Urban Ecology
mahsa samadpour shahrak; Mehrdad Karimimoshaver
Abstract
Highlights- The research considered the effect of planting patterns on thermal comfort.- The research addressed population increase and its effect on the morphology of cities.- The results of comparison between the scenario without trees and the others demonstrate that the thermal comfort conditions ...
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Highlights- The research considered the effect of planting patterns on thermal comfort.- The research addressed population increase and its effect on the morphology of cities.- The results of comparison between the scenario without trees and the others demonstrate that the thermal comfort conditions exhibit great changes, and all the scenarios create better environmental conditions than the scenario without trees.- The findings show that simply moving vegetation and trees without changing their nature and dimensions and the environment can improve comfort to some extent. IntroductionThe increasing population has changed the morphology of cities and caused changes in the surrounding environmental conditions. Green space per capita is about 4.5 square meters in Iran, which is quite different from the global standard: 20 to 25 square meters per person (Haashemi et al., 2016). As a result, it seems necessary to increase the amount of greenery in cities. Lee et al. (2016) introduce shading and ventilation as the main factors in the improvement of thermal comfort conditions in the environment using trees. Vegetation reduces mean radiant temperature and improves environmental conditions through evaporation and daylight control and reflection (Salata et al., 2017). It plays a major role in the regulation of weather conditions by controlling and conducting wind flow and reducing wind speed and pressure (Perini et al., 2018).Theoretical FrameworkThermal comfort involves conditions of perception in which the surrounding environment is thermally satisfactory (Ashrae, 1997). In their review of the studies conducted in the field of thermal comfort in outdoor spaces, Johnson et al. have introduced the predicted survey average index as one of the most widely used indices among ones such as SET and UTCI. (Johansson et al., 2013). This index has been widely used in different regions with different climates (El-Bardisy et al., 2016; Salata et al., 2015; Abdi et al., 2020).This model was designed by Fanger in 1970, considering factors such as air temperature, average radiant temperature, and relative humidity and two personal variables including clothing resistance and activity level, used as a composite index. This index specifies the coefficients that are measured according to Asher’s thermal scale and indicates the average thermal sensation of a large group of people in a certain space (Fanger, 1970). Therefore, considering and measuring this index causes other microclimatic factors to be taken into account and obtained through the following formulae:PMV=(0.303e-0.036m+0.028)[(M-W)-H-Ec-crec-Erec]E=3.05×10-3(256tsk-3373-pa)+EswEc=3.05×10-3[6.99×5733(M-W)-pa]+0.42(M-W-58.15)Crec=0.0014M(34-Ta)Erec=1.72×10-5M(5867-Pa).The value of H can be measured directly and calculated using the following equation:H=Kcl=tsk-tcl/Icl.Moreover, previous research has pointed out the importance of planting patterns, trees, and vegetation and their impact on the environmental and microclimatic conditions of the region. The question that arises now is what kind of tree planting pattern, among the common ones, can have a better impact on the environment. In this study, therefore, the four common planting patterns of sextuple, quadruple, row, and scattered were selected to be applied in the same conditions and with the same number of trees.MethodologyIn this research, the ENVI-met software was used because the output provides most of the parameters required for thermal comfort, such as Ta, Tmrt, and wind speed (Taleghani et al., 2015), and the results have been validated and used by researchers (Taleghani et al., 2018). For data measurement, five receptors were selected at the central points of the site. These receptors were located so as to be scattered in the site and be capable of expressing the general state thereof. Therefore, three receptors at the central points of the site and two located around the site were selected. Moreover, because the average human height between the positions of sitting and standing is 1.50 meters, the simulation measurement was carried out at this height. The environmental data and information on the receptors were extracted during the study hours (10 am to 9 pm), and the average value was calculated for the predicted survey average index.Results and DiscussionThe analysis of the data and figures extracted from the software demonstrates that a more uniform shade is created in the environment in the scattered pattern than in the others, and because the trees are scattered in most parts of the site, solar access is more limited there than in the other scenarios. Moreover, ventilation conditions are easier in the row pattern than in the scattered pattern, and the warm wind passes through the trees more easily there due to the regular arrangement. Therefore, the best planting pattern is the one that creates the more uniform shade and better ventilation conditions. However, the results of the scattered pattern are the same in most parts of the site, and there is only a little difference between them in some cases. As a result, the scattered and row patterns of tree planting are better than mass planting and concentrated in certain parts of the site.ConclusionThe results of comparing the treeless scenario to the others demonstrate that the thermal comfort conditions change to a large extent, and all scenarios create better environmental conditions than the treeless state. Moreover, because the row pattern exhibits a lower average PMV for most receptors and most hours of the day, it is the best pattern. The sextuple pattern has high indices in most cases, and the quadruple pattern has a similar function to the sextuple one. Therefore, it can be concluded that the row and scattered patterns create better comfort conditions than the others. The results of this research can be used by architects, landscape designers, and urban designers. In this research, different patterns of trees have been compared, so future research can involve comparison of other plantings such as grass and shrubs and of the effects of different planting patterns.
Urban Ecology
Pegah Yadegari; hassan sajadzadeh
Abstract
Highlights
The relative confinement of public open spaces of residential neighborhoods in cold climates plays an effective role in the thermal comfort of users.
Reducing wind speed plays a key role in increasing the thermal comfort of cold climates in winter.
Deciduous trees absorb sunlight during ...
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Highlights
The relative confinement of public open spaces of residential neighborhoods in cold climates plays an effective role in the thermal comfort of users.
Reducing wind speed plays a key role in increasing the thermal comfort of cold climates in winter.
Deciduous trees absorb sunlight during the day and reflect it to the environment in the evening and at night
Introduction
Because of the expansion of cities, it has become highly challenging to modify urban structures to address the drawbacks of the planning and design of open spaces, control microclimates, and improve thermal comfort conditions. Due to their effect on the quality of air in cities, urban microclimates are highly significant, and since urban spaces play an important role in creation of urban microclimates, urban designers and planners have the capacity and means to reduce the negative effects of climate on citizens’ health through implementation of proper designs.
Theoretical Framework
Urban spaces affect their users’ thermal comfort via their design elements. Various parameters can induce micro-climatic changes, such as the geometric patterns, vegetation, natural elements, and construction materials of the open spaces. These elements also play important roles in balancing urban thermal comfort during winter. While the effects of vegetation and geometric patterns on thermal comfort in public open spaces during winter have been studied independently, the cumulative impact of vegetation and geometric parameters during winter in cold and dry climates has not been investigated sufficiently. This article sought to address this shortcoming.
Methodology
The ENVI-met software was used for simulation and comparison of the thermal comfort conditions of the open spaces selected for this study. First, the design parameters of the selected sites were determined via field measurement, and were entered into the software for simulation of the thermal environments. The four climatic parameters of thermal comfort were measured during winter using ENVI-met . Then, a receptor was placed at the center of each selected site for investigation of thermal comfort at the pedestrian scale. Using these receptors, the parameters of space design and their impacts on thermal comfort were studied during the selected season.
Results and Discussion
The changes recorded for wind speed were larger than those in MRT, air temperature, and RH; hence, the differences in thermal comfort at the central points. According to the results, the Kolapa and Kolanj neighborhoods exhibited more favorable thermal conditions due to their higher PET values. Both Kalpa and Kolanj neighborhoods had north-south orientation. This type of orientation provides top-down access to the sunlight during winter. The H/W ratios at the central receptors of the Kolanj and Kalpa neighborhoods were 0.6 and 0.3, respectively. These H/W ratios provided greater enclosure than those of the other neighborhoods. While a H/W ratio less than one can be said to be suitable for cold climates during winter, it can cause thermal discomfort against wind speed if it lies below a certain threshold. This condition was observed in the Kababiyan neighborhood, where the H/W ratio at the central point was 0.13. As a result, the residents have to take protective measures against the winter wind and storms. In addition, dense vegetation caused a decrease in the SVF of the neighborhoods. The neighborhood centers with vegetation exhibited higher MRT values as well. The trees also raised the RH values of the neighborhoods. Because of the dry climate of Hamadan, Iran, vegetation can certainly improve thermal comfort in this city.
Conclusion
Recent climate studies have explored thermal comfort as an important quality of urban spaces. While thermal comfort can be achieved through a decrease in temperature in hot climates (as emphasized by most studies), it requires an increase temperature to provide thermal comfort in cold and dry climates. The presence of Hamadan’s citizens in the urban open spaces of the city always decreases in the second half of the year because of the cold mountainous climate. Limitation in or even lack of thermal comfort is one of the most important reasons for this change. With their high standards of sociability, the centers of the historical neighborhoods of Hamadan have always served as places for social interaction between the residents of the city. Therefore, this study attempted to assess the thermal characteristics of nine neighborhood centers in Hamadan using the notion of thermal comfort and the relevant variables.
Acknowledgment
This article has been extracted from a Master’s thesis in the field of Urban Design entitled Measurement and evaluation of thermal comfort in the centers of traditional neighborhoods with an emphasis on urban geometry and vegetation (historical neighborhoods of Hamadan), defended by the first author under the supervision of the second author at Bu-Ali Sina University.
Urban Sustainability
Samaneh Heidari; Golnaz Mortezaei
Abstract
Highlights The effect of some urban planning criteria on wind flow has been evaluated through a new method called Large Eddy Simulation. Simulation analysis of different scenarios confirmed that among density, lot coverage ratio and altitude, lot coverage ratio is the most influential parameter on the ...
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Highlights The effect of some urban planning criteria on wind flow has been evaluated through a new method called Large Eddy Simulation. Simulation analysis of different scenarios confirmed that among density, lot coverage ratio and altitude, lot coverage ratio is the most influential parameter on the air flow. Examining the effect of only density factor on air flow cant lead us to good conclusions about how wind flows. Fluctuations in different scenarios indicate that at the beginning and the end of the streets, the wind speed is faster than the middle. Introduction Along with the rapid growth of urbanization and the issues of global warming, environmental pollution, the urban heat island, and climate change, thermal comfort has turned into one of the most influential factors in adaptation of the design of climate-related urban open spaces. Today, the high temperature in human-made areas has doubled the need to consider thermal comfort in open urban spaces. Thus, wind flow is regarded as one of the most influential climatic parameters, where the speed and movement of the wind affect human thermal comfort. Theoretical Framework The traditional architecture and urban planning applied in the city of Isfahan, Iran makes up a unique local examples of Iranian architecture, which has been forced to provide many climatic solutions due to the hot, dry climatic conditions. In the past half century, however, a new pattern has emerged in building massing models as a result of the changes in the forms of housing space into different types of dense multi-family housing. Due to their extension and pervasiveness in Iran, these terraced housing models can be considered as part of the new urban planning trend in the country. Because of the increase in density and building surface ratios, however, part of the self-purification capacity of the urban environment has vanished, and certain construction models have become common in different climates with unfavorable conditions. As many cities are looking for solutions to apply compression and massing as far as possible, the drawbacks of the previous model have become more prominent, and a need has arisen for solutions to the current situation, in order to reduce the probable adverse consequences in the future. The consequences that may arise from this trend include a lack of thermal comfort in open urban spaces, an increase in heat exchange between indoor and outdoor spaces, and a rise in energy loss as a result. A master plan and an auxiliary force to urban designers and planners, the Booklet for Urban Planning and Building Regulations of the city of Isfahan always seeks to modify this pattern in the current situation. In the present study, therefore, attempts are made to consider the existing directions in the booklet and examine the role of physical factors in wind flow and its extent in the new fabric of the city. Methodology Due to its applied nature, this research uses the descriptive-analytical method and documentary and field techniques for data collection. Moreover, the large eddy simulation (LES) model is used for analysis of the defined scenarios. Results and Discussion. In order to achieve its purposes, the present study was designed in three phases. Thus, the effective physical indicators were first extracted through examination of the theoretical foundations related to thermal comfort, and their overlap with the directions in the Booklet for Urban Planning and Building Regulations of Isfahan was then studied. In the final step, LES was conducted through definition of the probable scenarios based on terrace housing models of the dominant line in the new fabric of Isfahan. An analysis of the simulation of different scenarios confirmed that an increase in lot coverage ratio, among the extracted indicators, caused a sharp decrease in speed ratio, while an increase in building height led to a decrease in speed ratio, and density exhibited a different effect, which could be interpreted along with the other criteria. Conclusion Based on the results, lot coverage ratio is the most effective parameter on air flow in the area, and density is not a suitable criterion for such measurement. Moreover, the effect of a change in lot coverage ratio on wind speed is greater than that of a change in building height. As for passage width, the fluctuations in speed ratio on narrow streets are far more limited than those on wide alleys and streets. Thus, speed is higher at the beginning and end of an alley than at the middle. In scenarios where building height is set between 10.5 and 14 meters, therefore, proper conditions are provided for urban air quality, ventilation, and air pollution.
Urban Sustainability
seyed majid mofidi shemirani; seyedeh maryam hoseini; haniyeh sanayeiyan; gholamreza japalaghi
Abstract
Throughout the past century, cities have lost their vital connection with the nature due to the fundamental changes in their functions and physical forms. The development of urbanization and attachment of villages to metropolises in recent years have led to destruction of vegetation in these regions. ...
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Throughout the past century, cities have lost their vital connection with the nature due to the fundamental changes in their functions and physical forms. The development of urbanization and attachment of villages to metropolises in recent years have led to destruction of vegetation in these regions. The importance of identifying the effects of cities on their climates can be indicated only through accurate research and quantitative assessment. The overall increase in air temperature as a result of urbanization is 1-3 degrees Celsius. In stable climatic conditions, however, the air temperature difference between urban and suburban areas can be as high as 10 degrees Celsius. Increasing the amount of vegetation, planting trees, and developing ecological networks are some of the effective passive methods available for improvement of microclimates. Similar methods have been used in the ancient cities of Iran, where the temperature inside the cities has always been lower than that of the surrounding areas due to the utilization of a special type of urban planning which has been capable of providing appropriate climatic conditions at micro scale by controlling climatic elements. Ozgol is one of the northern neighborhoods of Tehran, where green spaces have diminished as a result of the development process and space quality at the centralized focal points has decreased. This study attempted to identify the relationship between green areas and temperature decrease on the hottest day of the year to help improve the quality of the public spaces and increase thermal comfort at the focal points of the neighborhood. This research used a hybrid methodology based on logical reasoning and software-assisted assessment to study a site in the Ozgol neighborhood under two conditions: current status and optimal design. The data on the current situation of the neighborhood were obtained by field measurements, and those on the latter situation were obtained via computer simulation and addition of plants to the area. Then, the PMV model was used for assessment of the comfort conditions and specification of the exact effect of plants on microclimate elements. The two conditions were compared, and the impact of urban design with plants on environment quality was evaluated. The evaluation criteria included temperature and relative humidity. The measurements were made at a height of 1.65 meters to prioritize pedestrian comfort. The findings suggested that allocation of a low percentage of city space to greenery can greatly improve microclimatic conditions. The computations indicated that every square meter of green space added to the area under study would expand the comfort zone by 3.71 times. The results also demonstrated that retention of the amount of relative humidity can reduce air temperature by 1.5-2 degrees Celsius. The findings of this study highlighted the significance of preserving the current green spaces over the neighborhood and the necessity of avoiding any change in the land use of the remaining gardens (about 6,000 m2 in the 4-hectare area of the site). The computations also showed that addition of the existing green spaces over the area by 2.69% can expand the area within the range of thermal comfort to twice as wide as the pre-intervention area. One the other hand, the issue of global warming, the 1-degree rise in the world’s temperature during the past century, highlights the value and significance of this 1.5-degree temperature decrease. Thus, it is possible to make significant changes through extension of the results of this study to a larger scale to involve the entire city.
