Alexandria Engineering Journal (2017) 56, 533–543
H O S T E D BY
Alexandria University
Alexandria Engineering Journal www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
Urban design in favor of human thermal comfort for hot arid climate using advanced simulation methods Asmaa Barakat *, Hany Ayad, Zeyad El-Sayed Faculty of Engineering, Architecture Department, Alexandria University, Egypt Received 24 February 2017; revised 12 April 2017; accepted 13 April 2017 Available online 4 May 2017
KEYWORDS Thermal comfort; Urban design; Hot arid climate; Simulation methods; Envi-met
Abstract Improving outdoor human thermal comfort could be considered as one of the most important targets for achieving successful open space designs. In hot arid climate, residential neighborhoods are responsible for the high request of energy to provide cooling needs for the occupants’ comfort. The main problem is the non-responsive contemporary urban design to human thermal comfort and energy. In this context, this paper aims at testing specific landscape parameters that could enhance outdoor human thermal comfort. The study is limited to the microclimate at urban open space and will be conducted in New Borg El-Arab (hot arid city according to Middleton and others [1], Alexandria, Egypt). The adopted methodology is based on the use of ENVI-met 4.0 software to measure four thermal indices (air temperature, relative humidity, MRT and PMV) and assess outdoor human thermal comfort in an existing neighborhood. In addition, different design scenarios that emphasize different landscape elements were also assessed. The results of this analysis depict changing street networks, landscape design and materials could enhance the level of thermal comfort in the urban open spaces. Ó 2017 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction The increase in world population leads to an urgent need to diminish the energy footprint of humanity. In hot arid climate, residential neighborhoods are responsible for the high request of energy to provide cooling needs for the occupants’ comfort [2]. The main problem is the non-responsive contemporary urban design to human thermal comfort and energy efficiency. Due to recent changes in the urban density and street networks * Corresponding author. E-mail address:
[email protected] (A. Barakat). Peer review under responsibility of Faculty of Engineering, Alexandria University.
of contemporary urban context, controlling micro-climate of neighborhoods imposes difficult challenges to achieve human thermal comfort. Randomized and careless urban design leads to developing uncomfortable areas between building blocks [3]. In this respect, several recent researches explored bioclimatic strategies that may enhance outdoor human thermal comfort. A recent research by Alireza Monam and Klaus Ru¨ckert [4] suggested strategies for the development of low carbon ‘‘energy-efficient” and resilient housing districts in semi-arid climates. This was achieved through the designing of 35 ha area of southern Hashtgerd new town using passive strategies for 8000 inhabitants in 2000 residential units. Other researchers attempted to adopt a retrofitting approach, such as
http://dx.doi.org/10.1016/j.aej.2017.04.008 1110-0168 Ó 2017 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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Table 1 PMV ranges and physiological equivalent for different grades of thermal perception and physiological stress; internal heat production: 80 W, heat transfer resistance of the clothing: 0.9 clo [12]. PMV
Thermal perception
Grade of physiological stress
3
Very cold Cold Cool Slightly cool Comfortable Slightly warm Warm Hot Very hot
Extreme cold stress Strong cold stress Moderate cold stress Slight cold stress No thermal stress Slight heat stress Moderate heat stress Strong heat stress Extreme heat stress
Axarli and Teli [5], who redesigned an open space in a residential area in Thessaloniki Greece. According to Middleton and others [1] Egypt is located in the hot arid climate zones. In this context, many planning projects have been produced and implemented to cope with population growth. In Egypt, the overwhelming rate of population growth did not allow time for full environmental studies for both the built and the natural environments where buildings and open spaces have to be adequately climatic responsive [6]. Urban design is strongly dependent on climate interactions which can improve or moderate impacts on human thermal comfort. This brings us to the must of a deep understanding of all the forces affecting the thermal comfort in the urban environment. Moving one step ahead, this knowledge is used to support urban designers and planners in decision making. Thus, their designs will ensure reduced energy consumption and improve human thermal comfort. This study aims at testing specific landscape parameters that could enhance outdoor human thermal comfort in hot arid climate. In order to achieve this aim, the first part of this paper (theoretical study) investigates the literature review of the human thermal comfort in general. Particularly, this paper
Figure 1
focuses on two thermal variables: air temperature and relative humidity. In addition, the thermal indices that could be used to evaluate both cold and hot outdoor conditions, such as Predicted Mean Vote (PMV) and Mean Radiant Temperature (MRT) were analyzed. The second part of this paper (Empirical study) discusses the adopted methodology which is based on proposing three different scenarios for existing urban area in New Borg El-Arab, Egypt. These scenarios assume preservation of existing buildings and changing street networks, landscape design and materials. ENVI-met 4.0 software is used to measure four thermal indices (air temperature, relative humidity, MRT and PMV) and assess outdoor human thermal comfort in the existing neighborhood and the three proposed scenarios. The results of this analysis depict changing street networks, landscape design and materials could enhance the level of thermal comfort in the urban open spaces. 2. Human thermal comfort Achieving human thermal comfort is essential for hot arid regions. ‘‘Thermal comfort is generally defined as that condition of mind which expresses satisfaction with the thermal environment. Dissatisfaction may be caused by the body being too warm or cold as a whole, or by unwanted heating or cooling of a particular part of the body (local discomfort)” [7]. Air Temperature is the most common indicator of human thermal comfort. Nevertheless, air temperature alone is not an accurate indicator of thermal comfort. There are other environmental and personal parameters must be taken into account. According to ASHRAE Standard 55-2010, environmental parameters are air temperature, mean radiant temperature, wind speed and relative humidity. Personal parameters are activity level and clothing insulation. In general, outdoor thermal comfort is much more complex than indoor comfort. For example, the spatial and temporal microclimatic variations of meteorological variables are often very large. Other reasons for the difficulty include lack of climate control in outdoor spaces [8]. To help architects and urban designers for better design decisions, some thermal variable and indices are proposed
The adopted steps for this paper.
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Figure 2
Figure 3
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The location of the case study site.
Site plan of the current situation for Engineers’ buildings in New Borg El-Arab.
for assessment. This paper focuses on two thermal variables: air temperature and relative humidity. In addition, the thermal indices that could be used to evaluate both cold and hot outdoor conditions: such as Predicted Mean Vote (PMV) and Mean Radiant Temperature (MRT). 2.1. Air temperature variable This is the temperature of the air surrounding the body. It is the most important environmental factor, measured by the dry bulb temperature (DBT). It is usually given in degree Celsius (°C) [9]. The appropriate air temperature can be assessed
by reference to the comfort zone in Givoni’s Psychrometric chart (Givoni 1976 & 1998). 2.2. Relative humidity variable Relative humidity is the ratio between the actual amount of water vapor in the air and the maximum amount of water vapor that the air can retain at that air temperature. Relative humidity between 40% and 70% does not have a major negative impact on thermal comfort [9]. The appropriate relative humidity can be assessed by reference to the comfort zone in Givoni’s Psychrometric chart (Givoni 1976 & 1998).
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A. Barakat et al. 3. Methods and tools In order to achieve the previously mentioned aim, testing specific landscape parameters that could enhance outdoor human thermal comfort in hot arid climate by using advanced simulation methods, the following steps were adopted as shown in Fig. 1. 3.1. Simulation with ENVI-met 4
Figure 4
Low maintenance and neglected landscape.
2.3. Mean radiant temperature (MRT) index The mean radiant temperature is one of the most important factors assessing outdoor human thermal comfort. In open spaces, regarding radiative heat exchange between the human body and its environment must consider the following short-wave and long-wave radiant fluxes: direct solar radiation, diffuse solar radiation, reflected solar radiation, infrared radiation from the sky and infrared radiation from the surroundings. MRT varies temporarily and spatially in cities where urban surfaces interact with radiation, absorbing, reflecting, or emitting radiative energy at various wavelengths [10]. 2.4. Predicted Mean Vote (PMV) index Predicted mean vote (PMV) was developed for assessing thermal comfort. The PMV calculations consider four environmental parameters: air temperature, mean radiant temperature, wind speed and relative humidity; and two personal variables: clothing insulation and metabolic rate, as the inputs and predict thermal sensation. The Predicted Mean Vote (PMV) refers to a thermal scale that runs from Cold (3) to Hot (+3) as illustrated in Table 1 [11].
Figure 5
Several simulation models are used in the process of evaluating human thermal comfort in outdoor spaces, such as ENVI-met, OTC Model, Rayman, SOLWEIG-model, TownScope, Urbawind, IES VE and Ecotect. In this research, the threedimensional model ENVI-met 4 was applied. ‘‘This model takes into account the physical processes between atmosphere, ground, buildings and vegetation and simulates the climate within a defined urban area with a high spatial and temporal resolution, enabling a detailed study of microclimatic variations” [13]. The input data consist of physical characteristics of the urban area and meteorological data. The required input data for the buildings are dimensions, reflectivity and U-value. The model uses detailed soil properties, including thermal and moisture. Both the evapotranspiration and shading from vegetation are taken into account. The required geographical and meteorological input data are longitude and latitude, initial temperature and specific humidity of the atmosphere at 2500 m (upper model boundary), relative humidity at 2 m height, wind speed and direction at the 10 m height, and cloud cover. The model provides a large variety of output data, including wind speed, air temperature, relative humidity, MRT and PMV in version 4.0. 3.2. Study area A site in New Borg El-Arab City was selected. This site belongs to Alexandria Province in the North of Egypt and is located in an arid desert area. New Borg El-Arab is one of the newest cities of Egypt that was developed and redesigned in the 21st century. New towns like New Borg ElArab were planned for a variety of reasons: to help house the overflow population of major cities and halt their unchecked growth, to facilitate decentralization of the economy, to restrict informal settlement around the cities, to transfer industrial companies from the metropolises, and, finally, to
The place looks like abandoned desert.
Urban design in favor of human thermal comfort
Figure 6
Table 2
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Plants randomly located and do not serve the need for shading, cooling, or wind modification.
Input meteorological data applied in the ENVI-met simulations [15].
Date
6th February
6th May
6th August
6th November
Wind speed (m/s) Wind direction (deg) Relative humidity (RH %) Temperature (K)
4.3 315 50 288
3.5 315 50 302
3 315 50 315
3 315 50 295
Air Temperature (°C) 45 35 25 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
Figure 7
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5:00 PM
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7:00 PM
8:00 PM
9:00 10:00 11:00 12:00 PM PM PM AM
Air temperature analysis in 6th August (the mid-day in summer).
Relave Humidity (%) 80 60 40 20 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
Figure 8
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5:00 PM
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7:00 PM
8:00 PM
9:00 10:00 11:00 12:00 PM PM PM AM
Relative humidity analysis in 6th August (the mid-day in summer).
Mean Radiant Temp. (°C) 80 60 40 20 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
Figure 9
2:00 PM
3:00 PM
4:00 PM
5:00 PM
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7:00 PM
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9:00 10:00 11:00 12:00 PM PM PM AM
Mean Radiant Temperature analysis in 6th August (the mid-day in summer).
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Figure 10
Figure 11
Predicted Mean Vote analysis in 6th August (the mid-day in summer).
Site plan of 1st scenario design for Engineers’ buildings in New Borg El-Arab.
control suburbanization and its devastating effect on peripheral greenery and agricultural land. The stated goals of the new towns lead to achieve a balanced economic and social growth and to control [big cities’] aimless development by establishing new satellite towns in a proper distance from them. This not only rectifies big cities and decreases their attractiveness, but also changes them to a suitable center for regional economic, social, and spatial development [14]. New Borg El-Arab climate is extremely hot in summers and cold in winters; this area belongs to a hot arid climatic region [1]. The selected neighborhood Engineers’ Buildings geographical position is 30°530 3000 N Latitude and 29°340 2400 E Longitude. Fig. 2 indicates the location of the case study site. The selected site has an area of approximately 12 acres with built-up area accounts for nearly 40% of the total area and open space area makes up about 60% of the total area and the building heights are approximately 16 m as illustrated in
Fig. 3. The hard surfaces dominate the site, while the permeable surfaces are limited. There are some vegetation and green spaces but they are randomly located and do not serve the need for shading, cooling, or wind modification. Many areas are overheated during summer because of the lack of shading and cooling. Also, traffic from the adjacent streets and the air conditioning systems of the surrounding buildings charge the open space with the extra heating load. The neglected landscape, the lack of maintenance and thermal discomfort make the place looks like abandoned desert as indicated in Figs. 4–6. 3.3. Simulating thermal performance of current situation Simulation period is the mid-day of the mid-month of spring, summer, autumn and winter. The simulation time is 16 h starts at 9:00 AM and ends at 12:00 AM. The area around 4 ha pilot
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Figure 12
Site plan of 2nd scenario design for Engineers’ buildings in New Borg El-Arab.
Figure 13
Site plan of 3rd scenario design for Engineers’ buildings in New Borg El-Arab.
project has been transformed in the ENVI-met model grid with the dimension 60 l 60 l 30 grids with a resolution of 4 m l 4 m l 3 m. In this study, the simulations were initiated using data obtained from weather data Alexandria, Egypt (41.8 km) [15], as illustrated in Table 2. A Point in the middle of the neighborhood was selected to run the simulation on it. The selected point is located on asphalt road between two buildings and it is completely exposed to the sun and not shaded as illustrated in Fig. 3. The air temperature in mid-Summer exceeds 48 °C in after-
noon period as illustrated in Fig. 7, and this temperature by reference to Givoni’s Psychrometric chart (Givoni 1976 & 1998) is considered uncomfortable temperature. On the other hand, the relative humidity in afternoon period is lower than 30% as shown in Fig. 8, by reference to Givoni’s Psychrometric chart (Givoni 1976 & 1998) and these conditions are expressed as an extremely drought period, whereas Mean radiant temperature (MRT) is higher than 77 °C as shown in Fig. 9. While Predicted mean vote (PMV) reaches 7 as illustrated in Fig. 10, this value expresses extreme heat stress.
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Air Temperature (°C)
47
Current Situaon 1st Scenario
45 2nd Scenario 43
3rd Scenario
41 39 37 35 33 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
2:00 PM
Figure 14
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Air temperature comparison.
Relave Humidity (%) 80
Current Situaon
75
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3rd Scenario
60 55 50 45 40 35 30 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
2:00 PM
Figure 15
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Relative humidity comparison.
The results of the simulation showed outdoor thermal comfort was completely neglected. 3.4. Intervention strategies for improvement In order to achieve the aim of this paper, some interventions in open space will be proposed to take advantage of the positive elements of the climatic conditions and eliminate the negative ones. Temperature control, solar exposure, airflow modification and regulation of relative humidity are required for thermal comfort achievement. Firstly, the control of air temperature is essential for open spaces. In this context, the interventions aim at lowering the temperature, especially during summer time. Nevertheless, it cannot usually be changed significantly through design. The use of vegetation, the selection of appropriate materials (e.g. cool materials), and the utilization of water elements or special
features (e.g. Fountains) can modify the temperature, especially during summer. Secondly, the airflow modification aims at the creation of comfortable outdoor living spaces in summer by exploiting cooling breezes and guiding them in the livable areas. Various plants can be used to redirect or guide the wind. Thirdly, the regulation of relative humidity is extremely important during summer and can be accomplished through vegetation and using water surfaces. The possibilities given in the urban open spaces are abundant. 4. Results According to the intervention strategies for improvement, the coming three scenarios were applied for redesigning Engineers’ Buildings in New Borg El-Arab City
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Mean Radiant Temp. (°C) 75 Current Situaon 70
1st Scenario
65
2nd Scenario
60
3rd Scenario
55 50 45 40 35 30 25
Figure 16
Mean radiant temperature comparison.
PMV
Current Situaon
8
1st Scenario 7
2nd Scenario 3rd Scenario
6 5 4 3 2 9:00 10:00 11:00 12:00 1:00 AM AM AM PM PM
2:00 PM
Figure 17
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9:00 10:00 11:00 12:00 PM PM PM AM
Predicted mean vote comparison.
4.1. The first scenario According to intervention strategies for improvement, the first proposal for redesigning Engineers’ Buildings in New Borg ElArab City was developed. In the 1st proposed design, the hard surfaces are limited, while the permeable surfaces are increased. Car Parking is moved outside the neighborhood to decrease the surface area of asphalt and increase the area of green spaces. Trees were removed and only grass and bushes
of 50 cm high were used in order not to obstruct the wind. Fig. 11 illustrates site plan of 1st scenario design. 4.2. The second scenario The second developed proposal is similar to the first scenario except for the addition of trees with an area of approximately 10% of the full site area as shown in Fig. 12. The 2nd proposed design takes into account the relationship between wind
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Total area Buildings Pavement Asphalt Green cover Trees Water elements
Current situation
1st Scenario
2nd Scenario
3rd Scenario
50,994 m2 100% 20,192 m2 39.6% 17,208 m2 33.7% 9840 m2 19.3% 3754 m2 7.4% 2039.8 m2 4% 0
50,994 m2 100% 20,192 m2 39.6% 13,742 m2 27% 4216 m2 8.3% 12,846 m2 25.2% 0 0
50,994 m2 100% 20,192 m2 39.6% 13,742 m2 27% 4216 m2 8.3% 12,846 m2 25.2% 5099.4 m2 10% 0
50,994 m2 100% 20,192 m2 39.6% 13,742 m2 27% 4216 m2 8.3% 12,165 m2 23.9% 5099.4 m2 10% 681 m2 1.3%
direction and landscape design. In the direction of coming wind, the palm trees were planted in order to make wind penetrating site easily. 4.3. The third scenario The third developed proposal is similar to the second scenario except for the addition of fountains and water bodies with an area of approximately 7% of the full site area in order to increase relative humidity as shown in Fig. 13. The 3rd proposed design takes into account the relationship between wind direction and position of water elements. In the direction of coming wind, the water bodies were put in order to moisturize wind penetrating site. 4.4. Comparison between current situation and proposed scenarios To analyze the effect on the urban layout in thermal comfort, ENVI-met was applied. Simulation period is the mid-day of the mid-month summer. The simulation time is 16 h starts at 9:00 AM and ends at 12:00 AM. Simulation outputs are air temperature, relative humidity, mean radiant temperature (MRT) and predicted mean vote (PMV) as indicated in Figs. 14–17. 5. Discussion To improve thermal comfort in proposed scenarios, the use of vegetation, the selection of appropriate materials (e.g. cool materials), and the utilization of water elements or special features (e.g. Fountains) are considered as illustrated in Table 3. In the first scenario, it is noticed that decreasing pavements by approximately 5% and asphalt cover dropping by 50%, green cover of grass and bushes of 50 cm height has been increased to make up a quarter of total area and tall trees have been removed. These changes in 1st scenario compared to the current situation made air temperature decrease approximately 1 °C, while relative humidity increased about 3%, mean radiant temperature dropped about 3 °C and PMV decreased about 0.4. Moreover, the second scenario is similar to the first one except adding trees carefully and its relationship is considered with wind direction to make up 10% of the total area. These changes in 2nd scenario helped to create better conditions compared with the current situation, and air temperature decreases approximately 1.4 °C, while changes in relative humidity hadn’t noticeable differences from the 1st scenario, mean radiant temperature dropped about 4 °C and PMV decreased about 0.6. Furthermore, adding water elements to
the 2nd scenario in the direction of coming wind in order to moisturize wind penetrating site, this change made the 3rd proposed scenario the best one. These changes in 3rd scenario helped to create better conditions compared with the current situation, and air temperature decreases approximately 2 °C, while changes in relative humidity increased about 6%, mean radiant temperature dropped about 5.5 °C and PMV decreased about 1. 6. Conclusion The results of the simulation showed outdoor thermal comfort in proposed layouts is higher in comparison with current layout according to air temperature, relative humidity, mean radiant temperature and PMV. The result from this paper implied optimizing sub-neighborhood layout by testing specific landscape parameters that could enhance outdoor human thermal comfort. Landscape design has a positive impact on outdoor thermal comfort. The results, especially the 3rd scenario, confirmed good modifications of thermal comfort are possible in summer with few modifications of urban layout such as planting and materials. However, this modification couldn’t make PMV index reach the comfort zone, and decreasing PMV by only 1 could bring some thermal comfort. This research focused on the act of retrofitting which gained considerable enhancement of the outdoor thermal comfort. However, it is suggested for further research to experiment with more dynamic changes to other constraints such as building layout and height in order to compare the impact of retrofitting versus modifying the original design in the early design stage. References [1] N. Middleton, D. Thomas, World Atlas of Desertification, second ed., UNEP (United Nations Environment Programme), London, 1997. [2] Pius Fatona, Abiodun Abiodun, Adetayo Olumide, Adesanwo Adeola, Oladunjoye Abiodun, Viewing Energy, Poverty and Sustainability in Developing Countries Through a Gender Lens, InTech, Nigeria, 2013. [3] A.S. Nouri, A framework of thermal sensitive urban design benchmarks: potentiating the longevity of Auckland’s Public Realm, Buildings 5 (1) (2015) 252–281. [4] Alireza Monam, Klaus Ru¨ckert, The Dependence of Outdoor Thermal Comfort on Urban Layouts, vol. 88, Universita¨tsverlag der TU Berlin and Fasanenstr, Berlin, Germany, 2013. [5] K. Axarli, D. Teli, Implementation of bioclimatic principles in the design of urban open spaces: microclimatic improvement for the cooling period of an open space adjacent to the sea, in: 25th Conference on Passive and Low Energy Architecture, Dublin, 2008.
Urban design in favor of human thermal comfort [6] M. El Araby, Urban growth and environmental degradation. The Case of Cairo, Egypt, Cities 18 (2) (2002) 135–149. [7] ASHRAE, ASHRAE Standard 55-2010, Thermal Environmental Conditions for Human Occupancy, Atlanta: American Society of Heating, Refrigerating and AirConditioning Engineers, 2010. [8] Erik Johansson, Sofia Thorssonb, Rohinton Emmanuel, Eduardo Kruger, Instruments and methods in outdoor thermal comfort studies – the need for standardization, Urban Clim. 10 (2) (2014) 346–366. [9] Andris Auliciems, Steven V. Szokolay, Thermal Comfort, Australia: Passive and Low Energy Architecture International (PLEA) in Association with Department of Architecture, The University of Queensland, 2007. [10] Jianxiang Huang, Jose Guillermo, John D. Spengler, CityComfort: a simulation-based method for predicting mean radiant temperature in dense urban areas, Build. Environ. 80 (2014) 84–95.
543 [11] Arash Beizaee, Steven K. Firth, Keyur Vadodaria, Dennis Loveday, Assessing the ability of PMV model in predicting thermal sensation in naturally ventilated buildings in UK, in: Proceedings of 7th Windsor Conference: The Changing Context of Comfort In An Unpredictable World, London, 2012. [12] A. Matzarakis, H. Mayer, Heat stress in Greece, Int. J. Biometeorol. 41 (1997) 34–39. [13] M. Bruse, Envi–met 3.0: Updated Model Overview, ResearchGate, 2004. [14] Mohammad Reza Shirazi, New Towns — Promises Towards Sustainable From ‘‘Shushtar-No”to ‘‘Shahre Javan Community”, Young Cities Research Paper Series, Germany, 2012. [15] World Weather & Climate Information, Weather and Climate, 31 August 2016. [Online]. Available: .
