According to population growth, urban sprawl, as well as global warming, attention to the impact of design on thermal comfort in open spaces is important. Thus, it is essential to climate studies and understanding environmental features, as well as results usage in improving designs. The aim of this research is to use optimal climate knowledge to improve the quality of urban spaces; so with suitable use of natural resources can be achieved in a sustainable urban environment and responsive to the needs of human. With regard to the simulation and analysis by ENVI-met software, the result of this paper showed that, by choosing the suitable species and number of trees on outdoor, Ta and the MRT in the summer were reduced by 0.29 ˚C and 20.04 ˚C respectively and the RH increased by 3.51%. Overall, PET improved from 34.92 to 26.16 ˚C and PMV decreased from 2.31 to 0.86 in the summer which means that they are reached around comfort zones.
Research Article
Comparative Analysis of Urban Greening Design Scenarios on Microclimate and Thermal Comfort
https://doi.org/10.21203/rs.3.rs-3442900/v1
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Human thermal comfort
Number and Tree species
Open Space
ENVI-met
Residential Complex of Aseman-e-Tabriz
The most challenges that mankind is facing these days are population growth and global warming. Regarding projections by the Population Reference Bureau (PRB), around 55% of the global population is living in the cities and urban areas (Population Reference). On the other hand, Climate change is a critical challenge to the urban areas which creates a phenomenon known as the urban heat island (UHI). Thus, the influence of UHI and urbanization cause discomfort environment to people, especially during summertime (Kotharkar, Bagade, & Ramesh, 2019). These issues have forced policy makers to think more creative and bring the concept of sustainability to the forefront of their decision as never before. An important characteristic of cities is urban greenery that creates shading along streets and in residential areas and consists in the development of adaptation possibilities against climate change. Some recommendations about urban design strategies have provided by designers and climatologists to urban heat island mitigation (Mills, 1999). Urban heat island mitigation strategies such as urban trees planting and appropriate use of high-albedo surfaces create better outdoor thermal comfort. In this regard, Numerous studies provided ways and recommendations to improve urban microclimate and outdoor thermal comfort by planting trees.
The study of vegetation in the control of incident solar radiation, and as a regulator of urban climatic changes involves qualifying and quantifying the influence of trees on human thermal comfort (De Abreu-Harbich, Labaki, & Matzarakis, 2015). The use of patterns to measure the performance of spaces designed to benefit from climate elements will be of great help; as an example, tree species in Brazil can attenuate solar radiation from 76.3–92.8% in the summer months (L. Abreu-Harbich, Labaki, & Matzarakis, 2012; Bueno-Bartholomei & Labaki, 2003). In many studies, the positive effects of vegetation on the urban heat island by shading and increasing evaporation and transpiration along with its beauty benefits (Czáder, Balczó, & Eichhorn, 2009; Galvão, Gerritsma, & De Maerschalck, 2008; Gromke & Ruck, 2007). In Brazil, it was recently concluded that outdoor thermal comfort is closely related to urban tree management (Spangenberg, Shinzato, Johansson, & Duarte, 2008). have investigated the effect of vegetation on the pattern of distribution and volume of polluting particles of traffic with the ENVI-met (Bruse & Fleer, 1998) model, showing that urban vegetation (trees and shrubs) has little effect on reducing wind speed and optimal ventilation and uniform change of wind speed vertically through the levels of passageways and urban passageways. Urban trees can modify air temperature, increase relative humidity, reduce wind speed, and modify air pollutants (Streiling & Matzarakis, 2003). Morakinyo et al.(Morakinyo, Dahanayake, Adegun, & Balogun, 2016) analyzed the effectiveness of trees in improving thermal comfort using the ENVI-met model and the results show that the tree configuration, including leaf level index, tree height, trunk height, are effective to improve thermal comfort. Also, in a similar study by (Morakinyo, Kong, Lau, Yuan, & Ng, 2017), improving the thermal comfort conditions by providing a suitable placement of trees in a parking (Milošević, Milošević, & Glišić, 2013) concluded that the location of trees is also important for trees to improve and reduce thermal stress.
According to Teshnehdel et al. (Teshnehdel, Akbari, Di Giuseppe, & Brown, 2020) by adding trees can reduce mean radiant temperature significantly. Since the correlation between MRT with physiologically equivalent temperature is high and is the most important factor influencing PET in the urban environment (Teshnehdel, Mirnezami, Saber, Pourzangbar, & Olabi, 2020). These results in a summer PET improvement from 34.92°C to 26.16°C, thus moving from an original hot thermal sensation to a slightly warm one. Hami et al. (Hami, Abdi, Zarehaghi, & Maulan, 2019) have evaluated the effects of green spaces on thermal comfort. Their study reported that the cooling potential of trees depends on their specifications including leaf area index, tree height, trunk height, crown height and crown width. Results of analyzing in 165 studies by Koc et al. (2018) showed that little is known about the thermal benefits of green infrastructures in tropical and desert climates, developing countries, and southern-hemisphere regions which are experiencing significant urbanization and population growth and are severely affected by heatwaves. However, in a series of researches that have been conducted on the outdoor thermal comfort in tropical climates such as Dahaka, Bangladesh (Ahmed, 2003), Hong Kong (Cheng, Ng, Chan, & Givoni, 2012; Kong et al., 2017; Lau, Chung, & Ren, 2019), Selangor, Malaysia (Makaremi, Salleh, Jaafar, & GhaffarianHoseini, 2012), Colombo, Sri Lanka (Johansson & Emmanuel, 2006), and Singapore (W. Yang, Wong, & Jusuf, 2013). Deng et al. (Deng, Pickles, Smith, & Shao, 2020) studied on tree crown spectroscopy on the radiative performance of ten planted tree species in the UK. Their findings illustrated that tree species selection in reduction of urban heat depends on the leaf size, solar altitude and combination of tree crown morphology. In addition, infrared transflection towards buildings and pedestrians is considerable. Therefore, tree crown transflection should be primarily towards sky on the sunlit side of trees. In addition, the quantification of tree shading benefits, in terms of PET, provides an accurate measure of the real cooling effects for thermal comfort (De Abreu-Harbich et al., 2015; Teshnehdel, Gatto, Li, & Brown, 2022). The shape and size of trees can modify the effect in different climate regions (Shashua-Bar, Potchter, Bitan, Boltansky, & Yaakov, 2010). The evaluation of different commonly found arboreal species and their characteristics should be taken into account by professionals of the urban built environment. This would improve outdoor thermal comfort, reducing the effect of heat islands and ensuring a better quality of life for people in the urban environment (L. V. Abreu-Harbich, Labaki, & Matzarakis, 2014; Shashua‐Bar et al., 2010; Streiling & Matzarakis, 2003).
A few results of the research also have shown the effect of urban greening and trees on urban microclimate and thermal comfort in winter (Hami et al., 2019; B. Yang, Olofsson, Nair, & Kabanshi, 2017; Zhang, Zhan, & Lan, 2018).
The thermal comfort stresses are defined over 10 scales ranging from extreme heat stress to extreme cold stress. The thermal comfort zone is believed to be between 18 and 23 ˚C for PET and (-0.5 _ +0.5) for PMV (Table 1) (Matzarakis, Mayer, & Iziomon, 1999).
| PMV | PET | Thermal sensation | Grade of Physiological stress |
| Below − 3.5 | Below − 4 | ||
| Very cold | Extreme cold stress | ||
| -3.5 | 4 | ||
| Cold | Strong cold stress | ||
| -2.5 | 8 | ||
| Cool | Moderate cold stress | ||
| -1.5 | 13 | ||
| Slightly cold | Slight cold stress | ||
| -0.5 | 18 | ||
| Comfortable | Neutral | ||
| 0.5 | 23 | ||
| Slightly warm | Slight heat stress | ||
| 1.5 | 29 | ||
| Warm | Moderate heat stress | ||
| 2.5 | 35 | ||
| Hot | Strong heat stress | ||
| 3.5 Above + 3.5 | 41 Above + 41 | ||
| Very hot | Extreme heat stress |
The goal of this paper is to probe how species and number of trees influence the outdoor microclimates and human thermal comfort. Numerical simulation is used to address this question and to determine how choosing the suitable species and number of trees in the residential area. Therefore, we have focused on human thermal comfort based on the PET, PMV and PPD for assessing trees performance in residential areas as a passive cooling technique, to improve outdoor thermal comfort in local steppe climate of Iran.
2.1. Study area
Tabriz (Iran) is located at (38˚8ˊNorth, 48˚15ˊEast) and 1350 meters above sea level. Tabriz is influenced by the local steppe climate. In Tabriz, there is little rainfall throughout the year. This location is classified as BSk climate (Köppen & Geiger, 1930). The average temperature in Tabriz is 11.6°C. The average annual rainfall is 318 mm.
Aseman-e-Tabriz residential complex (Fig. 1) was designed and built on a land of 9.4 hectares, with 16 residential towers of 18 floors. (Table 2) shows the level and percentage of open space elements.
| Open space elements | Area (m2) | Percent (%) | |
|---|---|---|---|
| Apartment blocks | 19000 | 20.25 | |
| Green space (grass and vegetation) | 43875 | 46.65 | |
| Transit network (Asphalt) | 16963 | 18.04 | |
| waterfront | 420 | 0.44 | |
| Service spaces | 13750 | 14.62 |
2.2. Methods
The research method is descriptive-analytic and simulation. Data collection has been done through library studies, field surveys and computer modeling. In this research, the effect of number and tree species on climate characteristics, including air temperature, relative humidity, wind speed, radiant temperature and thermal comfort indexes such as PET, PMV and PPD by ENVI-met software have been investigated. First, four cases were analyzed by ENVI-met software based on the species and the number of trees according to (Table 3).
| Study Case | Material | Species of trees | Number of trees per hectare | The total number of trees on the site | Area for 1 tree |
|---|---|---|---|---|---|
| Current situation | Asphalt | Needle tree (pine-cypress) | 17 | 153 | 286 m2 |
| Case 1 | Asphalt | Deciduous tree (acacia- beech) | 17 | 153 | 286 m2 |
| Case 2 | Asphalt | Deciduous tree (acacia-beech) | 30 | 270 | 162 m2 |
| Case 3 | Asphalt | Deciduous tree (acacia-beech) | 45 | 405 | 108 m2 |
| Case 4 | Asphalt | Deciduous tree (acacia-beech) | 60 | 540 | 81 m2 |
2.2.1. Numerical simulation
Due to some limitations of the software, the hottest day of summer and coldest day of winter, which are considered as the summer and winter solstice, were selected as a case study. In this regard, the weather data of Tabriz points were taken from the site of the Iranian Meteorological Organization to use in data input of ENVI-met (Table 4).
| Data | 2017.06.22 | 2017.12.22 |
|---|---|---|
| Dry Bulb Temperature (˚C) | 24.2 | 2.9 |
| Relative Humidity (%) | 32 | 73 |
| Wind Speed (m/s) | 4.9 | 2.1 |
| Wind Direction (degree) | 120 | 250 |
| Cloud coverage | 0 | 0 |
Almost all of the trees planted in the site are coniferous species with a height of 7 meters and a diameter of 3 meters (Fig. 2). Physical features such as dimensions, number and position of apartment blocks, waterfront, the level of green space (grass) and the material of pedestrian level fixed were considered.
The parameters needed for modeling trees in the Albero (a subcategory of the ENVI-met):
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• The root geometry root
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• The tree crown geometry
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• Leaf Specifications
The physical specification of each tree for modeling was input using the measured data (Table 5). Leaf properties have been defined according to its species (coniferous-deciduous) and tree calendar (season profile). Due to a lack of specialized instruments, the root geometries of trees were default values.
2.2.2. Input parameters for ENVI-met
(Table 6) illustrate the information required for ENVI-met software to determine thermal comfort indices and the conditions used in the configuration file of this study.
| Simulations input parameters | Tabriz | ||
|---|---|---|---|
| Summer day | Winter day | ||
| Location | 38˚8ˊN 48˚15ˊE | ||
| Elevation | 1350 | ||
| Climate | BSk | ||
| Simulation day | 2017.06.22, 2017.12.22 | ||
| Simulation period | 9 Hour, from 9:00 am to 17:00 pm | ||
| Domain size | 90*60*60 | ||
| Grids spatial resolution | Horizontally: 6m Vertically: 2m | ||
| Personal characteristics | Age: 35 | Height: 175 cm | Weight; 75 kg |
| Cloths and Activity | Speed: 0.5 m/s | 0.9 | 0.4 |
To obtain more accurate results, 10 virtual receptors in ENVI-met simulation (A to J) as reference points for recording and receiving climatic information during the simulation period (9am -5pm) is defined. The comparison of simulation results can determine the performance of each tree on the thermal comfort conditions, especially on the site microclimate. The base model in the ENVI-met represents accurate outdoor microclimates with the current building, vegetation, and soil/surface conditions (Figs. 3, 4).
2.3. Model validation
To validate the ENVI-met model, the result of simulation and measuring compared for further analysis. The measuring instrument was placed 1.5m above the ground (Fig. 5). The information and technical data of the instrument have represented in (Table 7). Air temperature and relative humidity of the area were measured and simulated. The measured data were averaged at different times on 31 January, 2 and 3 February year 2017 from 09:00–17:00 in local time.
| Sensor type | Measuring range | Accuracy | Output resolution | Measuring rate |
|---|---|---|---|---|
| Testo 610 | -10 to + 50°C | ± 0.5°C | 0.1°C | 1 s |
| Testo 610 | 0 to 100%RH | ± 2.5%RH (5 to 95%RH) | 0.1%RH | 1 s |
3.1. Validation results
According to the simulation and measuring results, the average Ta difference between simulated and measured results is 0.5°C, while the difference around 1.5°C at the highest point. There is a very close agreement correlation coefficient between the measured and simulated data of Ta (R2≃0.92, RMSE≃0.98°C) and RH (R2≃0.88, RMSE≃2.76%) (Fig. 6).
3.2. Investigation of PMV and PET results
(Fig. 7) shows the average PMV (current situation) for each site in the summer and winter, which is calculated using the ENVI-met software. According to the defined zone, Zero is the ideal value, representing thermal neutrality, and the comfort zone is defined by the combinations of the six parameters (Metabolic rate, Clothing insulation, Air temperature, Radiant temperature, Air speed and Humidity) for which the PMV is within the recommended limits (-0.5 < PMV < + 0.5) (Table 1). According to this divisions, there are different conditions on the site. So that, in summer, point E is the maximum quantity of PMV with 2.73 (PPD: 97%), due to the distance from the buildings and the lack of trees. Since point G is located among the trees, it is the lowest amount (PMV: 1.64 _ PPD: 56%) in summer and the highest with − 3.62 (PPD: 100%) in winter. Also, the average total PMV of the ten points in the summer is 2.31 (PPD: 87%). In winter, the lowest value for point I (PMV: -2.6 _ PPD: 96%) it has the highest mean radiant temperature. Average points in this season are − 3.07 (PPD: 100%). (Fig. 8) shows the average PET index (current situation) for each point in the summer and winter. When the physiological equivalent temperature is between 18 and 23°C the thermal condition is in comfortable zone (Table 1). According to the (Fig. 8), in summer, physiological equivalent temperatures in all point are above 30°C, with the highest PET from point E at 37.33 ˚C, because of exposure to direct sunlight. Due to being in the shadow of buildings, point H is the lowest value (31.03°C); the average temperature of the physiological equivalent of 10 points is based on 34.92 ˚C. In winter, the highest point is J to the 7.81 ˚C, because of exposure to sunlight during a day and point G is still the lowest (3.87 ˚C). The average physiological equivalent temperature of all points in winter is 5.97°C. The results show that, points G, H and J are in hot zone in summer and the other points are in very hot zone. In the winter, all points except the point G are in a very cold area. Therefore, based on the Predicted mean vote and the physiological equivalent temperature index, the main problem of the site is hot tension in the summer and very cold tension in the winter.
The 9-hour average of climate variables include air temperature, relative humidity, wind speed, radiant temperature, as well as PET, PMV and PPD indices related to the receiving points located on the site from 9 am to 17 pm, respectively, summer in the (Table 8) and winter in the (Table 9) has been calculated.
| Alternative | Temp (˚C) | RH (%) | Wind Speed (m/s) | Tmrt (˚C) | PET (˚C) | PMV | PPD (%) |
|---|---|---|---|---|---|---|---|
| Current situation | 26.20 | 36.77 | 2.21 | 59.93 | 34.92 | 2.31 | 73.67 |
| Case 1 | 26.19 | 37.69 | 1.91 | 53.70 | 32.97 | 2.09 | 68.90 |
| Case 2 | 26.18 | 39.09 | 1.68 | 47.76 | 30.00 | 1.54 | 54.32 |
| Case 3 | 25.91 | 40.28 | 1.74 | 39.89 | 26.16 | 0.86 | 44.13 |
| Case 4 | 25.87 | 41.49 | 1.41 | 38.75 | 25.14 | 0.84 | 36.35 |
| Alternative | Temp (˚C) | RH (%) | Wind Speed (m/s) | Tmrt (˚C) | PET (˚C) | PMV | PPD (%) |
|---|---|---|---|---|---|---|---|
| Current situation | 6.28 | 84.00 | 1.09 | 23.47 | 5.97 | -3.07 | 94.70 |
| Case 1 | 5.94 | 84.30 | 1.01 | 17.87 | 4.97 | -3.29 | 98.09 |
| Case 2 | 6.77 | 83.88 | 0.81 | 14/80 | 5.07 | -3.24 | 97.73 |
| Case 3 | 6.92 | 83.80 | 0.82 | 13.22 | 5.34 | -3.19 | 97.76 |
| Case 4 | 6.75 | 84.15 | 0.97 | 12.69 | 5.08 | -3.24 | 98.27 |
In Case 1 calculations have been made from the needle leaf (pine-cypress) to the deciduous (Beech-acacia) species, and other physical features including the number of fixed trees are assumed. The results of the study show that in the summer season, points A, E, G and J are in the hot zone, and points B, D, F and H are in the warm zone and points C and I are in the slightly warm zone. In the winter, all the points pointed on the site except the points G and D, are in a very cold area (Fig. 9).
In Case 2, with the increase in the number of trees to 270 leafy trees (Beech-Acacia), calculations have been done and other physical features have been fixed. The results show in the summer, points D, E, F and J within a warm zone and points A, B, C, G, H, and I are in the hot zone. In the winter, G, C and D points are in the extremely cold zone and the rest of the points are in a very cold area (Fig. 10).
In Case 3 calculations have been done with 405 numbers of tree species (Beech-Acacia tree) increasing, and other physical features are assumed to be constant. The results of the study show that in the summer season, points D and H are in the warm zone, and points A, B, C, E and I are in the slightly warm zone and three points F, G and J are within the comfort zone. In the winter, C and G points are in the extremely cold zone and the rest of points are in a very cold area (Fig. 11).
In Case 4, the number of trees is estimated at 540 trees (Rush-Acacia), and other physical features are assumed to be constant. The results of the study show that in the summer of summer, points D and H are in the warm zone, and points B, C, E and I are in a slightly hot zone and four points A, F, G and J are within the comfort zone. In winter, C and G points are in the extremely cold zone and the rest of the points are in a very cold area (Fig. 12).
According to (Fig. 13), the sun and the shadow are significant in the calculation of thermal comfort. These differences have created a wide zone of "mean radiant temperatures" in different parts of the site. In summer, the mean radiant temperature in the site, with 153 leaf needles, is 59.93°C, and the proposed design, with 405 deciduous trees, is 39.89°C. Therefore, the mean radiant temperature in the proposal decreased to 20.04°C in summer and 10.25°C in winter.
This study evaluated the factors affecting thermal comfort in an open space-based study of the Tabriz Residential Complex. In the first stage, the climate variables and thermal indexes of the selected points of the site are calculated on the first day of summer (22th June) as the summer revolution and the first day of winter (22th December) as a winter revolution through simulation, and then calculate the thermal comfort of a particular person. Based on the analysis of the species and number of trees, the results show that the shade of trees decreases the mean radiant temperature in the summer and has a significant role in cooling the urban spaces. Also, the use of trees leads to increases in the relative humidity that has an effective role in reducing the temperature of the environment. So case 3 with 405 deciduous trees was selected as the most suitable case for the number and species of trees.
4.1. Selection of human thermal comfort model
The microclimates and human thermal comfort benefits from urban trees are significant while due to some limitations in this research, we only used influence of species and number of trees in a residential district. In this study, V4 of the ENVI-met model was utilized. The performance of Ta and RH simulation in ENVI-met V4 software was validated. In most previous studies (Acero & Herranz-Pascual, 2015; Middel, Häb, Brazel, Martin, & Guhathakurta, 2014; Skelhorn, Lindley, & Levermore, 2014; Srivanit & Hokao, 2013; Teshnehdel, Akbari, et al., 2020), validation of the ENVI-met model which mainly focused on Ta and RH have been verified. Overall, the performance of the ENVI-met model was satisfactory compared with early versions (Tsoka, Tsikaloudaki, & Theodosiou, 2018). The good performance of this software provides opportunities to researchers for presentation in multiple scenarios. Thanks to the user-friendly interface of ENVI-met. The users have the scientific power of physical climate simulation systems that make them forget they work with a sophisticated climate simulation Model. However, being time-consuming, costly and difficult to follow the analysis are among some limitations connected to the application of this software.
4.2. The effect of tree cover
In this study, we used the ENVI-met model to test four vegetation scenarios at the residential district in Tabriz. The results showed that, by adding tree cover in the study area, the air temperature at the pedestrian level reduce by 0.29 ºC in summer season which was lower than the results (McPherson, 2001; Milošević et al., 2013), they utilized the same model to study tree canopy influence on air temperature.
(Andreou, 2013; Taleghani, Sailor, & Ban-Weiss, 2016; Yahia & Johansson, 2014) propounded that by adding new trees improved the outdoor thermal comfort. Other tree features such as height, leaf area index, canopy density, and crown size may recommend different results (Armson, Rahman, & Ennos, 2013). The tree growing process can also be considered in the future research to understand how trees will influence the urban built environment in a long time period (Rahman, Armson, & Ennos, 2015). Our results suggest that by reducing the Tmrt from 59.93˚C to 39.89˚C, PET decrease 34.92˚C to 26.16 ˚C (c3) during summer day. There is a high correlation between the "MRT" with the thermal comfort indexes (Akbari & Teshnehdel, 2018; Teshnehdel, Bahari, & Mirnezami, 2019; Teshnehdel, Soflaei, & Shokouhian, 2020), therefore, MRT is the most important factor influencing human thermal comfort in the residential area which can control that by trees. According to results of this study, PET value in c3, improve about 8.76 ˚C. The cooling benefits from trees can reduce the thermal comfort level from “hot” to “warm” in hot summer day (Crewe, Brazel, & Middel, 2016). The quantification of tree shading benefits, in terms of PET, provides an accurate measure of the real cooling effects for thermal comfort. The shape and size of trees can modify the effect in different climate regions (Spangenberg et al., 2008). The evaluation of different commonly found arboreal species and their characteristics should be taken into account by professionals of the urban built environment. This would improve outdoor thermal comfort, reducing the effect of heat islands and ensuring a better quality of life for people in the urban environment (Shahidan, Shariff, Jones, Salleh, & Abdullah, 2010; Streiling & Matzarakis, 2003). Our results demonstrated that by adding new trees can decrease heat island and air temperature, greenery design especially appropriate selection of number and tree species lead to further decreased air temperature and sensible heat at the residential district (Shahidan et al., 2010).
The results of this study will help policymakers and designers to think more creative and bring the concept of sustainability to select and planting urban trees to improve thermal comfort in the residential districts.
This research studies the potential of trees to heat stress mitigation in a residential district in Tabriz, Iran which is located in BSk climate, is investigated. The micro-meteorological simulation model ENVI-metV4 was validated against Ta and RH data, on four different urban greening scenarios in this study. The results showed that trees play a significant role in outdoor thermal comfort regulation and mitigating urban heat islands. Therefore, it is imperative to use the principles that make tree species more selective and systematically in urban areas.
The results of this study showed that:
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• By choosing the appropriate species and density of trees in open space of residential complex, the air temperature and the mean radiant temperature in the summer were decreased by 0.29 ˚C and 20.04 ˚C respectively.
-
• Relative humidity, which is one of the factors affecting the cooling of urban open spaces, has increased in the microclimate zone of the site, up to 3.51 percent from the current summer season. In winter, the relative humidity was reduced by 0.2%
-
• By adding the number of trees, as well as changing the species of trees from leaf to deciduous species in the proposal, reduce the wind speed compared to the current situation, with a decrease of 0.47 and 0.27 m/s in summer and winter, respectively.
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• Based on the PMV, PPD and PET indexes, the main problem with the site is thermal overheating in summer, the Predicted Mean Vote is 2.31, the PPD index, which represents dissatisfied people, is 73.67% and the physiological equivalent temperature is 34.92°C. Using the proposed plan, the Predicted Mean Vote was reduced to 0.86, PPD reduced to 44.13% and the physiological equivalent temperature reached to 26.16°C which was closer to the comfort zone.
Results represented that trees as an effective strategy can improve outdoor thermal comfort in urban areas and provide some design recommendations and guidelines for urban designers and policymakers. I this study, we presented the impact of trees on outdoor thermal comfort at the neighborhood or block scale. It is evident that further studies are necessary in order to the spatial arrangement of trees at a large scale to support and confirm our results.
Data availability statement
The data that support the findings of this study are available on request from the corresponding author (Saeid Teshnehdel) upon reasonable request.
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|
PET |
Physiological equivalent thermometer |
|
PMV |
Predicted Mean Vote |
|
SET |
Standard Effective Temperature |
|
hPa |
Hectopascal (100 x 1 Pascal) |
|
kg |
kilogram |
|
RMSE |
Root Mean Square Error |
|
CC |
Correlation Coefficient |
|
Ta |
Air Temperature |
|
RH |
Relative Humidity |
|
MRT |
Mean Radiant Temperature |
|
°C |
Celsius degree |
|
m/s |
Meter/second |
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.