The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Andreas Matzarakis - One of the best experts on this subject based on the ideXlab platform.
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Accuracy of Mean Radiant Temperature Derived from Active and Passive Radiometry
Atmosphere, 2020Co-Authors: Henning Staiger, Andreas MatzarakisAbstract:The concept of the Mean Radiant Temperature (Tmrt) allows the study of radiative exchanges between a human and its environment. It presupposes that the Radiant effects on the person of the actual environment, which is generally heterogeneous, and the virtual environment, which is defined as homogeneous, are identical. ISO 7726 specifies the required accuracy in Tmrt as input of rational thermal indices, outdoors ±5 (K). Tmrt accounts for the Radiant heat absorbed by skin/clothing from the shortwave (SW) and longwave (LW) spectral bands. Most of the Radiant components are isotropic. However, there are anisotropic SW components; namely the direct irradiance and under clear or partly obstructed skies a significant circumsolar fraction (fcs) in the diffuse irradiance. Both originate from the close proximity of the solar disk. This study highlights the effect of fcs on Tmrt. In the scope of human biometeorology a standing body posture is standard. For unidirectional irradiances its Radiant cross-section varies dependent on the solar altitude. Active radiometry in deriving Tmrt is based on measured irradiances. One method is the Klima-Michel-Modell (KMM) that uses readily available measurements from standard meteorologically Radiant observations. KMM references Fanger’s area projection factors that are derived from precise measurements of real humans. Thus, KMM serves as reference in evaluation of further methods. One is the six-directional instrument (Tmrt,r,6−Dir). Slightly simplifying a standing human, it represents a subject as a rectangular solid. Tmrt,r,6−Dir is derived based on measured irradiances incident on the vertical and horizontal planes. In passive radiometry the energy balance equation of a black globe thermometer is solved that leads to Tmrt,Tg,BG. fcs significantly impacts Tmrt with noticeably reduced values for high and increased for low solar altitudes. Hence, accounting for fcs is essential for the accuracy of Tmrt. For KMM an extension to an existing algorithm is provided in order to include fcs into the Tmrt calculation that results in Tmrt,r,KMM. For Tmrt,r,6−Dir the Radiant cross-section of the solid depends to a minor extent on its azimuth relative to the solar azimuth. As a result Tmrt,r,6−Dir slightly scatters compared to Tmrt,r,KMM. However, it remains within ±2 (K). Tmrt,Tg,BG compared to Tmrt,r,KMM complies only at night with the ISO 7726 bin of ±5 K. Tmrt,Tg,BG significantly overestimates Tmrt,r,KMM during the daytime, because of its greater SW absorptance compared to skin/clothing and to a smaller extent because the standing posture is represented by a sphere. Particularly in sunny conditions, Tmrt,Tg,BG is subject to considerable variance. Thus, outdoors during the daytime, Tmrt,Tg,BG is unable to serve as an appropriate input for the calculation of rational-based thermal indices.
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Mean Radiant Temperature in urban canyons from solar calculations climate and surface properties theory validation and ʽmr tʼ software
Building and Environment, 2020Co-Authors: Shabtai Cohen, Andreas Matzarakis, Yaniv Palatchi, Danielle Potchter Palatchi, Victor Lukyanov, Yaron Yaakov, Limor Shashuabar, Josef Tanny, Oded PotchterAbstract:Abstract Mean Radiant Temperature (Tmrt) is important for human thermal comfort indexes, but is difficult to determine. Tmrt was calculated from measured Temperatures of buildings and vegetation surfaces in urban scenarios along with meteorological data (Temperature, relative humidity and global radiation). The method can be used for experimental work in the urban settings without the use of four-flux net radiometers. Differences in Tmrt for different positions in the urban canyon can be calculated. A software package named Mr.T was developed which allows determining Tmrt from data input manually or from EXCEL spreadsheets. The software was validated in two urban settings: in Tel Aviv University and a nearby urban canyon in summer and in the old city quarter of Beer Sheva at the end of winter. Results were close to those obtained with a four-flux net radiometer. Differences in calculated and measured fluxes are discussed as well as sources of errors in the calculations. Assumption of clear skies for the computation of atmospheric radiation did not introduce significant errors. A priori values of albedo and emissivity of the different urban surfaces can have large effects on fluxes and Radiant Temperatures, and the use of tables of those values is probably a large source of uncertainty when using the calculation procedure. In conclusion, the software developed can be a significant tool for the study of thermal comfort conditions in urban settings.
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Mean Radiant Temperature in urban canyons from solar calculations, climate and surface properties – Theory, validation and ʽMr.Tʼ software
Building and Environment, 2020Co-Authors: Shabtai Cohen, Andreas Matzarakis, Yaniv Palatchi, Danielle Potchter Palatchi, Victor Lukyanov, Yaron Yaakov, Josef Tanny, Limor Shashua-bar, Oded PotchterAbstract:Abstract Mean Radiant Temperature (Tmrt) is important for human thermal comfort indexes, but is difficult to determine. Tmrt was calculated from measured Temperatures of buildings and vegetation surfaces in urban scenarios along with meteorological data (Temperature, relative humidity and global radiation). The method can be used for experimental work in the urban settings without the use of four-flux net radiometers. Differences in Tmrt for different positions in the urban canyon can be calculated. A software package named Mr.T was developed which allows determining Tmrt from data input manually or from EXCEL spreadsheets. The software was validated in two urban settings: in Tel Aviv University and a nearby urban canyon in summer and in the old city quarter of Beer Sheva at the end of winter. Results were close to those obtained with a four-flux net radiometer. Differences in calculated and measured fluxes are discussed as well as sources of errors in the calculations. Assumption of clear skies for the computation of atmospheric radiation did not introduce significant errors. A priori values of albedo and emissivity of the different urban surfaces can have large effects on fluxes and Radiant Temperatures, and the use of tables of those values is probably a large source of uncertainty when using the calculation procedure. In conclusion, the software developed can be a significant tool for the study of thermal comfort conditions in urban settings.
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Modeling of Mean Radiant Temperature based on comparison of airborne remote sensing data with surface measured data
Atmospheric Research, 2016Co-Authors: Yu Cheng Chen, Chih-yu Chen, Andreas MatzarakisAbstract:Abstract Assessment of outdoor thermal comfort is becoming increasingly important due to the urban heat island effect, which strongly affects the urban thermal environment. The Mean Radiant Temperature (Tmrt) quantifies the effect of the radiation environment on humans, but it can only be estimated based on influencing parameters and factors. Knowledge of Tmrt is important for quantifying the heat load on human beings, especially during heat waves. This study estimates Tmrt using several methods, which are based on climatic data from a traditional weather station, microscale ground surface measurements, land surface Temperature (LST) and light detection and ranging (LIDAR) data measured using airborne devices. Analytical results reveal that the best Means of estimating Tmrt combines information about LST and surface elevation information with meteorological data from the closest weather station. The application in this method can eliminate the inconvenience of executing a wide range ground surface measurement, the insufficient resolution of satellite data and the incomplete data of current urban built environments. This method can be used to map a whole city to identify hot spots, and can be contributed to understanding human biometeorological conditions quickly and accurately.
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Comparison of different methods of estimating the Mean Radiant Temperature in outdoor thermal comfort studies
International Journal of Biometeorology, 2014Co-Authors: E. L. Krüger, F. O. Minella, Andreas MatzarakisAbstract:Correlations between outdoor thermal indices and the calculated or measured Mean Radiant Temperature T_mrt are in general of high importance because of the combined effect on human energy balance in outdoor spaces. The most accurate way to determine T_mrt is by Means of integral radiation measurements, i.e. measuring the short- and long-wave radiation from six directions using pyranometers and pyrgeometers, an expensive and not always an easily available procedure. Some studies use globe thermometers combined with air Temperature and wind speed sensors. An alternative way to determine T_mrt is based on output from the RayMan model from measured data of incoming global radiation and morphological features of the monitoring site in particular sky view factor (SVF) data. The purpose of this paper is to compare different methods to assess the Mean Radiant Temperature T_mrt in terms of differences to a reference condition (T_mrt calculated from field measurements) and to resulting outdoor comfort levels expressed as PET and UTCI values. The T_mrt obtained from field measurements is a combination of air Temperature, wind speed and globe Temperature data according to the forced ventilation formula of ISO 7726 for data collected in Glasgow, UK. Four different methods were used in the RayMan model for T_mrt calculations: input data consisting exclusively of data measured at urban sites; urban data excluding solar radiation, estimated SVF data and solar radiation data measured at a rural site; urban data excluding solar radiation with SVF data for each site; urban data excluding solar radiation and including solar radiation at the rural site taking no account of SVF information. Results show that all methods overestimate T_mrt when compared to ISO calculations. Correlations were found to be significant for the first method and lower for the other three. Results in terms of comfort (PET, UTCI) suggest that reasonable estimates could be made based on global radiation data measured at the urban site or as a surrogate of missing SR data or globe Temperature data recorded at the urban area on global radiation data measured at a rural location.
Sofia Thorsson - One of the best experts on this subject based on the ideXlab platform.
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The influence of anisotropic diffuse shortwave radiation on Mean Radiant Temperature in outdoor urban environments
Urban Climate, 2020Co-Authors: Nils Wallenberg, Björn Holmer, Fredrik Lindberg, Sofia ThorssonAbstract:Abstract During clear weather conditions the main part of the shortwave irradiance derives from sun direct-beam radiation. However, part of the shortwave radiation also originates from all-sky diffuse radiation (D), with a large part being circumsolar in origin. Many radiation models considers the sky as isotropic when estimating D. Here we implement an anisotropic model for D into the SOLWEIG model to examine the spatial patterns of D in a built-up environment, as well as its influence on Mean Radiant Temperature (Tmrt), a variable essential for estimating outdoor human thermal comfort. Comparisons between the anisotropic and the isotropic models indicates that the D in the isotropic model is overestimated in shaded areas and underestimated in areas close to sunlit walls. This is explained by the circumsolar origin of D during clear and semi-cloudy conditions and solar altitude. These over- and underestimations, consecutively, have implications for Tmrt, which can differ by up to 3 °C. The deviations in D thus signify the importance of using an anisotropic model when estimating D and Tmrt, especially since the areas with the highest reported Radiant loads receive even more radiation considering an anisotropic diffuse sky, i.e. the hottest areas are even hotter than previously reported.
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Present and projected future Mean Radiant Temperature for three European cities
International Journal of Biometeorology, 2017Co-Authors: Sofia Thorsson, Shannon Campe, David Rayner, Lutz Katzschner, Antje Katzschner, Janina Konarska, Fredrik Lindberg, Shiho Onomura, Ana Monteiro, Silva VelhoAbstract:Present-day and projected future changes in Mean Radiant Temperature, T _mrt in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air Temperature, T _ a , increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on T _mrt. The number of days with high T _mrt in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime Radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the Radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the Radiant heat load is outlined based on these findings and existing literature.
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the effect of urban geometry on Mean Radiant Temperature under future climate change a study of three european cities
International Journal of Biometeorology, 2015Co-Authors: Fredrik Lindberg, David Rayner, Sofia ThorssonAbstract:Future anthropogenic climate change is likely to increase the air Temperature (T a ) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T a , which give rise to high Radiant heat load, i.e. Mean Radiant Temperature (T mrt ). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T mrt as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T mrt is found in open areas in all three cities despite of the latitudinal differences in average daytime T mrt . In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T mrt in the winter. Although the T mrt averages are similar for the north–south and east–west street canyons in each city, the number of hours when T mrt exceeds the threshold values of 55.5 and 59.4 °C—used as indicators of moderate and severe heat stress—in the north–south canyons is much higher than that in the east–west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T mrt in the spring, while the reduction in T mrt is somewhat offset by increasing T a in other seasons. It suggests that changes in the T mrt under the future scenario are dominated by variations in T a . Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure can reduce daytime heat stress since it reduces the number of hours of high T mrt in the summer and does not cause substantial changes in average and minimum T mrt in the winter. In dense urban settings, a more diverse urban thermal environment is also preferred to compensate for reduced solar access in the winter. The extent to which the urban geometry can be optimized for the future climate is also influenced by local urban characteristics.
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Mean Radiant Temperature a predictor of heat related mortality
urban climate, 2014Co-Authors: Sofia Thorsson, Benedicte Dousset, Janina Konarska, Björn Holmer, Fredrik Lindberg, Joacim Rocklov, David RaynerAbstract:Health studies have repeatedly used air Temperature (Ta), sometimes adjusted for humidity, when analyzing the impact of weather on mortality. The aim of this study is to highlight the importance of Mean Radiant Temperature (Tmrt) and its impact on heat related mortality. Tmrt is an essential meteorological parameter that influences the thermal comfort (heat load) of humans. It is useful when assessing the impact of weather, especially heat, on people’s health. Tmrt is directly influenced by urban geometry and surface material, which also makes it a good measure to identify urban hot spots. The performance of models using Ta and Tmrt for daily mortality is compared for Stockholm County, Sweden. It is demonstrated that Tmrt models fit heat related mortality better than Ta models, which implies that health studies should consider using Tmrt rather than Ta. The use of Tmrt models allows us to determine more accurate thresholds for increased risks of heat related mortality, and thus to better identify adverse weather conditions and heat prone urban geometries. Such information is needed to implement heat-warning systems and mitigate harmful effects of heat stress.
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Characteristics of the Mean Radiant Temperature in high latitude cities—implications for sensitive climate planning applications
International Journal of Biometeorology, 2014Co-Authors: Fredrik Lindberg, Björn Holmer, Sofia Thorsson, David RaynerAbstract:Knowledge of how the Mean Radiant Temperature ( T _ mrt ) is affected by factors such as location, climate and urban setting contributes to the practice of climate sensitive planning. This paper examines how T _ mrt varies within an urban setting and how it is influenced by cloudiness. In addition, variations of T _ mrt in three high latitude cities are investigated in order to analyse the impact of geographical context and climate conditions. Results showed large spatial variations between sunlit and shaded areas during clear weather conditions, with the highest values of T _ mrt close to sunlit walls and the lowest values in the areas shaded by buildings and vegetation. As cloudiness increases, the spatial pattern is altered and the differences are reduced. The highest T _ mrt under cloudy conditions is instead found in open areas where the proportion of shortwave diffuse radiation from the sky vault is high. A regional comparison between three Swedish coastal cities showed that T _ mrt during summer is similar regardless of latitudinal location. On the other hand, large differences in T _ mrt during winter were found. Shadows, both from buildings and vegetation are the most effective measure to reduce extreme values of T _ mrt . However, extensive areas of shadow are usually not desired within outdoor urban environments at high latitude cities. One solution is to create diverse outdoor urban spaces in terms of shadow and also ventilation. This would provide individuals with access to a choice of thermal environments which they can use to assist their thermal regulation, based on personal needs and desires.
Fredrik Lindberg - One of the best experts on this subject based on the ideXlab platform.
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The influence of anisotropic diffuse shortwave radiation on Mean Radiant Temperature in outdoor urban environments
Urban Climate, 2020Co-Authors: Nils Wallenberg, Björn Holmer, Fredrik Lindberg, Sofia ThorssonAbstract:Abstract During clear weather conditions the main part of the shortwave irradiance derives from sun direct-beam radiation. However, part of the shortwave radiation also originates from all-sky diffuse radiation (D), with a large part being circumsolar in origin. Many radiation models considers the sky as isotropic when estimating D. Here we implement an anisotropic model for D into the SOLWEIG model to examine the spatial patterns of D in a built-up environment, as well as its influence on Mean Radiant Temperature (Tmrt), a variable essential for estimating outdoor human thermal comfort. Comparisons between the anisotropic and the isotropic models indicates that the D in the isotropic model is overestimated in shaded areas and underestimated in areas close to sunlit walls. This is explained by the circumsolar origin of D during clear and semi-cloudy conditions and solar altitude. These over- and underestimations, consecutively, have implications for Tmrt, which can differ by up to 3 °C. The deviations in D thus signify the importance of using an anisotropic model when estimating D and Tmrt, especially since the areas with the highest reported Radiant loads receive even more radiation considering an anisotropic diffuse sky, i.e. the hottest areas are even hotter than previously reported.
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Present and projected future Mean Radiant Temperature for three European cities
International Journal of Biometeorology, 2017Co-Authors: Sofia Thorsson, Shannon Campe, David Rayner, Lutz Katzschner, Antje Katzschner, Janina Konarska, Fredrik Lindberg, Shiho Onomura, Ana Monteiro, Silva VelhoAbstract:Present-day and projected future changes in Mean Radiant Temperature, T _mrt in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air Temperature, T _ a , increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on T _mrt. The number of days with high T _mrt in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime Radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the Radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the Radiant heat load is outlined based on these findings and existing literature.
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towards city wide building resolving analysis of Mean Radiant Temperature
urban climate, 2016Co-Authors: Britta Janicke, Fred Meier, Sebastian Schubert, Fredrik Lindberg, Dieter SchererAbstract:Abstract This study presents a method to simulate Tmrt building-resolving while considering both micro-scale urban structures and meso-scale atmospheric conditions. We extended the model SOLWEIG, one of the few methods to derive Mean Radiant Temperature (Tmrt) building-resolved and city-wide, to include spatial patterns of meteorological input. Based on a day within an extreme heat event (2003) in Berlin, Germany, we examined the effect of the new method on Tmrt, which uses gridded meteorological input data from a mesoscale weather model, compared to a standard set-up using ungridded data. Results indicted a considerable effect of spatially resolved air Temperature (up to 3.2 K) during midnight. Furthermore, we detected high sensitivity of Tmrt to the partitioning of direct and diffuse short-wave radiation. The spatial pattern of Tmrt revealed that at midday the city centre exhibited low values compared to open areas. We conclude that considering meso-scale atmospheric conditions and urban structure for simulating Tmrt city-wide can lead to a more appropriate description of heat-stress hazards and might also be valuable for climate-sensitive urban planning.
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influence of ground surface characteristics on the Mean Radiant Temperature in urban areas
International Journal of Biometeorology, 2016Co-Authors: Fredrik Lindberg, Shiho Onomura, C. S. B. GrimmondAbstract:The effect of variations in land cover on Mean Radiant Temperature (T mrt ) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface Temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of ground surface materials on T mrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction in T mrt to reduce the Radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused T mrt to be underestimated. The implications of using high temporal resolution (e.g. 15 minutes) meteorological forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites.
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the effect of urban geometry on Mean Radiant Temperature under future climate change a study of three european cities
International Journal of Biometeorology, 2015Co-Authors: Fredrik Lindberg, David Rayner, Sofia ThorssonAbstract:Future anthropogenic climate change is likely to increase the air Temperature (T a ) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T a , which give rise to high Radiant heat load, i.e. Mean Radiant Temperature (T mrt ). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T mrt as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T mrt is found in open areas in all three cities despite of the latitudinal differences in average daytime T mrt . In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T mrt in the winter. Although the T mrt averages are similar for the north–south and east–west street canyons in each city, the number of hours when T mrt exceeds the threshold values of 55.5 and 59.4 °C—used as indicators of moderate and severe heat stress—in the north–south canyons is much higher than that in the east–west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T mrt in the spring, while the reduction in T mrt is somewhat offset by increasing T a in other seasons. It suggests that changes in the T mrt under the future scenario are dominated by variations in T a . Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure can reduce daytime heat stress since it reduces the number of hours of high T mrt in the summer and does not cause substantial changes in average and minimum T mrt in the winter. In dense urban settings, a more diverse urban thermal environment is also preferred to compensate for reduced solar access in the winter. The extent to which the urban geometry can be optimized for the future climate is also influenced by local urban characteristics.
Helmut Mayer - One of the best experts on this subject based on the ideXlab platform.
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intra urban differences of Mean Radiant Temperature in different urban settings in shanghai and implications for heat stress under heat waves a gis based approach
Energy and Buildings, 2016Co-Authors: Liang Chen, Bailang Yu, Feng Yang, Helmut MayerAbstract:Abstract The Mean Radiant Temperature (Tmrt) is an effective indicator to characterize the urban thermal Radiant environment and assess outdoor thermal comfort and heat stress. In this study, the SOLWEIG model (SOlar and Long Wave Environmental Irradiance Geometry) was employed to investigate the spatial variation of Tmrt in different urban settings in Shanghai. The model was tested against six directional Radiant flux density measurements and showed good performance in Shanghai’s urban environment. Two different urban settings with different building geometry and vegetation cover were used as case study sites. A typical heat wave day in 2013 was selected to investigate the daytime Radiant heat stress intensity. Spatial analysis modules were developed and the Radiant Heat Stress Intensity index was defined. The study reveals that in Shanghai under heat waves the heat stress induced by the thermal Radiant environment is quite severe, with Tmrt commonly well above 60 °C in daytime, and intra-urban Tmrt differences are largely influenced by building density and height, street orientation and vegetation. Open paved spaces and space near sunlit walls are the places that have the highest Tmrt. The study shows that the spatial variation of Tmrt can be used to identify thermally vulnerable areas and hotspots in complex urban environment, and provide implications for urban design towards the mitigation of heat stress in high-density cities.
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validation of the Mean Radiant Temperature simulated by the rayman software in urban environments
International Journal of Biometeorology, 2016Co-Authors: Helmut MayerAbstract:The RayMan software is worldwide applied in investigations on different issues in human-biometeorology. However, only the simulated Mean Radiant Temperature (T mrt) has been validated so far in a few case studies. They are based on T mrt values, which were experimentally determined in urban environments by use of a globe thermometer or applying the six-directional method. This study analyses previous T mrt validations in a comparative manner. Their results are extended by a recent validation of T mrt in an urban micro-environment in Freiburg (southwest Germany), which can be regarded as relatively heterogeneous due to different shading intensities by tree crowns. In addition, a validation of the physiologically equivalent Temperature (PET) simulated by RayMan is conducted for the first time. The validations are based on experimentally determined T mrt and PET values, which were calculated from measured meteorological variables in the daytime of a clear-sky summer day. In total, the validation results show that RayMan is capable of simulating T mrt satisfactorily under relatively homogeneous site conditions. However, the inaccuracy of simulated T mrt is increasing with lower sun elevation and growing heterogeneity of the simulation site. As T mrt represents the meteorological variable that mostly governs PET in the daytime of clear-sky summer days, the accuracy of simulated T mrt is mainly responsible for the accuracy of simulated PET. The T mrt validations result in some recommendations, which concern an update of physical principles applied in the RayMan software to simulate the short- and long-wave Radiant flux densities, especially from vertical building walls and tree crowns.
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Significance of 3-D Radiant flux densities for the determination of the Mean Radiant Temperature: synopsis of experimental investigations in Freiburg, Southwest Germany, during summer
2014Co-Authors: Hyun Jung Lee, Helmut MayerAbstract:This investigation deals with the role of Radiant flux densities from different directions in complex urban settings for human thermal comfort in summer. The major aim is to analyze the various impacts of the 3-D short- and long-wave Radiant flux densities absorbed by the standardized human-biometeorological reference person on the Mean Radiant Temperature (Tmrt) and physiologically equivalent Temperature (PET). Data from human-biometeorological measuring campaigns conducted in different street canyons within Freiburg (Southwest Germany) on clear-sky summer days 2007-2010 are the basis of this investigation. The results point to the different importance of the absorbed 3-D Radiant flux densities for Tmrt and PET. While the magnitude of Tmrt is mainly determined by the total of the absorbed 3-D long-wave Radiant flux densities, the fluctuations of Tmrt are mainly governed by the total of the absorbed 3-D short-wave Radiant flux densities. Their variance can be well explained by the variance of the sky view factor related to the southern part of the upper half space. Taking account of the different impact of the 3-D Radiant flux densities, Tmrt can be quite well estimated by a multiple regression using the total of the absorbed 3-D short-wave Radiant flux densities and the absorbed long-wave Radiant flux density from the lower half space as independent variables. PET can be well estimated by a multiple regression with Tmrt and near-surface air Temperature Ta as independent variables.
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Modelling radiation fluxes in simple and complex environments: basics of the RayMan model
International Journal of Biometeorology, 2010Co-Authors: Andreas Matzarakis, Frank Rutz, Helmut MayerAbstract:Short- and long-wave radiation flux densities absorbed by people have a significant influence on their energy balance. The heat effect of the absorbed radiation flux densities is parameterised by the Mean Radiant Temperature. This paper presents the physical basis of the RayMan model, which simulates the short- and long-wave radiation flux densities from the three-dimensional surroundings in simple and complex environments. RayMan has the character of a freely available radiation and human-bioclimate model. The aim of the RayMan model is to calculate radiation flux densities, sunshine duration, shadow spaces and thermo-physiologically relevant assessment indices using only a limited number of meteorological and other input data. A comparison between measured and simulated values for global radiation and Mean Radiant Temperature shows that the simulated data closely resemble measured data.
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Modelling radiation fluxes in simple and complex environments—application of the RayMan model
International journal of biometeorology, 2009Co-Authors: Andreas Matzarakis, Frank Rutz, Helmut MayerAbstract:Short- and long-wave radiation flux densities absorbed by people have a significant influence on their energy balance. The heat effect of the absorbed radiation flux densities is parameterised by the Mean Radiant Temperature. This paper presents the physical basis of the RayMan model, which simulates the short- and long-wave radiation flux densities from the three-dimensional surroundings in simple and complex environments. RayMan has the character of a freely available radiation and human-bioclimate model. The aim of the RayMan model is to calculate radiation flux densities, sunshine duration, shadow spaces and thermo-physiologically relevant assessment indices using only a limited number of meteorological and other input data. A comparison between measured and simulated values for global radiation and Mean Radiant Temperature shows that the simulated data closely resemble measured data.
Ariane Middel - One of the best experts on this subject based on the ideXlab platform.
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Validation of seasonal Mean Radiant Temperature simulations in hot arid urban climates.
The Science of the total environment, 2020Co-Authors: Peter J. Crank, Ariane Middel, Melissa Wagner, Dani Hoots, Martin Smith, Anthony J. BrazelAbstract:Abstract We validated seasonal RayMan and ENVI-met Mean Radiant Temperature (TMRT) simulations to assess model performance in a sensitivity analysis from cold to extremely hot conditions. Human-biometeorological validation data were collected in Tempe, Arizona via transects during five field campaigns between 2014 and 2017. Transects were conducted across seven locations in two to three-hour intervals from 6:00 to 23:00 LST with a Kestrel meter and thermal camera (2014–2015) and the mobile instrument platform MaRTy (2017). Observations across diverse urban forms, sky view factors, and seasons covered a wide range of solar radiation regimes from a minimum TMRT of 8.7 °C to a maximum of 84.9 °C. Both models produced large simulation errors across regimes with RMSE ranging from 8 °C to 12 °C (RayMan) and 11.2 °C to 16.1 °C (ENVI-met), exceeding a suggested TMRT accuracy of ±5 °C for heat stress studies. RayMan model errors were largest for engineered enclosed spaces, complex urban forms, and extreme heat conditions. ENVI-met was unable to resolve intra-domain spatial variability of TMRT and exhibited large errors with RMSE up to 25.5 °C for engineered shade. Both models failed to accurately simulate TMRT for hot conditions. Errors varied seasonally with overestimated TMRT in the summer and underestimated TMRT in the winter and shoulder seasons. Results demonstrate that models should not be used under micrometeorological or morphological extremes without in-situ validation to quantify errors and assess directional bias due to model limitations.
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Modelling the impact of increased street tree cover on Mean Radiant Temperature across Vancouver’s local climate zones
Urban Forestry & Urban Greening, 2019Co-Authors: Mehdi Aminipouri, Kirsten Zickfeld, E. Scott Krayenhoff, Anders Knudby, Ariane MiddelAbstract:Abstract Extensive impervious surface cover, anthropogenic heat emissions, and lack of vegetation contribute to the formation of distinct urban microclimates where higher air and surface Temperature as well as lack of shade intensify outdoor heat exposure and thermal discomfort for humans. Modifications to the thermal environment via urban design can be used to mitigate this effect. In this study, the potential for increased street tree coverage to reduce Mean Radiant Temperature (Tmrt) 1 across six different local climate zones (LCZs) 2 in Vancouver, Canada, was examined using the Solar and LongWave Environmental Irradiance Geometry (SOLWEIG) 3 model. The Radiant cooling effect of increased street tree coverage during the hottest day on record for Vancouver (July 29, 2009) was quantified by spatiotemporal changes to Tmrt. SOLWEIG was evaluated successfully prior to implementation of a street tree cover increase equivalent to 1% of plan area in each of six Vancouver LCZs investigated. Results indicate 3.2–6.3 °C reduction in spatially-averaged daytime (9:00 – 18:00) Tmrt and 3.3–7.1 °C reduction during the hottest period of day, 11:00-17:00. During the hottest period of day, the largest spatially-averaged Tmrt reduction (7.1 °C) was modelled in a low-rise residential area. Modelling suggested that a pedestrian standing directly under a tree canopy would experience Tmrt reductions of 15.5–17.3 °C in all LCZs. Also, under current conditions with no increase in tree cover, the compact high-rise and the large low-rise areas are shown to be the most and least comfortable environments regarding human thermal exposure with spatially-averaged Tmrt of 41.9 °C and 47.9 °C, respectively. We conclude that increases to Vancouver’s street tree cover by 1% of plan area can substantially reduce Tmrt during extreme hot weather. The results of this study show that the cooling potential of added street trees is greater in lower density residential neighborhoods with 1–2 storey buildings compared to higher density neighborhoods occupied by high-rise or mid-rise buildings.
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modelling the impact of increased street tree cover on Mean Radiant Temperature across vancouver s local climate zones
Urban Forestry & Urban Greening, 2019Co-Authors: Mehdi Aminipouri, Kirsten Zickfeld, Scott E Krayenhoff, Anders Knudby, Ariane MiddelAbstract:Abstract Extensive impervious surface cover, anthropogenic heat emissions, and lack of vegetation contribute to the formation of distinct urban microclimates where higher air and surface Temperature as well as lack of shade intensify outdoor heat exposure and thermal discomfort for humans. Modifications to the thermal environment via urban design can be used to mitigate this effect. In this study, the potential for increased street tree coverage to reduce Mean Radiant Temperature (Tmrt) 1 across six different local climate zones (LCZs) 2 in Vancouver, Canada, was examined using the Solar and LongWave Environmental Irradiance Geometry (SOLWEIG) 3 model. The Radiant cooling effect of increased street tree coverage during the hottest day on record for Vancouver (July 29, 2009) was quantified by spatiotemporal changes to Tmrt. SOLWEIG was evaluated successfully prior to implementation of a street tree cover increase equivalent to 1% of plan area in each of six Vancouver LCZs investigated. Results indicate 3.2–6.3 °C reduction in spatially-averaged daytime (9:00 – 18:00) Tmrt and 3.3–7.1 °C reduction during the hottest period of day, 11:00-17:00. During the hottest period of day, the largest spatially-averaged Tmrt reduction (7.1 °C) was modelled in a low-rise residential area. Modelling suggested that a pedestrian standing directly under a tree canopy would experience Tmrt reductions of 15.5–17.3 °C in all LCZs. Also, under current conditions with no increase in tree cover, the compact high-rise and the large low-rise areas are shown to be the most and least comfortable environments regarding human thermal exposure with spatially-averaged Tmrt of 41.9 °C and 47.9 °C, respectively. We conclude that increases to Vancouver’s street tree cover by 1% of plan area can substantially reduce Tmrt during extreme hot weather. The results of this study show that the cooling potential of added street trees is greater in lower density residential neighborhoods with 1–2 storey buildings compared to higher density neighborhoods occupied by high-rise or mid-rise buildings.