Post on 18-Jan-2017
transcript
Microclimate surface interventions
Professor Maria Kolokotroni
Research Institute of Energy Futures
Leader: Resource Efficient Future Cities Group
Brunel University London
08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 2
Pollution is one of the difference between high density cities and suburban areas/countryside
air, thermal, noisepollution
Brunel University London
Thermal pollution causes:
– Heat capacity
– Heat conductivity
– Solar absorptivity
– Sky factor
– Wind patterns
– Energy consumption
– Vegetation
Brunel University London
Heat island intensity in London08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 4
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
0 3 6 9 12 15 18 21 24
Time, hours
DT
, °C
Source: Watkins R, Palmer J, Kolokotroni M and Littlefair P, (2002). The London Heat Island – results from summertime monitoring,
Proc. Chartered Institution of Building Services Engineers, Series A, Building Services Engineering Research &Technology, Vol (23). No 2 pp97-106.
Brunel University London
Effect on night air temperature
Minimum Temperatures Variations (1999)
8
10
12
14
16
18
20
Satur
day
Sun
day
Mond
ay
Tuesd
ay
Wed
nesday
Thurs
day
FridayM
inim
um
Tem
pe
ratu
res
°C
London
Rural
M a x im u m T e m p e ra tu re s V a ria tio n s (1999)
2 2
2 4
2 6
2 8
3 0
3 2
3 4
Sat
urda
y
Sun
day
Mon
day
Tues
day
Wed
nesd
ay
Thur
sday
FridayM
ax
imu
m T
em
pe
ra
ture
s °
C
L o n d o n
Ru r a l
M in im u m Te m p e ra tu re s Var ia tio n s (2000 )
8
1 0
1 2
1 4
1 6
1 8
2 0
Satu
rday
Sunday
Monday
Tuesday
Wednesday
Thursday
FridayM
inim
um
Te
mp
era
ture
s °
C
L o n d o n
R u ra l
M axim u m Te m p e ra tu re s Var ia tio n s (2000 )
2 2
2 4
2 6
2 8
3 0
3 2
3 4
Satu
rday
Sunday
Monday
Tuesday
Wednesday
Thursday
FridayM
ax
imu
m T
em
pe
ra
ture
s °
C
L o n d o n
R u ra l
Source: Kolokotroni M, Giannitsaris I and Watkins R, (2006). The effect of the London Urban Heat Island on building summer
cooling demand and night ventilation strategies, Solar Energy, Vol 80 (4) pp 383-392.
Brunel University London
Hourly mean UHI value with wind speed
less than 5 m/s for Core Area (zone-1)
0
0.5
1
1.5
2
2.5
3
3.5
4
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6
hours
UH
I in
degC
clear sky partially cloudy cloudy
Source: Kolokotroni M and Giridharan R, (2008). Urban Heat Island Intensity in London: An investigation of the impact of physical characteristics
on changes in outdoor air temperature during summer, Solar Energy Vol 82, pp. 986-998
Brunel University London
Impact on building internal temperatures
Source: Kolokotroni M, Zhang Y and Watkins R, (2007), The London Heat Island and building cooling design, Solar Energy, Vol 81 pp 102-110.
Brunel University London
Buildings’ energy use trends
In the UK at present, most buildings are not air-
conditioned 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
Source: Kolokotroni M., Ren X., Davies M., Mavrogianni A (2012). London’s urban heat island: impact on current and future energy consumption
for heating and cooling. Energy and Buildings, Vol 47, pp 302-311
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
Brunel University London
Improve external thermal environment to
mitigate thermal pollution
Reduce anthropogenic heat from buildings and
transport;
Increase vegetation
Increase albedo of surfaces
Brunel University London
Effect of vegetation08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 11
0.0
5.0
10.0
15.0
20.0
25.0
30.0
07:00 09:00 11:00 13:00 15:00 17:00 19:00
Time, hours (BST)
Air
te
mp
era
ture
, °C
0.0
0.5
1.0
1.5
2.0
2.5
3.0
ΔT
, °C
Streets
Park
ΔT
Hourly mean air temperature
Source: Watkins R, Palmer J, Kolokotroni M and Littlefair P, (2002).
The London Heat Island – surface and air temperature measurements
in summer 2000, ASHRAE Trans, Vol 108, Pt1, pp419-427.
Brunel University London
Effect of albedo08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 12
British
Museum
Bloom
sbury
Montag
ue Plac
e
Great
Russell
St
Montague St
PARK
Fo
Fi
Mean gorge surface temperature and air
temperature (Montague St.)
y = 0.83x + 1.4
r2 = 0.98
n = 21
0
5
10
15
20
25
30
0 5 10 15 20 25 30 35 40
Mean gorge surface temperature, °C
Go
rge a
ir t
em
pera
ture
, °C
Tair-cloudy day
Tair-sunny day
Regression (all data)
The positions of the measurement sites
around the British Museum.
Fi and Fo are two particular façades
chosen for comparison.
Brunel University London
Impact of greeness08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 13
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
16
16.5
17
17.5
18
18.5
19
19.5
20
20.5
21
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Pe
rce
nta
ge
of
Gre
en
ne
ss (
%)
Te
mp
era
ture
in d
eg
C
Measuring point
Daytime Night Percentage of Greenness
Brunel University London
08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 14
16
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12h 13h 14h 15h 12h 13h 14h 15h 12h 13h 14h 15h
Tem
pe
ratu
re i
n d
eg
C
Day 1 Day 2 Day 3
Open Daytime Built Daytime Green Daytime
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13
14
15
16
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20
21
21h 22h 23h 21h 22h 23h 21h 22h 23h
Tem
per
atu
re i
n d
egC
Day 1 Day 2 Day 3
Open Night Built Night Green Night
Source: Maciel C R, Kolokotroni M, Nogueira, M C J A, Giridharan R and Watkins R., (2013, doi:10.1093/ijlct/ctt016).
The impact of surface characteristics on ambient temperature at urban micro- scale: comparative field study in two climates, International Journal of Low Carbon Technologies.
Brunel University London
Impact on building surfaces
0
5
10
15
20
25
30
35
40
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
Tem
pe
ratu
re o
C
Hours
External Air Temperature Roof Surface Temperature Internal Ceiling Temperature
1 June 2009 16 August 2009
Avg day global solar radiation: 351 W/m2
Avg day external temperature 19.5 oCAvg day global solar radiation: 350 W/m2
Avg day external temperature: 19 oC
Source: Kolokotroni M, Gowreesunder B and Giridharan R, (2013). Cool roof technology in London: an experimental and modelling study,
Energy and Buildings Vol 67, pp658-667. doi:10.1016/j.enbuild.2011.07.011
Brunel University London
Urban albedo
• Urban albedo is the reflectivity of the urban mosaics i.e. multiple surfaces.
• The characteristics of this mosaic are determined largely by urban geometry
• Urban albedo is the ratio of incoming to outgoing radiation at upper edge of the canyon
08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 16
Source: Giridharan Reganathen, Kent University
Brunel University London
Urban Albedo Depends on………..
• Building block geometry
• Reflectance of the roof
• Reflectance of the ground
• Reflectance of the wall
• Urban vegetation
• Solar altitude
• Solar azimuth
• Soil moisture
08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 17
Urban albedo research work is mostly based on numerical models
Brunel University London
Numerical models have shown….08 January 2017
CIBSE Resilient Cities Group Event – 6 January 2017 18
Source: Yang and Li, The impact of building density and building height heterogeneity on average urban albedo and street surface temperature, Building and Environment, 2015
Brunel University London
Summary
Urban buildings use more energy than rural buildings because of urban
thermal pollution
We have 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
We have less knowledge on how to improve thermal environment in
cities, especially in moderate climates where requirements for
heating might fight requirements for cooling.
In this context, knowledge and tools of urban albedo (based on
empirical and numerical work for high latitude locations such as
London) can allow us to make specific interventions
Brunel University London
Thank you
08 January 2017
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