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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
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Sky factor
reduced effectiveness of long-wave radiation for cooling
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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
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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
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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
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rural
16000
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UHI, energy use and climate change
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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.
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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.
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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
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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
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Cool Materials: how do they work?
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And other colours
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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
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