The Writing’s on the WallRecent Cool Wall Research and Measures

February 22, 2018Hosted by:

U.S. EPA Heat Island Reduction Program

Building Energy and Greenhouse Gas Benefits

Ronnen M. LevinsonLawrence Berkeley National Lab

LBNL Heat Island Group

Source: Lea Suzuki, San Francisco Chronicle, 10 February 2013

Ronnen Levinson*, Pablo Rosado,Sharon Chen, and Hugo Destaillats

Lawrence Berkeley National Lab (LBNL)* RMLevinson@LBL.gov

12

13

A “cool” wall reflects sunlight to reduce cooling load, save energy, and lower emissions

Wall solar reflectance

• Conventional ≈ 25%• Cool color ≈ 40%• Off or dull white ≈ 60%• Bright white ≈ 80%

14

We used EnergyPlus to model cool-wall heating, ventilation, and air conditioning (HVAC) energy savings

Apartment building Single-family home Large hotel

Small office Medium office Large office

Stand-alone store Strip mall Restaurants (sit-down and fast-food)

15

We evaluated annual energy, cost, and emission savings in each California and U.S. climate zone (> 100K simulations!)

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Cool walls save energy, carbon dioxide in homes, offices, and stores in all California climates + U.S. climates 1 - 4

17omes

Example: Single-family home in Houston, TX

Single-family home

N

Floor area: 220 m² (2,400 ft²)Net wall area: 180 m² (1,900 ft²)Wall albedo: 0.25 → 0.60Building orientation: averaged

$58 (6%) $74 (5%)

$129 (7%)

329 kg (6%)

421 kg (5%)

736 kg (7%)

0

100

200

300

400

500

600

700

800

New (2012) Older (1980s) Oldest (pre-1980)

Annual HVAC energy cost savings ($)

Annual HVAC carbon dioxide equivalent savings (kg)

Savings in pre-1980 homes over 2 times that in new h

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Can scale savings by Solar Availability Factor (SAF)to adjust for shading & reflection by neighboring buildings

Single-family homes (each 6 m tall)

E

S

W

N

30 m6 m

3 m

3 m

𝑅𝑅 = 2SAF ≈ 0.5

𝑅𝑅 = building height 𝐻𝐻 / separation 𝑊𝑊

𝑅𝑅 = 0.2SAF ≈ 0.9

𝑅𝑅 = 1SAF ≈ 0.6 𝑅𝑅 = 2

SAF ≈ 0.5

0.2 1 2 10

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Cool wall products with high solar reflectance (SR) are sold today

Conv

entio

nal

SR 0.0 – 0.1 0.1 – 0.2 0.2 – 0.3 0.3 – 0.4 0.4 – 0.5 0.5 – 0.6 0.6 – 0.7 0.7 – 0.8 0.8 – 0.9

Spec

tral

ly s

elec

tive

L*=34, a*=2, b*=4 dark brown

L*=32, a*=3, b*=7 dark brown

L*=47, a*=1, b*=-1 dark purple-gray

L*=47, a*=0, b*=7 green-gray

0.49 0.51

light gray L*=67, a*=-1, b*=1

0.65

light brown L*=67, a*=5, b*=18

dark brown L*=32, a*=2, b*=6

0.14

0.20

0.81

0.28

0.53

0.36

0.33

0.31

0.24

0.39

0.62

0.66

0.88

off white L*=88, a*=0, b*=12

dark purple-gray L*=48, a*=2, b*=0

0.06

dull white L*=85, a*=-1, b*=1

silver metallic L*=79, a*=-1, b*=-3

L*=32, a*11, b*=3 burgundy

bright white L*=94, a*=-1, b*=3

L*=81, a*=-4, b*=8 light green

bright white L*=98, a*=-1, b*=2

L*=72, a*=1, b*=5 light gray

L*=68, a*=5, b*=17 light brown

lower-tier cool walls(0.40 ≤ SR < 0.60)

higher-tier cool walls(SR ≥ 0.60)

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Wall products are undergoing 2 year exposure in California, 5 year exposure at U.S. sites

04

15

4

46

69

4 611

4

30

55

0

10

20

30

40

50

60

70

retroreflector Al-plasticcomposite

factory-appliedcoating

fabric, vinyl field-appliedcoating

total

CA Exposure US Exposure

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Solar reflectance losses modest (≤ 0.05) after15 months in California, 12 months in U.S.

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(18

mo.

)

Initial albedo

woodconcretemetalfiber cement

Berkeley

Field-applied coatings on...

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(18

mo.

)

Initial albedo

woodconcretemetalfiber cement

Los Angeles

Field-applied coatings on...

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(18

mo.

)

Initial albedo

woodconcretemetalfiber cement

Fresno

Field-applied coatings on...

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(12

mo.

)

Initial albedo

woodconcretemetalfiber cement

Arizona

Field-applied coatings on...

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(12

mo.

)

Initial albedo

woodconcretemetalfiber cement

Florida

Field-applied coatings on...

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Alb

edo

loss

aft

er fi

eld

expo

sure

(12

mo.

)

Initial albedo

woodconcretemetalfiber cement

Ohio

Field-applied coatings on...

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