D3. Thermal comfort, cooling and pollution
Urban design and thermal comfort outdoors in warm-humid climates
Aims and method:
Investigates the relationship between urban design, urban microclimate, and outdoor comfort across different street patterns and in low-, medium-, and high-rise buildings in Dar es Salaam, Tanzania. Air temperature, wind speed, mean radiant temperature, and the physiologically equivalent temperature are simulated using ENVI-met to highlight the strengths and weaknesses of the existing urban design.
Key findings:
· Areas with low-rise buildings suffer from greater heat stress in urban spaces than areas with high-rise buildings.
· The use of dense trees helps to enhance the thermal comfort conditions by reducing reduce heat stress.
· Provision of shade is a more efficient way to reduce physiologically equivalent temperature than increases in wind speed.
Reference:
Yahia, M. W., Johansson, E., Thorsson, S., Lindberg, F., & Rasmussen, M. I. (2017). Effect of urban design on microclimate and thermal comfort outdoors in warm-humid Dar es Salaam, Tanzania. International Journal of Biometeorology, 1-13.
Cool towns and cities
Aims and method:
Reviews evidence about the relationship between urban greening and the cooling of towns and cities in the light of climate change. A systematic review methodology was used to evaluate the available evidence on the subject, with a meta-analysis of available data on the cooling effect of parks and green spaces
Key findings:
· Most studies investigated the air temperature within parks and beneath trees and are broadly supportive that green sites can be cooler than non-green sites.
· Meta-analysis of data from different studies suggested that, on average, an urban park would be around 1°C cooler than a non-green site during the day.
· Studies that measured temperature from multiple parks in the same urban area showed that larger parks were cooler.
· Shade from trees has been shown to be important for lowering temperatures; but temperatures are also cooler in unshaded green sites or above short vegetation, which suggests evaporative cooling may also play a role.
· The extension of the cooling effect of a green area beyond its boundary is supported by data from a few studies and is particularly important for the likely public health consequences
Reference:
Bowler, D. E., Buyung-Ali, L., Knight, T. M., & Pullin, A. S. (2010). Urban greening to cool towns and cities: A systematic review of the empirical evidence. Landscape and urban planning, 97(3), 147-155.
http://www.sciencedirect.com/science/article/pii/S0169204610001234
The cooling and energy saving effect of landscape
Aims and method:
Investigates the cooling and energy saving effect of landscape parameters in an urban park of Beijing during a hot summer. Continuous on site microclimate data of the impact of individual parameters including grass, water bodies, trees and artificial shading devices and different combinations were collected. The thermal perception of people as effected by each parameter was studied according to both the measured data and thermal sensation votes from a questionnaire survey.
Key findings:
· Whilst it is possible to build manmade shading devices to deliver optimum cooling and energy saving effects, natural elements such as grass, trees and water can have similar impacts.
· Optimal benefits can be obtained by a combination of manmade and natural elements, notably designed shading and trees
Reference:
Xu, X., Sun, S., Liu, W., García, E. H., He, L., Cai, Q., & Zhu, J. (2017). The cooling and energy saving effect of landscape design parameters of urban park in summer: A case of Beijing, China. Energy and Buildings.
http://www.sciencedirect.com/science/article/pii/S0378778816319764
Tree canopy, comfort and value
Aims and method:
Aimed to calculate the value street trees provide in Australian cities and to gain better insights into their benefits. The research considered more than 500 publications, policies, street tree programmes and other relevant literature and analysed the impact of tree canopies on property prices and the average summer temperature in the Sydney suburbs of Annandale, Blacktown, and Willoughby. The analysis focused on the relationship between the size of the tree canopy, the price of land and property, and temperature.
Key findings:
· In Annandale, the air temperature was 4 degrees Celsius lower in streets with 28% canopy coverage than in streets with 20% canopy coverage. The surface temperature of concrete and asphalt was also at least 14 degrees cooler in the shade making pedestrians more comfortable.
· A 10% increase in the size of the canopy across Blacktown showed an increase in the value of property of 7.7%, or $55,000 for the average house. A 10% increase in the canopy aligned with an average increase in property prices of $33,152 in Willoughby, and $60,761 in Annandale.
· Trees can protect asphalt pavements, halving the number of times maintenance workers must seal the pavement over a 30-year period, although they also have costs associated with their maintenance.
Reference:
Swinbourne, R. & Rosenwax, J. (2017) “Green Infrastructure: a vital step to brilliant Australian cities” 2017 AECOM.
Energy, cool surfaces and shade trees
Aims and method:
Explores the relation between the existence of trees and other non-absorbent surfaces in urban areas and the energy demand for cooling and associated impacts on pollution in American cities. A range of simulation models were used to simulate energy use against different three dimensional ground conditions.
Key findings:
· Cool surfaces (cool roofs and cool pavements) and urban trees can have a substantial effect on urban air temperature and, hence, can reduce cooling-energy use and smog.
· About 20% of the national (USA) cooling demand can be avoided through a large-scale implementation of heat-island mitigation measures, with major impacts on liveability through reducing smog and urban heat island effects
· This amounts to 40 TWh/year savings, worth over $4 billion per year by 2015, in cooling-electricity savings alone. Once the benefits of smog reduction are accounted for, the total savings could add up to over $10 billion per year (2001 prices).
Reference:
Akbari, H., Pomerantz, M., & Taha, H. (2001) Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas, Solar Energy, 70(3), 295-310
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.155.1477&rep=rep1&type=pdf
Surface cover and energy use
Aims and method:
Develops and tests a model to assess the response of the urban environment across Greater London to changes in surface characteristics, population and energy use; explains the routes by which these changes affect the urban climate; and presents a methodology which may be applied to other cities. Evaluated nine different scenarios (changes in surface composition, tree cover, traffic use, populations, building cover, and climate sensitivity) using the Surface Urban Energy and Water balance Scheme (SUEWS).
Key Findings:
· Well-watered vegetation is a key control on urban energy partitioning and important for moderating elevated urban temperatures
· Consequently, building upwards has a smaller impact on the urban energy balance than building on vegetated areas
· Adding vegetation has greatest impact in sparsely vegetated area
· A range of meteorological conditions should be considered when assessing the impact of scenarios.
Reference:
Ward, H. C., & Grimmond, C. S. B. (2017). Assessing the impact of changes in surface cover, human behaviour and climate on energy partitioning across Greater London. Landscape and Urban Planning, 165, 142-161.
http://www.sciencedirect.com/science/article/pii/S0169204617300749
Urban form and reducing energy load through cooling
Aims and method:
Develops and tests a statistical model for estimating space-cooling energy use in residential homes by incorporating variables that represent external built form in the US. The study integrates a variety of quantitative data including geographic information systems (GIS) and light detecting and ranging data (LiDAR) to extract high resolution variables to represent urban form. These are combined with occupant behaviour, property and sociodemographic data to form 2D and 3D spatial data.
Key Findings:
· Higher population density, east-west street orientation, higher green space density within 100 ft radius, and a higher sum of tree heights on the east, south and west side of houses have statistically significant effects on summer cooling energy consumption.
· Building at greater density; planting more trees and greenspace at community level; and east-west street orientation, can all reduce energy load through cooling.
Reference:
Ko, Y., & Radke, J. D. (2014). The effect of urban form and residential cooling energy use in Sacramento, California. Environment and planning B: Planning and Design, 41(4), 573-593.
Urban geometry, greening and outdoor thermal comfort
Aims and method:
Examines how the combination of urban geometry (aspect ration, street orientation, sky view factor and local and neighbourhood scale) and urban green space (street trees and urban parks) affect the metrological comfort of pedestrians. The paper syntheses these diverse literatures to explore the combined effects of these two design features on the local environment for users.
Key Findings:
· The placement, density and distribution of buildings affects the creation of heat islands by the shaping the flow of air and sunlight exposure.
· Street-level greening cools urban environments by providing shade and mitigating heat build-up.
· The combined effects appear positive for pedestrians, but further research about how the interaction operates is required.
Reference:
Jamei, E., Rajagopalan, P., Seyedmahmoudian, M., & Jamei, Y. (2016). Review on the impact of urban geometry and pedestrian level greening on outdoor thermal comfort. Renewable and Sustainable Energy Reviews, 54, 1002-1017.
http://www.sciencedirect.com/science/article/pii/S1364032115011831
Pollution and resident behaviours
Aims and method:
Examines the impacts of traffic noise, air pollution and lack of public green space on self-reported health and well-being of Berlin residents. The study combines quantitative measures including a combination of GIS mapping of the environmental indicators and a survey of residents to analyse the relations between multiple neighbourhood burdens and health indicators, incorporating both ambient stressors and lack of environmental resources.
Key Findings:
· Traffic noise is the only statistically significant relationship with self-reported health behaviour
· Approximately a third of the variation in neighbourhood satisfaction scores was explained by the levels of traffic noise, air pollution and availability of green space.
· Perceived air pollution has the biggest impact on health behaviours.
Reference:
Honold, J., Beyer, R., Lakes, T., & van der Meer, E. (2012). Multiple environmental burdens and neighborhood-related health of city residents. Journal of Environmental Psychology, 32(4), 305-317.
http://www.sciencedirect.com/science/article/pii/S027249441200028X
Traffic noise exposure and health
Aims and method:
Outlines evidence linking housing conditions to health for twelve housing risk factors including traffic noise. Reports on a meta-analysis of studies linking traffic noise, hypertension and heart disease, with due consideration to confounding factors, including air pollution.
Key findings:
· Road traffic noise is a significant risk factor for ischaemic heart diseases, causing ca. 3% of all myocardial infarction in Germany, according to 1999 exposure data
· The risk increases when the average noise levels is greater than 60 dB(A) during the day, which corresponds with noise levels during the night of approximately 50 dB(A).
Reference:
Braubach, M., & World Health Organization. (2011). Environmental burden of disease associated with inadequate housing: A method guide to the quantification of health effects of selected housing risks in the WHO European Region.
http://www.euro.who.int/__data/assets/pdf_file/0003/142077/e95004.pdf
Community noise exposure and stress in children
Aims and method:
Examines the stress outcomes of typical, everyday community noise exposure among children. The work examined multi-methodological indices of stress among young children living under 50 dB or above 60 dB in small towns in Austria.
Key findings:
· Children living in relatively noisy neighbourhoods had raised blood pressure, heart rates and levels of stress hormones, effects that happen at noise levels far below those required to damage hearing.
· Increased background noise also seemed to reduce child motivation, especially amongst girls and to ‘learned helplessness’ syndrome.
Reference:
Shield, B. M., & Dockrell, J. E. (2003). The effects of noise on children at school: a review. Building Acoustics, 10(2), 97-116.
http://journals.sagepub.com/doi/abs/10.1260/135101003768965960