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Civil, Environmental, and Architectural EngineeringThe University of Kansas
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“Radiant Barrier Technology – A Must in Green Architecture”
Mario A. Medina, Ph.D., P.E.
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Introduction
““Preventing the sun's radiation from entering through the roof can make a significant contribution to comfort and reduction in cooling bills/needs.””
From: Sustainable Building Sourcebook Chapter: Energy
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Definition
A radiant barrier consists of a layer of metallic foil, with low emittance, that significantly reduces the transfer of heat energy radiated from “hotter” surfaces to “colder” surfaces (e.g., the deck of an attic to the attic floor). Among the benefits of installing radiant barriers are energy savings, $ savings, and comfort.
(Source: Florida Solar Energy Center)
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Radiant Barriers
Installation Configurations
Pre-laminated Roof Sheathing
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Radiant Barriers
How are they installed?
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Radiant Barriers
How are they installed?
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Radiant Barriers
How they work:– Radiant barriers reduce radiated heat transfer rate by
the combination of the low emittance/high reflectance properties of the foil.
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Radiant Barriers
Modes of Heat Transfer
(Source: Btubusters)
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Radiant Barriers
Heat transfer schematic
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Radiant Barrier
Radiant Barrier
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Radiant Barriers
In the present study, the performance of radiant barriers was assessed via:– Experiments
• Side by side monitoring of pre- and post-retrofit data.
– Modeling• Mathematical representation of thermal sciences that describe
the processes that take place. • Implemented using computer programming (e.g.,
FORTRAN).
– Model/Experiment Validation
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Radiant Barriers
Experiments: Test Houses
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Radiant Barriers
Experiments: Sensors
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Radiant Barriers
Experiments: Monitoring Equipment
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Radiant Barriers
Experimental Results: Calibration (No RB Case)Ceiling Heat Flux Indoor Air
Temperature
< 3 % < 0.3 oF
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Radiant Barriers
Experimental Results: Calibration (RB Case)Ceiling Heat Flux Indoor Air
Temperature
< 3 % < 0.3 oF
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Radiant Barriers
Experimental Results: Effect of Radiant Barriers (~28% Daily Heat Flow Reduction)
37.5%
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Radiant Barriers
Experimental Results: Installation ComparisonsHorizontal Configuration vs. Truss Configuration?
Slight Advantage for the Horizontal Configuration
~ 5 %
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Radiant Barriers
Experimental Results: Shingle Temperatures Horizontal Configuration Truss Configuration
vs. No RB Case vs. No RB Case
No difference in shingle temperature
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Radiant Barriers
Experimental Results: Effects of Daily Solar Radiation
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Radiant Barriers
Experimental Results: Effects of Attic Ventilation
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Radiant Barriers
Experimental Results: Effects of Attic Insulation Level
42%
34%
25%
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Radiant Barriers
Modeling: Based on Energy Balance Approach at Each Enclosing Surface
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Radiant Barriers
ModelingEnergy Balance (General)
Energy Balance (Heat Transport Processes)
Outdoor Energy Balance
Indoor Energy Balance
Q Q Q Qconducted to from convected to from radiated net latent condensation evaporation( / ) ( / ) ( ) ( / ) 0
Y Tsi Tr X Tso Tr
CR q ho T Tsohro T Tso q
i jj i
N Si n j i j
j i
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i o i n i amb i n
i sky surr i n sol i
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Z Tsi Tr Y Tso Tr
CR q hi Tsi T
hri Tsi Tsi q
i jj i
N Si n j i j
j i
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i i i n i i n attic air n
i k i nk i
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Radiant Barriers
Modeling: Solar Modeling
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Radiant Barriers
Verification of Model/Experiments (No RB Case)
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Radiant Barriers
Verification of Model/Experiments
Horizontal Configuration Truss Configuration
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Radiant Barriers
Verification of Model/Experiments (Winter)
No Radiant Barrier Configuration Horizontal Configuration
15 % Reduction in Heat Leaving Across the Attic
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Radiant Barriers
Verification of Model/Experiments
No Radiant Barrier Configuration Horizontal Configuration
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Radiant Barriers
Computer Simulations: Yearly Performance
Horizontal Configuration Truss Configuration
34 %Jun - Aug
32 %Jun - Aug
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Radiant Barriers
Computer Simulations: Yearly Performance
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Radiant Barriers
Computer Simulations: Attic Ventilation Pattern (Soffit/Soffit)
Jun - Aug
33.1% 31.6%
Horizontal
Truss
No RB
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Radiant Barriers
Computer Simulations: Attic Ventilation Pattern (Roof/Soffit)
Jun - Aug
31.4% 26.2%
Horizontal
Truss
No RB
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Radiant Barriers
Computer Simulations: Attic Ventilation Pattern (Soffit/Ridge)
Jun - Aug
32.3% 28.2%
Horizontal
Truss
No RB
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Radiant Barriers
Computer Simulations: Impact of Radiant Barrier on Cooling Demand as a Function of Insulation Degradation
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Radiant Barriers
Computer Simulations: Climate Influence
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Radiant Barriers
Computer Simulations: Climate Influence
Climate
SummerMonthly
Dry Bulb Air Temperature
oC(oF)
SummerMonthly RelativeHumidity
(%)
Summer Monthly Wind
Speedkm/h(mi/h)
Area Covered
km2
(mi2)
Percent Area
Covered(%)
Humid Subtropical 29(84) 68 13.7
(8.5)1,939,636(750,430) 24.03
Humid Continental Warm Summer
25(77) 70 14.1
(8.8)1,655,112(640,350) 20.50
Desert 28(83) 47 13.0
(8.1)1,223,467(473,350) 15.16
Humid ContinentalCool Summer
21(70) 67 14.0
(8.7)905,291
(350,250) 11.21
Steppe 17(62) 43 12.7
(7.9)739,043
(285,930) 9.15
Marine West Coast 15(59) 80 13.3
(8.3)560,259
(216,760) 6.94
Mediterranean 17(63) 74 16.1
(10.0)508,837
(196,865) 6.30
Western High Areas 20(68) 50 13.7
(8.5)481,581
(186,320) 5.97
Tropical Savanna 28(83) 77 12.9
(8.0)59,484
(23,014) 0.74
TOTAL 8,072,711(3,123,269) 100.00
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Radiant Barriers
Computer Simulations: Climate Influence
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Radiant Barriers
Computer Simulations: Climate Influence
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Radiant Barriers
Computer Simulations: Climate Influence
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Radiant Barriers
Computer Simulations: Climate Influence
0
50
100
SIPR PHPR
0
50
100
SIPR PHPR 0
50
100
SIPR PHPR
0
50
100
SIPR PHPR
0
50
100
SIPR PHPR
0
50
100
SIPR PHPR 0
50
100
SIPR PHPR
0
50
100
SIPR PHPR
0
50
100
SIPR PHPR
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Radiant Barriers
Computer Simulations: Climate Influence
Climate Sample Station
Sample Summer
Integrated Percent
Reduction(SIPR)
(%)
Average
Peak-Hour Percent
Reduction (PHPR)
(%)
Humid SubtropicalSan Antonio, TXNew York- NY
Atlanta, GA
34.332.538.5
35.1 31
Humid ContinentalWarm Summer
Topeka, KSIndianapolis, IN
30.030.1 30.5 46
Desert Las Vegas, NVTucson, AZ
19.223.0 21.1 23
Humid Continental CoolSummer
Minneapolis, MNDetroit, Michigan
25.724.3 25.0 54
Steppe Pocatello, IDHelena, MT
16.013.7 14.9 36
Marine West Coast Astoria, OR 9.6 9.6 ~100
Mediterranean San Francisco, CA 2.3 2.3 97
Western High Areas Boulder, CO 19.7 19.7 44
Tropical Savanna Miami, FL 36.8 36.8 42
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Radiant Barriers
Parametric Analyses: Outdoor Air Temperature
0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50 60 70 80 90
Average Hourly Ambient Temperature for Period (deg F)
Perc
enta
ge R
educ
tion
in C
elin
g He
at F
lux
for P
erio
d(%
)
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Radiant Barriers
Parametric Analyses: Mean Hourly Relative Humidity
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Radiant Barriers
Parametric Analyses: Mean Hourly Global (H) Radiation
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200
Mean Hourly Global Horizontal Solar Radiation for period(Btu/h-sf)
Perc
enta
ge R
educ
tion
in C
eilin
g He
at
Flux
for P
erio
d(%
)
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Radiant Barriers
Parametric Analyses: Latitude
0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50
Latitude of Location(deg N)
Perc
enta
ge R
educ
tion
in C
eilin
g He
at
Flux
for P
erio
d(%
)
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Radiant Barriers
Parametric Analyses: Altitude
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Radiant Barriers
Parametric Analyses: Roof Solar Absorptivity
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Radiant Barriers
Parametric Analyses: Radiant Barrier Emissivity
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Radiant Barriers
Parametric Analyses: Attic Airflow Rate
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Radiant Barriers
Parametric Analyses: Roof Slope
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Radiant Barriers
In Conclusion….
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THANK YOUTHANK YOU