Human Thermal Comfort Research Articles

High-temperature and thermal radiation affecting human thermal comfort and physiological responses: An experimental study

Hot environments with high temperatures and thermal radiation are to be found in heat treating, glass melting workshops, etc., which impacts worker thermal comfort and physiological responses. The motivation of this study was to explore the changes of thermal comfort in a high-temperature and thermal radiation environment. Four experimental cases were designed to simulate high temperatures and thermal radiation. Physiological parameters such as skin temperature, ear cancel temperature, heart rate, and weight loss were investigated. Evaporative heat losses and skin wettedness were calculated by Gagge's two node model or weight loss. The results showed that local and mean skin temperatures increased by approximately 4 °C during the exposure. Thermal sensation vote was positively correlated with WBGT. The dynamic relationship between human heat gain, evaporative heat loss and potential thermal risk was framed as Stage A, Stage B, and possibly Stage C. This study could provide the basic information and theoretical evidence for the thermal comfort and thermal risk in high-temperatures and thermal radiation environment.

Molecular dynamics study of paraffin/polyethylene blends as phase change materials for energy efficiency in buildings

ABSTRACT The greenhouse gas emissions and global energy consumption associated with construction materials can be greatly reduced by incorporating phase change materials into buildings. These materials can absorb and release energy during a phase transition, thus reducing the energy consumption while achieving human thermal comfort. Molecular dynamics simulations were used to study the miscibility of both linear and branched polyethylene with two types of paraffin (octadecane and hexatriacontane) at two different temperatures. The results showed that blending was better at high temperatures for both polymers, and branched polyethylene was more miscible with both paraffins than linear polyethylene was. Hexatriacontane exhibited better blending characteristics. From the molecular dynamics results, we concluded that linear polyethylene/paraffin blends were more suitable as phase change materials in buildings than branched polyethylene/paraffin blends, as they were miscible at high temperatures but separated into two phases at ambient temperature. The optimal blends were subsequently incorporated into a cement model to study their influence on the mechanical properties of this construction material. The introduction of the blends into the cement model deteriorated its mechanical properties.

Research on indoor thermal environment evaluation and thermal adaptation in winter of Japanese wood-framed detached houses

Indoor space is the place where human beings live, and how to meet people's indoor thermal comfort needs in the context of energy scarcity is one of the important issues for sustainable development of buildings, and the evaluation of the indoor thermal environment has become the key to it. In the case of Japanese wood-framed detached houses, which contain different types of space forms, it is difficult to accurately apply the existing thermal environment evaluation results. In this study, detached houses in Kitakyushu City, Japan, were selected as the research object, and continuous measurements and subjective questionnaires of the indoor thermal environments were conducted based on three modes of no heating, continuous heating, and intermittent heating, in order to grasp the current information of the thermal comfort in detached houses. The results showed that: 1. The average indoor temperatures in both Washitsu and Yoshitsu were lower than the human thermal comfort range; 2. The thermally neutral temperature of 15.9 °C in Washitsu was lower than that of 17.7 °C in Yoshitsu, and the acceptable temperature zones were (14.3–17.5 °C) and (15.6–18.9 °C), respectively; 3. Develop modified models (PMVe) and adaptive predicted mean vote (aPMV) model suitable for thermal comfort evaluation of detached houses in Japan. The results of this study will help to improve the indoor thermal environment and thermal comfort evaluation system of Japanese detached houses, and provide a useful reference for the study of the renewal and renovation of houses in this area.

The Effects of Exterior Glazing on Human Thermal Comfort in Office Buildings

As a major component of the building envelope, the energy-saving design of exterior windows is key to energy savings in office buildings. The conventional design of exterior windows mainly focused on their impact on heating and cooling energy but ignored the indoor thermal comfort problems caused by the direct solar radiation transmitted by windows and the fluctuation of their internal surface temperatures. This study analyzed the influence of exterior windows on the indoor thermal environment of office buildings by carrying out field experiments. The experiments were carried out in a typical office building in Xi’an during December and January. The impact of exterior windows on human thermal comfort was studied from two perspectives: longwave radiation from the surface of window glass and solar shortwave radiation. It was found that solar radiation was the main cause of temperature fluctuations on the internal surface of windows and created non-uniform thermal environments. The mean radiant temperature fluctuations in the near-window area could reach up to 7.8 °C due to outdoor solar radiation in winter. Solar radiation transmitted by windows directly affects thermal sensations. Since conventional thermal comfort models or indices underestimated the thermal sensations of occupants in the presence of solar radiation, the additional thermal loads caused by solar radiation needed to be taken into account. The allowable operative temperature range for maintaining thermal comfort should be reduced by 0.5 °C when occupants are exposed to solar radiation.

Climate projections of human thermal comfort for indoor workplaces

Climate models predict meteorological variables for outdoor spaces. Nevertheless, most people work indoors and are affected by heat indoors. We present an approach to transfer climate projections from outdoors to climate projections of indoor air temperature (Ti) and thermal comfort based on a combination of indoor sensors, artificial neural networks (ANNs), and 22 regional climate projections. Human thermal comfort and Ti measured by indoor sensors at 90 different workplaces in the Upper Rhine Valley were used as training data for ANN models predicting indoor conditions as a function of outdoor weather. Workplace-specific climate projections were modeled for the time period 2070–2099 and compared to the historical period 1970–1999 using the same ANNs, but ERA5-Land reanalysis data as input. It is shown that heat stress indoors will increase in intensity, frequency, and duration at almost all investigated workplaces. The rate of increase depends on building and room properties, the workplace purpose, and the representative concentration pathway (RCP2.6, RCP4.5, or RCP8.5). The projected increase of the mean air temperature in the summer (JJA) outdoors, by + 1.6 to + 5.1 K for the different RCPs, is higher than the increase in Ti at all 90 workplaces, which experience on average an increase of + 0.8 to + 2.5 K. The overall frequency of heat stress is higher at most workplaces than outdoors for the historical and the future period. The projected hours of indoor heat stress will increase on average by + 379 h, + 654 h, and + 1209 h under RCP2.6, RCP4.5, and RCP8.5, respectively.

Quantifying the effects of indoor non-uniform solar radiation on human thermal comfort and work performance in warm season

Window-through solar radiation significantly affects indoor thermal environments as well as human thermal comfort and health. This study aims to investigate occupants’ thermal comfort and work performance with indoor solar radiation conditions in warm season. 24 subjects participated in six field tests with varying solar radiation conditions, while recording environmental, physiological, and psychological parameters. Results indicate that strong solar radiation significantly impacts physiological, psychological responses, and work performance. Specifically, compared to no direct solar radiation condition (only weak diffuse radiation), mean skin temperature increased by 0.6–1.6 °C, while local skin temperature increased by up to 2.7 °C. Additionally, SpO2 decreased and PR increased with higher solar radiation intensity. Besides, averagely, at the same operative temperature (Top) (28 °C), the percentage of thermal discomfort was approximately 18 % higher with direct solar radiation compared to without. The upper limit of the optimal Top range (less than 20 % of the subjects felt thermal discomfort and unproductive) with direct solar radiation (25.1 °C) is about 3 °C lower than without direct solar radiation (28.0 °C). For high willingness to work (90 %), the upper limits of the optimal Top range with and without exposure to direct solar radiation are 24.2 °C and 26.8 °C, respectively.

Numerical study of human thermal comfort in changing environments of high and low temperature

A great temperature difference (GTD) in changing environments has a great impact on human comfort and health. Thus, the optimization of human comfort in the GTD environment becomes extremely important. In this paper, the human thermal regulation and clothing heat transfer in the GTD environment were simulated. The predicted skin temperature was verified by the experimental results in the GTD environment. The absolute error percentage of skin temperature was less than 5 %, indicating that the model has good accuracy for prediction of skin temperature in the GTD environment. Influencing factors of thermal comfort in the GTD environment were studied by the validated model. It was found that the influence of clothing thermal resistance had a critical value on the thermal comfort. When the effective thermal resistance was less than the critical value, increasing clothing thermal resistance improved the thermal comfort, and vice versa. The influence of metabolic equivalent change on the thermal comfort in a low-temperature environment was greater than that in a high-temperature environment. Finally, the thermal comfort time of human was predicted by the model, which could predict the duration of thermal comfort state under different GTD environments. The findings have great significance to adjust the comfortable dress of human under the GTD environment.

Heat transfer simulation of electric heating fabric system and parametric design: Towards human thermal comfort and energy efficiency

A 3D heat transfer model was developed to optimize the design of electric heating garments (EHGs) towards human thermal comfort and energy efficiency. The model deals with the thermal interaction between human skin, a three-layer electrical heating fabric system, and cold environments, allowing analysis of the heating process and resultant skin temperature. Three heat transfer mechanisms, namely conduction, convection and radiation, were considered. The real-time and final skin temperatures from simulation and measurement exhibited a difference below 4%, demonstrating the efficiency of the model. A steady-state parametric study was conducted using the validated numerical model. Five parameters, such as heating temperature, thermal resistance of the inner and outer fabrics, wind speed, and environmental air temperature, were involved. The results indicate that the heating temperature and thermal resistance of the inner fabric have a more noticeable effect on the temperature of the skin surface below the heated area compared to the other three factors. Apart from the heating temperature, the other four factors have a greater impact on the skin temperature of non-heated regions than that of the heated region. Multiple linear regression analysis was performed to establish a relationship between skin temperature and the five factors. Based on this analysis, a prediction model for skin temperature was developed and subsequently used to determine relevant parameters for EHGs. A method for optimizing the design of electrically heated clothing is proposed, which can achieve the dual goals of human thermal comfort and energy efficiency.

Modeling the Normalized Urban Heat Island for the City of Karlsruhe by Linking Urban Morphology and Green Infrastructure

Citizens in urban areas are affected by the urban heat island (UHI) effect, resulting in increased thermal heat compared to rural areas. This threat is exacerbated by global climate change. Therefore, it is necessary to assess human thermal comfort and risk for decision making. This is important for planners (climate resilience), the health sector (information for vulnerable people), tourism, urban designers (aesthetics), and building architects. Urban structures modify local meteorological parameters and thus human thermal comfort at the microscale. Knowledge of the pattern of a city’s UHI is typically limited. Based on previous research, generalized additive models (GAMs) were built to predict the spatial pattern of the UHI in the city of Karlsruhe. The models were trained with administrative, remotely sensed, and land use and land cover geodata, and validated with measurements in Freiburg. This identified the hot and cold spots and the need for further urban planning in the city. The model had some limitations regarding water bodies and anthropogenic heat production, but it was well suited for applications in mid-latitude cities which are not topographically characterized. The model can potentially be used for other cities (e.g., in heat health action plans) as the training data are freely available.

Research on the Heating Effect of a Convection Radiator Based on a Human Thermophysiological Model

Forced convection is the most effective way to improve the thermal efficiency of a radiator under low-temperature conditions. This technical method differs significantly from the heating effects of general radiation and natural convection. Few studies have applied the objective evaluation method based on quantitative calculation to evaluate the effectiveness of indoor heating or optimize the technical parameters (air flow rate, air supply method, etc.) of heating systems. This article couples human metabolic factors with heating environmental factors and uses a 57-node human thermal physiological model to evaluate the effectiveness of forced convection radiator heating from the perspective of the local thermal comfort of the human body and demonstrates the feasibility of this scheme by comparing it with floor radiation heating. The research shows that the air supply speed of a radiator affects human thermal comfort. Continuing to increase the wind speed, at a speed of 3 m/s, the surface temperature of the human body reaches a high value and will then decrease, leading to a decrease in thermal comfort. Research on indoor air distribution shows that the use of bottom-side air supply provides better thermal comfort compared to top air supply. The local skin temperature distribution of the human body indicates that when the indoor average temperature is higher than 20 °C, the overall thermal comfort of convective radiator heating and floor radiant heating is comparable. The article provides a way of objectively calculating and directly quantifying the effect of heating equipment on human thermal physiological parameters.

Effects of large skylights on lighting and thermal environments in underground public transport hubs: A case study in Shenzhen

Large skylights in underground public transport hubs are designed to introduce natural light and reduce the energy consumed by artificial lighting. Although large skylights can improve the lighting environment of underground public transport hubs, they also increase energy consumption due to solar radiation. Therefore, there is an urgent need to balance the improved lighting and energy consumption associated with large skylights and to determine the optimal design scheme. There are few studies on the lighting and thermal environments of underground public transport hubs, and the optimal design scheme for large skylights is unclear. Therefore, in the current study, field tests were conducted to analyze the lighting and thermal environments of two underground public transport hubs located in Shenzhen: Shenzhen North Station and Futian Station. In addition, multiobjective optimization was carried out for the large skylight at Futian Station. The results showed that most passengers were satisfied with the lighting and thermal environment under large skylights, but they were less satisfied in the summer than in the winter. Therefore, appropriate shading measures should be considered to reduce the effect of large skylights on passengers’ thermal comfort in the summer. Furthermore, the results of multiobjective optimization indicated that the large skylight at Futian Station led to a 28.1 % reduction in annual air conditioning-induced energy consumption, a 31.5 % increase in the lighting performance index (UDI), and a 43.8 % increase in the human thermal comfort index (CTR). The results of this study could provide guidance for the design of large skylights in underground public transport hubs.

Analysis of thermal discomfort associated with synoptic conditions in the city of Pelotas, southernmost region of Brazil.

Here, we evaluated the influence of outdoor environmental conditions (synoptic weather conditions) on human thermal discomfort in the five macro-regions of Pelotas city, located in the southernmost region of Brazil. To do this, meteorological sensors (HOBO MX2301A) were installed outside the residences to measure the air temperature, dew point temperature, and relative humidity between 18 January and 20 August 2019. Two well-established simplified biometeorological indices were examined seasonally: (i) humidex for the summer months and (ii) effective temperature as a function of wind for the autumn and winter months. Our findings showed seasonal differences related to human thermal discomfort and outdoor environmental conditions. The thermal discomfort was highest in the afternoons during the summer months and at night during the winter months. The seasonal variation in human thermal discomfort was highly associated with the meteorological conditions. In summer, the presence of the South Atlantic Subtropical Anticyclone (SASA) contributed to heat stress. The SASA combined with the continent's low humidity contributed to the perceived sensation of thermal discomfort. In the winter, thermal discomfort was associated with the decrease in air humidity caused by high atmospheric pressure systems, which led to a decrease in both air temperature and air moisture content. Our findings suggest that a better understanding of the complex interplay between outdoor environmental factors and human thermal comfort is needed in order to mitigate the negative effects of thermal discomfort.

Spatiotemporal variability in human thermal comfort perception in open-air spaces: application to the state of Minas Gerais, Brazil.

The objective of this study was to propose bioclimatic zoning to classify human thermal comfort and discomfort in the state of Minas Gerais, Brazil; both historical and future scenarios are considered. Thus, historical series (1961 to 2017) of the effective temperature index as a function of the wind (ETW) were obtained as a function of the monthly average values of the minimum, mean, and maximum dry-bulb air temperatures (tdb,min, tdb,mean, and tdb,max, respectively), in addition to the mean relative humidity ([Formula: see text], %) and mean wind speed ([Formula: see text], m s -1). The data were obtained from 34 weather stations and subjected to trend analysis by using the nonparametric Mann-Kendall test, thus enabling the simulation of future scenarios (for 2028 and 2038). Then, to define the thermal ranges of the bioclimatic zoning, maps of ETWmin, ETWmean, and ETWmax were created from geostatistical analysis. Overall, the results show warming trends for the upcoming years in Minas Gerais municipalities. All climatic seasons showed an increase in the frequency of new classifications in the upper adjacent classes, which indicates climate warming. Therefore, when considering future scenarios for the autumn and winter seasons, attention should be given to changes in predicted thermal sensation, especially in the Central Minas Gerais, Belo Horizonte Metropolitan, South/Southwest Minas, Campo das Vertentes, and Zona da Mata.

Improving Pedestrian Thermal Comfort Using Optimized Urban Trees Pattern in Aswan City

For long periods last years, the majority of cities suffer from exceptionally hot- dry climate. However, the most urban patterns within these cities are unsuitable for these severe occurrences and raise the value of the Urban Heat Island (UHI). The goal of this study is to see how UHI mitigation options affect outdoor human thermal comfort in three different forms of frequent urban trees patterns in the world’s most populous city in Egypt, Aswan. The ENVI-met model was utilised to assess meteorological using simulation climate program (Ecotect Analysis), buildings and vegetation distribution, using Pupulus Alba. All measurements were taken in a pedestrian walkway at the microclimate case study (case 1. without trees, case 2. distribution trees each 8m total coverage 50%, case 3. distribution trees each 12m total coverage 21.5% were conducted to measure, relative humidity, mean radiant temperature, wind speed, air temperature and prediction mean vote as a key indicator for human thermal comfort. This study provided a better understanding of the role of Urban Heat Island UHI mitigation strategies on human thermal comfort in the outdoor spaces of Aswan’s residential neighborhoods. The simulation results revealed high thermal comfort and discomfort after setting 3 cases for trees pattern for the climate and the possible vegetation (trees patterns). This result indicate that an optimized percentage of urban trees pattern can mitigate (UHI) effect and clear the role that urban trees serve in modifying microclimates.

Simulation-based thermal analysis and validation of clothed thermal manikin

Human thermal comfort within various environmental conditions is of paramount importance in a wide range of industries, including clothing design, indoor climate control, and occupational safety. Researchers are always in search the sophisticated tools and techniques that simulate the thermal regulation of human body under different environmental conditions. The present research aims to present a precise methodology for the simulation of clothed thermal manikin in controlled environmental conditions. A comprehensive method is recommended that consists of the use of 3D body scanning technology, different 2D and 3D CAD as well as thermal simulation software. The results of the simulations are very satisfactory, which are later validated with the wear trials with the help of the same clothed thermal manikin and under the same environmental conditions. The comparative analysis shows some deviations that are discussed thoroughly and the need for further research is highlighted in the papers as well. Furthermore, the present research gives us a digital platform to understand the clothing's thermal comfort and the parameters that affect it with the consideration of the draping behavior of the clothing, microclimate, thermal properties, and surrounding environmental conditions.

Special Section on Health, Urban Climate and Complexity in Urban Design and Planning

This journal section welcomes contributions addressing new knowledge through research, practice examples and experimentation related to public spaces for all. The section calls for contributions to a discourse within and across the nexus of:- Urban health to enable holistic and equitable communities- Urban climate analysis and environmental performance concerning, for example, city form, green infrastructure and human thermal comfort- Exploring urban complexities, particularly regarding the consideration of the system-wide interdependencies of sociotechnical and socioecological relationships.To date, there is very little discourse and research on public space undertaken from these perspectives and paradigms and their intersection. Hence, we seek contributions that embrace complexity, examine ambiguities and in-betweens, and contradictions in policies. We also welcome experimental methodologies that can have a practical impact and achieve an ontological shift towards transformative change in communities transcending the conceptual Global North and South, East and West dualism. We appreciate theoretical and practical investigations that demonstrate entanglement with multifaceted aspects ranging from visualisation, communication, or arts-based expressions. We seek to explore the environmental, social, and technical conditions that contribute to an urban climate conducive to health and well-being in the broadest sense. Selected contributions and case studies will need to demonstrate the successful application of at least two of the three focus themes. These manuscripts will allow space for discussion regarding scale-ability and practice application to achieve equitable public spaces.

Urban tree canopies drive human heat stress mitigation

Climate warming and urbanisation compound the public health risk posed by heat. Heat can be mitigated at local scales through urban greening, which provides shade and reduces surface and air temperatures. Yet, the relative effectiveness of different greening options on human thermal comfort based on physiology-based indices is understudied. We installed microclimate stations at 17 locations covering a gradient of tree canopy cover and perviousness in the city of Ghent, Belgium, and monitored the modified Physiologically Equivalent Temperature (mPET) during 195 days over Spring and Summer. We assessed the canopy cover, pervious surface fraction and building sky fraction based on field measures and hemispherical pictures. Unpaved locations with trees experienced a 2.4-fold reduction in the number of days with strong heat stress (mPET > 35 °C) compared to paved, treeless locations. Based on mixed models and our selected environmental variables, cooling effects were predominantly driven by tree canopy cover, where locations with 100% canopy cover had temperature maxima 5.5 °C mPET lower than treeless locations throughout the monitoring period. When air temperatures rose to 40 °C, cooling by tree canopies increased to 8.8 °C mPET. The pervious surface fraction and building view factor were less influential, generating variation of at most 1.7 °C and 1.1 °C mPET, respectively. In contrast, night-time temperatures were rather determined by the regional-scale urban heat island effect than by aforementioned local factors. Still, tree canopies slightly cooled the warmest nights only, whereas the vicinity of buildings led up to 1.2 °C mPET warming on average. Expanding the urban tree cover may therefore be the best solution for improving local thermal comfort levels when daytime heat peaks, but will provide little relief at night.

Direct Synthesis of Polyimide Curly Nanofibrous Aerogels for High-Performance Thermal Insulation Under Extreme Temperature.

Maintaining human body temperature is one of the basic needs for living, which requires high-performance thermal insulation materials to prevent heat exchange with external environment. However, the most widely used fibrous thermal insulation materials always suffer from the heavy weight, weak mechanical property, and moderate capacity to suppress heat transfer, resulting in limited personal cold and thermal protection performance. Here, an ultralight, mechanically robust, and thermally insulating polyimide (PI) aerogel is directly synthesized via constructing 3D interlocked curly nanofibrous networks during electrospinning. Controlling the solution/water molecule interaction enables the rapid phase inversion of charged jets, while the multiple jets are ejected by regulating charge density of the fluids, thus synergistically allowing numerous curly nanofibers to interlock and cross-link with each other to form porous aerogel structure. The resulted PI aerogel integrates the ultralight property with density of 2.4mg cm-3, extreme temperature tolerance (mechanical robustness over -196 to 300 °C), and thermal insulation performance with ultralow thermal conductivity of 22.4mW m-1 K-1, providing an ideal candidate to keep human thermal comfort under extreme temperature. This work can provide a source of inspiration for the design and development of nanofibrous aerogels for various applications.

Local Thermal Comfort and Physiological Responses in Uniform Environments

The thermal perception of different body parts can vary greatly throughout the human body and have different influences on overall thermal sensation and comfort. Various personal comfort systems (PCS) have been developed to stimulate local body parts for the purpose of enhancing human thermal comfort, yet the most effective body parts for intervention remain undetermined. Therefore, a series of climate chamber experiments under five uniform environments with three sets of suits were conducted in this study. The results showed that the head, chest, belly, and hands tended to feel no cooler than overall in cooler environments, but arms and legs felt generally no warmer than overall in warmer environments. The head, trunk and upper arms were more likely to be the comfort-dominant body parts. Additionally, the upper arms and upper back expected temperature regulation measures the most under non-neutral environments, thus they seem to be the two most needed and effective targeted body parts that a PCS could be applied to. The skin temperature and thermal sensation of limbs were more sensitive to indoor air temperatures than those of the torso. However, variations in the skin temperature of the head, chest, upper back, and calves had the strongest correlation with overall sensation vote changes. The above results and conclusions can not only serve as the basis for the future studies of local thermal comfort, but also provide theoretical guidance for the design of future PCS products.

Effects of interactions between thermal and acoustic environments on subjective comfort evaluations in outdoor public spaces

ABSTRACT In this study, five outdoor open areas were selected as the study sites to investigate the effects of thermal and acoustic environments, physical activity levels, and pleasantness on evaluations of the thermal and acoustic comfort in outdoor open spaces. Survey questionnaires and on-site measurements were used to quantitatively assess human thermal and acoustic comfort in outdoor spaces. The following findings were obtained in this study. The acoustic environment affected the thermal sensation, where reducing excessive outdoor noise levels could enhance thermal comfort. Increasing the physiological equivalent temperature amplified the acoustic sensation. Individuals reported the most comfortable acoustic perception outdoors at a physiological equivalent temperature of 30.1°C. Reducing both the thermal and acoustic indices improved the overall comfort to some extent. Decreasing physical activity levels by an appropriate amount enhanced the thermal comfort, acoustic comfort, and overall comfort. Finally, maintaining a sense of pleasantness was conducive to increasing the thermal comfort, acoustic comfort, and overall comfort. In states of moderate and pleasurable feelings (pleasantness level = 0, 1, 2, 3), increased acoustic comfort and pleasantness combined significantly enhanced the thermal comfort.