Radiant Barrier Performance

A Summary of Fifty Years of Radiant Barrier
Research
Mario Medina and Bill Lippy
Presentation Outline
 Introduction to RIMA International
 Introduction to Radiant Barriers
 Radiant Barrier Installations
 Related Technologies

Radiant Barrier Performance
 Ceiling Heat Flows: Summer and Winter
 Space Cooling and Heating Loads
 Attic Temperature Reductions
 Parameterization
 HERS Ratings
 Conclusions
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RIMA-I
The Reflective Insulation Manufacturers Association
International (RIMA-I) is the only trade association
representing the reflective insulation, radiant barrier,
and interior radiation control coating (IRCC) industries.
For more information visit www.RimaInternational.org
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Introduction to Radiant Barriers
What is the Problem?
Summer Example
• Radiant Heat Gain & Loss on Buildings
• Roof Temperatures reach 160º in
Summer and very cold in the Winter
• Common building materials, such as
wood, masonry, and fiberglass insulation
have average surface emittances of
approximately 0.85;
• The hot roof radiates to cooler ceiling in
the summer
• The warm ceiling insulation radiates to
the cold roof deck in the winter
• Increase in Ceiling Heat Flux
• Higher Loads for HVAC mounted ducts
and equipment
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Radiant Barriers - Basics
• Radiant barriers function by primarily reducing heat transfer by radiation.
• Reduces Summer Heat Gain & Winter Heat Loss
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Reduced Radiant Load on Ceiling and HVAC
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Radiant Barrier Installations
Horizontal Radiant
Barrier
Truss Radiant Barrier
Deck Applied Radiant
Barrier
Draped Radiant Barrier
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Radiant Barrier Installations
“Truss Radiant Barrier”
(TRB)
“Deck Applied Radiant Barrier”
(DARB)
“Draped Radiant Barrier”
(DRB)
“Horizontal Radiant Barrier”
(HRB)
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Other Radiant Barrier Installations
Radiant Barrier on Knee Walls
Radiant Barrier on Gables
Radiant Barrier on a Ceiling
Radiant Barrier used as an
Insulation Baffle
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Radiant Technologies –
Internal Radiation Control Coatings (IRCC’s)
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Performance
Radiant Barriers & IRCC’s
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Radiant Barrier Performance
• Products defined as radiant barriers
have surface emittances less than or
equal to 0.1 and products defined as
interior radiation control coatings
convert surface emittances to 0.25 or less.
• The thermal performance or the
reduction of radiant heat transfer is
proportional to the surface emittance of
the radiant barrier material.
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Radiant Barrier Performance

% Reduction = Test Period
q Control dt -
q
Retrofit
dt
Test Period
q
x 100
Control dt
Test Period
qControl: Ceiling heat flux from the control attic [Btu/hr-ft2, W/m2]
qRetrofit: Ceiling heat flux from the retrofit attic [Btu/hr-ft2, W/m2]
Test Period: Testing period used in the integration
Shaded area = % Reduction
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Radiant Barrier Performance
U.S. Climate Zone Map (ASHRAE Standard 169-2006, 2006)
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Radiant Barrier Performance
Ceiling Heat Flow
Results archived in ASHRAE Transactions, Volume 118, Part 1, 2012
“A Comprehensive Review of Radiant Barrier Research Including Laboratory and Field
Experiments”
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Radiant Barrier Performance
Ceiling Heat Flow
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Radiant Barrier Performance
Ceiling Heat Flow
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Radiant Barrier Performance
Space Cooling Load
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Radiant Barrier Performance
Space Heating Load
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Radiant Barrier Performance
Space Cooling and Space Heating Load
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Radiant Barrier Performance
Attic Temperature Reductions
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Radiant Barrier Performance
Shingle Temperature Increase: Experimental
Results archived in ASME Journal of Solar Energy Engineering, Vol. 114, No. 1,1992
"Effects of Attic Ventilation on the Performance of Radiant Barriers"
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Radiant Barrier Performance
Effects of Daily Solar Irradiation: Experimental
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Radiant Barrier Performance
Effects of Attic Ventilation: Experimental
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Radiant Barrier Performance
Effects of Shingle Solar Absorptivity: Simulated
Results archived in ASME Journal of Solar Energy Engineering, Vol. 120, No. 1, 1998
“A Transient Heat and Mass Transfer Model of Residential Attics Used to Simulate Radiant Barrier
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Retrofits - Part II: Validation and Simulations”
Radiant Barrier Performance
Effects of Radiant Barrier Emissivity: Simulated
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Radiant Barrier Performance
Effects of Outdoor Air Temperature: Simulated
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Percentage Reduction in Celing
Heat Flux for Period(%)
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
Average Hourly Ambient Temperature for Period (deg F)
Results are archived in the ASCE Journal of Energy Engineering, Vol 134, No. 1, 2008
“Evaluating the Sensitivity of Attic Radiant Barrier Performance to Climate Parameters”
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Radiant Barrier Performance
Effects of Outdoor Relative Humidity: Simulated
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HERS Ratings – Example
Sample House Specifications
House Specifications:
· Single-story, rectangular-style house with the orientation facing north/south. The house size is 1,540 square feet.
· Vented attic.
· Ducts in the attic, “not-insulated” (use R-0.50). Energy Gauge requires a minimum R-value.
· Ceiling insulation R19.
· Wall construction: Frame, insulated to R19. Wall height 8 feet.
· Slab on grade – no floor insulation.
· Double-pane vinyl windows. Window area 15% of each wall.
· Door – metal with foam core at 20 square feet per door – 2 doors.
· Mechanical System: Cooling efficiency is SEER13, heat pump HSPF 7.7.
· Electric water heater EF 0.92.
Additional Assumptions for RemRate
· 35x44 foot print - 1540 ft^2
· 3 Bedrooms
· 2x6 8-ft wood frame walls, R-19 cavity insulation, medium exterior color
· Double pane vinyl windows, U-value 0.46, SHGC 0.57
· 2 Steel-polyurethane core doors, R 2.6; 20-ft^2 each
· Vented Attic, R-19 or R-30 blown insulation, dark colored roof
· 50-gal electric water heater EF=0.92, located in conditioned area
· 2-ton air source heat pump, 13 SEER, 7.7 HSPF, 10kW resistance heat backup, located in attic
· Thermostat setting: 70F heating, 75F Cooling
· Ductwork in Attic, one central return, 0.5 R insulation, RESNET/HERS default leakage (supply area = 415.8 ft^2; return area = 77.0 ft^2)
· Infiltration, 2009 IECC default, 7.00 ACH@50 Pa
· Electric dryer and range
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HERS Ratings – Example using RemRate
Zones
City
HERS Index
Without Radiant
Barrier
HERS Index
With Radiant
Barrier
∆HERS
Index
1
Miami
102
97
5
2
Austin
93
90
3
3
Atlanta
92
90
2
4
Baltimore
105
104
1
5
Chicago
112
111
1
6
Minneapolis
116
115
1
7
Fargo
120
118
2
8
Fairbanks
124
124
0
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Performance Conclusions
 On average, RBs reduce summer ceiling heat flows by approximately 23
to 45% depending on the insulation level. Winter ceiling heat flow
reductions are approximately 40% of the summer values for the same
insulation levels.
 Space cooling loads are reduced by 6 to 20% and space heating load
reductions would be approximately 40% of the space cooling load
reductions for the same insulation levels.
 DARBs and TRBs would reduce attic temperatures by an average of 13 oF,
while RBs in the HRB configuration would reduce the attic temperature
by an average of 4 oF. No negative effects on shingles were observed.
 Radiant barrier emissivity and a mix of outdoor air temperature with
relative humidity had first order effects.
 Radiant Barriers impact HERS ratings
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THANK YOU!
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