ASI3_Lecture 2_9/12/2011
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning1
photo
Implementing Urban Climatology in the 'Real World' - Theory and Practice
• Evyatar Erell• Associate Professor• Ben Gurion University of the Negev
Croucher Advanced Study Institute 2011-2012Urban Climatology for Tropical & Sub-tropical Regions
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning2
Acknowledgements
Prof. Terry Williamson
Adelaide University
Prof. David Pearlmutter
Ben Gurion University of the Negev
ASI3_Lecture 2_9/12/2011
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning3
Asking the right questions is the
key to setting appropriate
objectives.
Academic research does not
necessarily focus on the ‘right’
questions (from the perspective of
the planner).
However, although planning
questions are typically ‘wicked
problems’ 1, we still expect
academic research to be the key
to answering them…
Context
Image from Search Patterns by Peter Morville and Jeffery Callender
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning4
1. To create a planning framework for the urban area (or part of it) that will allow optimal exposure of individual buildings so that they may employ measures for improved thermal control, either to conserve energy or to improve comfort in the absence of AC (although these aims
may be mutually exclusive!).
In accordance with the local climate
In accordance with the building’s function
2. To design public open space that supports pedestrian activity in a comfortable environment (thermal & visual comfort, air quality)
In accordance with the local climate
In accordance with expected activities
Objectives
ASI3_Lecture 2_9/12/2011
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning5
Paradigm
Clear definition of goals
Unambiguous benefits
Integration in the design process
Complexity
Subsidiarity
Economics and sustainability
Adaptability
Variety
Manage expectations
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning6
Process
1. Analysis of local climate
2. Analysis of life styles and requirements of the project’s occupants, and identification of main environmental problems
3. Definition of planning objectives, with reference to
spatial scale: urban/neighborhood/building
elements dealt with: buildings/open space
temporal scale, on the annual cycle (summer-winter) or diurnal cycle (day-night)
4. Selection of appropriate design strategies
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning7
Climatic planning strategies
Land use allocation (location)
Street orientation
Building density
Building typology (e.g. pavillion, row, courtyard)
Street cross-section
Vegetation
Colour (albedo?)
Special landscaping elements
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning8
Drawbacks:
The similarity between environmental conditions in the existing and planned settlements may not be sufficient.
The modern adaptation may differ critically in some aspects from the traditional solution.
The existing traditional solutions may not encompass the whole range of possible plans.
Generating solutions (i)
Study existing settlement patterns typical of specific environments to see which appears to be the most successful, and try to emulate the main features in new design.
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning9
Analyze the processes occurring in urban regions to develop a model capable of predicting conditions in any given environment.
Generating solutions (ii)
Drawbacks:
Unless the model is complete and accurate, conclusions may be misleading.
Modeling the microclimate does not generate architectural form…
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning10
Scales of intervention
level policy project
who planning authority(ies) property developer or owner (buildings)
public utilities (infrastructure)
what establish objectives at an urban scale
integration in detailed project plans
define specific measures cost assessment
specify performance metrics implementation
check compliance maintenance
evaluate of progress feedback (to planning authorities)
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning11
Planning authorities (or why cities are like camels)
“a camel is a horse designed by committee…”
Sir Alec Issigonis (or VOGUE Magazine)
modern architecture and urban planning are carried out by groups of professionals from diverse fields
information from multiple and sometimes conflicting sources must be reconciled
the problem is not to produce an idealized plan derived from climatic considerations
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning12
Application of computer modeling
Required:
A model to predict the air temperature at a given point in the urban canopy layer with sufficient accuracy to be a useful practical tool for use in simulation of building energy or thermal comfort.
The model should be simple to use
It should require only publicly available inputs: standard weather data and a simple morphological description of site
The CAT model deals with the intra-urban variations in canopy air temperature, at a spatial scale that is smaller than the resolution of meso-scale models.
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning13
T_base T_base=
Conceptual basis of CAT model
T_metT_urb
Turb = Tbase + T urbT_urb
Tbase = Tmet + T met
T_met
Erell & Williamson, 2006
A surface energy balance is calculated for the canyon volume at each of the two sites, and an empirical resistance is applied to estimate the effect of stability on energy exchange with the air above roof height.
Parameterizations are used to simplify the inputs.
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning14
Methodology: Model flow chart
reference site
canyon site
weather file
view factors
INPUTS SENSIBLE HEAT FROM CANYON SURFACES
SW (solar) radiation: dir, dif, reflected
LW radiation: sky, terrestrial
wind speed & convection
moisture availability (advection)
anthropogenic heat
heat storage
sensible heat flux
anthropogenic heat
TURBULENT MIXING
canyon geometry
thermal (buoyancy)
mixing coeff.
DBT PREDICTION
mechanical (wind)
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning15
Validation
N
View of Adelaide Centre and measurement sitesurban canyon
Kent Town BoM
reference
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning16
CAT model validation - Adelaide
BoM urban
observed predicted
Absolute minimum 5.6 7.3 7.3
Mean daily minimum 9.5 10.5 10.2
Monthly mean 13.0 14.6 14.6
Mean daily maximum 17.1 17.3 17.8
Absolute maximum 22.0 22.0 22.3
CAT simulation results for May 2000
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning17
y = 0.71x + 0.48
R2 = 0.70
-2
-1
0
1
2
3
4
5
6
7
-2 -1 0 1 2 3 4 5 6 7
measured UHI (K)
pre
dic
ted
UH
I (K
)CAT model validation (ii)
D = 0 if model results are no better than the trivial estimate (Tcanyon = Tref)
D = 1 if model results give a perfect fit with measured data
D < 0 if model results are worse than the trivial estimate
Williamson Degree of Confirmation (D) = 0.58
cool island
heat island
Williamson, 1995
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning18
CAT validation (iii): Gothenburg
Williamson Degree of Confirmation: 0.52Wind data in input file suspect
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning19
Application example (i): Building energy consumption
(Erell Soebarto and Williamson, 2007)
The need for urbanized weather data in simulation
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning20
Predicted canyon heat island intensity (based on Australian BoM data for 1987):
Simulated diurnal and seasonal patterns
-4
-2
0
2
4
6
8
0 3 6 9 12 15 18 21 24
time of day
pre
dic
ted
tem
per
atu
re
dif
fere
nce
(K
)
Daytime cool island as well as marked nocturnal heat island
Canyon heat island is stronger in winter
-4
-2
0
2
4
6
8
1 2 3 4 5 6 7 8 9 10 11 12
month
pre
dic
ted
te
mp
era
ture
d
iffe
ren
ce
(K
)
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning21
Building energy simulations
Performance Simulated with ENERWIN‐EC:
‐ Hourly thermal/energy simulation program
‐ Taking into account hourly weather, building geometry, envelope properties, internal loads and operations, HVAC operations
‐ Predicting hourly, monthly, and annual heating and cooling loads, energy end uses, energy costs, thermal comfort.
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning22
‐ Total floor area: 6,536 m2
‐ Envelope: insulated masonry walls (U=0.79); concrete roof (U=0.33), double glazed low‐e windows (U=1.8)
‐ Occupancy: 5 days/week
‐ Ventilation: 0.7 l/sec/m2
‐ Infiltration: 0.4 ach
‐ Internal gains: 18 W/m2 lighting and equip.
‐ HVAC system: Central cooling (COP 2.64); gas heating (COP 0.7)
‐ Thermostat settings, occupied (unoccupied): summer ‐ 24 (26); winter – 22 (20).
View of Case Study Building
Case study building
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning23
peak
coolingkW
heatingkW
403345BoM data
391325CAT modified input
-12-20difference
annual
coolingGJ
heatingGJ
5721060BoM data
671842CAT modified input
+99-118difference
Small reduction in peak loads (cooling too!) is due to the moderating effect of urban thermal mass on air temperature.
Using ‘urbanized’ temperature in energy simulation
Annual energy budget reflects urban heat island, with increased cooling load and reduced heating requirement.
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning24
Application example (ii): Density
The effect of density on
a. building energy consumption for heating and cooling (Williamson, Soebarto and Erell, 2009)
b. Climate cooling potential(williamson & Erell, 2008)
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning25
the urban street canyonThe basic unit
A semi infinite canyon, defined by its 2‐D section: width (W) and height of two sides (H)
Methodology
Generate climate data for different H/W ratios, from 0.25‐4. (1)
Choose a building.
Run simulation program to calculate energy performance with “standard” climate data.
Compare results for simulations carried out with ‘urbanized’ climate files.
Change location and re‐do experiment (Adelaide, Glasgow, Sde Boqer).
H
W
(1) Anthropogenic heat input was varied for each canyon width in an attempt to represent a realistic scenario of different development, traffic and pedestrian densities.
Density and building energy consumption
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning26
Simulated modification of air temperature (CAT)
LocationCanyon Aspect Ratio
4 2 1 0.5 0.25
Adelaide 5.9 5.5 5.2 3.7 3.1
Glasgow 4.1 3.8 3.3 2.9 2.4
Sde Boqer 4.6 4.3 3.9 3.6 2.5
Average Monthly Maximum Canyon Heat Island (K)
Average monthly maximum canyon cool island (K)
LocationCanyon Aspect Ratio
4 2 1 0.5 0.25
Adelaide 1.8 1.7 1.6 1.4 1.2
Glasgow 1.1 1.0 1.2 1.1 1.1
Sde Boqer 1.3 1.0 1.0 .8 .6
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning27
ADELAIDE GLASGOW SDE BOQER
H/W heating cooling total heating cooling total heating cooling total
4 402 558 960 1167 164 1331 314 703 1017
2 411 550 961 1181 164 1345 320 693 1013
1 423 543 965 1208 161 1369 328 685 1013
0.5 437 539 976 1241 159 1400 339 676 1015
0.25 446 538 984 1265 158 1422 343 674 1017
Note: Calculation assumes NO mutual shading by similar adjacent buildings.
Annual energy budget (EnerWin)
* all values in GJ/year
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning28
ADELAIDE GLASGOW SDE BOQER
H/W heating cooling total heating cooling total heating cooling total
4 402 558 960 1167 164 1331 314 703 1017
2 411 550 961 1181 164 1345 320 693 1013
1 423 543 965 1208 161 1369 328 685 1013
0.5 437 539 976 1241 159 1400 339 676 1015
0.25 446 538 984 1265 158 1422 343 674 1017
Annual energy budget (EnerWin)
984623361141913112889654954700.25
953578375140511612899484594890.5
91750741013978913089313975341
89239849514574614119032886152
11112478641840241816117416710064
984623361141913112889654954700.25
953578375140511612899484594890.5
91750741013978913089313975341
89239849514574614119032886152
11112478641840241816117416710064
NO
mut
ual s
hadi
ngm
utua
l sha
ding
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning29
-1750
-1500
-1250
-1000
-750
-500
-250
0
0 1 2 3 4
aspect ratio (H/W)
Ch
ang
e in
CC
P [
Kh
]
London Adelaide Sde Boqer
Effect of canyon aspect ratio on the absolute
change in the CCP of London, Adelaide and Sde
Boqer for the three-month summer period, based
on air temperature predicted by CAT with
anthropogenic heat input set to zero.
)(1
,,,,,1
hne
h
hhhnbhn
N
n
TTmN
CCPf
i
{ m=1h if Tb-Te ≥ Tcrit
m=0 if Tb-Te < Tcrit
)24
2cos(5.25.24,i
hb
hhT
h - Time of day
Tb - Building temperature
Te - External temperature
Tcrit - Fixed arbitrarily at 3K
* Artmann et al (2007)
Urban density and climate cooling potential *
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning30
-1750
-1500
-1250
-1000
-750
-500
-250
0
0 1 2 3 4
aspect ratio (H/W)
Ch
ang
e in
CC
P [
Kh
]
London Adelaide Sde Boqer
-1750
-1500
-1250
-1000
-750
-500
-250
0
0 1 2 3 4
aspect ratio (H/W)
Ch
ang
e in
CC
P [
Kh
]
London Adelaide Sde Boqer
Right: The addition of even a modest amount of anthropogenic
heat (representing a traffic flow rate corresponding to 20
vehicles per hour per meter of street width) exacerbates the
reduction in climate cooling potential in dense urban locations.
Urban density and anthropogenic heat
ASI3_Lecture 2_9/12/2011
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning31
Comments on urban density
Radiant exchange often has a greater impact on building energy
consumption than air temperature
The effect of density on building performance depends on
whether the building is air conditioned (fixed temperature) or
free-running
Although dense cities promote warmth (i.e. UHI) – energy costs
for cooling typical office buildings may actually be smaller in
certain dense urban configurations
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning32
Application example (iii): Colour
The effect of albedo modification on outdoor thermal comfort
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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Correlation between calculated thermal stress and subjective thermal sensation
Givoni, 1963
ITS – Index of Thermal Stress (warm climates)
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning34
Rn - net radiation
C - convection
M - metabolic heat
W – mechanical work
Givoni, 1963
Calculation of ITS (i)
fEITS
1
)( WMCRE n )]12.0(6.0exp[1
max
E
E
f
)42(3.0max aPvpVE
p – clothing coefficient
V – wind speed
Pva – vapour pressure of air
ITS - the sweat rate required for thermal equilibrium, expressed as equivalent latent heatE - required cooling rate by sweatingf - sweat efficiency
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning35
Pearlmutter, Shaviv and Berliner (2007)
Calculation of ITS (ii): Radiant exchange
Net Radiation (W m-2 of body area):
Short-wave (incident fluxes):Kdir = direct radiationKdif = diffuse radiationhKh= horizontal reflected radiationvKv= vertical reflected radiation
1-s= skin absorptivity
Long-wave (absorbed fluxes):Ld = downward sky radiationLh = horizontally emitted radiationLv = vertically emitted radiation
εTs4 = radiation emitted by body
Rn = (Kdir+ Kdif + hKh+ vKv)(1-s)+ Ld+Lh+ Lv - εTs
4
Radiant energy exchanges between cylindrical body and urban environment
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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Calculation of ITS (iii): Convective exchange
Convection (W m-2 of body area):
Temperature difference (oC):
T=Ts-Tz
Ts=body skin temperature (35oC)
Tz = air temperature (oC)
Heat transfer coefficient (W m-2 K):
hC= 8.3uz0.6
uz = wind speed (m/s)
Cz = hC ∆T
Convective energy exchanges between cylindrical body and urban environment
Pearlmutter, Shaviv and Berliner (2007)
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Desert Architecture & Urban Planning37
Pedestrian heat stress
-200
0
200
400
600
800
1000
6 8 10 12 14 16 18
time of day
he
at
str
es
s (
W)
0.20
0.45
0.70
-200
0
200
400
600
800
1000
6 8 10 12 14 16 18
time of day
hea
t st
ress
(W
)
0.20
0.45
0.70
N-S canyon with H/W=2 Open space (represented by a N-S ‘canyon’ with H/W=0.1)
Calculations of heat stress carried out for an open space and a street canyon
in Adelaide using site data generated by CAT, with all surfaces having uniform
albedos of 0.2, 0.45, 0.7 (weather data for the day of Nov. 25, 1987).
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning38
Pedestrian heat stress
Calculations of heat stress carried out for N-S and E-W street canyons in
Adelaide using site data generated by CAT, with all surfaces having uniform
albedos of 0.2, 0.45 or 0.7 (weather data for the day of Nov. 25, 1987).
N-S canyon with H/W=2 E-W canyon with H/W=2
-200
0
200
400
600
800
1000
6 8 10 12 14 16 18
time of day
hea
t st
ress
(W)
0.200.450.70
-200
0
200
400
600
800
1000
6 8 10 12 14 16 18
time of day
he
at s
tre
ss
(W
)
0.200.450.70
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning39
Canyon air temperature prediction with CAT
15
20
25
30
35
40
24 4 8 12 16 20 24
time of day
DB
T (
oC
)
ref0.200.450.70
-3
-2
-1
0
1
2
3
4
6 8 10 12 14 16 18
time of day
T
( o
C)
0.20
0.45
0.70
N-S street canyon in Adelaide with H/W=2; all surfaces have uniform
albedos of 0.2, 0.45, or 0.7 (weather data for the day of Nov. 25, 1987).
Temperature difference relative to weather station
Air temperature at the reference weather station (measured) and at street canyon (predicted).
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning40
External heat load on a pedestrian
N-S canyon in Adelaide with H/W=2, at noon, for surfaces with different albedos (0.2, 0.45, 0.7)
Notes:
External fluxes were calculated per unit area of the pedestrian body (represented by a cylinder).
The graph does not show dissipation of heat in the form of LW radiation given off by the person or latent heat loss by sweat. -100
100
300
500
700
900
1100
0.20 0.45 0.70
surface albedo
ex
tern
al f
lux
es
(W
/m2 )
SW reflected
SW sun
LW terrestrial
LW sky
convection
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning41
External heat load on a pedestrian
N-S canyon
-100
100
300
500
700
900
600 800 1000 1200 1400 1600 1800
time of day
flux
(W/m
2 )
SW (reflected)
SW (sun)
LW (terrestrial)
LW (sky)
convection
Street canyon in Adelaide with H/W=2 withuniform surface albedos of 0.45.
(weather data for the day of Nov. 25, 1987)
E-W canyon
-100
100
300
500
700
900
600 800 1000 1200 1400 1600 1800
time of day
flu
x (W
/m2 )
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning42
Scenario testing
What if urban scale albedo modification reduced air temperature by 2K (as some models suggest)?
-200
0
200
400
600
800
1000
6 8 10 12 14 16 18
time of day
hea
t st
ress
(W
)
-2K
base N-S canyon, H/W=2
Base case:
- reference DBT not modified
- albedo of canyon surfaces = 0.45
‘-2K’ case:
- reference DBT reduced by 2K
- albedo of canyon surfaces = 0.7
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Shading and air movement
Raffles Hotel, Singapore 7th Ave. Mall, Beer Sheva
Effective microclimate modification in small, well-defined urban spaces:
Clarke Quay, Singapore
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning44
Layered building facades
Arcades provide shade (and protection from rain): Israel (left), Portugal (above).
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Desert Architecture & Urban Planning45
Modeling complex street cross-sections
basic street canyon street with overhangs
street with pergolas
street with sidewalk trees
boulevard with center treesrecessed colonnades
Simulate each with respect to - air flow; temperature; thermal comfort; air quality; visual comfort; accoustics… for different aspect ratios, wind speed and direction etc.
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning46
Application example (iv): Vegetation
The effect of vegetation on outdoor thermal comfort
(Shashua-Bar, Erell and Pearlmutter, 2010)
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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MeshExposedTrees
Bare
Grass
Gro
un
d co
ver
Overhead cover
Trees-Bare Exposed-Bare Mesh-Bare
Mesh-GrassExposed-GrassTrees-Grass
Configurations monitored
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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Normalized* air temperature
* Courtyard air temperature at a given hour was adjusted proportionally for the ratio between simultaneously measured ambient temperature, and average ambient temperature for that hour over the entire study period
Clear / GrassClear / Bare
Trees / GrassTrees / Bare
Shade / GrassShade / Bare
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ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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Exposed-Grass
Exposed-Bare
Thermal comfort
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
Desert Architecture & Urban Planning50
Trees-Bare
Mesh-Bare
Mesh-Grass
Trees-Grass
Thermal comfort
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Comments on vegetation
Vegetation may make a substantial contribution to thermal comfort
even when its effect on air temperature is small.
This is done by reducing the exposure of a pedestrian to radiation –
both solar and long wave
Reduction of surface temperature is often the primary contribution of
vegetation to thermal comfort
To the extent that reduction in air temperature is due to evapo-
transpiration, there is an equivalent increase in the latent heat of the
air – so in humid climates the net effect on building energy
consumption may be negligible.
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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In buildings as well as for pedestrians outdoors, dissipating excess heat is a problem: Available environmental sinks are ineffective in warm humid climates.
High air temperatures are often perceived as the problem – yet, unlike cold climates, convective exchange contributes only a small part of the environmental load on a person or on a building, which is dominated by radiant loads.
Therefore, reduction of environmental loads is an essential pre-requisite for good climatic design, which means control of radiant loads –primarily by shading (of people and surfaces), but also through selective use of high albedo materials and vegetation.
Final thoughts on UMC in warm humid climates
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A cascade of models at appropriate scales
global climate change
regional resolution
urban effects
street canyons
buildings
thermal comfort
X
Spatial scales
Time scales
1-way vs. 2-way coupling?
Processes (physical, chemical etc.)
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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Final thoughts on computer modeling and simulation
There is much to be learned from models of different kinds at different scales (in time and space) – but care must be taken to avoid drawing the wrong conclusions from inappropriate use of any particular model.
Formulating the question appropriately is the first step
Building energy simulation must take into account the effects of the surrounding urban environment.
The problem is complex, but the analysis needs to address all relevant factors: Focusing on one, e.g. air temperature, risks erroneous conclusions.
How do atmospheric models link to models employed by other disciplines (e.g. transport)?
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Evyatar ErellBen Gurion University of the NegevDesert Architecture and Urban Planning,Jacob Blaustein Institutes for Desert Research,Sde Boqer Campus, 84990ISRAELTel: +972 8 6596878 Email: [email protected] Website: www.bgu.ac.il/CDAUP/evyatar-erell.html
End, Thank You
ASI 3: CLIMATE CHANGE AND URBAN DESIGN School of Architecture, The Chinese University of Hong Kong, Hong Kong, 9-10 Dec 2011
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References and additional reading
Artmann N., Manz H. and Heiselberg P. (2007). "Climatic potential for passive cooling of buildings by night-time ventilation in Europe", Applied Energy 84:187-201.
Erell, E. and Williamson, T. (2006). Simulating air temperature in an urban street canyon in all weather conditions using measured data at a reference meteorological station, International Journal of Climatology, 26, 1671-1694.
Erell E., Soebarto V. and Williamson T. (2007). “Accounting for urban microclimate in computer simulation of building energy performance”. In Wittkopf S. and Tan B. K. (Eds.) Sun, Wind and Architecture, Proceedings of PLEA 2007, 24th International Conference on Passive and Low Energy Architecture, Singapore, November 22-24, 2007, pp. 593-600.
Erell E. (2008). “The application of urban climate research in the design of cities”, Advances in Building Energy Research, 2:95-121.
Erell E., Pearlmutter D. and Williamson T. (2010). Urban climate: Designing Spaces Between Buildings. Earthscan/James & James Science Publishers, London, 266p.
Givoni B (1963). Estimation of the effect of climate on man — development of a new thermal index. PhD thesis, Technion-Israel Institute of Technology.
Mills G., Cleugh H., Emmanuel R., Endlicher W., Erell E., McGranahan G., Ng E., Nickson A., Rosenthal J. and Steemer K. (2010). "Climate Information for Improved Planning and Management of Mega Cities (needs perspective)". Procedia Environmental Sciences, 1:228-246.
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References and additional reading
Pearlmutter D., Shaviv E. and Berliner P. (2007). "Integrated modeling of pedestrian energy exchange and thermal comfort in urban street canyons", Building & Environment, 42:2396-2409.
Ritchey, Tom (2005). "Wicked Problems: Structuring Social Messes with Morphological Analysis“. Swedish Morphological Society, www.swemorph.com.
Shashua-Bar L., Pearlmutter D. and Erell E. (2011). "The influence of trees and grass on outdoor thermal comfort in a hot-arid environment". International Journal of Climatology, 31(10): 1498–1506.
Williamson, T. J. (1995)."A confirmation technique for thermal performance simulation models", Building Simulation '95, Madison, Wisconsin, U.S.A.
Williamson T. and Erell E. (2008). “The Implications for Building Ventilation of the Spatial and Temporal Variability of Air Temperature in the Urban Canopy Layer”. International Journal of Ventilation, 7(1):23-35.
Williamson T.J., Erell E. and Soebarto V. (2009). "Assessing the error from failure to account for urban microclimate in computer simulation of building energy performance". In Building Simulation 2009, Proceedings of the 11th International IBPSA Conference, Glasgow, Scotland, July 27-30, 2009, pp. 497-504.
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‘wicked problems’
In social studies, a ‘wicked problem’ is a problem that is difficult or impossible to solve because of incomplete, contradictory, and changing requirements that are often difficult to recognize.
1. There is no definitive formulation of a wicked problem (defining wicked problems is itself a wicked problem).
2. Wicked problems have no stopping rule.3. Solutions to wicked problems are not true-or-false, but better or worse.4. There is no immediate and no ultimate test of a solution to a wicked problem.5. Every solution to a wicked problem is a "one-shot operation"; because there is no opportunity to
learn by trial and error, every attempt counts significantly.6. Wicked problems do not have an enumerable (or an exhaustively describable) set of potential
solutions, nor is there a well-described set of permissible operations that may be incorporated into the plan.
7. Every wicked problem is essentially unique.8. Every wicked problem can be considered to be a symptom of another problem.9. The existence of a discrepancy representing a wicked problem can be explained in numerous ways.
The choice of explanation determines the nature of the problem's resolution.10. The planner has no right to be wrong (planners are liable for the consequences of the actions they
generate).Ritchey, 2005
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Williamson degree of confirmation
),(),( meUvmUCs
U(m,v) is the Theil inequality factor between the measured value and the trivial guess
U(e,m) is the Theil inequality factor between the estimated value and the measured one
),(
),(),(
vmU
meUvmUD
The Williamson degree of confirmation (D) is the confirmation factor Cs normalized by the likely magnitude of the error, represented by the Theil inequality factor between the measured values and the trivial guess.
Williamson, 1995