cool pavements: urban heat island mitigation issues & strategies
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Cool Pavements
Urban Heat Island Mitigation Issues & Strategies—Hard Surfaces
Kamil Kaloush, Ph.D., P.E.Arizona State University
Tuesday, March 10, 2009
ASTER ThermalImaging Satellite
Mobile Transects
Laboratory Testing
31.6°C
61.8°C
40
50
60
IR Thermal Imagery
Embedded Thermocouples
UHI Evaluation Techniques
4
Time lapse infrared view of Chicago near Millennium Park
July 14 – 15, 2007
5:00AM
8:00AM
11:00AM
1:00PM
3:00PM
6:00PM
9:00PM
• Environmental considerations:
– air, surface, and subsurface temperatures, cloud cover, direct sun light / solar radiation, humidity level, wind velocity, and surrounding land cover.
• Physical parameters:
– material constituents, surrounding materials and anthropogenic heat sources, ground heat flux.
• Age and traffic.
Influencing Factors
Source of thermophysical properties: literature, laboratory and field tests.
Fundamental Properties
• Albedo, α
• Emissivity, ε– controls the far-infrared re-radiation from the surface back
to the sky.
• Convection Coefficient, h
• Thermal Conductivity, k
• Specific Heat, C
• Density, ρ
• Thermal Diffusivity, α,κ
• Porosity, φ
reflectedemitted
heat transfer to
air (convection)
Base material
Surface material conduction
incoming solar
radiation
(insolation)
reflectedemitted
heat transfer to
air (convection)
Base material
Surface material conduction
incoming solar
radiation
(insolation)
9December 2, 2008 9
Thin and Ultra-Thin Whitetopping PCC
Parking Areas
• Many options
– Reflective (high albedo) Pavements
• Increased operation life
• Improves thermal comfort for customers
Portland Cement Concrete
Comparing Surface Temperatures
10
Surface Chip Seals and Coatings:using reflective / light-colored chip / paints
“Gritting”:reflective chipsand aggregate
Shot-Blasting:abrading surface binder
Reflective Asphalt Pavements
Synthetic Binders:using reflective aggregates
December 2, 2008
Heat Transfer between Pavement and its Surroundings
Pavement
Solar Radiation,q”sol
Convection,h (To-T )
Irradiation,(To
4 –T4sky)
Ground (Natural Soil) Ground)
Air @T
Initial Condition: @t = 0s, T(0) = Tinitial
Boundary Condition: @x , T(t) Tinitial
Conduction to Deep Earth, kgrd T(t)
x
To
Tm
Ti
Tn
L
Tools - Models
- No. of Pavement Layers
- Density
- Specific Heat Capacity
- Thermal Conductivity
- Pavement Layer Thickness
- Pavement Layer Interface
Thermal Contact Resistance
- Albedo of Top Layer
- Emissivity of Top Layer
- Deep Ground Properties
- Temperature
- Depth
- Sky View Factor
- Solar View Factor
Simulation Runs
15
0
100
200
300
400
500
600
700
800
900
1000
28
32
36
40
44
48
52
56
60
64
68
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00
Solar R
adiatio
n Flu
x (Wm
-2)
Tem
pe
ratu
re (o
C)
Time
(1) PPCC
(2) PPCC*
(3) PCC
(4) UTW
(5) HMA
Air Temp
Solar
16
U-haul : Permeable Pavement Evaluation
subbase
geotextile
Sub grade soil
Plastic grid and
membrane
decorative rock filler
Other ?
• Improve our understanding of how paving materials
interact with the urban climate.
• Advance the state of knowledge regarding technologies
and practices to mitigate UHI impacts.
• Address model and design practices, testing and standard
development, technological approaches, and planning and
policy considerations.
• Provide a home for TRB related activities (sessions,
workshops, reports, ..)
TRB AF000(2)
Pavement Materials and the Urban Climate
Thank You!
kaloush@asu.edu www.asuSMART.com
60,000 ft2 & NCE Home - LEED Silver
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