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Evaluation of outdoor thermal comfort in sunlight, building shade, and pergola shade during summer in a humid subtropical region
Abstract
This study evaluated outdoor thermal comfort during summer in a humid subtropical region. Meteorological inspections were conducted in sunlight, building shade, and pergola shade. The participants included 42 collegiate male subjects who completed questionnaires on thermal sensation and thermal comfort. To evaluate the thermal environments, we used three thermal indices: the universal effective temperature (ETU), the universal thermal climate index (UTCI), and the outdoor standard effective temperature (OUT_SET*). We confirmed that the ETU model is a suitable index for evaluating outdoor thermal comfort in the range of this study. Thermal neutral temperatures, as measured by ETU, UTCI, and OUT_SET*, were 33.1 °C, 34.0 °C, and 28.9 °C, respectively. Under sunlight, intense solar radiation raised the ETU value considerably; however, humidity and air velocity lowered it due to increased skin wettedness from the hot environment. The ETU model can provide a more detailed understanding of the various parameters affecting thermal comfort in the outdoor environment. At 800 W/m2 of total solar radiation in sunlight, the building shade and pergola shade with plants provided cooler thermal environments with ETU reductions of 18.4 °C and 16.2 °C, respectively, compared with sunlight. In cloudy conditions with total solar radiation of 300 W/m2, the building and pergola shades had ETU reductions of 9.3 °C and 6.8 °C, respectively.
... Natural and artificial shade provided by trees, buildings, and corridors is crucial for improving pedestrian thermal comfort, and their influence varies over time [49][50][51][52][53]. In our study, high values of TCV (i.e., more uncomfortable) were observed along the more City. ...
... Among these, the building coverage ratio played the most important role. Building height is often closely related to shading effects [50,64]. However, in this study, the mean building height strongly affected thermal comfort indicators in the early afternoon and late afternoon ( Table 6). ...
Urban populations face increasing heat stress in cities. However, the influence of the built environment of new and old urban blocks on pedestrian thermal comfort remains unclear. This study selected typical old (Yongqingfang) and new urban areas (Knowledge City) in Guangzhou, China, as our research sites. Through field monitoring and surveys, we used physiological equivalent temperature (PET) and thermal comfort vote (TCV) to evaluate outdoor thermal comfort by thermal walk experiments. We analyzed the relationships between built environment variables, meteorological variables, and pedestrian thermal comfort at the two sites. Our analysis revealed significant differences in the built environment and meteorological conditions between the new and old urban blocks within the 60-m buffer zone. PET and TCV showed noticeable spatiotemporal variations in both sites, and their correlation was stronger in the morning (r = 0.87–0.89) than late afternoon (r = 0.60–0.70). Our stepwise regression model indicated that sky view factor and building coverage ratio significantly affected outdoor thermal comfort in old and new urban blocks. Built environment variables explained a higher percentage of the variance in PET (Yongqingfang R2: 0.59–0.82, Knowledge City R2: 0.32–0.81) than TCV (Yongqingfang R2: 0.45–0.57, Knowledge City R2: 0.48–0.69). In short, built environment variables affected thermal indices more than thermal perception. The impact of built environment variables on TCV is also greater in new urban areas than in old urban blocks. Our findings provide insights into the complex relationship between built environments and outdoor thermal comfort in different urban landscapes, which informs climate-resilient urban design.
... In thermal perception research, the predicted mean vote (PMV) was first proposed by Professor Fanger in Denmark [34]. In order to further deepen the research on human thermal sensation, more relevant human comfort indexes emerged, such as wet bulb black globe temperature (WBGT) [35], physiological equivalent temperature (PET) [36], habitual thermal climate index (UTCI) [37], and standard effective temperature (SET) [38]. It has been found that the perception of the thermal environment is not only related to the physical environment of the microclimate, but also linked to the subjective consciousness of the human body. ...
... #0 Outdoor thermal comfort biodiversity (10); vegetation (26); forest (6); community (7); national park (4); pattern (9); biodiversity (22); vegetation (65); forest (7); community (12); national park (15); pattern (14); biodiversity (36); vegetation (134); forest (14); community (6); national park (11); pattern (25); vulnerability (2); shade (2); management (5); vulnerability (7); shade (10); management (20); ecosystem service (16) (21); air pollution (7); wind (4); street canyon (17); numerical simulation (6); cfd (40); air flow (46) air pollution (21); wind (22); street canyon (83); numerical simulation (23); prediction (10); pollution dispersion (2); cfd simulation (4); prediction (13); pollution dispersion (24); cfd simulation (14); mitigation strategy (24) (28); sensation (28); physical activity (10); From 2017 to 2022, testing the accuracy, applicability, and validity of human thermal indicators has become a systematic issue. It becomes another important segment of the landscape microclimate. ...
With the increasing requirements of healthy habitat environments, landscape microclimates have been widely concerned. To comprehensively grasp the development history and research status of the landscape microclimates in China and other countries, CiteSpace software was used to comparatively analyze and visually present the literature related to landscape microclimates in CNKI and WOS databases for the past 20 years. The results show that: (1) The number of publications on landscape microclimate research shows an increasing trend in China and other countries, and the number of publications increased significantly after 2016. Although the number of publications by Chinese scholars is less than that of foreign scholars, they have developed rapidly in recent years, and their international influence has increased significantly. (2) A positive exchange has been formed among international scholars, and the number of collaborative studies has been increasing. China’s microclimate research has formed relatively stable teams that have conducted numerous studies in the fields of urban communities, street greening, and plant communities, respectively. Although the links between research teams and institutions in China and other countries are relatively close, they still need to be further strengthened. (3) In the past decade, the theoretical system of landscape microclimates has been improved, and the research themes have become more concentrated, but it still has remained close to the early basic research. (4) Future research will remain centered on “mitigating the urban heat island effect” and “optimizing human heat perception”. New topics such as “biodiversity”, “carbon cycle”, and “climate change” have been added. In conclusion, the research needs to continue to explore the evaluation system of microclimates and verify the evaluation index of outdoor thermal comfort for human thermal adaptation in different regions. The standards and systems of human habitat adapted to different regional characteristics should be formed.
... Several studies have examined urban forms, such as building overhangs [12,13] and building setbacks [14,15]. Different shade materials have been explored, such as nylon sun sail [16][17][18], polyvinyl chloride (PVC) umbrella [19,20], glass cover [21], aluminium structure [22], concrete shelter [23], pergola [24] and photovoltaic canopies [8]. Other studies about engineered shade have focused on the transparency of glass shading devices, which affects the reflection and transmission of solar radiation [25,26]. ...
... Fourthly, we used sunny conditions as our experimental and simulation conditions. The performance of shading devices is different in sunny and cloudy conditions [20,24]. Future studies can compare the effects of shading devices on thermal and visual comfort under sunny, partly cloudy, and cloudy conditions. ...
Shading effectively alleviates heat stress caused by heatwaves and urban heat islands. Artificial shading is a viable alternative to urban greenery when tree planting is impracticable. While tree shade has been studied extensively, the effects of shading devices on the microclimate and illuminance are not well understood. To examine the influence of shading devices on outdoor thermal and visual comfort, we conducted on-site meteorological observations and surveys (n = 1272) on a university campus in Guangzhou during the summer of 2018. In ENVI-met simulations, various shading device properties were compared, including materials, transparency, and size. Simulation results indicate that shading devices reduced mean radiant temperature, Physiological Equivalent Temperature (PET), and Universal Thermal Climate Index (UTCI) up to 24.8 °C, 12.0 °C and 5.9 °C, respectively. However, there was a negligible reduction in air temperature and wind speed. Opaque materials and glass covers with 10% transparency decreased illuminance by 73%–83% and 65%–75%, respectively. Moreover, the size threshold for optimal cooling effects differs in locations with different sky view factors and tree shade. Our survey reveals that reducing the illuminance by > 90,000 lux and sun sensation vote from +2.5 to +1 can lower the thermal sensation vote by up to one vote. As shading devices decrease illuminance and thermal indices, the cross-modal effect between visual and thermal comfort would need to be considered in optimizing the design of shading devices. Further observation and numerical simulation of outdoor microclimate and illuminance are necessary to validate this cross-modal effect in other climatic regions.
... The adverse environmental conditions related to climate change and the need to adapt outdoor public space to these constraints mean that certain types of architectural elements are necessary to optimise the quality of a given urban space (Ou and Lin 2023;Watanabe et al. 2014). Although the assessment of urban walls was not applicable, it is important to briefly mention this important architectural element, which would certainly be an asset to the square and to the urban comfort of its users. ...
The application of an effective and efficient model for the assessment of construction design solutions for outdoor public spaces is currently necessary for cities to obtain high quality urban spaces, be it a street, a square or a park. The characteristics of a given outdoor public space are defined by the appropriate choice of materials and construction techniques used, which must tend towards sustainable solutions. It is therefore imperative that these places are attractive in terms of urban comfort, safe to use and economically viable throughout their useful life. The model presented in this study is applicable to the design of new outdoor public spaces, as well as to the renovation of the built environment. The model has been applied to a square in the city of Maia, Portugal, which also serves to test and further develop the analysis and calculation methodology. As a main result, the square has been classified as a “good quality” outdoor public space, which is reflected in level 4 according to the proposed scale. Therefore, to further improve this space and reach the maximum level, specific improvement indicators are provided.
... Material choices and design considerations are, therefore, critical to fulfilling both aesthetic and protective functions, adding a layer of practicality to the broader goal of creating resilient and visually pleasing urban environments. With regard to shade structures and shelters, critical for user comfort and safety, demand thorough assessment of construction solutions (Watanabe et al. 2014;Turnbull and Parisi 2005). This is driven by the need to consider the durability of materials, design innovation and adaptability to different environmental conditions. ...
This research explores the synergy between modernity and tradition in the creation of sustainable construction solutions for outdoor public spaces, with the aim of optimising urban quality. The comprehensive methodology includes pre-assessment, categorisation of construction solutions and strategic optimisation. Key urban elements, from pavements to waste management, are examined, highlighting their unique strengths and challenges. The study highlights the importance of a balanced approach, integrating smart technologies with traditional or vernacular solutions. The results show the transformation of outdoor public spaces into vibrant, inclusive, and sustainable environments. Significant achievements include innovative urban design, ecologically balanced green spaces, and a comprehensive framework for holistic urban development. Beyond the physical structures, the research emphasises community nurturing, cultural preservation, and the creation of a sustainable legacy for future generations.
... The extreme heat, particularly during the summer when recorded highest temperature reaches 50°C in July 7, 9 , makes walking outdoors uncomfortable and potentially hazardous. Research shows that shade from buildings and trees is essential for improving outdoor thermal comfort [10][11][12][13] . Ideally, sidewalks should be fully shaded by trees to provide continuous relief throughout the day. ...
In recent decades, the population boom in Middle Eastern cities has led to increased motorization and consequent carbon emissions. Cities have been expanding their public transportation systems and promoting walking and biking. However, the scorching temperatures make the active-mobility choice challenging. This study investigates the alignment of the shortest and shadiest paths within 500 and 1000-meter walksheds of metro stations in Dubai, where commuters often walk to their destinations. We developed an optimal shading path method that assigns dynamic rewards to buildings, trees, and indoor shade, which better reflects real-world conditions than existing models that only give shade a constant reward. The results reveal that, on average, the shadiest path is 1.3% longer than the shortest path, with an 8.9% increase in building shade and an 8.8% decrease in sun exposure compared to the shortest path. The findings provide valuable information to planning agencies about where to prioritize shade provision, ultimately enhancing pedestrian comfort and promoting active mobility in warmer cities.
... As the greenery volume increases, the temperature rise decreases. This clearly demonstrates that greenery volume plays a crucial role in reducing temperatures in the microclimate of street spaces [48,49]. When the three-dimensional greenery volume of street trees is too low, it fails to provide thermal comfort improvements. ...
In the context of increasingly extreme high temperatures during the summer in cold regions, the spatial vitality of urban blocks is significantly affected. In order to enhance the summer vitality of sustainable urban neighborhoods, this study explores the mechanisms of street elements and vitality under the guidance of thermal comfort. Taking an urban pedestrian street in Sanlitun, Beijing, during a summer day as the research subject, this study systematically analyzed the impact of environmental factors such as street orientation, aspect ratio, three-dimensional greenery of trees, and tree spacing on the thermal comfort of street space. By quantitatively analyzing the relationship between thermal comfort and pedestrian vitality in different street spaces, this study reveals the mechanisms by which environmental factors enhance the summer usability and spatial vitality of pedestrian streets. The research results indicate that street vitality shows a gradually increasing trend throughout the day, particularly between 12:00 and 16:00, when thermal comfort significantly affects people’s vitality. Furthermore, univariate analysis reveals that the street aspect ratio is the primary factor influencing the spatial vitality of the southern section of the Sanlitun Taikoo Li pedestrian street, with a characteristic average of 8.28 over a week. Finally, the results of the multi-factor analysis show that, when enhancing street vitality, priority should be given to the interactions between street aspect ratio, tree greenery, temperature, and physiological equivalent temperature, where the correlation coefficient between street aspect ratio and vitality is 0.70, and that between temperature and physiological equivalent temperature is 0.63, both showing positive correlations. Research shows that, in street planning, a reasonable building aspect ratio (1:2 to 1:4) and scientific green design are key. By carefully controlling the planting density and greenery configuration of trees, optimal street space effects can be achieved. This study proposes sustainable urban design strategies by optimizing street space design and improving environmental thermal comfort, aiming to enhance the summer vitality of urban blocks in cold regions and advocate for a sustainable development model that combines ecological and social benefits.
... , carbon footprint accounting (C. Z. , building shade studies (Watanabe et al., 2014), and building stock analysis (Frantz et al., 2023). These studies can further contribute to addressing critical environmental challenges related to urbanization, thereby promoting the achievement of sustainable development. ...
Understanding urban vertical structures, particularly building heights, is essential for examining the intricate interaction between humans and their environment. Such datasets are indispensable for a variety of applications, including climate modeling, energy consumption analysis, and socioeconomic activities. Despite the importance of this information, previous studies have primarily focused on estimating building heights regionally at the grid scale, often resulting in datasets with limited coverage or spatial resolution. This limitation hampers comprehensive global analysis and the ability to generate actionable insights at finer scales. In this study, we developed a global building height map at the building footprint scale by leveraging Earth Observation (EO) datasets and advanced machine learning techniques. Our approach integrated multisource remote-sensing features and building morphology features to develop height estimation models using the extreme gradient boosting (XGBoost) regression method across diverse global regions. This methodology allowed us to estimate the heights of individual buildings worldwide, culminating in the creation of the three-dimensional (3D) Global Building Footprints (3D-GloBFP) dataset for the year 2020. Our evaluation results show that the height estimation models perform exceptionally well at a global scale, with R2 values ranging from 0.66 to 0.96 and root-mean-square errors (RMSEs) ranging from 1.9 to 14.6 m across 33 subregions. Comparisons with other datasets demonstrate that 3D-GloBFP closely matches the distribution and spatial pattern of reference heights. Our derived 3D global building footprint map shows a distinct spatial pattern of building heights across regions, countries, and cities, with building heights gradually decreasing from the city center to the surrounding rural areas. Furthermore, our findings indicate disparities in built-up infrastructure (i.e., building volume) across different countries and cities. China is the country with the most intensive total built-up infrastructure (5.28×1011m3, accounting for 23.9 % of the global total), followed by the USA (3.90×1011m3, accounting for 17.6 % of the global total). Shanghai has the largest volume of built-up infrastructure (2.1×1010m3) of all representative cities. The derived building-footprint-scale height map (3D-GloBFP) reveals the significant heterogeneity in urban built-up environments, providing valuable insights for studies on urban socioeconomic dynamics and climatology. The 3D-GloBFP dataset is available at 10.5281/zenodo.11319912 (Building height of the Americas, Africa, and Oceania in 3D-GloBFP; Che et al., 2024c), 10.5281/zenodo.11397014 (Building height of Asia in 3D-GloBFP; Che et al., 2024a), and 10.5281/zenodo.11391076 (Building height of Europe in 3D-GloBFP; Che et al., 2024b).
... During the simulation period, the overall utilization rate of facilities in the site is only 37.5%. Considering the simulation day is in the summer, neutral UTCI is set at 34°C as a reference, considering studies in the same climatic zone with similar air temperatures on the simulation date (Watanabe et al., 2014). It can be seen that only 22.8% of the facilities are in a state of thermal comfort. ...
... Meanwhile, in addition to tree canopies, various types of shades feature perforated or porous structures, including pergolas [113,114] and louvers [115,116]. The presence of these diverse shading objects with transmissive properties in built environments underscores the importance of developing scalable and accurate methods to estimate transmittance. ...
Street-view-based techniques for assessing the sky view factor (SVF) and solar irradiance under trees are gaining attention as tools for evaluating trees as nature-based solutions to mitigate urban heat risks. Although these metrics significantly depend on the morphology of trees and resulting canopy transmittance, an existing approach, termed the Solid Canopy Method (SCM), assumes zero transmission and has not accounted for these variations. This paper advances the computation of both metrics, improving their accuracy and application — we developed the Transmissive Canopy Method (TCM), a panorama-based approach that integrates semantic segmentation and binarization to evaluate SVF and solar irradiance while accounting for transmittance of tree canopies. Using a study area on a university campus in Singapore, we collected data on solar irradiance and 360°imagery to validate our method. The results indicated improved accuracy with MAE, RMSE, and R values of 77.8 Wm−2, 105.0 Wm−2 and 0.90, respectively — significantly outperforming the SCM. We showcased two use cases of our method: (1) high-resolution mapping of SVF and solar irradiance in a field with trees, and (2) walking route optimization considering sunlight exposure. Our findings highlight the strong capability of our TCM to evaluate the effects of trees in mitigating urban heat more accurately than the existing method. Additionally, the TCM has potential applications in urban planning and management, enabling strategic tree planting prioritizing areas lacking sufficient shading and developing tools for optimizing walking routes to minimize sunlight exposure.
... UTCI effectively captured the thermal sensations reported by participants, reflecting its comprehensive approach to accounting for environmental variables and human physiological responses. The consistent performance of UTCI aligns with its widespread acceptance and validation in diverse climatic contexts [24][25][26] . www.nature.com/scientificreports/ ...
This study evaluates the applicability of three thermal comfort indices—Physiologically Equivalent Temperature (PET), Standard Effective Temperature (SET), and Universal Thermal Climate Index (UTCI)—in various outdoor environments on the campus of Xi’an University, China. Meteorological data were collected on sunny days using a portable weather station at a height of 1.5 m, and subjective questionnaires were administered to 25 healthy university students over three months to gather Thermal Sensation Votes (TSV) and Thermal Comfort Votes (TCV). The study was conducted at four distinct outdoor locations: a lakeside area (Location 1), a shaded path (Location 2), a sports field (Location 3), and a plaza (Location 4). PET, SET, and UTCI values were calculated from the collected data using Rayman software. The analysis revealed significant differences in thermal comfort across the four locations, with the highest proportion of subjects feeling hot at the sports field (54.4%) and the highest proportion feeling cold at the lakeside (39%). The shaded path had the highest proportion of subjects feeling comfortable (79.4%), while the lakeside had the lowest (60.1%). The results indicated that SET underestimated thermal sensation at Locations 1, 3, and 4, necessitating calibration. PET was suitable for Locations 2, 3, and 4 but failed to reflect the thermal sensation at Location 1 due to prolonged sun exposure. In contrast, UTCI demonstrated applicability across all locations. To enhance accuracy, revised indices SET’ and PET’ were formulated using the mean-median method, providing more precise thermal comfort assessments. These findings underscore the limitations of SET and PET under specific conditions and highlight the robustness of UTCI, offering valuable insights for urban planning and design aimed at improving outdoor thermal comfort and well-being.
... Later, in 1988, some researchers (De Dear & Pickup, 2000;Jendritzky, et al., 2012;Honjo, 2009) compared several thermal indices and reached a decision that SET* is highly capable to evaluate outdoor comfort even the convective and radiant heat exchange is limited (Chen & Matzarakis, 2018). Further, the SET* has been extended again to make specifically for outdoor conditions (Jeong, et al., 2016;Shimazaki, et al., 2011;Watanabe, et al., 2014;Xi, et al., 2012). OUT_SET* is the outdoor variation of SET* which Complimentary Copy streamlines the complex MRT conditions along with an MRT with all other variables provided as in SET*. ...
... Later, in 1988, some researchers (De Dear & Pickup, 2000;Jendritzky, et al., 2012;Honjo, 2009) compared several thermal indices and reached a decision that SET* is highly capable to evaluate outdoor comfort even the convective and radiant heat exchange is limited (Chen & Matzarakis, 2018). Further, the SET* has been extended again to make specifically for outdoor conditions (Jeong, et al., 2016;Shimazaki, et al., 2011;Watanabe, et al., 2014;Xi, et al., 2012). OUT_SET* is the outdoor variation of SET* which Complimentary Copy streamlines the complex MRT conditions along with an MRT with all other variables provided as in SET*. ...
... Urban shading is generally categorized into building shade, tree shade and lightweight/artificial shade (Kántor et al., 2018;Lee et al., 2018;Middel et al., 2021;Watanabe et al., 2014). The latter two both provide options for targeted interventions at the street scale, compared to shading from buildings, which, although having the greatest cooling effect (Lee et al., 2018), is best suited to new urban developments. ...
... At the same time, trees set up for shading should be able to adapt to a high-altitude climate. In addition, flower beds and enclosed seats can be set up in appropriate locations to provide college students with a place to rest (40,41). ...
Introduction
Research on the outdoor thermal comfort (OTC) of a university campus is beneficial to the physical and mental health of college students.
Methods
In this study, the OTC of students attending Tibet University in Lhasa, which experiences high-altitude cold climate conditions, under different activity intensities was studied using field measurements and a questionnaire survey.
Results
With the increase in activity intensity, the comfort physiologically equivalent temperature (PET) value gradually increased in summer, while the comfortable PET value gradually decreased in winter. The most comfortable PET value is 17.6°C in summer and 11.5°C in winter. The neutral PET of Tibetan college students during outdoor activities in summer was 16.3°C, and the neutral PET of outdoor activities in winter was 12.1°C. Gender and ethnicity had different effects on thermal sensation under different activity intensities. Under vigorous-intensity activities, PET in winter and summer had the greatest influence on thermal sensation. The situation was different under moderate-intensity activity. PET had the greatest influence on thermal sensation in summer, and Tmrt had the greatest influence on thermal sensation in winter.
Discussion
These findings provide a basis for an improved design of the outdoor environment under different outdoor activity intensities in high-altitude areas.
... In recent years, extensive investigations on OTC have been conducted in various climatic zones worldwide (Eludoyin and Adelekan, 2013;Lai et al., 2020b), including many renowned coastal cities or regions such as Shanghai (Huang et al., 2019), Hong Kong , Nagoya (Watanabe et al., 2014), Melbourne (Nogueira et al., 2020), Singapore (Acero et al., 2022), and Umeå (Yang et al., 2017). However, most of these studies focused on squares, schools, parks, streets, or scenic areas located in central urban areas and did not consider the potential impacts of coastal climatic environments on outdoor thermal comfort. ...
Coastal outdoor spaces serve as public venues where individuals engage in water-related activities, admire scenic views, embark on tourist excursions, and partake in social gatherings. Enhancing thermal comfort is a crucial prerequisite for increasing the attractiveness of these spaces. This study investigated the outdoor thermal comfort (OTC) in a coastal park called Xinghai Park located in a cold region of China over a period of five days during the spring and autumn seasons. The universal thermal climate index (UTCI) was employed to establish the thermal benchmark. Through on-site measurements and questionnaire surveys, both single-factor and multi-factor analyses were conducted to assess the microclimate and thermal perception in four representative coastal spaces, thereby identifying the thermal benchmark and factors influencing thermal perception in the Coastal Park. The findings indicated that: (1) during the transition seasons, the neutral UTCI (NUTCI) of the Coastal Park was 15.3 °C, with neutral UTCI range (NUTCIR) ranging from 9.3 °C to 21.4 °C, and there were significant variations in the thermal benchmarks among different types of spaces; (2) the primary factors influencing thermal perception during the transition seasons in the Coastal Park were physical factors (Ta, Tg, RH, Va, G), while individual, social, and psychological factors also exerted varying degrees of influence on respondents' thermal perception; (3) there were substantial spatial differences in the factors influencing respondents' thermal perception. The findings of this study provide valuable references for determining thermal environmental design strategies for transitional season coastal outdoor recreational spaces and enhancing the quality of urban life.
... Asv Actual Sensation Vote Lamarca, C., Qüense, J., and Henríquez, C. (2018) [57] Etu Universal effective temperature Watanabe, S., Nagano, K., Ishii, J., and Horikoshi, T. (2014) [58] H Figure 12 depicts the number of works that employed questionnaire data collecting and the number of participants questioned. ...
The exponential growth of urban populations and city infrastructure globally presents distinct patterns, impacting climate change forecasts and urban climates. This study conducts a systematic review of the literature focusing on human thermal comfort (HTC) in outdoor urban environments. The findings indicate a significant surge in studies exploring HTC in open urban spaces in recent decades. While historically centered on Northern Hemisphere cities, there is a recent shift, with discussions extending to various metropolitan contexts in the Southern Hemisphere. Commonly employed urban categorization systems include Sky View Factor (SVF), Height × Width (H/W) ratio, and the emerging Local Climate Zones (LCZs), facilitating the characterization of urban areas and their usage. Various thermal indices, like Physiological Equivalent Temperature (PET), Predicted Mean Vote (PMV), Universal Thermal Climate Index (UTCI), and Standard Effective Temperature (SET), are frequently utilized in evaluating external HTC in metropolitan areas. These indices have undergone validation in the literature, establishing their reliability and applicability.
... Ouyang et al. [57] simulated the area with a 250 x 225 grid model at a 2 m horizontal resolution, while Sinsel et al. [42] used a 152 x 120 grid at a 1.5 m horizontal resolution. The majority of the research efforts with ENVI-met restrict simulation durations ranging from 4 to 12 [35,58,59] or constrain their focus on two to three morphological scenarios over a 24-h timeframe [60], or have concentrated on urban canyon or vegetation configurations [43,61]. These only provide a limited picture of the behavior of urban morphologies, whereas extended simulation periods of 24-48 h can generate more accurate climate results [62]. ...
... With regard to shade structures and shelters, critical for user comfort and safety, demand thorough assessment of construction solutions (Watanabe et al. 2014;Turnbull and Parisi 2005). This is driven by the need to consider the durability of materials, design innovation and adaptability to different environmental conditions. ...
... Furthermore, the transition between seasons contributes to longterm changes in human thermal history. Comparing this study (Table 5) with Liu et al.'s research [83] on transitional seasons in Hong Kong and Guangzhou, as well as year-round scale adjustments in studies like Guangzhou [80], Nagoya [81], and Wuhan [82], it is evident that despite belonging to the same climate region, significant variations exist in the TI values corresponding to the same TSV category. The TI values derived from this study are significantly higher compared to those from year-round and transitional season studies, while the discrepancies among the year-round and transitional season studies themselves are relatively minimal. ...
The urban heat island effect intensifies, leading to increased thermal exposure for city residents. Variations in thermal sensation are observed among individuals with different short-term thermal experiences, challenging the reliability of Thermal Sensation Vote (TSV) scales. This study investigates TSV disparities in Shanghai, China, between two groups: individuals with Short-Term Air Conditioning Usage Experience (STACUE) and those Lacking Short-Term Air Conditioning Usage Experience (LSTACUE). Through questionnaire surveys and environmental monitoring, the study evaluates the performances of various ensemble learning models for predicting TSV. The selected Random Forest Regressor is employed to calibrate TSV scales for Physiologically Equivalent Temperature, Standard Effective Temperature (SET*), Universal Thermal Climate Index, and Perceived Temperature. Using Shapley values from game theory, we reveal how environmental variables contribute to TSV differences among individuals with varying short-term thermal histories. Results indicate higher Thermal Unacceptable Vote and greater Environmental Expectation Vote for STACUE individuals versus LSTACUE ones. Calibrated TSV scales, particularly SET*, exhibit significant enhancements over original scales: a 35.04 % increase in prediction accuracy percentage and a 0.57 correlation increase. Explainable analysis underscores that air temperature (28.8%) has a stronger impact on TSV among STACUE individuals, whereas mean radiant temperature (32.2%) is the primary factor affecting TSV among LSTACUE. Furthermore, we found gender interacts with thermal environmental parameters concerning TSV. This study sheds light on how short-term thermal history influences TSV among residents, informing customized urban thermal management strategies.
... Understanding thermal and visual comfort is therefore crucial to designing attractive outdoor spaces and improving the quality of outdoor living. A study by Watanabe et al. (2014) shows how the shadows of buildings and pergolas provide cooler environments than sunlight in summer. Therefore, an important aspect to be considered is the different social activities related to the use of outdoor public spaces when comparing the summer and winter seasons, where not all summer activities should be abandoned in winter (Pressman 1996). ...
The aim of the present study is the development of a model for the assessment of construction design solutions for outdoor public spaces, specifically for streets, squares, and parks, sustained by the analysis of the most important criteria in the urban space. Each of these criteria is divided into sub-criteria, that are very relevant in defining the rigour of the respective model, where materials and construction solutions play a very important role in the quality of a given outdoor public space and are decisive in obtaining a good classification. Through the approach of the assessment model, it is possible to define a matrix of relationships between the criteria and the sub-criteria of the analysis, allowing the perception of which sub-criteria have more influence in the assessment of the outdoor public space. The overall result of the assessment of a given outdoor public space is presented on a qualitative scale defined by quality levels, and improvements can be identified to move to a higher quality level.
... The extracted results indicate that trees can provide an environment with a lower T mrt by an average of 12.62 °C and a maximum of 24.79 °C at 16:00, whereas an extended cooling effect is created by an architectural shade as well as the combination of tree and architectural shade that decline T mrt by 25.3 °C on average and a peak of 32.6 °C at 8:00. The findings of this study reveal the impacts of shade on outdoor thermal comfort improvement at the pedestrian level during the hot season that is in good agreement with previous studies [18,[53][54][55][56][57]. Also it is observed that an architectural shade creates a cooler environment than trees. ...
Thermal comfort is one of the most important factors affecting the quality of outdoor space. This work investigates the effect of shade on outdoor thermal comfort during the hot season. For this purpose, meteorological measurement and questionnaire surveys are conducted simultaneously at four points of the university campus in the cold semi-arid climate of Shahrood, Iran. Then the ENVI-met V4 is validated and implemented to examine the impact of different shading scenarios on outdoor thermal comfort. The neutral physiological equivalent temperature (PET) and the upper boundary of the PET comfort range are obtained at 21.9 °C and 26.9 °C , respectively. The results demonstrate that the plant shade creates the most acceptable thermal environment. Also shading cause a significant reduction in the PET value and thermal stress, while increasing the comfort levels and the comfort hours during the sunny days. Furthermore, the simulation results indicate that creating shade in the open space by trees contribute to lower level of mean radiant temperature up to 24.79 °C and up to 13.7 °C for PET. Moreover, a maximum mitigation effect of an architectural shade is obtained at 32.6 °C for mean radiant temperature and 17 °C for PET. The highest reduction of PET (17.2 °C) is achieved by the combination of trees and the architectural shade. The outcomes of this research work provide useful design recommendations to improve outdoor thermal comfort.
... With the rapid development of the economy, urban construction and expansion are exerting a significant influence on the climate and environment of urban areas [1,2]. This causes environmental pollution, the greenhouse effect, extreme weather, and other problems [3][4][5]. The contradiction between urban environmental problems and residents' need for healthy and comfortable living spaces is becoming increasingly prominent. ...
The urban heat island phenomenon in large cities is becoming increasingly serious as urbanization continues to develop, seriously affecting the lives of urban residents. Rivers can effectively alleviate urban heat islands and improve the thermal comfort of riverfront space in summer. Thus, the effect of rivers on the urban microclimate environment is studied in this work. A section of the Fu River in the inland city of Chengdu was selected as the research object, and a combination of experimental and numerical simulation methods was employed. ENVI-met software was used to study the river’s influence on the air temperature, relative air humidity, and the thermal comfort of the riverfront space. The measured experimental parameters are first used to verify the accuracy of the ENVI-met software simulation results, which are then employed to carry out simulation research. The simulation results suggest that the different types of underlying surfaces have varying impacts on the air temperature and relative air humidity. Rivers have a significant cooling effect on the regional thermal environment, and roads have a warming effect on the air temperature. The order of influence of different underlying surfaces on air temperature is as follows: rivers > roads > trees. Rivers have an obvious humidifying effect on the air, and roads have little effect on relative air humidity. The order of influence of different underlying surfaces on relative air humidity is as follows: rivers > trees > roads. The results of the outdoor predicted mean vote (PMV) reveal that rivers, trees, and green plants can effectively improve the comfort of individuals downwind.
... By comparing the PET value before and after the transformation at the same time of the day, it can be seen that the PET value after the transformation had decreased, and the thermal comfort had significantly improved. The shading structure can effectively block solar radiation and have a significant cooling effect in summer [73]. Effective tree placement and arrangement can improve outdoor microclimate and thermal comfort. ...
As a main place for student activities on campus, outdoor spaces have positive impacts on students’ physical and mental health. Namely, outdoor heat and comfort are of great significance to improve activity quality. Here, four unique outdoor spaces were studied to explore the varying effects on human thermal comfort during hot-summer and cold-winter periods. Distinct outdoor spaces (fully open, semi-open, semi-enclosed, and fully enclosed areas) from the southern campus of Anhui Jianzhu University were chosen. The PET was used as a metric for measuring thermal comfort and analyzing correlated spatiotemporal distributions. The results showed that outdoor thermal comfort was derived from multiple factors, including vegetation, underlying surface materials, building presence, and wind-heat environment. Notably, high correlations between Tmrt and thermal comfort were revealed, where such temperatures of places with trees or building shade were low; thus, PET was low. Further, Ws showed a significantly negative correlation with PET. Of the four outdoor space forms, the fully enclosed location had the lowest thermal comfort level, while the semi-enclosed spaces showed the highest level of body comfort. Therefore, semi-enclosed space (U-shaped) is recommended in campus planning and construction. Accordingly, an improved strategy was proposed based on experimental transformation for fully enclosed spaces. The thermal comfort after optimization was simulated to provide references for outdoor space thermal comfort improvement during seasonal extremes.
... Another noteworthy method for measuring the outdoor T mrt is the upper-and-lower-hemisphere method, which uses a four-component netradiometer to observe long-and short-wave radiant flux densities of the upper and lower hemispheres, requiring the separation of diffuse radiation from total solar radiation [34,35]. The practical utility of this method is illustrated in the literature. ...
Beach areas are characterized by unique underlying surfaces, contributing to a thermal environment with
thermal radiation that differs from urban areas. However, existing studies have not considered the estimation
bias of the black-globe thermometer method in the thermal evaluations of beach areas. Thus, for thermally
characterizing beach areas, this paper aimed to appraise the accuracy of estimation results of mean radiant
temperatures (Tmrt) by the black-globe thermometer method and upper-and-lower-hemisphere method based on
the results of the six-directional method; to verify correction formulas for the thermometric method; and to
compare coastal radiation and biometeorological indices across anthropometric heights and locations. Numerous
findings were noteworthy. Firstly, the beach area exhibited a higher Tmrt than other urban underlying surfaces,
while sea breezes lowered coastal air temperatures, thus mitigating thermal stress. Secondly, relative to the
benchmark Tmrt values, the thermometric method exhibited over-estimations while the hemispheric method
exhibited the least variability. Thirdly, the two Tg-correction-based thermometric methods registered substantial
Tmrt deviations, whereas the direct correction equation registered only modest deviations. Lastly, the thermal
environment differed significantly across three heights, of which the height of 0.1 m exhibited greater thermal
stress. Conversely, the thermal environment differed little across the three beach locations. This study offers
analytical insights into the thermal characterization of beach environments and accuracy of different Tmrt-esti-
mation methods, providing robust evidence-based methodological guidance to future studies on coastal thermal
comfort.
... More contemporary versions of berceaux, also known as pergolas or arbour walkways, are nowadays constructed in Dutch private gardens and public parks, but are not yet commonly used for microclimate amelioration in urban public spaces. Despite this, research shows that pergolas can significantly reduce radiant temperature by casting shade (Hoyano, 1988;Katsoulas et al., 2017;Watanabe, Nagano, Ishii, & Horikoshi, 2014). Some studies also found a reduction in air temperature below pergolas (Ch afer, Pisello, Piselli, & Cabeza, 2020; Katsoulas et al., 2017). ...
Current solutions for climate amelioration require excessive amounts of energy, such as air conditioners and patio heaters. Yet, historical energy-passive climate-responsive design solutions exist that have a potential for outdoor microclimate control. Regarding these solutions, there was no overview of historical vegetation for microclimate amelioration in oceanic climate zones. We therefore explored historical vegetation types for microclimate amelioration in the Netherlands, for the example of oceanic climate zones. We identified six vegetation types: espaliered trees, tree lanes, berceaux, shelterbelts, green walls and umbrella trees. For each type we described their historical microclimatic function(s) and discussed their quantitative microclimatic effects based on available literature. Whilst tree lanes and green walls are currently applied to ameliorate urban microclimate, this seemed not to be the case for umbrella trees, espaliered trees, shelterbelts and berceaux. We therefore recommend urban designers to also consider these other historical vegetation types for passive outdoor microclimate amelioration.
As key urban infrastructures, urban lakeside parks are vital recreation and leisure spaces for city residents. However, creating a comfortable microclimate in these parks is challenging, particularly in cities with scorching summers and significant diurnal temperature differences, such as Zhengzhou (characterised by hot and humid summers). Addressing this challenge is a critical objective in urban planning, as it directly affects the well-being and park usage of residents. From July 11 to 16,2023, Longzi Lake Park was taken as the research object, and the peak period of crowd activity from 9 a.m. to 7 p.m. was selected for observing tourists behaviour. During this period, the microclimate factors, including air temperature, solar radiation, relative humidity, wind speed, and wind direction, were continuously observed by measuring instruments at a height of 1.5 m from the ground. The research indicates several key findings: (1) Both solar radiation and air temperature significantly affect human thermal comfort in the park. As solar radiation intensifies, individuals experience the most comfortable thermal sensations in fully shaded areas. Hence, it can be noted that provision of shading is an important factor in reducing heat stress. (2) The presence of water bodies also significantly enhances thermal comfort during the summer months. Water features contribute to a cooling and humidifying effect, and improved thermal comfort levels in water-adjacent areas. Therefore, park visitors tend to seek out waterside spaces for activities and relief from the heat. (3) The study identifies a negative correlation between PET (Physiologically Equivalent Temperature) and the number of visitors with tendency to visit waterside areas. This suggests that the perception of thermal comfort is affected by the type of activity, with park visitors engaged in physical exercises appearing to be reduced.
The urban environment is threatened by urban heat island (UHI) effect and air pollution events which have been worsened by population increase, heat waves, and wildfire smoke. It is important to understand that urban air quality and thermal environment are mutually dependent, meaning that the alteration in one can affect the other. This two-way interaction is described in our review through a detailed analysis of physics-based models and their synergistic processes. Then, drawing on the literature, we categorized mitigation plans into four major strategies: modification of urban morphology, integration of urban greenery, incorporation of water bodies, and utilization of cooling materials. The identified mitigation strategies were evaluated for their effectiveness in achieving various reduction targets, such as overheating, strong wind events, and gaseous and aerosol pollutants. These assessment results can be helpful in developing a practical guide for establishing climate-resilient buildings and cities. This study also conducts a co-benefits and conflicts analysis associated with these mitigation strategies, discussing their application potentials for designers, planners, and policymakers in preparing cities to become thermally resilient and healthy. The review emphasizes the need for the formulation of numerical coupling models that will address the “thermo–pollutant” coupling to better comprehend the magnitude of synergies.
Outdoor thermal comfort affects occupants’ well-being and building energy use. A reliable thermal index tailored to diverse climates is crucial for improving outdoor conditions. Current calibration methods for the neutral thermal range typically set a Thermal Sensation Vote threshold between −0.5 and 0.5. However, this threshold was derived from the indoor-focused Predicted Mean Vote model, which may not be applicable to outdoor conditions. To address this limitation, a revised calibration framework for outdoor scenarios is proposed, taking subtropical hot-humid campus as a case study. The key aspect of this framework is refining the neutral Thermal Sensation Vote interval for outdoor settings. First, an evaluation of the original outdoor thermal comfort index identified the necessity for recalibration. Next, the correlation between Thermal Comfort Vote and Thermal Sensation Vote was established to accurately localize context-specific neutral Thermal Sensation Vote interval. Finally, the proposed framework was applied to UTCI calibration, yielding a modified neutral UTCI range of 4.5–27.2°C through localized regression analysis. This study also highlights the impact of spatial configurations on outdoor thermal comfort, finding higher thermal tolerance within natural landscapes. It provides insights into creating outdoor thermal settings in subtropical hot-humid locations, especially for campus construction or renovation.
Thermal comfort is a significant aspect of human well-being and productivity, particularly in tropical and subtropical regions where high temperatures and humidity prevail yearly. However, research on indoor and outdoor thermal comfort in those regions is lacking when compared to other areas, and a significant gap exists in the comprehension related to the suitability and application of existing thermal comfort indices. This study intends to provide insights into existing human thermal comfort indices based on their applications in tropical and subtropical regions of Koppen climates for indoor and outdoor. PRISMA guidelines are used for conducting a systematic literature review using 86 articles. Of these, 38 were original thermal comfort indices articles and 48 were case studies (indoor and outdoor). This research discussed the most and least preferred indices as well as the approaches and parameters considered by the thermal comfort indices. The result shows that most efforts were made in temperate and continental climates to derive thermal comfort indices. For outdoor thermal comfort assessment, 72% of studies used Physiological Equivalent Temperature; 21% used Discomfort Index and Universal Thermal Climate Index. Whereas for indoors, > 90% of studies used the Predicted Mean Vote index and Operative Temperature. Overall, the used thermal comfort indices in reviewed studies underestimate the comfortable ranges observed in tropical and subtropical regions. The findings of this study can be utilized by researchers, urban designers, and planners to increase understanding related to human thermal comfort in tropical and subtropical climates.
Rising global temperatures have resulted in urban heat waves in recent years,
endangering residents' health and even their lives. As a result, accurate outdoor thermal comfort prediction is critical. The goal of this research is to develop highly accurate and interpretable machine learning models of outdoor thermal comfort. We created a summer outdoor thermal comfort dataset for cold regions using microclimate parameter measurements and questionnaires, and divided it into two datasets: without and with shading. The prediction performance of nine machine learning models was compared, as well as their prediction performance following Bayesian optimization. Finally, the SHAP model was used to explain the important features of the best machine learning models and their impact on thermal comfort. The results show that after partitioning the dataset by shading, the accuracy of the best machine learning prediction models for Thermal sensation vote (TSV), Thermal acceptable vote (TA), and Thermal comfort vote (TCV) in the unshaded space improves by 9.2%, 9.31%, and 6.16%, respectively, while the prediction accuracy in the shaded space remains basically unchanged. Extreme gradient boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), and categorical boosting (CatBoost) outperform other methods. After Bayesian optimization (BO), the machine learning models' TSV, TA, and TCV prediction accuracies improved by 6.83%, 4.05%, and 2.55%, respectively. CatBoost model with Bayesian optimization (CatBoost+BO) was the best model in most cases. TSV, TA, and TCV predictions were heavily influenced by microclimate parameters, with mean radiant temperature being the most important in unshaded spaces and air temperature being critical in shaded spaces. Furthermore, age, body mass index, and emotional state all had a significant impact on TA and TCV. This research will contribute to improving the quality of life of urban residents by providing a scientific foundation for the design and planning of urban open space.
Urban outdoor space is an important activity place for residents, and its thermal environment directly affects residents’ quality of life and physical and mental health. Due to global climate change and the acceleration of urbanization, the outdoor thermal comfort of urban residents has seriously declined, causing more and more scholars to pay attention to this problem and to carry out research. This paper summarizes the development history and evaluation principles of outdoor thermal comfort evaluation indices and sorts out the methods for achieving outdoor thermal comfort. This paper reviews the effects of urban climate, local microclimate, physiological, psychological, social, and cultural factors on outdoor thermal comfort. In addition, strategies for improving thermal comfort in urban outdoor spaces are discussed from the aspects of urban geometry, vegetation, surface materials, and water bodies. Finally, the existing problems and development directions of current urban outdoor space thermal comfort studies are pointed out. This review paper can provide a reference for the scientific planning and construction of urban outdoor spaces to improve people’s thermal comfort.
This book is a learning material for architecture students about outdoor thermal design. This book contains the basic principles of thermal design, from the concept of heat and its transfer, to its influence on building design. We hope that this book can provide a better understanding for architecture students regarding outdoor thermal comfort, as well as assist in developing better and more effective outdoor design skills which can guide their research activities.
Alongside rapid urbanization, the warm, humid tropical climate of Colombo exerts pressure on the city intensifying thermal discomfort. This could further create a negative influence on performing outdoor activities restricting the quality of life of urban dwellers. Therefore, creating a thermally comfortable urban space is significant. Yet, identifying the suitable tree species to provide better thermal comfort in Colombo has seldom been discussed. This study evaluates the impact on outdoor thermal comfort based on the physiologically equivalent temperature (PET) of five common species in Colombo; Cassia fistula, Tectona grandis, Plumeria obtuse, Mangifera indica, and Terminalia catappa. The field data collection was conducted on the sites of five selected species under both sunny and cloudy conditions. The parameters that contribute to assessing the urban thermal environment; sky view factor, relative humidity, air temperature, surface temperature, wind speed, solar radiation, and cloud cover were measured. The RayMan model was used to estimate thermal comfort by calculating PET values. The results indicated that the shading of trees can considerably influence outdoor thermal comfort expressed by PET. The lower PET values under the tree canopies indicated a lower level of thermal discomfort compared to an adjacent site, which was not directly shaded. Moreover, the one-way ANOVA test (p = 0.027) indicated that thermal comfort under Terminalia catappa was statistically different compared to Plumeria obtuse on sunny days. Additionally, among the selected species, Terminalia catappa was identified to be the most suitable species for improving thermal comfort in outdoor urban settings. The findings assist in the identification of species that offer greater thermal comfort in Colombo. As the use of appropriate tree species for shading is critical in alleviating heat stress, the results achieved can be employed as a measure of enhancing outdoor thermal comfort and as a vital initiative to achieve sustainability in Colombo.KeywordsUrban MicroclimateOutdoor thermal comfortUrban greeningSky View Factor (SVF)Physiologically equivalent temperature (PET)Colombo
This study investigated the applicability of expanded metal meshes (EMMs) in horizontal shading devices. We performed simulations and experiments with EMMs with different opening ratios and directions. We established various experimental and control groups to measure air temperature, surface temperature, and black globe temperature. After the comparison of simulation and experimental data, we used Grasshopper to simulate long-term climate situations. The research results can serve as reference for users in Tainan and provide customized suggestions. The findings can serve as a paradigm for parametric design to analyze EMMs. In design projects involving outdoor horizontal shading devices, these results can be used in the design phase for evaluation. Full-day measurements revealed that EMMs with small openings exhibited favorable shading effects. In the Tainan area, we suggest using north-facing EMMs; in our simulations result, 70% of sunshine did not pass through the mesh in a day. For shading equipment in the morning, west-facing EMMs should be used because they blocked 50-90% of sunshine. For recreational areas in the afternoon and evening, east-facing EMMs can block 50-90% of sunshine after noon. In Taiwan, south-facing EMMs are not advised because their shading performance is suboptimal in the morning and afternoon.
This chapter presents a comprehensive literature review of peer-reviewed papers on the UTCI with special focus on its applications. A search in Scopus and Web of Science has been conducted in February 2021 yielding 320 and 304 documents, respectively, for the time frame from 2000 to March 2021. Results have been classified according to 8 different categories, which roughly define the areas of application of the index: (1) Outdoor Thermal Comfort (OTC) and thermal stress; (2) Urban Climate and Planning studies; (3) Climate-related impacts on human health; (4) Bioclimate; (5) Comparisons with other thermal comfort indices; (6) Meteorological analyses; (7) Climate change research; (8) Tourism. The bulk of research carried out on the UTCI is primarily concentrated on the first two topics, reaching about 60% of papers output. Clusters identified in VOSviewer from co-occurrences of author keywords closely match the main areas of application of the index. Research output shows an intrinsic multidisciplinary nature but it is still concentrated in a few countries. Areas of application such as public weather service and climate-related impacts on the health sector still need to become aware of the potentialities and practicalities of the UTCI.KeywordsUTCILiterature reviewVOSviewerBibliometric analysis
Thermal comfort is an important indicator for evaluating the environment of urban public space, and appropriate thermal comfort can effectively prolong the duration of outdoor activities. In the existing studies, there is a lack of thermal comfort comparison between hot spots and cold spots. In this study, we selected the coastal city of Dalian in China as our study area and conducted field investigations on the thermal comfort of two landmark resorts, namely, a downtown commercial street and coastal leisure park. The study was conducted on typical summer days and consisted of interviewing several residents to understand their thermal comfort requirements. We investigated the thermal expectations of the interviewees through meteorological measurements and questionnaires. The universal thermal climate index (UTCI) was used to determine the thermal benchmarks of the on-site subjects. The results indicated that (1) globe temperature and air temperature were the most important factors that affected thermal comfort, followed by relative humidity and wind speed in summer daytime. (2) Shaded spaces are more comfortable than open spaces, and tree shade is preferred over artificial shade in coastal park. (3) The neutral UTCI (NUTCI) of the respondents were 24.1°C (coastal park) and 26.0°C (commercial street); the neutral UTCI ranges (NUTCIR) were 20.8–27.4°C (coastal park) and 23.3–28.7°C (commercial street). (4) The upper thermal acceptable range limits of the coastal park and commercial street were 30.2 and 32.1°C, respectively, which were substantially higher than the upper NUTCIR limit, indicating that the residents in Dalian were well-adapted to hot weather. The results can provide a good reference for determining ideal design strategies to optimize the thermal environment of urban outdoor recreation spaces in summers and improve the quality of life in coastal cities.
Providing thermally comfortable semi-outdoor and outdoor environments is essential to multi-functional public spaces such as museums, cultural centers and university campuses. Given the difficulty of controlling the thermal conditions, individuals may have reduced expectations regarding the thermal comfort of outdoor environments. An extensive field survey of five public places in Taiwan obtained 8077 sets of data. This study discussed thermal sensitivity and proposed thermal comfort ranges, neutral temperatures, and preferred temperatures for semi-outdoor and outdoor environments. The results show that occupants of semioutdoor and outdoor environments are more tolerant regarding thermal comfort than are occupants of indoor environments. Furthermore, global radiation appears to have greater potential to change subject thermal sensation than air movement. In a hothumid region such as Taiwan, semi-outdoor and outdoor environments, applied with sunshine eliminating design strategies, can effectively increase occupant thermal comfort.
Proceedings of the 15th International Congress of Biometeorology and International Conference on Urban Climatology, edited by R. de Dear and J. Potter (Macquarie University; Sydney) (ISBN 1 86408 5436). pp.ICB9.4.1-6.
Outdoor spaces play important roles in daily lives, and the use of these spaces is determined largely by outdoor thermal comfort. Few studies have been conducted on outdoor thermal comfort in northern China. Using microclimatic monitoring and subject interviews at a park in Tianjin, China, this investigation studied outdoor thermal comfort under different climate conditions. Although outdoor thermal environment varied greatly with air temperature from -5.0 to 34.5oC, 83.3% of respondents consider it “acceptable”. Preferences in solar radiation, wind speed, and relative humidity were related to air temperature. The higher the air temperature was, the higher the wind speed and the lower the solar radiation and relative humidity desired by the occupants, and vice versa. The data were also used to evaluate three indices. The Universal Thermal Climate Index (UTCI) satisfactorily predicted outdoor thermal comfort, while the Predicted Mean Vote (PMV) overestimated it. The neutral Physiological Equivalent Temperature (PET) range found in this study was 11-24oC, which was lower than the ranges in Europe and Taiwan. Our study indicated that residents of Tianjin were more adapted to cold environment.
Existing procedures for the assessment of the thermal environment in the fields of public weather services, public health systems, precautionary planning, urban design, tourism and recreation and climate impact research exhibit significant shortcomings. This is most evident for simple (mostly two-parameter) indices, when comparing them to complete heat budget models developed since the 1960s. ISB Commission 6 took up the idea of developing a Universal Thermal Climate Index (UTCI) based on the most advanced multi-node model of thermoregulation representing progress in science within the last three to four decades, both in thermo-physiological and heat exchange theory. Creating the essential research synergies for the development of UTCI required pooling the resources of multidisciplinary experts in the fields of thermal physiology, mathematical modelling, occupational medicine, meteorological data handling (in particular radiation modelling) and application development in a network. It was possible to extend the expertise of ISB Commission 6 substantially by COST (a European programme promoting Cooperation in Science and Technology) Action 730 so that finally over 45 scientists from 23 countries (Australia, Canada, Israel, several Europe countries, New Zealand, and the United States) worked together. The work was performed under the umbrella of the WMO Commission on Climatology (CCl). After extensive evaluations, Fiala's multi-node human physiology and thermal comfort model (FPC) was adopted for this study. The model was validated extensively, applying as yet unused data from other research groups, and extended for the purposes of the project. This model was coupled with a state-of-the-art clothing model taking into consideration behavioural adaptation of clothing insulation by the general urban population in response to actual environmental temperature. UTCI was then derived conceptually as an equivalent temperature (ET). Thus, for any combination of air temperature, wind, radiation, and humidity (stress), UTCI is defined as the isothermal air temperature of the reference condition that would elicit the same dynamic response (strain) of the physiological model. As UTCI is based on contemporary science its use will standardise applications in the major fields of human biometeorology, thus making research results comparable and physiologically relevant.
A variety of research has linked high temperature to outdoor thermal comfort in summer, but it remains unclear how outdoor meteorological environments influence people's thermal sensation in subtropical monsoon climate areas, especially in China. In order to explain the process, and to better understand the related influential factors, we conducted an extensive survey of thermally comfortable conditions in open outdoor spaces. The goal of this study was to gain an insight into the subjects' perspectives on weather variables and comfort levels, and determine the factors responsible for the varying human thermal comfort response in summer. These perceptions were then compared to actual ambient conditions. The database consists of surveys rated by 205 students trained from 6:00 am to 8:00 pm outdoors from 21 to 25 August 2009, at Nanjing University of Information Science & Technology (NUIST), Nanjing, China. The multiple regression approach and simple factor analysis of variance were used to investigate the relationships between thermal comfort and meteorological environment, taking into consideration individual mood, gender, level of regular exercise, and previous environmental experiences. It was found that males and females have similar perceptions of maximum temperature; in the most comfortable environment, mood appears to have a significant influence on thermal comfort, but the influence of mood diminishes as the meteorological environment becomes increasingly uncomfortable. In addition, the study confirms the strong relationship between thermal comfort and microclimatic conditions, including solar radiation, atmospheric pressure, maximum temperature, wind speed and relative humidity, ranked by importance. There are also strong effects of illness, clothing and exercise, all of which influence thermal comfort. We also find that their former place of residence influences people's thermal comfort substantially by setting expectations. Finally, some relationships between thermal perception and amount of exercise, thermal experience, mood, clothing, illness and microclimate, etc., are established. Our findings also shed light on how to resist or adapt to outdoor hyperthermic conditions during summer in subtropical monsoon climate areas.
Over the past century more than 100 indices have been developed and used to assess bioclimatic conditions for human beings. The majority of these indices are used sporadically or for specific purposes. Some are based on generalized results of measurements (wind chill, cooling power, wet bulb temperature) and some on the empirically observed reactions of the human body to thermal stress (physiological strain, effective temperature). Those indices that are based on human heat balance considerations are referred to as "rational indices". Several simple human heat balance models are known and are used in research and practice. This paper presents a comparative analysis of the newly developed Universal Thermal Climate Index (UTCI), and some of the more prevalent thermal indices. The analysis is based on three groups of data: global data-set, synoptic datasets from Europe, and local scale data from special measurement campaigns of COST Action 730. We found the present indices to express bioclimatic conditions reasonably only under specific meteorological situations, while the UTCI represents specific climates, weather, and locations much better. Furthermore, similar to the human body, the UTCI is very sensitive to changes in ambient stimuli: temperature, solar radiation, wind and humidity. UTCI depicts temporal variability of thermal conditions better than other indices. The UTCI scale is able to express even slight differences in the intensity of meteorological stimuli.
Recognising that modifications to the physical attributes of urban space are able to promote improved thermal outdoor conditions and thus positively influence the use of open spaces, a survey to define optimal thermal comfort ranges for passers-by in pedestrian streets was conducted in Curitiba, Brazil. We applied general additive models to study the impact of temperature, humidity, and wind, as well as long-wave and short-wave radiant heat fluxes as summarised by the recently developed Universal Thermal Climate Index (UTCI) on the choice of clothing insulation by fitting LOESS smoothers to observations from 944 males and 710 females aged from 13 to 91 years. We further analysed votes of thermal sensation compared to predictions of UTCI. The results showed that females chose less insulating clothing in warm conditions compared to males and that observed values of clothing insulation depended on temperature, but also on season and potentially on solar radiation. The overall pattern of clothing choice was well reflected by UTCI, which also provided for good predictions of thermal sensation votes depending on the meteorological conditions. Analysing subgroups indicated that the goodness-of-fit of the UTCI was independent of gender and age, and with only limited influence of season and body composition as assessed by body mass index. This suggests that UTCI can serve as a suitable planning tool for urban thermal comfort in sub-tropical regions.
This paper presents the findings of an outdoor thermal comfort study conducted in Hong Kong using longitudinal experiments--an alternative approach to conventional transverse surveys. In a longitudinal experiment, the thermal sensations of a relatively small number of subjects over different environmental conditions are followed and evaluated. This allows an exploration of the effects of changing climatic conditions on thermal sensation, and thus can provide information that is not possible to acquire through the conventional transverse survey. The paper addresses the effects of changing wind and solar radiation conditions on thermal sensation. It examines the use of predicted mean vote (PMV) in the outdoor context and illustrates the use of an alternative thermal index--physiological equivalent temperature (PET). The paper supports the conventional assumption that thermal neutrality corresponds to thermal comfort. Finally, predictive formulas for estimating outdoor thermal sensation are presented as functions of air temperature, wind speed, solar radiation intensity and absolute humidity. According to the formulas, for a person in light clothing sitting under shade on a typical summer day in Hong Kong where the air temperature is about 28°C and relative humidity about 80%, a wind speed of about 1.6 m/s is needed to achieve neutral thermal sensation.
This review comprehensively examines scientific literature pertaining to human physiology during exercise, including mechanisms of heat formation and dissipation, heat stress on the body, the importance of skin temperature monitoring, the effects of clothing, and microclimatic measurements. This provides a critical foundation for microclimatologists and biometeorologists in the understanding of experiments involving human physiology. The importance of the psychological aspects of how an individual perceives an outdoor environment are also reviewed, emphasizing many factors that can indirectly affect thermal comfort (TC). Past and current efforts to develop accurate human comfort models are described, as well as how these models can be used to develop resilient and comfortable outdoor spaces for physical activity. Lack of suitable spaces plays a large role in the deterioration of human health due to physical inactivity, leading to higher rates of illness, heart disease, obesity and heat-related casualties. This trend will continue if urban designers do not make use of current knowledge of bioclimatic urban design, which must be synthesized with physiology, psychology and microclimatology. Increased research is required for furthering our knowledge on the outdoor human energy balance concept and bioclimatic design for health and well-being in urban areas.
The physiological equivalent temperature, PET, is a thermal index derived from the human energy balance. It is well suited to the evaluation of the thermal component of different climates. As well as having a detailed physiological basis, PET is preferable to other thermal indexes like the predicted mean vote because of its unit ( degrees C), which makes results more comprehensible to urban or regional planners, for example, who are not so familiar with modern human-biometeorological terminology. PET results can be presented graphically or as bioclimatic maps. Graphs mostly display the temporal behaviour of PET, whereas spatial distribution is specified in bioclimatic maps. In this article, some applications of PET are discussed. They relate to the evaluation of the urban heat island in cities in both temperate climates and warm climates at high altitude. The thermal component of the microclimate in the trunk space of a deciduous forest is also evaluated by PET. As an example of the spatial distribution of PET, a bioclimatic map for Greece in July (Mediterranean climate) is presented.
Bioclimate conditions at Sun Moon Lake, one of Taiwan's most popular tourist destinations, are presented. Existing tourism-related climate is typically based on mean monthly conditions of air temperature and precipitation and excludes the thermal perception of tourists. This study presents a relatively more detailed analysis of tourism climate by using a modified thermal comfort range for both Taiwan and Western/Middle European conditions, presented by frequency analysis of 10-day intervals. Furthermore, an integrated approach (climate tourism information scheme) is applied to present the frequencies of each facet under particular criteria for each 10-day interval, generating a time-series of climate data with temporal resolution for tourists and tourism authorities.
In urban planning it has become more important to consider climatic comfort in the outdoor open spaces such as parks, streets, etc., to make up higher-grade residential environment. However, relation between human thermal sensations and surrounding climatic conditions or thermal indices is not yet made so clear in the outdoor environment as in the indoor ones. Thus the experiments on human thermal sensation were conducted in the shade of trees and in sunshine during summer season. This paper mainly describes Comfort sensation in relation to other thermal sensations and thermal indices. Temperature sensation is most highly correlated with Comfort sensation and Sweatiness and Radiation sensations are next to this. Wetness sensation has low relation with Comfort as a whole. Air Flow sensation is moderately related in treeshade but low in sunshine. ASHRAE's Standard New Effective Temperature, SET*, is recommended as a fairly good thermal index for out-door environment, having high correlation with Comfort sensation in comparison with Discomfort Index and Wet-Bulb Globe Temperature Index. SET* from 27℃ to 28℃ is considered to be the threshold for comfort in the out-door environment, based on the cumulative frequency distribution of SET* for each category of Comfort sensation. Comfortable temperature, T_<a・cal>, calculated by Penwarden's comfort equation is inclined to be less than measured value, T_<a・meas・> R_b, thermal resistance of body tissue, equal to 0.04 m^2℃/W (onset of sweating) gives better agreement between T_<a・cal> and T_<a・meas・> rather than R_b equal to 0.065 m^2℃/W (no sweating, i.e., most comfortable) does. The better T_<a・cal> agrees with T_<a・meas・>, the higher wind speed, the higher comfortable level of Comfort sensation and the lower Sweatiness sensation.
There are few studies on the microclimate and human comfort of urban areas in hot dry climates. This study investigates the influence of urban geometry on outdoor thermal comfort by comparing an extremely deep and a shallow street canyon in Fez, Morocco. Continuous measurements during the hot summer and cool winter seasons show that, by day, the deep canyon was considerably cooler than the shallow one. In summer, the maximum difference was on average 6K and as great as 10K during the hottest days. Assessment of thermal comfort using the PET index suggests that, in summer, the deep canyon is fairly comfortable whereas the shallow is extremely uncomfortable. However, during winter, the shallow canyon is the more comfortable as solar access is possible. The results indicate that, in hot dry climates a compact urban design with very deep canyons is preferable. However, if there is a cold season as in Fez, the urban design should include some wider streets or open spaces or both to provide solar access.
Consideration of urban microclimate and thermal comfort is an absolute neccessity in urban development, and a set of guidelines for every type of climate must be elaborated. However, to develop guidelines, thermal comfort ranges need to be defined. The aim of this study was to evaluate the behaviour of different thermal indices by investigating different thermal environments in Damascus during summer and winter. A second aim was to define the lower and upper limits of the thermal comfort range for some of these indices. The study was based on comprehensive micrometeorological measurements combined with questionnaires. It was found that the thermal conditions of different outdoor environments vary considerably. In general, Old Damascus, with its deep canyons, is more comfortable in summer than modern Damascus where there is a lack of shade. Conversely, residential areas and parks in modern Damascus are more comfortable in winter due to more solar access. The neutral temperatures of both the physiologically equivalent temperature (PET) and the outdoor standard effective temperature (OUT_SET*) were found to be lower in summer than in winter. At 80 % acceptability, the study defined the lower comfort limit in winter to 21.0 °C and the upper limit in summer to 31.3 °C for PET. For OUT_SET*, the corresponding lower and upper limits were 27.6 °C and 31.3 °C respectively. OUT_SET* showed a better correlation with the thermal sensation votes than PET. The study also highlighted the influence of culture and traditions on people’s clothing as well as the influence of air conditioning on physical adaptation.
A thermal comfort study has been carried out in outdoor urban spaces in Singapore. The field study was carried out from August 2010 to May 2011. There were 2059 respondents from 13 different outdoor spaces participated in this study and 2036 effective questionnaire responses were collected. Thermal comfort perceptions and preferences were analyzed in this study. The neutral operative temperature occurred at 28.7 °C and preferred temperature was found to be 26.5 °C. Thermal acceptability analysis shows the acceptable operative temperature range was 26.3–31.7 °C in outdoor urban spaces in Singapore. Correlation analysis indicates that sun sensation/solar radiation has the most significant influence on human thermal sensation in outdoor spaces. This study also explores the impact of thermal adaptation on human thermal sensation in outdoor spaces, which could be useful for future researchers. Comparative analysis shows that people may expect a higher temperature in outdoor conditions than in semi-outdoor or indoor conditions in Singapore, suggesting that people in outdoor conditions could be more tolerant with the heat stress than people in indoor conditions in tropical climate.
In an outdoor environment, thermal comfort is affected by various factors, in particular solar radiation. Quantifying the solar absorptance of a human body is necessary for accurately assessing outdoor thermal comfort. Numerous studies have measured the solar absorptance of skin and fabrics. However, these measurements do not represent the solar absorptance of clothed humans. This study intends to determine the average solar absorptance of the human body wearing a combination of specific black and white garments and measure the average solar absorptance of Japanese, college-aged male subjects wearing casual summer, autumn, and winter clothing. The solar absorptance of the entire clothed human body was derived from these measurements. The solar absorptance of a black-shirt and black-trousers combination was found to be 0.76. For the combination of a white-shirt and white-trousers, the minimum solar absorptance was 0.38. Furthermore, the average solar absorptances of 30 Japanese, college-aged male subjects wearing casual clothing in summer, autumn, and winter were 0.66, 0.69, and 0.77, respectively. In summer, the average solar absorptance of the subjects in casual clothing depended on the color of tops. The average solar absorptances were suggested to be 0.76, 0.56, and 0.68 for subjects wearing black tops, white tops, and tops with Munsell values between 2 and 8, respectively.
Tree-shaded outdoors can reduce the heat effect by ameliorating the microclimate and enhancing the human thermal comfort outdoors; for this reason, they are main places for rest, recreation and social activity in Taiwan's cities. Field comfort surveys of 3839 interviewees were conducted in tree-shaded spaces throughout a year. The aims were to obtain a better understanding of human thermal comfort response outdoors and to propose an adaptive comfort model for tree-shaded spaces. A comfort zone, centering on neutral operative temperature which is an empirically derived linear function of mean monthly outdoor temperature, of 6 °C for 90% acceptability and 8 °C for 80% acceptability was suggested for tree-shaded spaces from surveyed data, adding that a non-linear function of the temperature difference between actual operative temperature and neutral operative temperature was established that aims to predict the percentage of heat or cold discomfort at a particular outdoor thermal condition. An application of the established adaptive comfort model on an actual tree-shaded space was demonstrated to show its practicality in long-term evaluation of a particular thermal environment.
This paper aims to clarify the handling technique of the solar radiation in an element of the thermal environment evaluation indices and to add expansions and improvements to conduction-corrected modified effective temperature ETF (Kurazumi et al., 2009) that can quantify the comprehensive effect on sensational and physiological sense and the effect of individual meteorological elements on the same evaluation axis applicable to an outdoor environment. Mean radiant temperature and radiant heat transfer coefficient of the outdoor space was defined. Enhanced conduction-corrected modified effective temperature ETFe that is ETF including short-wave solar radiation in outdoor space was defined. This sensational and physiological climatic environment index can make temperature convert each effect of difference in posture; air velocity; long-wave radiation in the outdoor space; short-wave solar radiation; contact surface temperature and humidity into individual meteorological elements. The addition of each temperature-converted factor is possible and quantifying the composite effect on sensational and physiological sense in the outdoor spaces as well as the discrete effect of each meteorological element is possible on the same evaluation axis. Consequently, it is possible to make the climate modification effects due to tree shade and areas of water that improve the urban thermal environment quantitatively explicit.
The purpose of this study is to propose new thermal index for outdoor and non-uniform environments with heat conduction, such as when a person sits on a bench at a park. This paper describes mathematically the theory of how solar radiation and heat conduction, as well as air temperature, humidity, air velocity and longwave radiation, are incorporated into the new index and how these thermal factors that may not be uniform are treated. Another important feature is that separate indices are generated for each factor while the new index is derived. It is expected that the new index will help us to understand how much each factor affects the human thermal comfort in outdoor and non-uniform environments with heat conduction.Highlights► New index for human thermal comfort is proposed theoretically. ► This index takes solar radiation and heat conduction into consideration. ► This index can indicate effects on local body area(s) as well as a whole body simultaneously. ► The index can also indicate universal and separate effects of the environmental factors simultaneously.
The mean radiant temperature (Tmrt) is one of the most important meteorological parameters governing human energy balance. In this paper, three different methods of obtaining the Tmrt in an outdoor urban setting are compared. Method A is based on integral radiation measurements and angular factors, method B is based on measurements with a 38-mm flat grey globe thermometer and in method C makes use of the Rayman 1.2 software is used. Measurements were performed in a large open square in a high latitude city—Göteborg, Sweden—during clear to overcast weather conditions in October 2005 and in July and August 2006.
Results show that the difference between Method A and Method B was generally relatively small. Most of the discrepancy, caused by rapid changes in radiation, temperature and wind speed was smoothed out using 5 min mean values. By systematically and empirically changing the mean convection coefficient, the accuracy of Method B was improved and a new equation expressing the Tmrt was obtained. With this new equation the 38 mm flat grey globe thermometer could successfully be used to estimate the Tmrt in an outdoor urban setting provided that the wind speed and the air and globe temperatures are measured accurately. The study also shows that the flat grey colour of the globe thermometer slightly underestimates the level of short-wave radiation (i.e. sunshine). Method C works very well during the middle of the day in July, i.e. at high sun elevations. However, the model considerably underestimates the Tmrt in the morning and evening in July and during the whole day in October, i.e. at low sun elevations.
In outdoor urban settings where thermal comfort researchers or urban planners and designers require an easy and reliable method of estimating mean radiant temperature, the 38 mm flat grey globe thermometer provides a good and cheap solution. Copyright
The influence of climatic and geometric variables on the hourly diffuse fraction has been studied, based on a data set with 22,000 hourly measurements from five European and North American locations. The goal is to determine if other predictor variables, in addition to the clearness index, will significantly educe the standard error of Liu- and Jordan-type correlations (). Stepwise regression is used to reduce a set of 28 potential predictor variables down to four significant predictors: the clearness index, solar altitude, ambient temperature, and relative humidity. A piecewise correlation over three ranges of clearness indices is developed to predict the diffuse fraction as a function of these four variables. A second piecewise correlation is developed for predicting the diffuse fraction as a function of the clearness index and solar altitude, for use when temperature and relative humidity are not available. A third piecewise correlation of the Liu- and Jordan-type is developed from the same data set. Comparing this correlation with the new correlations provides a direct measure of the value of added predictor variables. The full diffuse fraction correlation reduced the residual sum squares by 14% when compared to the correlation that is a function of the clearness index only. The correlation including the clearness index and solar altitude diminished the residual sum squares by 9%. The correlations exhibited some degree of location dependence. This is expected, as the climates are quite different. The correlations also showed some seasonal dependence; the errors are higher in the fall and winter than on an annual basis.
In the absence of empirical outdoor thermal comfort studies it has been widely assumed that indoor thermal comfort theory generalises to outdoor settings without modification. Many indoor models were developed to describe thermal discomfort, not stress, therefore their relevance to conditions that vary greatly from neutrality, as many outdoor climatic conditions do, has not been critically validated in the field to date. The thermal comfort of 1018 subjects in outdoor and semi-outdoor locations in subtropical Sydney was investigated by a questionnaire and a comprehensive package of micro-meteorological instruments. The thermal neutrality in terms of the thermal comfort index of 26.2°C was significantly higher than the indoor counterpart of 24°C (ASHRAE Trans. 92 (1986) 709).
This paper presents some of the findings of the European project, RUROS, primarily concerned with the environmental and comfort conditions of open spaces in cities. The results of the microclimatic and human monitoring, in relation to the thermal environment and comfort conditions in open spaces, are presented. The database consists of nearly 10,000 questionnaire guided interviews from field surveys in 14 different case study sites, across five different countries in Europe. The findings confirm a strong relationship between microclimatic and comfort conditions, with air temperature and solar radiation being important determinants of comfort, although one parameter alone is not sufficient for the assessment of thermal comfort conditions. Overall comfort levels are over 75% for all cities on a yearly basis. There is also strong evidence for adaptation taking place, both physically, with the seasonal variation in clothing and changes to the metabolic rate, as well as psychologically. Recent experience and expectations play a major role and are responsible for a variation over 10 °C of neutral temperatures, largely following the profile of the respective climatic temperatures on a seasonal basis, across Europe. In this context, perceived choice over a source of discomfort is another important parameter for people in open spaces.
With considerably increased coverage of weather information in the news media in recent years in many countries, there is also more demand for data that are applicable and useful for everyday life. Both the perception of the thermal component of weather as well as the appropriate clothing for thermal comfort result from the integral effects of all meteorological parameters relevant for heat exchange between the body and its environment. Regulatory physiological processes can affect the relative importance of meteorological parameters, e.g. wind velocity becomes more important when the body is sweating. In order to take into account all these factors, it is necessary to use a heat-balance model of the human body. The physiological equivalent temperature (PET) is based on the Munich Energy-balance Model for Individuals (MEMI), which models the thermal conditions of the human body in a physiologically relevant way. PET is defined as the air temperature at which, in a typical indoor setting (without wind and solar radiation), the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor conditions to be assessed. This way PET enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors. On hot summer days, for example, with direct solar irradiation the PET value may be more than 20 K higher than the air temperature, on a windy day in winter up to 15 K lower.
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