Top PDF The effect of asymmetrical street aspect ratios on urban wind flow and pedestrian thermal comfort conditions

The effect of asymmetrical street aspect ratios on urban wind flow and pedestrian thermal comfort conditions

The effect of asymmetrical street aspect ratios on urban wind flow and pedestrian thermal comfort conditions

Fig. 4. 4: Velocity magnitude for Aswan and Farafra Models in hot arid Egyptian climate. Decreasing the passage between buildings while using wider street canyons. Source: Rizk and Henze (2010). However, the model‘s results were based on high wind velocity input values of between about 12 to 13m/s, which may not be applicable for the current research of Madinah where the yearly average maximum wind speed was found to be 3.5m/s (refer to Chapter 2 for more detail). Nevertheless, the researchers found that a chess-board design arrangement for buildings rows can also increase wind velocity at both windward surfaces and narrow passages of the next row by increasing street canyon width to as much as 20m (Rizk and Henze, 2010). Similarly, it was found that in the Farafra model, which uses narrow distances between passages of buildings (i.e. 6m) at the same row and rectangular shapes that have trapezoid courtyards that face the wind, it is possible to achieve 33-41% of wind velocity at the windward surfaces and 38-70% at the second and third row, by using the chess-board design arrangement and increasing the canyons width. This evidence emphasises the importance of narrow passages which can increase wind velocity by venturi effect (channel effect, i.e. the effect where wind speed increases as it passes through a smaller openings) (e.g. Blocken and Carmeliet, 2004b), as increasing wind speeds is demanding in areas that suffer from very low wind to achieve thermal comfort (Qaid and Ossen, 2014). However, these case studies of Egypt of multiple rows of buildings did not consider the effect of increasing the urban street H/W aspect ratios (particularly increasing the height of buildings) on urban pedestrian microclimate or pedestrian thermal comfort conditions.
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Effect of urban street canyon aspect ratio on thermal performance of road pavement solar collectors (RPSC)

Effect of urban street canyon aspect ratio on thermal performance of road pavement solar collectors (RPSC)

The urban heat island (UHI) effect is a form of accumulated heat caused by urbanisation when build- ings, roads and other infrastructure elements replace open land or water areas. These elements tend to absorb the heat from the sun rather than reflect it, causing the surface temperature and air temperature to elevate. Several studies suggested that one of the causes of the UHI effect is the reduction of the air ve- locity in narrow space in between buildings (courtyards and street canyons) which decreases convective heat transfer and urban ventilation [1-4]. Studies [5, 6] on RPSC (road pavement solar collectors) have highlighted the potential of reducing the UHI effect by dissipating the heat from the pavement for energy harness. The study [5] suggested that using RPSC or a hydronic pipe system for pavement heat reduction can potentially extend the lifecycle of pavements up to 5 years by reducing surface temperature by 5°C. In the authors’ previous study [6], the effect of urban street canyon on the RPSC performance was inves- tigated and compared against the simulation without the street canyon (replicating rural area). Results have shown higher potential thermal collection (PTC) and surface temperature reduction (STR) was ob- tained by RPSC in urban conditions. The study also highlighted the reduction of the convective heat transfer from the surface due to the wind flow pattern across long facades which can significantly lower the air circulation in the canyon. In this study, investigation of the impact of various canyon geometries on the RPSC performance was carried out, extending the study of [6] which showed improved thermal performance of RPSC in urban as compared to suburban or rural.
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CFD MODELING AS A TOOL FOR ASSESSING OUTDOOR THERMAL COMFORT CONDITIONS IN URBAN SETTINGS IN HOT ARID CLIMATES

CFD MODELING AS A TOOL FOR ASSESSING OUTDOOR THERMAL COMFORT CONDITIONS IN URBAN SETTINGS IN HOT ARID CLIMATES

The Reynolds Averaged Navier Stokes (RANS) approach is a modeling method in which the major variables such as temperature and velocity are divided into time-averaged and turbulent fluctuation, and then the turbulent model is used to model the turbulent fluctuation (Nielsen et al., 2007). Blocken and Persoon (2009) used RANS in studying an urban setting to evaluate wind comfort on pedestrian level around a large football stadium to study the effects of adding new high-rise buildings in the surroundings. The advantages of RANS include its availability in all CFD codes, inexpensive and widely validated, but it is not as accurate as LES because of the lack of capturing smaller length scale (eddy scale) in RANS. Blocken et al. (2009) and He and Song (1999) indicated another shortfall of RANS, which is that RANS solves only the mean flow and small eddies, whereas the LES solves the large and most important turbulent eddies. Santiago et al. (2010) have used LES model and RANS model to evaluate the effect of the direction of incident wind on the flow plume dispersion. It was noticed that LES requires greater computational cost than RANS, and the use of RANS with turbulent kinetic energy (k- ɛ) model is reasonably suitable for simulating wind flow in urban environments, and has increasingly been used for wind studies at pedestrian level (e.g. Blocken et al., 2004; Yoshie et al., 2007; Blocken and Persoon, 2009). In LES model, large scale structures in turbulent flow are created directly, this is due to unsteadiness of the mean flow (shear or buoyancy effects) that are simulated directly as they are problem reliant, anisotropic and play a key part in transportation of mass, momentum and energy. LES modeling is most appropriate for the simulation of air pollutant, which is because of its ability to solve the large eddies in the field of the fluid flow (e.g. Walton et al., 2002). In contrast, small scale structures can be modeled in LES with less effect on the prediction value (Uddin, 2008). The grids in LES are more refined compared to RANS and hence need more computational power for simulation. The employment of LES in urban environment studies could be seen in Salim et al. (2011), Li et al. (2009), and Tominaga, et al. (2008). Researchers such as Tominaga et al. (2008) applied LES simulation to high-rise building geometry to study the wind flow around it within the surface boundary layer, flow within an urban complex and around a tree.
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Effect of urban street canyon aspect ratio on thermal performance of road pavement solar collectors (RPSC)

Effect of urban street canyon aspect ratio on thermal performance of road pavement solar collectors (RPSC)

The urban heat island (UHI) effect is a form of accumulated heat caused by urbanisation when build- ings, roads and other infrastructure elements replace open land or water areas. These elements tend to absorb the heat from the sun rather than reflect it, causing the surface temperature and air temperature to elevate. Several studies suggested that one of the causes of the UHI effect is the reduction of the air ve- locity in narrow space in between buildings (courtyards and street canyons) which decreases convective heat transfer and urban ventilation [1-4]. Studies [5, 6] on RPSC (road pavement solar collectors) have highlighted the potential of reducing the UHI effect by dissipating the heat from the pavement for energy harness. The study [5] suggested that using RPSC or a hydronic pipe system for pavement heat reduction can potentially extend the lifecycle of pavements up to 5 years by reducing surface temperature by 5°C. In the authors’ previous study [6], the effect of urban street canyon on the RPSC performance was inves- tigated and compared against the simulation without the street canyon (replicating rural area). Results have shown higher potential thermal collection (PTC) and surface temperature reduction (STR) was ob- tained by RPSC in urban conditions. The study also highlighted the reduction of the convective heat transfer from the surface due to the wind flow pattern across long facades which can significantly lower the air circulation in the canyon. In this study, investigation of the impact of various canyon geometries on the RPSC performance was carried out, extending the study of [6] which showed improved thermal performance of RPSC in urban as compared to suburban or rural.
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Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers

* Correspondence: lupwai@mit.edu Received: 10 July 2017; Accepted: 22 August 2017; Published: 25 August 2017 Abstract: Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a “reversed wind catcher” has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas.
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Prioritizing Underserved Communities for Thermal Comfort Street Retrofit in Eugene, OR

Prioritizing Underserved Communities for Thermal Comfort Street Retrofit in Eugene, OR

Yet, the major discussion of environmental justice began only 3 decades ago. It started when North Carolina planned to move contaminated soil from the states’ roadsides to a landfill located in Warren County, one of only few counties in the states with a majority of black population in 1982 (Office of Legacy Management, n.d.). (Palmer, 2016). The decision triggered protests by environmental advocates seeking social justice and environmental protection (Palmer, 2016). Even though the advocates lost the battle, the event started the controversy that “the nation’s environmental problems disproportionately burden its low-income people of color” (Palmer, 2016). President Clinton issued Executive Order 12898 to “make environmental justice a part of the federal decision-making process” (Office of Legacy Management, n.d.). The order also fo- cuses on “the health and environmental conditions in minority, tribal, and low-income communities”, aiming to achieve environmental justice and foster nondiscrimination (Office of Legacy Management, n.d.). Federal agencies need to “make environmental justice as an integral part of their missions and to establish an environmental justice strategy” (Office of Legacy Management, n.d.).
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Urban outdoor thermal comfort of the hot-humid region

Urban outdoor thermal comfort of the hot-humid region

Conclusion The proposed comfort zone of the outdoor environment of Kuala Lumpur can be used to monitor the climatical environmental condition. If the climate range falls within the zone, then it is suggested that the outdoor environment is thermally comfortable most of the time for users.

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The influence of bioclimatic urban redevelopment on outdoor thermal comfort.

The influence of bioclimatic urban redevelopment on outdoor thermal comfort.

The influence of bioclimatic urban redevelopment on outdoor thermal comfort Karakounos I., Dimoudi A.*, Zoras S. Department of Environmental Engineering, Democritus University of Thrace, 67132 Xanthi, Greece One of the greatest environmental challenges for the sustainability of future cities is the mitigation of the urban heat island phenomenon and thus, improvement of outdoor comfort conditions for people. The emphasis of this work is to analyze how mitigation techniques in a dense urban environment affect microclimate parameters and outdoor thermal comfort. The quantitative differentiation of outdoor thermal comfort conditions through bioclimatic urban redevelopment for an area in the city of Serres, Greece is investigated. The main bioclimatic interventions concern the application of cool paving materials, the increase of vegetated areas and the creation of water surfaces. The analysis and comparison are performed for a hot summer day with the ENVI-met model. Software simulations regarding microclimatic and outdoor thermal comfort conditions are performed for the daytime period 06.00 to 20.00 (14 hours) at the height of 1.8m from the ground. The examined parameters are air temperature, surface temperature and mean radiant temperature (T mrt ).
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Thermal comfort in urban green spaces in arid environments.

Thermal comfort in urban green spaces in arid environments.

El “confort térmico” es concebido como la ausencia de malestar con el ambiente térmico (ASHRAE, 2014). Para el estudio del confort en los EVU de la ciudad de San Juan, se aplica el índice racional UTCI (Universal Thermal Climatic Index) (Jendritzky, de Dear y Havenith, 2012) para espacios abiertos, basado en la valoración de la respuesta fisiológica de la persona. El UTCI define 10 escalas de estrés térmico, que abarcan desde el estrés por calor extremo al causado por mucho frío. La escala de valoración se presenta en la Tabla 1.

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Urban outdoor thermal comfort of the hot-humid region

Urban outdoor thermal comfort of the hot-humid region

2 Associate Professor, Institute of Building Technology, Faculty of Engineering, The University of Nottingham, University Park, NG7 2RD, UK Abstract. The study on outdoor comfort is becoming popular due to the fact that the thermoregulatory model is seen as inadequate in explaining outdoor thermal comfort conditions. Hot-humid region can be said as experiencing a critical environmental condition because of its constantly high temperature and humidity throughout the year. Thus, this study focus on the assessment of thermal comfort of outdoor urban spaces in Kuala Lumpur, Malaysia (3° 9’N and 101° 44’E). Survey on human response towards outdoor thermal comfort in hot-humid climate of Kuala Lumpur, Malaysia was carried out during day time between 0900h to 1800h along with measurement of environmental parameters such as air temperature (°C), wind velocity (m/s), radiant temperature (°C), relative humidity (%) and solar radiation (lux). A total of 123 samples were involved in this study which took place within four sites around Kuala Lumpur. Survey results were then correlated with the environmental parameters to further develop the comfort zone for hot-humid outdoor environment specifically for Kuala Lumpur and, generally, for hot-humid regions.
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Potential Contribution of Urban Developments to Outdoor Thermal Comfort Conditions: The Influence of Urban Geometry and Form in Worcester, Massachusetts, USA

Potential Contribution of Urban Developments to Outdoor Thermal Comfort Conditions: The Influence of Urban Geometry and Form in Worcester, Massachusetts, USA

In this study the existence of UHI is tested in four locations. First, a total of four measuring stations, representing different forms and geometries were chosen and were investigated in terms of climatic parameters in order to demonstrate the existence of Urban Heat Island (UHI). The magnitude of spatial and temporal variations of mean radiant temperature, outdoor air temperature, wind speed and relative humidity were quantified using ENVI-met model and thermal comfort was assessed using Physiologically Equivalent Temperature (PET) index via RayMan. Secondly, the thermal comfort level of one of the locations will be measured after applying mitigation strategies and results will be compared. Thirdly, the performance of downtown Worcester in terms of walkability will be examined using Urban Modelling Interface (UMI). Any kind of intervention in urban settings can change the outdoor thermal conditions. This study intends to measure the impact of new developments on existing urban areas via comparing thermal condition in two scenarios, before and after development. Figure2 illustrates this concept.
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Thermal comfort of heterogeneous and dynamic indoor conditions — An overview

Thermal comfort of heterogeneous and dynamic indoor conditions — An overview

goals for emission reductions [6] , a heterogeneous and more flex- ible comfort zone could be consequential by providing further latitude for reducing building energy requirements. This work is an attempt to summarise works in the field of human thermal comfort, as related to different spatial and temporal transients and the consequent comfort implications. Fig. 1 gives an impression of this work's layout, with thermal comfort of hetero- geneity at the centre, surrounded by the sub-topics deliberated upon and their perceived interconnections. Section 2 discusses inputs from current international standards d along with any supporting literature d regarding allowable variations and non- uniformities in indoor environments and on those salient features of the standards that advocate a broadening of comfort zone. Starting with broad search parameters such as ‘human thermal comfort ’ and ‘thermal sensation’, Section 3 summarises such works that involved human participants being exposed to dynamic or non-uniform thermal environments, both under field and labora- tory conditions. Related literature on thermal sensation and com- fort of local body parts are also summarised. We further discuss some recent works on the concept of alliesthesia and what it im- plies for comfort under heterogeneous situations.
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The role of sky view factor and urban street greenery in human thermal comfort and heat stress in a desert climate

The role of sky view factor and urban street greenery in human thermal comfort and heat stress in a desert climate

3 Iran has diverse climates. There are limited days in a year which meet thermal comfort conditions (Daneshvar et al., 2013). Roshan et al. (2017) determined new threshold temperatures for cooling and heating degree days index for different parts of Iran. The results showed that southern coasts and central plateau of Iran have more Cooling Degree Days (CDD) and need maximum cooling energy. One of the passive design strategies recommended in such climates is human-biometeorological oriented design (Snir et al., 2016, Middel et al., 2019, Taleghani et al., 2019, Zamani et al., 2012). Solar radiation, wind speed and evaporation are three important factors of climate design in such desert climates. Greenery is one of the most effective elements of a human-biometeorological oriented design which plays an important role in improving thermal comfort (Middel et al., 2015, Taleghani and Berardi, 2018, Lee et al., 2016, Lee and Mayer, 2018). There are many studies that showed the heat mitigation impacts of vegetation in traditional courtyards (Foruzanmehr and Vellinga, 2011, Nasrollahi et al., 2017, Taleghani et al., 2012), and in urban scale (Akbari and Kolokotsa, 2016, Yan et al., 2018) in arid climates. Due to the water shortage in such climates, urban greenery needs to be designed in the most efficient way.
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Effect of Variation in Outlet Air Grilles location on Thermal Comfort and Air Flow Patterns

Effect of Variation in Outlet Air Grilles location on Thermal Comfort and Air Flow Patterns

Many steps in fluent part are used in (CFD) program . At the begging simulation Problem setup and included Model as shown in Fig-6.Also,The solution to a flow field problems (temperature, pressure, velocity, etc) is defined at nodes for each cell.The number of elements for three cases were 701528, 694643 and 315525 respectivelyas shown in Fig(6). Materials setup which included material properties used in simulation such as density (ρ), specific Heat (Cp)and thermal Conductivity (k)with values1.225, 1005 and0.0454 respectively. The Boundary conditions which has a significant impact on CFD simulation success in giving a reliable results for solved problem. Boundary conditions that imposed in CFD simulation implemented in this work consist of three types:, velocity inlet and outflow as tabulated in table 9. wall boundary included Walls with constant temperatures and also constant heat fluxes from other internal source such as Person, Computer and Light are45, 74.38 and 1000 respectively.
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Wind characteristics and outdoor thermal comfort assessment in East Malaysia

Wind characteristics and outdoor thermal comfort assessment in East Malaysia

Not only the values and trends of wind velocity, but the prevailing wind is also important in assessing the possibilities of outdoor thermal comfort conditions. The results of wind characteristic analysis can be very useful especially for design team to finalise their design of building orientation and position in relation to other surrounding buildings. This in order to enhance building permeability for greater induction of wind that can reduce heat. Table 2 shows the trends of prevailing wind in Kuching from South-Southeast direction (150°), and from East-Southeast direction (110°) in Kota Kinabalu, with an average frequency of about 4.59% and 19.81% respectively. These results also indicated that both locations have different prevailing wind velocities throughout the years. However, their prevailing wind directions remained the same every year for each of the locations, except in 2014 where the prevailing wind direction in Kuching was from North (0°). In short, yearly weather data analysis for the three-year period show different wind directions. A more precise wind directions for both locations can be obtained if a longer study period is considered.
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Thermal comfort conditions in airport terminals: Indoor or transition

spaces?

Thermal comfort conditions in airport terminals: Indoor or transition spaces?

and CO 2 and was reflected in the correlation between the two variables ( Table 3 ) (r ¼ 0.44, p < 0.01). The correlation between operative temperature and CO 2 concentration was weaker for MAN T1 (r ¼ 0.06, p < 0.05) and MAN T2 (r ¼ 0.13, p < 0.01), while also implying the tendency for higher temperatures with increased occupancy levels. The effect was significant in the smaller spaces within LCY, where a highly variable traffic was handled within the day. Occupancy changes in LCY explain 40% of the temperature variance in summer and nearly 30% in winter (r ¼ 0.62, p < 0.01 for summer, r ¼ 0.55, p < 0.01 for winter). The overall effect was weaker for MAN T1 and MAN T2 due to the considerably larger volume of spaces and the use of air quality controls in the latter. Seasonally, the correlation was significant only for the busy sum- mer period (r ¼ 0.29 for MAN T1 and r ¼ 0.37 for MAN T2, p < 0.01), as occupancy volumes did not vary much during the winter sur- veys; passenger traffic in MAN T2 was very low during winter, while in the busier MAN T1 traffic had very little variance within the day.
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Thermal comfort conditions in airport terminals: Indoor or transition spaces?

Thermal comfort conditions in airport terminals: Indoor or transition spaces?

There has been limited work, however, on the evaluation of the thermal environment in airport terminals and the investigation of the thermal comfort requirements for the different user groups. Balaras et al. took spot measurements of the thermal and visual conditions in three Greek airports for a week during summer. The study reported lack of proper humidity control and problems with temperature regulation in all three buildings, while through 285 questionnaires it highlighted the different satisfaction levels be- tween passengers and staff with all IEQ parameters [22] . The satisfaction with IEQ was also evaluated in eight Chinese airports where subjective and objective data were collected over a year. The study highlighted thermal issues such as overcooling and over- heating in several terminal spaces, however, the buildings were shown to underperform more in terms of acoustic environment and indoor air quality [23] . Environmental and subjective data were also collected from passengers in Terminal 1 at Chengdu Shuangliu International Airport, China, over a period of two weeks in summer and winter. Neutral temperature was 21.4  C in winter and 25.6  C in summer, with the respective comfort zones at 19.2 e23.1  C and 23.9 e27.3  C. Based on 569 questionnaires, the study reported that 78.3% of passengers were generally satis fied with the thermal environment and 95.8% considered the thermal conditions acceptable [24] . Another study surveyed 128 staff and passengers in the terminal of Ahmedabad airport, India, during the summer, and found a very high comfortable temperature range in the air- conditioned part of the building, 24 e32  C [25] . Ramis and dos Santos collected temperature and humidity data from three air- ports in Brazil. The temperature was found below the acceptable
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Urban heat island of Madrid and its influence over urban

thermal comfort

Urban heat island of Madrid and its influence over urban thermal comfort

Fig. 4 Selection of case studies from the comparison of temperatures in the two periods con- sidered, 1985 and 2015, respectively. Source: Elaboration by the authors 4.1 Case Study 1. Barrio de las Rejas This suburb is located in the district of San Blas, northeast of Madrid. Its geo- graphical location, south of the airport of Barajas, between the A-2, M-40 and M- 21 railways, as well as the abundance of industrial estates, industrial and give it an isolated character. Historically the residential population is concentrated in the western part of the neighborhood, specifically in Ciudad Pegaso. Urban develop- ment considered by the Urban Plan of 1997 led to the construction of over 1,600 homes, greatly increased its population and occupation in recent years 1 .
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Effect of architectural adjustments on pedestrian flow at bottleneck

Effect of architectural adjustments on pedestrian flow at bottleneck

Abstract – In the last decades, a series of terrible accidents happened within pedestrian crowds, which makes crowd dynamic a significant issue to be investigated. Literature reviews show that pedestrian flow presents different features within different architectural layout. In this paper, pedestrian movement properties at bottleneck are studied by carrying out series of experiments under laboratory condition. The influence of door sizes and exit locations on pedestrian crowd flow is investigated. It was found that larger door width resulted in shorter evacuation time and faster flow rate. By comparing the fundamental diagram among crowd evacuation, the average velocity increases as the width increases under the same density condition. Interestingly, the influence of the boundary layer, as well as the effective width on pedestrian crowd dynamic, was clearly observed. Our results suggest that the combination of exit width and location resulted in a synergistic effect, but the exit widths gradually became the most important factor influencing the flow rate.
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Thermal Comfort in a Naturally Ventilated and Air Conditioned Urban Arcade

Thermal Comfort in a Naturally Ventilated and Air Conditioned Urban Arcade

recorded information such as age, sex, and length of time lived in Cleveland, clothing levels, and level of activity before the survey. Current status of thermal comfort questions used standard comfort scales common to field studies of thermal comfort such as the ASHRAE 7pt. Thermal Sensation Scale, the McIntyre 3pt. Preference Scale, a 6pt. General Comfort Scale, and questions about direct acceptability in which subjects were asked to reply “acceptable” or “unacceptable” about their current thermal conditions. Questions about humidity, air movement, and direct sunlight also used preference and acceptability scales. Thermal expectation questions asked the subject to
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