Microclimate surface interventions

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


Thermal pollution causes:

– Heat capacity

– Heat conductivity

– Solar absorptivity

– Sky factor

– Wind patterns

– Energy consumption

– Vegetation


Heat island intensity in London08 January 2017


-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.


Effect on night air temperature

Minimum Temperatures Variations (1999)

8

10

12

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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.


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


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.


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


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


Improve external thermal environment to

mitigate thermal pollution

Reduce anthropogenic heat from buildings and

transport;

Increase vegetation

Increase albedo of surfaces


Effect of vegetation08 January 2017


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.


Effect of albedo08 January 2017


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.


Impact of greeness08 January 2017


0

0.1

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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


08 January 2017


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12h 13h 14h 15h 12h 13h 14h 15h 12h 13h 14h 15h

Tem

pe

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eg

C

Day 1 Day 2 Day 3

Open Daytime Built Daytime Green Daytime

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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.


Impact on building surfaces

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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

http://dx.doi.org/10.1016/j.enbuild.2011.07.011


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


Source: Giridharan Reganathen, Kent University


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


Urban albedo research work is mostly based on numerical models


Numerical models have shown….08 January 2017


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


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


Thank you

08 January 2017

20

Microclimate surface interventions

Environment

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