GSEP’S Cool Roofs and Pavements Working Group 2
01
2
Global Climate Benefits of Cool Roof
Vishal Garg, IIIT- Hyderabad
Vishal Garg, IIIT- Hyderabad
M.L. Fischer1, F. Salamanca1, S. Menon1,2, S. Tonse3, V. Garg4, J. Mathur5, K. Niranjan4, B. Shah6, M. Naja7, KP Singh8
1LBNL, 2Climateworks, 3TST Consulting, 4IIIT Hyderabad, 5 MNIT Jaipur, 6Winbuild Consulting, 7 ARIES,
8GB Pant University
Acknowledgements We gratefully acknowledge the ARM program, Dr. Ram Sagar (ARIES), and Rao Kotamarthi (GVAX, PI) for advice and assistance. This work is supported by the US Dept. of Energy Offices of Efficiency and Renewable Energy , and Science under contract DE-AC02-05CH11231
Earth System Cooling with Reflective Roofs
ARIES Obsevatory
Pantnagar University
Vishal Garg, IIIT- Hyderabad
EERE/SC study verifies predicted global cooling benefit of white roofs in warm urban climates • USDOE-Indian collaboration measured
atmospheric radiation and building heat budgets at two sites in N. India, June 2011- March 2012
• Combination of satellite remote sensing, airborne, and surface measurements show
1) Heat loads are reduced to buildings, improv ing indoor comfor t fo r occupant s o f un -cond i t ioned buildings in warm climates
2) Radiative transfer models capture predicted benefit of white roofs
Original and White Coated Roofs
Maximum alCtude ~30 km
Balloon-‐Borne Sounding System: Thermodynamic state of atmosphere, wind speed and direcCon
ISRO aircraO (~7-‐8 km flying alCtude)
Ground-‐based instruments
Satellite footprint ranges from 1 m to 1 km
Roof-‐top instruments
Earth System Cooling with Reflective Roofs
Vishal Garg, IIIT- Hyderabad
Earlier work • Menon et.al (2010)
• Negative radiative forcing – 18.2 W/m2 for 0.1 increase in Albedo • uncoupled global land surface model
• Millstein et.al (2011) • Negative radiative forcing– 18.4 W/m2 for 0.1 increase in Albedo • coupled global land surface model
Scope of the project • To experimentally verify the increase in out going solar radiation at TOA • Predict the outgoing solar radiation using a Radiative Transfer Model
(RRTMG)
Introduction
Vishal Garg, IIIT- Hyderabad
• Pantnagar; 29.03 0N, 79.49 0E, 235m above sea level
• Agricultural and Industrial area • Aerosol and Gaseous emissions
• residential cooking, • diesel vehicles
Methodology
Surface monitoring: 2 white roofs and 2 dark roofs
Four-component radiometers During the process of Whitening Data monitoring on dark roof
Heat flux sensor
Vishal Garg, IIIT- Hyderabad
Methodology
• Nainital; 29.36 0N, 79.46 0E, ~ 1940 m above sea level
• Central Himalayan region • Site has lower aerosol loading compared
to Pantnagar but still significant AOD relative to background sites
Surface monitoring: 2 white roofs and 2 dark roofs
Data monitoring on dark roof Data monitoring on white roof
Temperature sensor on Dark roof
Vishal Garg, IIIT- Hyderabad
Pantnagar • 21st October • 26th December • 20th March
Methodology
Naintal • 13th October • 21st December • 20th March
True color image of light (PW1, PW2) and dark (PD1, PD2) roofs at the Pantnagar site taken the
21st OCT 2011
True color image of light roofs (NW1, NW2) and dark roofs (ND1, ND2) at the Nainital site taken the
20th MARCH 2012.
Satellite Measurements of SW↑TOA Radiation: 6 shots
Vishal Garg, IIIT- Hyderabad
Soiling of Roof
Pantnagar Nainital
• Roof reflectivity increased by paint application • Continuous measurements capture temporal variations
White roofs=W1, W2 Black roofs=B1, B2
Vishal Garg, IIIT- Hyderabad
Shortwave Outgoing Solar Radiation - Pantnagar
0
100
200
300
400
500
PW1 PW2 PD1 PD2
21st October
0
50
100
150
200
250
PW1 PW2 PD1 PD2
26th December
Reflected Solar RadiaCon at surface Reflected Solar RadaCon at TOA
0
50
100
150
200
250
300
350
400
PW1 PW2 PD1 PD2
20th March
α=0.41
α=0.56
α=0.1 α=0.28
α=0.3 α=0.08
α=0.67 α=0.62
α=0.3
α=0.11
α=0.44 α=0.42
Incoming Solar RadiaCon 637 W/m2
Incoming Solar RadiaCon 472 W/m2
Incoming Solar RadiaCon 639 W/m2
Reflected Solar RadiaCon at surface
Reflected Solar RadiaCon at TOA
Vishal Garg, IIIT- Hyderabad
Shortwave Outgoing Solar Radiation - Nainital
0
100
200
300
400
500
600
NW1 NW2 ND1 ND2
13th October
0 100 200 300 400 500 600
NW1 NW2 ND1 ND2
21st December
0 100 200 300 400 500 600 700
NW1 NW2 ND1 ND2
20th March
α=0.34
α=0.76
α=0.06 α=0.12
α=0.38 α=0.71
α=0.06 α=0.1
α=0.11 α=0.07
α=0.7
α=0.39
Incoming Solar RadiaCon 665 W/m2
Incoming Solar RadiaCon 802 W/m2
Incoming Solar RadiaCon 826 W/m2
Reflected Solar RadiaCon at surface
Reflected Solar RadiaCon at TOA
Vishal Garg, IIIT- Hyderabad
IKONOS Quantifies Global Cooling Benefit
Earth System Cooling with Reflective Roofs
Vishal Garg, IIIT- Hyderabad
• White roofs reduce total (shortwave & thermal) net radiation loading by ~ 200 W m-2 in fall, 2011 (many times typical building heat loads)
• Only part of net radiation is returned to space, requiring space-borne measurements and model evaluation
White Roofs Reduce Net Radiation Loading and Heat Flux to Building
~ 200 W m-‐2
Time of day (GMT)
Earth System Cooling with Reflective Roofs
Vishal Garg, IIIT- Hyderabad
Successful Prediction of Global Cooling Benefit
Close agreement of measured (IKONOS) and modeled (RRTMG) top-of-atmosphere SW radiance for both sites and three seasons demonstrates method can be applied to urban scales
(Salamanca et al., accepted and in press)
Earth System Cooling with Reflective Roofs
Vishal Garg, IIIT- Hyderabad
W2 B2 Block B
W1 B1 Block A
Center for Basic Sciences and Humanities, Pantnagar University, Uttarakhand
Block A – Biophysics center wing Block B – Environmental science wing W1 & W2: White roofs,B1 & B2: ExisCng roofs
Thermocouple covered with cement and coated white
Pantnagar Site (Concrete Roof)
Warm and Humid (29°C – 4°C) 29.01°N, 79.29°E
Vishal Garg, IIIT- Hyderabad
Temperature and Heat Flux (6-31 May 2012)
12°C
04°C
2.3°C
20 W/m2
Vishal Garg, IIIT- Hyderabad
y = 1.4177x + 12.079 R² = 0.60923
-‐40
-‐30
-‐20
-‐10
0
10
20
30
40
50
60
-‐40 -‐30 -‐20 -‐10 0 10 20 30 Da
rk ro
of (
W/m
2)
Cool roof (W/m2)
Heat Flux
Cool roof -‐ Dark roof Linear (Cool roof -‐ Dark roof)
Heat Flux (May 2012)
Vishal Garg, IIIT- Hyderabad
0 5 10 15 20 25 30 35 40 45
Tem
pe
ratu
re °
C
Month
Monthly mean outside surface temperature
0 5 10 15 20 25 30 35 40 45
Tem
pe
ratu
re °
C
Month
Monthly mean Inside Surface temperature
Monthly mean Temperature and Heat Flux
-‐15
-‐10
-‐5
0
5
10
15
20
He
at
Flu
x (W
/m2)
Month
Monthly mean Heat Flux
Dark roof Cool roof
Vishal Garg, IIIT- Hyderabad
Daytime monthly mean Temperature and Heat Flux
0
10
20
30
40
50
60
Dec Jan Feb Mar Apr May Jun Jul
Tem
pe
ratu
re °
C
Month
Daytime Monthly mean outside surface temperature
0 5
10 15 20 25 30 35 40
Dec Jan Feb Mar Apr May Jun Jul
Tem
pe
ratu
re °
C
Month
Daytime Monthly mean Indoor surface temperature
Day time – 8:00 to 18:00
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
15
Dec Jan Feb Mar Apr May Jun Jul
He
at
Flu
x (W
/m2)
Month
Daytime Monthly mean Heat Flux
Vishal Garg, IIIT- Hyderabad
Energy balance of roof (4th March, 2012, Pantnagar)
White Roof surface
Incoming short wave 738 W/m2
Reflected short wave 362 W/m2
Dark Roof surface
Incoming short wave 707 W/m2
Reflected short wave 76 W/m2
Heat Flux through the roof 21 W/m2
Heat Flux through the roof 43 W/m2
Vishal Garg, IIIT- Hyderabad
A
B
Aryabhatta Research Institute of Observational Sciences
Nainital site (Metal Roof)
Cold Climate (Summer: 27°C – 10°C, Winter: 15°C – 0°C) 29.22°N, 79.27°E
Vishal Garg, IIIT- Hyderabad
Temperature and Heat Flux (1-21 Dec 2011)
0
10
20
30
40
50
0:00
13:15
2:30
15:45
5:00
18:15
7:30
20:45
10:00
23:15
12:30
1:45
15:00
4:15
17:30
6:45
20:00
9:15
22:30
Tem
pe
ratu
re °
C
Time (Hours)
Underdeck surface temperature
0
10
20
30
40
50
0:00
13:15
2:30
15:45
5:00
18:15
7:30
20:45
10:00
23:15
12:30
1:45
15:00
4:15
17:30
6:45
20:00
9:15
22:30
Tem
pe
ratu
re °
C
Time (Hours)
Overdeck surface temperature
0
10
20
30
40
50
0:00
10:30
21:00
7:30
18:00
4:30
15:00
1:30
12:00
22:30
9:00
19:30
6:00
16:30
3:00
13:30
0:00
10:30
21:00
7:30
18:00
4:30
15:00
1:30
Tem
pe
ratu
re °
C
Time (Hours)
Air temperature
-‐200
-‐100
0
100
200
300
400
500
0:00
21:25
18:50
16:15
13:40
11:05
8:30
5:55
3:20
0:45
22:10
19:35
17:00
14:25
11:50
9:15
6:40
4:05
1:30
22:55
20:20
17:45
15:10 He
at
Flu
x (W
/m2)
Time (hours)
Heat Flux
Vishal Garg, IIIT- Hyderabad
y = 1.6226x + 35.494 R² = 0.84874
-‐200
-‐100
0
100
200
300
400
500
-‐150 -‐100 -‐50 0 50 100 150 200
Dark(W
/m2)
White(W/m2)
Dark(Green) -‐ White roof
Heat Flux - Dark-Cool roof (1-21 Dec 2011)
Vishal Garg, IIIT- Hyderabad
Energy balance of roof (21st December, 2012,Nainital)
White Roof surface
Incoming short wave 701 W/m2
Reflected short wave 239 W/m2
Dark Roof surface
Incoming short wave 665 W/m2
Reflected short wave 40 W/m2
Heat Flux through the roof 34 W/m2
Heat Flux through the roof 82 W/m2
Vishal Garg, IIIT- Hyderabad
Results* for Pantnagar
• Daily mean benefit for albedo increase of 0.1 is ~ 20 Wm-2 for Pantnagar (~ 40 Wm-2 for Nainital)
• Heat flux reduction of ~ 20 Wm-2 is observed in the month of May
• Over deck Temperature reduction of 12oC
• Under deck Temperature reduction of 4oC
• Indoor temperature reduction of 2-3oC
* These are the preliminary results, further analysis is being carried out for final results