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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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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Experiments: Test Houses
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Experiments: Sensors
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Experiments: Monitoring Equipment
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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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Experimental Results: Installation ComparisonsHorizontal Configuration vs. Truss Configuration?
Slight Advantage for the Horizontal Configuration
~ 5 %
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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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Experimental Results: Effects of Daily Solar Radiation
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Experimental Results: Effects of Attic Ventilation
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Experimental Results: Effects of Attic Insulation Level
42%
34%
25%
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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
N Si n j
i o i n i amb i n
i sky surr i n sol i
,,
,, ,
,
,,
( , ) ,
/ , ,
( ) ( )
" ( )( ) "
0 1 0 1
1
0
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
N Si n j
i i i n i i n attic air n
i k i nk i
s sk n latent i
,,
,, ,
,
,,
( , ) , ,
, ,,
,, ,
( ) ( )
" ( )
( ) "
0 1 0 1
1
1 10
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Modeling: Solar Modeling
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Verification of Model/Experiments (No RB Case)
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Verification of Model/Experiments
Horizontal Configuration Truss Configuration
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Verification of Model/Experiments (Winter)
No Radiant Barrier Configuration Horizontal Configuration
15 % Reduction in Heat Leaving Across the Attic
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Verification of Model/Experiments
No Radiant Barrier Configuration Horizontal Configuration
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Computer Simulations: Yearly Performance
Horizontal Configuration Truss Configuration
34 %Jun - Aug
32 %Jun - Aug
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Computer Simulations: Yearly Performance
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Computer Simulations: Attic Ventilation Pattern (Soffit/Soffit)
Jun - Aug
33.1% 31.6%
Horizontal
Truss
No RB
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Computer Simulations: Attic Ventilation Pattern (Roof/Soffit)
Jun - Aug
31.4% 26.2%
Horizontal
Truss
No RB
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Computer Simulations: Attic Ventilation Pattern (Soffit/Ridge)
Jun - Aug
32.3% 28.2%
Horizontal
Truss
No RB
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Computer Simulations: Impact of Radiant Barrier on Cooling Demand as a Function of Insulation Degradation
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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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Computer Simulations: Climate Influence
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Computer Simulations: Climate Influence
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Computer Simulations: Climate Influence
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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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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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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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Parametric Analyses: Mean Hourly Relative Humidity
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Parametric Analyses: Mean Hourly Global (H) Radiation
0
5
10
15
20
25
30
35
40
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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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Parametric Analyses: Latitude
0
5
10
15
20
25
30
35
40
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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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Parametric Analyses: Altitude
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Parametric Analyses: Roof Solar Absorptivity
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Parametric Analyses: Radiant Barrier Emissivity
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Parametric Analyses: Attic Airflow Rate
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Parametric Analyses: Roof Slope
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In Conclusion….
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THANK YOUTHANK YOU