plan based on the character of the road will be beneficial in terms of achieving the determined goals. Eventually, the adaptation to UHI should be achieved to plan short-, medium- and long-term changes.

Can retro-reflective materials replace diffuse highly reflective materials for urban buildings’ wall to improve outdoor thermal comfort?

In recent years, there have been numerous studies on the application of retroreflective (RR) materials to exterior building walls to relieve the urban heat island (UHI) phenomenon and save building energy consumption instead of diffuse highly reflective (DHR) materials. Experimental measurements were undertaken to investigate the impact of applying DHR and RR materials to building exterior walls on the outdoor thermal environment. DHR and RR walls were tested with three canyon aspect ratios (H/ D) of 0.5, 1.0, and 1.5, respectively, with seven environmental indexes recorded and compared, including air temperature (Ta), relative humidity (RH), sol-air temperature (SAT), operative temperature (OT), standard effective temperature (SET*), change in operative temperature (COT), and real-time solar reflectance (ρ). The results show that the RR wall is more effective in improving the outdoor thermal environment, where SAT decreased by 4.5 °C, SET* decreased by 0.5 °C, and COT decreased by 1.2 °C, on average, while it can also improve the real-time solar reflectance (ρ) by 12% on average compared to the DHR wall. Moreover, it gets more effective in scenarios with a higher canyon aspect ratio.

Relevance of Urban Geometry and Outdoor Thermal Comfort in Urban Heat Island Mitigation – A Review

UHIs’ environmental and energy implications are well-known, but their significance in aggravating heat stress in populations is only recently being recognised. Planners, health managers, and public administrators now prioritise UHI prevention. Urban geometry, material finishes, and green and blue infrastructure are prominent UHI mitigation options. This paper examines urban geometry as a key parameter and reviews UHI research. This report also identifies information gaps and emphasizes the need for this type of research in key Indian metropolitan centers. The anticipated study will help public health planners and administrators. Methods: Authors compiled extensive literature on UHI and related concepts. The outcome intent was to understand the relevance of urban geometry parameters in UHI intensity and how it impacts outdoor thermal comfort. Various electronic databases were searched for publications meeting the criteria of outdoor thermal comfort and urban planning characters (urban geometry) as a mitigation strategy, ranging from 2000 to 2020. Summary: The impact of UHI on human comfort conditions cannot be ignored. Appropriate planning measures at the initial stages of city planning via urban geometry parameters can certainly yield encouraging results to reduce the intensity of UHI and improve outdoor thermal comfort conditions.

Building form and outdoor thermal comfort: Inverse design the microclimate of outdoor space for a kindergarten

Thermally comfortable mircoclimate is essential for creating high-quality outdoor spaces that attract citizens and boost city vitality. Previous design efforts to improve outdoor thermal comfort were usually conducted at large scales, such as city scale, neighborhood scale, urban block scale. Few researchers focused on the building scale. This study proposes an optimization framework based on genetic algorithm to determine the building shape, orientation, and location during early design stage that reduces the overall thermal stress in the target outdoor space. Solar radiation and wind fields were simulated to obtain the outdoor Universal Thermal Climate Index (UTCI) as the performance indicator. The simulations were validated against the experimental data. This investigation applied the proposed optimization framework to design the outdoor space for a kindergarten under the climate of Tianjin and Shanghai, respectively. The results showed that optimization reduced the overall thermal stress. The most favourable kindergarten forms were suggested through optimization. Moreover, solar radiation has been proved to contribute more to outdoor thermal comfort than wind field and heat stress is more important than cold stress during optimization. This study supplements the inverse design of outdoor thermal comfort at building scale and provides suggestions to create comfortable urban outdoor spaces.

Improving outdoor thermal comfort of a kindergarten by optimizing its building shape with genetic algorithm

Thermally comfortable mircoclimate is essential for creating high-quality outdoor spaces that attract citizens and boost city vitality. Previous design efforts to improve outdoor thermal comfort were usually conducted at large scales, such as city scale, neighborhood scale, urban block scale. Few researchers focused on the building scale. This study proposes an optimization framework based on genetic algorithm to determine the building shape, orientation, and location during early design stage that reduces the overall thermal stress in the target outdoor space. Solar radiation and wind fields were simulated to obtain the outdoor Universal Thermal Climate Index (UTCI) as the performance indicator. The simulations were validated against the experimental data. This investigation applied the proposed optimization framework to design the outdoor space for a kindergarten under the climate of Tianjin and Shanghai, respectively. The results showed that optimization reduced the overall thermal stress. The most favourable kindergarten forms were suggested through optimization. This study supplements the inverse design of outdoor thermal comfort at building scale and provides suggestions to create comfortable urban outdoor spaces.

Thermal Resilience of Citizens: Comparison between Thermal Sensation and Objective Estimation in Outdoor Spaces: A Case Study in Seville, Spain

Sanitary issues, combined with the effects of climate change, emphasize the comfort of outdoor spaces in cities. Numerous comfort models exist and can predict thermal sensation. However, these comfort indices need to be validated in hot zones and quantify the neutral range considering people’s thermal resilience. The present study investigates the outdoor thermal comfort of people who live in hot areas and are accustomed to this and quantifies this effect. For that, predictions provided by the COMFA thermal comfort model were compared with the occupants’ perceptions given in the field campaigns’ questionnaires. The field campaigns were associated with on-site monitoring of local climate variables. It was observed that during the survey period, the entire space was predicted to be uncomfortable by the COMFA model. On the contrary, the results of the questionnaires showed that the most frequently encountered thermal sensations were distributed between the comfort zone and the hot zone. The proposed methodology has been designed to be used by other researchers, and it is adaptable to other outdoor thermal comforts such as PET or ITS. The comparison between the model’s predictions and the users’ responses to space highlighted the tendency of the COMFA to overestimate the thermal sensations. This work’s results allow extending the neutral comfort band from 50 W/m2 (value of literature) to 80 W/m2. So, the paper quantifies that the effect of the thermal resilience of the people increases the thermal band of comfort by around 60%. These results will allow an accurate assessment of the effectiveness of future mitigation solutions implemented to improve outdoor thermal comfort in other world areas. It is due to the propose of a higher neutrality range researchers or designers could achieve outdoor thermal comfort in effective and reliable ways, even in hot climates.

Simulation framework for early design guidance of urban streets to improve outdoor thermal comfort and building energy efficiency in summer

Global warming and the urban heat island effect have led to the deterioration of the outdoor thermal environment and the rise of building cooling demand, calling for urban design with high environmental quality. However, little has been changed in the practice of urban street design. This paper bridges this gap by developing a framework of parametric simulation for design guidance of urban streets with an advanced urban canopy model that can simulate the interactive indoor-outdoor environment. Case studies are conducted at the neighborhood scale for six cities to improve outdoor thermal comfort and building energy efficiency in summer. The influence of street and building design parameters has been investigated based on 31104 simulations. Results reveal the conflict between optimizing outdoor thermal comfort and optimizing building energy efficiency. In the majority of the investigated cities, window-to-wall ratio, window type, and street orientation are the most influential parameters. Strategies by adjusting these parameters can significantly improve outdoor thermal comfort, as quantified by thermal stress hours, at a cost of increasing the building cooling load. Planting bigger and denser roadside trees always moderately reduces the thermal stress hours and building cooling load. These results demonstrate the potential of this framework to identify the design trade-offs between thermal comfort and building energy efficiency. The framework can be extended to various cities to help designers and policymakers at the early design stage.

Assessment of outdoor shading strategies to improve outdoor thermal comfort in school courtyards in hot and arid climates

• To encourage students to perform different activities and interact in open spaces of school • to improve OTC for students in school courtyards located in a hot, arid climate. • Significant reduction in the PET for courtyard temperatures based on the ENVI-met model reached 18.5°C • To integrate hybrid scenarios of staggered shading and trees whether in the current schools or in the early design stages Schools in hot arid climate depend on courtyard to encourage students’ for social activity. In order to improve Outdoor Thermal Comfort (OTC), applying passive mitigation strategies in the courtyard is critical issue. This paper aims to improve students’ thermal comfort in school courtyards throughout the study of a public school with an E-shaped style in New Assiut City. Hence, different shading strategies (shading with different heights, vegetation, and hybrid) are simulated by using ENVI-met model v 5.0.0 to improve OTC for students in school courtyards. Firstly, monitoring was conducted inside outer courtyards. Then nine scenarios of passive strategies were implemented inside two courtyards with a ratio H/W = 0.4 and 0.7. After that, Physiological Equivalent Temperature (PET) was used to compare different scenarios. The results found, by applying hybrid orthogonal and diagonal staggered shading with trees in wide canyons, significant reductions of PET values reached 18.5°C and 18.6°C respectively. In addition, the shading at height= 4 m hybrid with trees achieves the best OTC improvement in the school courtyards. Thus, PET values were located in comfortable and slightly warm ranges for wide courtyard with H/W ratio = 0.4, and this result is more sufficient than in deep canyon with H/W = 0.7. Hence, the study provides information for architects and planners to integrate hybrid scenarios of staggered shading and trees whether in the current schools or in the early design stages for them to reduce heat stress and improve students’ thermal comfort.

Linking landscape spatial heterogeneity to urban heat island and outdoor human thermal comfort in Tokyo: Application of the outdoor thermal comfort index

Rapid urbanization and high-density development are major drivers of global warming. The associations of spatial landscape patterns with urban thermal environments have been extensively investigated. Meanwhile, quantifying the cooling effects of landscape patterns on street-level outdoor thermal comfort has been less attempted. This study examined the relationship between the spatial heterogeneity of landscape patterns and urban residents’ outdoor thermal comfort in Tokyo, Japan. The cooling effects of the greenery pattern – configurations and compositions – on thermal comfort were explored while considering the interaction effects of greenery patterns with water bodies and urban densities. Our study findings indicated that spatial landscape patterns have a statistically significant impact on outdoor thermal comfort, showing 69% of explanatory power (Adj-r2) in the spatial error model. The cooling effects of greenery were improved when their spatial patterns were in a more aggregated, less fragmented, and less complex shape. Furthermore, outdoor thermal stress was relatively lower when there was simple shape greenery in low-density areas or complex shapes but in high-density areas while indicating synergies between them. Our findings would provide microclimatic urban planning and design implications of how to spatially configure urban greenery to improve outdoor thermal comfort.