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Urban Heat Island in London and impact on buildings energy demand Professor Maria Kolokotroni Research Institute of Energy Futures Leader: Resource Efficient Future Cities Group What is the difference between cities and countryside? Urban Pollution air, thermal, noise Brunel University London Air pollution 29 February 2016 London, Friday 10 April 2015 Example of photo of air pollution in the press Brunel University London 3 Thermal pollution causes: – Heat capacity – Heat conductivity – Solar absorptivity – Sky factor – Wind speed – Energy consumption – Vegetation Brunel University London Heat capacity & conductivity RURAL URBAN ground is less dense high density materials with high heat capacity and high thermal conductivity has a lower heat capacity and has an insulating layer above Brunel University London Solar absorptivity Albedo (solar reflectivity) varies in both rural and urban areas Brunel University London Sky factor reduced effectiveness of long-wave radiation for cooling Brunel University London Wind speed Mean rural wind speeds are higher than urban ones because the ground surface is smoother The “rougher” urban surfaces reduce wind speeds, but there are local variations Wind flowing across a deep narrow street canyon will create little disturbance at ground level Brunel University London Energy consumption releases heat Rural energy use is small compared to the energy received from the sun Energy use density in urban areas is much higher Brunel University London Vegetation To evaporate water requires energy - this helps keep plants and the air around them cool Urban areas are “harder”. They have less vegetation, less evaporative cooling and less shading of the ground parks can provide “rural” oases in the city Brunel University London What is the effect of these factors? It is known as Urban Heat Island effect Brunel University London http://www.lucid-project.org.uk Source: The LUCID project Land Surface Temperature, 12 July 2006, 21.00 UT ASTER satellite image RICHMOND WIMBLEDON COMMON PARK Brunel University London Urban Heat Island in London Body of work in hot climates, US, Europe and Asia What happens in moderate climates such as London? We measured it! Brunel University London Measurement station Brunel University London GLA report: London’s Urban Heat Island Brunel University London Example of the variation in heat island intensity across London Brunel University London Hourly mean UHI value with wind speed less than 5 m/s for Core Area (zone-1) 4 3.5 UHI in degC 3 2.5 2 1.5 1 0.5 0 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 hours clear sky Brunel University London partially cloudy cloudy 1 2 3 4 5 6 Variation in annual heating & cooling load y = -1.40x + 55600 r2 = 0.56 n = 24, p=0.001 40000 35000 25% increase Cooling load, kWh 45000 30000 12000 22% 13000reduction 14000 15000 Heating load, kWh Brunel University London rural 16000 Brunel University London UHI, energy use and climate change Brunel University London Using future weather files we used CIBSE weather files for London 2050 (medium-high scenario, according to UKCP02) these were constructed using the method developed by Hacker and Blecher to predict parameters on an hourly basis we adapted air temperature based on the results of LSSAT model developed by Brunel. Everything else was kept the same over London. Brunel University London Brunel University London UHI, energy use and climate change HW-Cooling load kWh/m2/year, 2050 HW-Cooling load,kWh/m2/year, 2000 50 50 45 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 -40 -30 -20 -10 Brunel University London 0 0 10 20 30 40 -40 -30 -20 -10 0 10 20 30 40 UHI, ventilation and climate change HW- Heating load, kWh/m2/year, 2050 HW-Heating load, kWh/m2/year, 2000 50 50 45 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 -40 -30 -20 Brunel University London -10 0 10 20 30 40 -40 -30 -20 -10 0 10 20 30 40 Buildings’ energy use trends In the UK at present, most buildings are not airconditioned so UHI is a ‘good’ effect in winter Building will be air conditioned in the future because of higher temperatures and even higher in the city Once AC is introduced internal temperatures will be regulated at 21-22 oC. At present, we tolerate higher. Estimations indicate a five-fold increase in carbon emissions by city buildings in 2050 This should be set against commitments of carbon reductions – international and country specific. Brunel University London What can be done? Improve energy efficiency of buildings – already regulated Generate heat and electricity by building integrated renewables nearly zero carbon buildings Improve external thermal environment – mitigate urban heat island Brunel University London Mitigate urban heat island Reduce anthropogenic heat from buildings and transport; reduce air-conditioning, increase insulation etc, reduce cars, use electric vehicles etc Increase vegetation, parks, green roofs, green walls Increase albedo of surfaces, cool roofs and pavements Brunel University London Cool Materials: how do they work? Brunel University London And other colours Brunel University London Does it work in temperate regions such as London? External Air Temperature Roof Surface Temperature Internal Ceiling Temperature 40 35 30 Temperature oC 25 20 15 10 Avg day global solar radiation: 351 W/m2 Avg day external temperature 19.5 oC 5 Avg day global solar radiation: 350 W/m2 Avg day external temperature: 19 oC 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 1 June 2009 Brunel University London Hours 16 August 2009 Cool Roofs and hot climates 29 February 2016 SR = 0.90 120 112.5 Energy Demand (kWh/m²) 99.9 100 93.5 104.6 102.2 SR = 0.70 Abu Dhabi – no heating demand 80 SR = 0.55 60 40 Green Roof 20 0 Base Typical (SR=0.30) Wuhan, China – hot summer/cold winter Brunel University London 31 Summary Urban buildings use more energy than rural buildings because of the Urban Heat Island Effect Technical knowledge on how to improve energy efficiency and integrate renewables to achieve nearly zero carbon buildings; this is encouraged by legislation and financial initiatives Less knowledge on how to improve thermal environment in cities, now and in the future, in particular moderate climates (such as London) and cold winter/hot summer climates (such as Wuhan in China) where requirements for heating might fight requirements for cooling. Brunel University London 29 February 2016 Thank you Brunel University London 33