Hui Li, Ph.D., P.E. Yuan He, Ph.D. John Harvey, Ph.D., P.E. 2016/16-1367-Cool Pavement_Hui Li... · Create a livable & walkable communities during hot summer (mitigated ... Albedo

Hui Li, Ph.D., P.E.Yuan He, Ph.D.

John Harvey, Ph.D., P.E.

UC Pavement Research Center (UCPRC) University of California, Davis & Berkeley

January 13th, 20161

TRB 95th Annual Meeting. Jan 10th – 14th, 2016Lectern Session 756: Research Progress on Cool Pavement Strategies

Outline Urbanization & Environmental Impacts

Cool Pavement & Potential Strategies

Cool Pavement Pilot Study at UCPRC

Main Results & Conclusions

Policy Effort & Research Needs2

3Research Highlights 2010, http://www.walker‐institute.ac.uk

Heat Island Effectwas first identified in the early 1800s in London

Heat Island Effect:• Increase heat stress• Compromise human thermal comfort and health • Impair air quality (ground‐level ozone, i.e. smog)• Increase cooling energy consumption

• Total energy use• Peak demand for energy

Types of heat island effect Urban Near‐surface air Surface (hot spot)

4

Impervious Surface:• Create stormwater runoff• Pollute the waterbody• Reduce groundwater recharge• Increase risk of flooding• Contribute to heat island effect

Flooding & Water Pollutionfrom impervious surface

5Chicago, IL

40% + Pavement,Dark(hot) &

Impervious(flood)

Low Impact Development Restore Natural Process & Ecological Function

To make pavement Cool & Permeable.






Potential Cool Pavement StrategiesStrategy Mechanism Co-Benefits

1. Modify material thermal properties1.1 Increase albedo/emissivity (?) Increase reflected/emitted

radiationEnhance illuminationOffset radiative forcing (?)

1.2 Increase heat capacity/density Increase heat capacity --

1.3 Reduce thermal conductivity Reduce transfer readiness --

2. Evaporation/evapotranspiration2.1 Permeable pavements

(+ vegetation)Increase latent heatIncrease thermal insulationIncrease convection

Reduce stormwater runoff Reduce water pollutionReduce flooding risk Recharge groundwaterIncrease greening

2.2 Water-retentive pavements (+ sprinkling)

Increase latent heat Reuse wastewater

3. Shading3.1 Canopy cover (+ trees) Reduce absorbed heat Increase greening (+ tree)

3.2 PV panels Reduce absorbed heat Reduce land use for solar farms

4. Enhance convection4.1 Ventilation paths Increase convection --

7






Goal & Scope of Pilot Study Explore thermal behavior of several potential cool pavement strategies (particularly permeable pavement) Asphalt, concrete vs. paver (different albedos) Permeable vs. impermeable Dry vs. wet (irrigation)

Evaluate effectiveness and applicability when applied in different contexts Surface and near‐surface heat effect Human thermal comfort Building thermal load

9Experiment + Modeling

Construction of Test Sections

10

Instrumentation

11

View of Test Sections

12

N

Field Measurements

• Permeability

• Albedo (i.e. solar reflectivity) & effect on pavement thermal performance

• Thermal behavior of permeable pavements under dry and wet conditions

• Thermal impact of pavement on near‐surface air

• Thermal interaction between pavement and wall

13






Permeability

15

A2 A3 B2 B3 C2 C3

0.0

0.2

0.4

0.6

0.8

1.0

Section

Hyd

raul

ic C

ondu

ctiv

ity (c

m/s

)

Permeameter (ASTM)

Permeability (a.k.a. hydraulic conductivity or infiltration rate)

A: Block Paver B: Asphalt C: Concrete

Albedo (Solar Reflectivity)

16

A1 A2 A3 B1 B2 B3 C1 C2 C3

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Section

Albe

do

A-Interlocking Concrete Pavement; B-Asphalt Pavement; C-Concrete Pavement.

1-Impermeable Design; 2 & 3-Permeable Designs.

Albedometer

A: Block Paver B: Asphalt C: Concrete

Albedo Change over Time

17

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

00:00 04:00 08:00 12:00 16:00 20:00 00:00Time

Alb

edo

0

200

400

600

800

1000

Rad

iatio

nW

m2

AlbedoIncident Solar RadiationReflected Solar Radiation

Change of albedo over time (nine test sections, only weathered)

Diurnal variation of albedo (B2)

albedo

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

9/4/11 11/3/11 1/2/12 3/2/12 5/1/12

Alb

edo

Time (m/d/yy)

A1A2A3B1B2B3C1C2C3

A: Block Paver (dash line)

B: Asphalt

C: Concrete

C: Concrete (C2)

18

y = -61.29x + 68.96R² = 0.91

y = -27.06x + 26.47R² = 0.78

0

10

20

30

40

50

60

70

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Tem

pera

ture

(°C

)

Albedo

Tmax_SummerTmin_SummerTmax_WinterTmin_Winter

Asphalt Concrete & Block Paver

Surface Temperature vs. Albedo

Thermal Behavior of Permeable Pavement under Dry & Wet Conditions (e.g. B3).

19(mm/dd)

B1

Air

B3

B3: permeableB1: impermeable

Irrigation

0.0 0.5 1.0 1.5 2.0 2.5 3.0

-10

-8

-6

-4

-2

0

Wind speed (m/s)

Coe

ffici

ent C

C = -5.13 + ( -0.57 *WS) R 2̂ = 0.29

Thermal Impact on Near‐surface Air

20

Influence of wind speed

10 20 30 40 50 60 70T (C)

B1_Air @ 07/31/2012

0:002:004:006:008:0010:0012:0014:0016:0018:0020:0022:0024:00

0

25

51

76

102

Hei

ght (

cm)

0

10

20

30

40

Hei

ght (

in)

Thermal Impact on Wall

21Lighter is hotter: legend range of 30 to 65 °C

Asphalt (B1), 60 °C

Concrete (C1), 45 °C

Wall, 52 °C

Wall, 55 °C

13:00 8/15/2012

Human Thermal Comfort Index

22

Mean Radiant Temperature (MRT) Defined as the uniform temperature of an imaginary environment in which radiant heat transfer from/to the human body is equal to the radiant heat transfer in the actual non‐uniform environment.

Physiological Equivalent Temperature (PET) Defined as the equivalent air temperature at which, in a typical indoor setting (Tmrt=Ta; VP=12 hPa; v=0.1 m/s,), the heat balance of the human body is maintained with core and skin temperatures equal to those under the actual complex conditions being assessed.

0.25

1

1 ( ) 273n

i hbmrt i hb i hb hb

i hb hb

D SVF IT E VF F

Modeling & Simulation for Temperature

23

The model considers :• Energy balance on the pavement surface;• Coupled processes of radiation,

conduction, convection, shading and evaporation.

Finite Element Method implemented in ABAQUS.

24M is the metabolic rate (W/m2). W is the rate of mechanical work (W/m2). S (W/m2) is the total storage heat flow in the body.

Energy Balance on Human Body

25

Inputs Parameters

26

Example pavement surface temperatures for three climates (baseline, summer)

27

Human Thermal Comfort Index, PET

28

0

10

20

30

40

50

60

70

Tem

pera

ture

(°C)

Scenario

Ts Tmrt PET Sacramento, CA

Ts: Surface TemperatureTmrt: Mean Radiant TemperaturePET: Physiological Equivalent Temperature

Human Thermal Comfort Index, PET

29

Ts: Surface TemperatureTmrt: Mean Radiant TemperaturePET: Physiological Equivalent Temperature

0

10

20

30

40

50

60

70

Tem

pera

ture

(°C

)

Scenario

Ts Tmrt PET Phoenix, AZ

0

10

20

30

40

50

60

70

Tem

pera

ture

(°C)

Scenario

Ts Tmrt PET Los Angeles, CA





Policy Effort & Research Needs

30

Main Conclusions from Pilot Study Reflective Pavement

Albedo has significant effects on the pavement temperature. Greatly increasing albedo might cause negative impacts on human thermal comfort and building/vehicle energy use.

Permeable Pavement Permeable pavement is a cool pavement strategy with many environmental benefits.

Evaporation from permeable pavement plays an important role in reducing daytime UHI.

High thermal resistance of porous materials helps reduce UHI, especially during nighttime.

Permeable pavements with a designed albedo are a promising cool pavement strategy for mitigating UHI.

31






Potential Benefits of Cool & Permeable Pavement

Mitigate heat island Create a livable & walkable communities during hot summer (mitigated

local heat stress) Reduce energy use for building and vehicle cooling Improve air quality (ground‐level ozone)

Reduce stormwater runoff Improve water quality Recharge groundwater Reduce flooding risk Reduce need for drainage/retention systems

Reduce pavement distress Rutting Cracking

33

Cool Pavements Research and Implementation Act

34http://www.leginfo.ca.gov/cgi‐bin/postquery?bill_number=ab_296&sess=CUR

Research Needs on Cool Pavement Challenges & uncertainties in the technologies

Albedo & durability of reflective cement/binder & coating/treatment Durability of porous materials Permeability vs. wicking/evaporation of porous materials Tradeoff between different seasons & different goals

Comprehensive impact evaluation (what‐if analysis) Human comfort; energy use (building & vehicle) Air quality; groundwater quality Climate (e.g. rainfall) Life cycle cost analysis Environmental life cycle assessment (on‐going)

Evaluating impacts at different scales (multi‐scale modeling) Local/street level Small/block scale Large/city/regional scale

35

Sponsors for Cool Pavement Study

Collaborators:

36

37

Hui Li, [email protected]

Documents

Hui Li, Ph.D., P.E. Yuan He, Ph.D. John Harvey, Ph.D., P.E. 2016/16-1367-Cool Pavement_Hui Li... · Create a livable & walkable communities during hot summer (mitigated ... Albedo