1
Windows MatterWindows Matter
(Plus: A Few Reminders About The Importance of Building
Energy Performance) Our Motto for the
Evening…
The End in MindThe End in Mind•The Worst Window…•Performance Beyond the Worst…•Why Windows Matter…
•The Energy Megatrend
Who Am I?Who Am I?– Building Scientist and Educator
• How Do Buildings Work?– Standards Writer on Building Performance
• How Do We Test Them?– Building Code Developer and Trainer
• How Do We Ensure Delivered Performance?
– A Beekeeper…• Learning from the ultimate building scientists…
Today We…Today We…
• Will Cover– Performance
Fundamentals– Glass Fundamentals– Thermal Performance– Some Building &
Window Modeling– Comfort Issues– Carbon Implications
• Won’t Cover– Dynamic Glazing– Material Distinctions– Non-Residential (though
the lessons are transferable)– Future Technologies
Efficient Windows?Efficient Windows?
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Early Energy Code SolutionsEarly Energy Code Solutions How Do We Pick a Window?How Do We Pick a Window?• Aesthetics• Cost• Heat Loss• Heat Gain• Air Leakage• Water Penetration• Wind Load Resistance• Sound Transmission• Fabric Fading Potential• Condensation Resistance
• Visible Light Transmission
• Daylighting• Ventilation Efficiency• Operating Characteristics• Maintenance & Durability• Code Compliance• Warranty Considerations• Other Issues
Macro versus MicroMacro versus Micro• Macro Thinking
– Southeast– North Carolina– Asheville– “Energy Star Windows”
• Micro Thinking– North Asheville on a
site facing due west, overlooking a lake, near the highway, open to prevailing NW winds, primarily west and east-facing glass and a black-topped driveway to the south
– Best window for MY job
Macro ThinkingMacro Thinking
…a good place to START
…but, alone, often lead to least common denominator results.*
…can help avoid some of the more location-specific potential problems.*
Micro DecisionsMicro Decisions Microclimate is PersonalMicroclimate is Personal
• Comfort– Physical– Emotional– Safety– Environmental– Financial
3
Microclimate ConsiderationsMicroclimate Considerations• Temperatures
– Summer Peak– Winter Peak– Diurnal Swing
• Moisture– Rain, snow, sleet– Relative Humidity– Condensation
• Wind– Peak Gusts– Sustained Gusts
• Radiation– Heat Gain– Heat Loss
• Relative Humidity– Ventilation
considerations• Local Pollutants
– Smog, Acid rain– Sand, dust– Highway or industrial
particulates– Noise
More Microclimate IssuesMore Microclimate Issues• Security (climate?)
– Human– Animal– Wind-borne debris
• Seasonal Climate issues– Monsoons– Hurricanes– Tornadoes– Blizzards– Locusts
• Movement– Earthquakes– Settling/expansive
Soils– Wind
• View(s)– Orientations– Reflections
• Privacy– Proximity
• Other
Microclimate WaterMicroclimate Water• Rain• Rain Direction• Lakes, Streams• Snow• Steam• Sleet• Fog
Privacy is a microclimate consideration
More microclimate concernsMore microclimate concerns• View• Scenery• Nature• Beauty• Privacy
Protection from Wild AnimalsProtection from Wild Animals
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More “Micro” ConsiderationsMore “Micro” Considerations•Component Performance
– Glass Performance (IGs, laminates, coatings)– Frame Performance (Monolithic or
composites)– Hardware Performance (Operators, locks,
balances, etc.)• Integration (on-site)
– Water management, security, etc.
But first, we have to meet the requirements of the
The Building Code!
What is the Code?What is the Code?•Least safe…•Least strong…•Least energy efficient…
…building allowed by law.
We’re not allowed to build it any crappier…
Disaster Breeds CodesDisaster Breeds Codes
Disaster Breeds Codes…Disaster Breeds Codes…•Code of Hammurabi – 1750 BC
– One of the first “Building Codes”– “Failure” put the builder’s life and property
at risk
•Let’s get a quick refresher in what ol’ Ham had to say…
Code of Hammurabi <snip>Code of Hammurabi <snip>• 229: If a builder has built a house for a man and
his work is not strong, and if the house he has built falls in an kills the householder, that builder shall be slain.
• 232: If goods have been destroyed, he shall replace all that has been destroyed; and because the house was not made strong, and it has fallen in, he shall restore the fallen house of his own material.
• 233: If a builder has built a house for a man, and his work is not done properly and a wall shifts, then that builder shall make that wall good with his own silver.
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Disaster Breeds Codes…Disaster Breeds Codes…•The Burning of Rome – 64 AD
– Nero didn’t like the slums and stench– Established fire safety and sanitation
requirements for all buildings following the fire
Europe Learns…Europe Learns…•The Great London Fire – 1666 AD
– Black Plague, raw sewage, tightly spaced buildings…
– Two-thirds of the city destroyed– “London Building Act” adopted after the fire
US Code Milestones…US Code Milestones…•The Chicago Fire – 1871 AD
– Mrs. O’Leary’s cow…– Destroyed 17,000 buildings, killed 250
people, left 100,000 homeless. – Bankrupted the insurance industry – New code adopted in 1875 regulating
building construction and fire prevention.
More US Code MilestonesMore US Code Milestones•The San Francisco Earthquake –
1906 AD– What the earthquake didn’t get, the fire did– One of the major influencers of today’s
structural, fire and life safety codes
First Energy Code MilestoneFirst Energy Code Milestone•Arab Oil Embargo – 1973-4
– President Carter’s Fireside Chat (“Turn your thermostat down to 65 and wear a sweater”and “Drive 55”)
– Precipitated the first energy codes for buildings – ASHRAE 1975
Hurricane AndrewAugust, 1992175 mph wind gusts$25 billion damage
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Recent Code MilestonesRecent Code Milestones•Hurricane Andrew – 1992 AD
– 90% of all homes in Dade County Florida had roof damage
– 117,000 homes were destroyed or had major damage
– Primary driver of today’s hurricane protection codes
More Recently…More Recently…
Katrina’s Legacy…Katrina’s Legacy…•Hurricane Katrina – 2005 AD
– Costliest hurricane in history – est. $80 billion
– Over 1300 confirmed deaths– 3200 still missing
•Louisiana and Mississippi? – Just considering their first Building Code!
Disaster TeachesDisaster Teaches
I-35W Bridge Construction in 1967
We Wait for DisasterWe Wait for Disaster•History has shown that we WAIT for
disaster, THEN we react.
There are consequences to waiting…
Sea Level +1M
New Orleans
Lake CharlesBeaumont
Baton Rouge
Weiss and Overpeck, University of Arizona
What if we wait for sea level to rise 1 meter
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Sea Level + 6MMiamiFt. Lauderdale
Daytona Beach
Jacksonville
St. Petersburg
Fort Meyers
Panama City
Weiss and Overpeck, University of Arizona
What if we wait for sea level to rise 6 meters? What About Energy Codes?What About Energy Codes?•“Disaster” is not as easy to define
•“Pain” is relative– $3 per gallon gasoline? $6? $10?– $0.15 per kWh electricity? $0.25? $0.50?– $50 per barrel of oil? $75? $100?
Another kind of pain…
Before we go too deeply into the specifics about window performance…
“Understanding the Size of Things…”
Buildings & EnergyBuildings & Energy
Source: EIA 2007
Buildings > 40%
Transportation28%
Industrial32%
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The Size of Things…The Size of Things…• There are over 110 million existing
residential buildings – (From US census data)
• ~64% of all windows are Single Pane – Replacement assumed at 14 per home– (Source: USDOE Core Data Book)
• Using “Chris Math” this means that we have about 1 Billion single pane windows that need to be replaced!
Fixing the “Problem”Fixing the “Problem”•1 Billion Single Pane Windows in
Existing Homes•We install about 35 million windows
in replacement per year– Half of these are clear glass!
• It will take 40 to 60 years to replace these energy hogs (old and new) with energy efficient ones
This assumes that we INCREASE the rate of market penetration of GOOD Windows!
Window Market SegmentationWindow Market Segmentation
Remodeling New
Replacement
Source: Ducker Research 20060
5
10
15
20
25
30
35
40M
illio
n U
nits
.
New Construction
34.1
Remodeling 17.2
Replacement 19.2
Manufactured Housing
1.8
Residential Window Sales - 200572.3 Million Units
The “Problem” Continues…The “Problem” Continues…•48% of today’s window sales have
clear glass – (Source: Ducker Research 2006)
•Over 35 million residential windows each year are produced without good glazing!– New and Replacement
Frame TypesFrame Types
Wood 19.2Vinyl 40.6
Aluminum 8.7
Other 1.9
Source: Ducker Research 2006
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Commercial 463MM
Residential 1,339MM
Glazing by Construction TypeGlazing by Construction Type
Total: 1,803 Million Square Feet
Source: Ducker Research 2006
Residential Glass TypesResidential Glass Types
Low-E56%
Non-Low-E44%
Source: Ducker Research 2006
Commercial Is Even WorseCommercial Is Even Worse
Low-E37%
Non-Low-E63%
Source: Ducker Research 2006
Every Project Is DifferentEvery Project Is Different
• Design Loads are Project Specific
• Wind Loads are Project specific
• Exposures are Project specific
Longaberger Basket Corporate HeadquartersNewark, OH
Now, let’s talk about Windows and Energy
Old (Wrong) “Rules of Thumb”Old (Wrong) “Rules of Thumb”•Windows are Bad
– Too much heat loss– Too much heat gain– They leak (air, water,
heat)•Skylights are Bad
– Same reasons– Overhead!
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More Old Wrong “Rules”More Old Wrong “Rules”•Glass performance = Window
performance•To save the most energy, minimize
window area•Only four glass options available
– Single, Double, Tint, Low-e•Low-e = Energy Efficient•All Low-e glazings are the same
Old Window Material “Rules”Old Window Material “Rules”•“Wood is good”•“Vinyl is new”•“Steel is safe”•“Aluminum is strong”•“That’s all the options you get….”
Today, over 50% of the windows sold are of some type of
composite material or composite construction...
Specification ChallengesSpecification Challenges• Can no longer just specify “wood
windows” or “aluminum” or “vinyl”• Sometimes two, three even as many as
20 different materials may make up a window
• All of these materials perform differently
Yet PERFORMANCE is what you are really seeking in
specification and product selection...
Old Performance “Rules”Old Performance “Rules”•“Performance Values are Reliable”•“Higher R-values are better”•“Windows Don’t Leak”•Glass Seals Will Last “A Long Time”
(Translation: “Forever”)•“Not Much More Area for
Performance Improvement….”
Energy Performance BasicsEnergy Performance Basics•U-factor•Solar Heat Gain Coefficient•Visible Transmittance•Air Leakage
But before we go TOO far...
Chris’s Rule # 1Chris’s Rule # 1
“Compare WHOLE PRODUCTWHOLE PRODUCTPerformance Values”
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Comparing PerformanceComparing Performance
?Whole Product vs. Center of Glass PerformanceWhole Product vs. Center of Glass Performance Frame area
Edge-of-glass area
Center-of-glass area
Different Materials:•Wood•Vinyl•Aluminum•Glass•Steel•Sealants•Gases•Laminates•Coatings•etc.
Specification Basics: EnergySpecification Basics: Energy•U-factor•Solar Heat Gain
Coefficient•Visible
Transmittance•Air Leakage
•Project specific•High rise? Low-rise?•Residential? Industrial?•Office? School?
•Climate specific•Hot? Cold? Mixed?•Dry? Humid?•Sandy? Snowy?•Altitude?
•Microclimate specific•Orientation•End Use
Methods of Heat TransferMethods of Heat Transfer
1. Conduction (∝ ti – to)
2. Convection (∝ ti - to )
3. Radiation (∝ t14 - t2
4 )
First, let’s talk about heat loss...
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ConductionConductionHeat transfer
through materialscaused by atemperaturedifference
70°FRoom Temp.
0°FAir Temp.
5°F
68°F
Qcond∝ Δt Heat transferdue to airmovement
70°FRoom Temp.
0°FAir Temp.
Qconv∝ Δt
ConvectionConvection
Heat transfer betweensurfaces of differenttemperatures.
70°FRoom Temp.
ColderSurfaces
RadiationRadiation
Qrad∝ t14 - t2
4
Windows Windows exhibit each exhibit each type of heat type of heat transfer transfer ––both summer both summer and winter!and winter! Convection –
inside, outside and between the glass
Wintertime Heat Loss
Conduction –through the frame, spacer, and glass
Radiation –direct, re-radiated, inside, outside and between the glass
Heat Loss in WinterHeat Loss in Winter
0°F 70°F
Heat Loss & WindowsHeat Loss & Windows
0
0.3
0.6
0.9
1.2
1.5
U-Factors
Existing New
• Common aluminum-framed, single glazed windows lose 3 to 4 times more heat in winter than today’s most basic energy efficient technologies
• Cold glass surfaces with recurring condensation
• BIG impact on comfort• BIG impact on heating
costs
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“U-Factor”“U-Factor”• Amount of heat transmitted through the
window due to a temperature difference between inside and out.– Includes Conduction, Convection and Radiation heat
transfer through the unit• The lower the value, the less heat is lost
through the window in the winter• Simple Rule for heating climates:
– Look for products with a U-factor < 0.35
Now, let’s talk about heat gain...
Of course, there are many types of solar control...
Solar Control Fundamentals…Solar Control Fundamentals…
More Solar Control...More Solar Control... Add-on Solar Control…Add-on Solar Control…
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A Southern Art Form…A Southern Art Form…LengthSummer
sunWinter
sun
Height
Solar Heat GainSolar Heat GainDiffuseradiation
DirectradiationReflected
radiation
Windows Windows exhibit each exhibit each type of heat type of heat transfer transfer ––both summer both summer and winter!and winter! Convection –
inside, outside and between the glass
Summertime Heat Gain
Conduction –through the frame, spacer, and glass
Radiation –direct, re-radiated, inside, outside and between the glass
Heat Gain & WindowsHeat Gain & Windows
0
0.2
0.4
0.6
0.8
1Solar Heat Gain
Existing New
• Air conditioning energy is very expensive
• New window technologies are over three times more efficient at blocking unwanted heat gain than common aluminum-framed, single glazed windows
• Windows generally drive the air conditioning load (residential)
• Windows generally determine the perimeter load (commercial)
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Homes Have ChangedHomes Have Changed
49%
91%
40%
50%
60%
70%
80%
90%
100%
1973 2005
New Single Family Homes with Air Conditioning
Window solar gain is the single largest contributor to cooling loads
Source: US Census 2005
“Solar Heat Gain Coefficient”“Solar Heat Gain Coefficient”•The fraction of the incident solar
radiation (at direct normal incidence) that is actually transmitted through the window in the form of heat
•The lower the value, the less heat gain into the space
•Simple rule for cooling climates:– Look for SHGC values <0.35
Well, what if I just specify “low-e windows”? Isn’t
that good enough?
NO!Different low-e glazings perform differently!
Spectral SelectivitySpectral Selectivity
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5
Wavelength (microns)
Tran
smitt
ance
(%)
ClearGray / BronzeHigh Transmittance Low-ESpectraly selective tint and Low-ESpectrally selective Low-E
IRUV VIS
What Flavor is Your Glass?What Flavor is Your Glass?
0%
10%
20%
30%
40%
50%
60%
70%
80%
300
380
780
2500
UV Visible Near Infrared
Clear HSLE1 HSLE2 MSLE LSLE1 LSLE2
Tran
smis
sion
%
Dee’s Door Shows ThisDee’s Door Shows This
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Visible TransmittanceVisible Transmittance•How much of the VISIBLE portion of
the solar spectrum is transmitted•The higher the value, the more
“clear” the window appears•Simple Rule:
– Look for Tvis values greater than 0.50
Then, of course, there is air leakage...
WINDWIND
““Air LeakageAir Leakage””Window Type, Placement and Partitions Impact Ventilation
Window air leakage is NOTNOT a good ventilation strategy!
Pollutant Control?Pollutant Control? “Air Leakage”“Air Leakage”• A measure of a window’s air tightness
under a fixed set of laboratory conditions– Currently at constant temperature and pressure,
may evolve to testing at differential temperatures• The lower the value, the tighter the
window– Tradeoffs may occur between tightness and ease of
operations• Simple rule:
– Look for air leakage less than 0.20 cfm/sq.ft.
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Recap of Rule #1Recap of Rule #1•Specify and Compare Whole Product
Performance Values•Chris’s Simple Specification Rules:
– U-factor < 0.35– SHGC < 0.35– Visible Transmission > 0.50– Air Leakage < 0.20
All Buildings Are Similar?All Buildings Are Similar?
A Brief History Lesson
How Did We Get Here?How Did We Get Here?•1973 Revisited
– Automobile Efficiency, Industrial Efficiency and Building Efficiency
•Solutions– EPA MPG’s, Appliance Standards, Utility Rate
Increases– More Insulation
• New Construction Standards• Weatherization Programs for Existing Construction
Rating CertificationRating Certification
R30InsulationInsulation
AutomotiveAutomotive
28 City30 Highway
Your actual mileage may vary dependingon driving conditions and other factors
1998 ToyotaCorrolaSedan4 Speed2L Engine
AppliancesAppliancesA Means of Comparison…
What About the Windows?What About the Windows?•Big Energy Losers
– Especially after insulated walls and attics•Limited Solutions
– “Double Pane”, Storm Windows, Tinted Glass•No Reliable Energy Performance
Ratings– Outrageous and illegal performance claims
•Code “Solutions” = Less Windows– Most approaches “traded out” windows
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Window Industry Responds...Window Industry Responds...•Innovation
– Low-e glazings– Gas filled IG units– Low conductivity spacers– New frame designs– Variety of new glazing transmission
properties
But a lot of these innovations are INVISIBLE!
Well, what if I just specify “low-e windows”? Isn’t
that good enough?
NO!Different low-e glazings perform differently!
Two “Low-E” WindowsTwo “Low-E” Windows
Message: They may LOOK the same - but can perform very differently.
Two Solar Control OptionsTwo Solar Control Options
Message: They may LOOK different - but can perform the same!
Chris’s Rule # 2Chris’s Rule # 2
DonDon’’t Trust Your Eyes!t Trust Your Eyes!––Can look the same, but Can look the same, but perform differently;perform differently;
––Can look different, but Can look different, but perform the same.perform the same.
Tinted
Clear
Color
0.2540%LSLE20.2766%LSLE10.4172%MSLE0.6378%HSLE20.7175%HSLE10.7882%Clear
SHGCVisible Light
New Style GlassNew Style Glass
Don't trust your eyes - read the label!
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Low-E LocationLow-E Location
On surface 2:• reduces solar
gain• roomside glass is
cool
On surface 3• absorbed sunlight
goes into room• HOT glass! Inside Glass Temperatures –
Winter DayInside Glass Temperatures –Winter Day
MSLE HSLE Clear
Frame, Edges and Seals?Frame, Edges and Seals? Window Industry Responds...Window Industry Responds...•Reliable Energy Ratings
– State-of-the-art Testing and Evaluation– Third Party Certification Authorization– Working with builders, architects and
regulators– Like MPG’s, R-values and Energy Guide
Labels•New Code Solutions
Window Energy Ratings?Window Energy Ratings?•National Fenestration Rating Council
(NFRC)•Formed in 1989 to provide a fair,
accurate and credible energy rating and labeling system for windows, doors and skylights
•Coordinates certification and labeling of energy performance
•Certified Energy Ratings
NFRC LabelNFRC Label• Certified Energy
Performance– U-factor– SHGC– Tvis– Air Leakage
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AdvantagesAdvantages•Instant, Accurate, Directly
Comparable Energy Ratings•Rating Applies to all Types of
Products•Eliminates Confusion Deciphering
Manufacturer’s Literature•Demonstrates Compliance to Local
Codes•Accurate HVAC System Sizing
Why is Certification Important?Why is Certification Important?
•Independently-determined ratings•Checked and verified by an
independent, third party•Assurance of “getting what you pay
for”•Manufacturer’s commitment to its
customers•Code Compliance
Chris’s Rule # 2Chris’s Rule # 2
“Don’t Trust Your Eyes”leads to.....
Chris’s Rule # 3Chris’s Rule # 3
“Require Performance Certification
and Labeling.”
If It’s Not Labeled… ?If It’s Not Labeled… ?•Does it have…
– Low-E coatings? • Which one?
– Gas fills? Which one?– Low-conductivity
spacers?•Does it meet…
– Local codes?– Performance
expectations?– Comfort expectations?
Chris’s RulesChris’s Rules•Compare Whole Product
Performance– Not center of glass
•Don’t Trust Your Eyes– Can look the same but perform differently– Can look different but perform the same
•Require Performance Certification and Labeling
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Safety Glazing 101Safety Glazing 101•Glass breaks•It can hurt you•It can hurt others•The code attempts to regulate that•Hollywood ignores these regulations
for dramatic effect…
“Ghost” Sequence“Ghost” Sequence Types of Safety GlazingTypes of Safety Glazing•Laminated Glass•Tempered Glass•Safety Insulating Unit•Others
– Plastic Glazing– Organic-Coated Glass– Wired Glass
Laminated GlassLaminated Glass
• Glass Retention• Qualifies as Safety Glass• Increased Burglar Resistance• Increased Impact Resistance• Improved Sound Control (STC)
Glass
Glass
Plastic Interlayer
Single LiteForced EntryBomb BlastHurricaneAcoustical
Safety
Laminated InsulatedSame as Single Plus:Energy ConservationEnhanced Acoustical
- Can be Double Laminated
Multiply LaminatedSame as Single Plus:
Enhanced Forced EntryBullet Resistance
Enhanced Blast Resistance
Laminate ConfigurationsLaminate Configurations
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Laminate ExamplesLaminate Examples
Monolithic Impact Resistant Glazing
Insulating Impact Resistant Glazing
Different NeedsDifferent Needs•Some jobs may need additional
– Safety performance• Like your car windshield
– Security performance• Resistant to intrusion
– Sound performance• Quiet
Bag TesterBag Tester SG Specialty ApplicationsSG Specialty Applications•Hurricane•Bomb Blast•Earthquake
Safety Glazing RealitySafety Glazing Reality•Three photos of an important
moment in safety glazing history
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So… Let’s Design a WindowSo… Let’s Design a Window•What Forces?•How to Best Meet Those Forces?•Priorities?
•Class Participation
Unit Size
Importance factorExposure
Wind Speed
Location in Wall
Mean Roof Height
MRH
Six basic elements are used to calculate design pressure requirements:
Design Pressure ElementsDesign Pressure Elements
Coastal Design Example…Coastal Design Example…•One in seven Americans live along
the Atlantic and Gulf coasts•140 coastal counties make up 52%
of the U.S. housing supply•Over 1500 residential building
permits are issued every day in coastal counties
Why Does This Matter?
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Hurricanes and Housing…Hurricanes and Housing…•Hurricane Andrew caused over $30
billion in insured loses•New York ranks 2nd in
cost/disasters – Florida ranks 1st.• Insurers forced to suspend or
terminate underwriting activity in certain areas of the state.
Still Closer…
Opening Protection?Opening Protection?•To protect against wind-borne
debris in high wind areas•Testing and certification required
– Yes, we get to break things…– Only this time we use a cannon…– And we load it with lumber…
No, this is not a joke…
Loading the CannonLoading the Cannon
Annealed GlassAnnealed Glass Laminated GlazingLaminated Glazing
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Pressure CyclingPressure Cycling Not Just a Coastal Issue…Not Just a Coastal Issue…
The Need for StandardsThe Need for Standards
Historical Perspective…Historical Perspective…
Past as PrecedentPast as Precedent1975 1985
Arab Oil Embargo - 1973
ASHRAE 1975 -Restricts Window Area
Energy Policy Act of 1992References NFRC
MEC 1995 – Introduced First Prescriptive Window Requirements
Model Energy Code (circa 1985)HDD Driven, Windows Part of Wall
1995
What Actions Did We Take?What Actions Did We Take?•Tried to Save Energy
– Developed Standards• Buildings, Cars, Appliances, Industrial Processes
– Innovated (new technologies)– Adopted Minimums (codes)– Provided Incentives
• Utility Programs, etc.
26
Why Standards?
AppliancesAppliances
A Means of Comparison…
AutomotiveAutomotive
How Far Can We Go?How Far Can We Go?
Recap: What is the Code?Recap: What is the Code?•Least safe…•Least strong…•Least energy efficient…
…building allowed by law.
We’re not allowed to build it any crappier…
Total Window U-factor requires knowledge of glass andframe properties.
27
Many Low-E CoatingsMany Low-E Coatings
0.250.04
0.240.02
0.260.08
0.310.20
0.48Uncoated (0.84)
Emittance Double Pane Glass U-Factor
The Rule of PanesThe Rule of Panes
Every Layer of Glass
in a Multi-Pane Unit
Equates to
1 Point
in
R-Value
U & Temperature vs. No. of PanesU & Temperature vs. No. of Panes
0.10
0.20
0.30
0.40
0.500.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6 7 8Number of Panes
25
30
35
40
4550
55
60
65
70
Roo
msi
de G
lass
Tem
pera
ture
U-Factor 0F Outdoor
Cen
ter o
f Gla
ss U
-Fac
tor
Air Space Heat TransferAir Space Heat Transfer
RADIATION– 2/3 of heat transfer– blocked with “low-E” coatings
Conduction/Convection– 1/3 of heat transfer– retarded with gas fill (argon)
Air Space Heat TransferAir Space Heat Transfer
2
2
22
21
16
19
10
13
0 5 10 15 20 25 30 35
Low-E, ArgonFilled
Low-E, Air Filled
Clear Glass,Argon Filled
Clear Glass, AirFilled
Btu/hr/ft2 @ 70° F ΔT
RadiationConduction
New Glass MathNew Glass MathGlass Type Approximate R-Value
1st layer of glass 1
2nd layer of glass 1
Low-Emissivity coating 1
Argon Gas fill 1
Total 4Quad pane performance with double glazing!
28
Advanced Glass MathAdvanced Glass Math
0.100.200.300.400.500.600.700.800.901.00
Single Pane
Double Pane
Triple Pane
Doublew/LoĒ &argon
Triplew/1 LoĒ& argon
Triplew/2 LoĒ& argon
25303540455055606570
Roo
msi
de G
lass
Tem
p
U-Factor 0F Outdoor
Cen
ter o
f Gla
ss U
-Fac
tor
What About 2 Low-E Coatings?What About 2 Low-E Coatings?
.25Low-E (0.04)Uncoated
.25UncoatedLow-E (0.04)
.28Mid-E (0.20)Mid-E (0.20)
.31Mid-E (0.20)Uncoated
32Glass
U-FactorSurface #
1 2 3 4
U vs. Gap Width & EmittanceU vs. Gap Width & Emittance
0.100.150.200.250.300.350.400.450.500.55
1/4"(6.5mm)
3/8"(9.8mm)
1/2"(13.0mm)
5/8"(16.0mm)
3/4"(19.5mm)
Airspace Gap Width
Clear Double Mid-E (0.20) Low-E (0.04)
Cen
ter o
f Gla
ss U
-Fac
tor
U-Factor Air vs. ArgonU-Factor Air vs. Argon
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
1/4" (6.5mm) 3/8" (9.8mm) 1/2" (13.0mm) 5/8" (16.0mm) 3/4" (19.5mm)Gap Width
Mid-E Air Mid-E Argon Low-E Air Low-E Argon
Cen
ter o
f Gla
ss U
-Fac
tor
U-Factor Argon vs. KryptonU-Factor Argon vs. Krypton
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
1/4" (6.5mm) 3/8" (9.8mm) 1/2" (13.0mm) 5/8" (16.0mm) 3/4" (19.5mm)
Gap Width
2P LE + Argon 2P LE + Kyrpton 3P (2)LE + Argon 3P (2)LE + Kyrpton
Cen
ter o
f Gla
ss U
-Fac
tor
U-Factor vs. Gas FillU-Factor vs. Gas Fill
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Argon Fill Level
Clear Double Mid-E (0.20) Low-E (0.04)
Cen
ter o
f Gla
ss U
-Fac
tor
29
Translating Glass Performance Into Window
Performance...
Understanding U-factor Limits
Translating Glass Performance Into Window
Performance...
Understanding U-factor Limits
Table 4 Close-upTable 4 Close-up
Source: ASHRAE Handbook of Fundamentals
Scatter Plot of Table 4Scatter Plot of Table 4
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.10 0.20 0.30 0.40 0.50Glass U-Factor
Aluminum Aluminum TB Clad Wood Wood / Vinyl Ins Vinyl
Linear (Aluminum) Linear (Aluminum TB) Linear (Clad Wood) Linear (Wood / Vinyl) Linear (Ins Vinyl)
Who
le W
indo
w U
-Fac
tor
Operable WindowOperable Window
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0.10 0.20 0.30 0.40 0.50
Glass U-Factor
Aluminum Alum TB CladWood Wood or Vinyl Insulated
Who
le W
indo
w U
-Fac
tor
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.10 0.20 0.30 0.40 0.50Glass U-Factor
Aluminum Alum TB CladWood W/V (1995) Improved W/V Insulated
Updated Operable WindowUpdated Operable Window
R4R8
Who
le W
indo
w U
-Fac
tor
R2
30
Total Window SHGC requires knowledge of glass propertiesandframe area.
50%
60%
70%
80%
90%
1 2 3 4 5 6 7 8Number of Clear Glass Panes
0.50
0.60
0.70
0.80
0.90
Layers Reduce Transmission!Layers Reduce Transmission!
Visi
ble
Tran
smis
sion
%
Solar Heat G
ain Coefficient
“Un-obtanium”
0.5048%0.6362%Tint
0.2218%------Reflective
0.7280%0.7882%Clear
SHGCVisibleSHGCVisible
6 mm Glass3 mm Glass
Old Style GlassOld Style Glass
What you see is what you get!
What Flavor is Your Glass?What Flavor is Your Glass?
0%
10%
20%
30%
40%
50%
60%
70%
80%
300
380
780
2500
UV Visible Near Infrared
Clear HSLE1 HSLE2 MSLE LSLE1 LSLE2
Tran
smis
sion
%
They look different - but have the same solar gain!They look different - but have the same solar gain!
Tinted
Clear
Color
0.2540%LSLE20.2766%LSLE10.4172%MSLE0.6378%HSLE20.7175%HSLE10.7882%Clear
SHGCVisible Light
New Style GlassNew Style Glass
Don't trust your eyes - read the label!
31
Low-E LocationLow-E Location
On surface 2:• reduces solar
gain• roomside glass is
cool
On surface 3• absorbed sunlight
goes into room• HOT glass! Inside Glass Temperatures –
Winter DayInside Glass Temperatures –Winter Day
MSLE HSLE Clear
More on Translating Glass Performance
into Window Performance...
Understanding Solar Heat Gain Limits
More on Translating Glass Performance
into Window Performance...
Understanding Solar Heat Gain Limits
Frame Area is the DriverFrame Area is the Driver
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
Glass SHGC
Alum, Fixed Alum, Operable W/V, Fixed W/V, Operable
Frame AreaAL Fixed =12%AL Operable=15%Wood/Vinyl Fixed =15%W/V Operable=25%
Win
dow
SH
GC
32
NFRC Certification
U-Factor
SHGC
Certified Energy Performance Certified Energy Performance
Windows&
Air Conditioner Sizing(if we have time)
Windows&
Air Conditioner Sizing(if we have time)
Air Conditioner and Heat Pump
Sizing Chart
Instructions:1. Stand at the curb and look at the house through cut outs. 2. Pick the hole that best fits the house.3. Choose the unit size shown at the bottom of that cutout.
Trim out on dotted lines carefully. Then follow instructions below.
1½ to 2 tons
2½ to 3½tons
4 to 5 tons
(cut out)(cut out)
(cut out)
Another Visual Sizing MethodAnother Visual Sizing Method
Complex Sizing MethodComplex Sizing Method
300+ pagesof
tabular data!
The "Window" PerspectiveThe "Window" Perspective
Solar GainThe “Other Stuff”
33
"Other Stuff" Expanded "Other Stuff" Expanded
•Heat Gain– Roof and Walls: U*A*ΔT– Infiltration– Internal Gains– Latent Gains
•Distribution System Efficiency– Duct Leakage– Thermal Gains
U * A * ΔTU * A * ΔT
•Get U-Factor from climate zone
•Area is simple math– Length, Width, Height– Stories
•Delta T is location dependent– Use climate zone "average"
IECC Climate
Zone
Window U Wall R Ceiling R
7-8 0.35 21 496 0.35 19 495 0.35 19 384 0.40 13 383 0.65 13 302 0.75 13 301 1.20 13 30
Single Story House UASingle Story House UA
0
100
200
300
400
500
600
700
800
900
1,000
2,000 2,500 3,000 3,500 4,000
Conditioned Floor Area, ft2
UA
CZ2 CZ3 CZ4 CZ5 CZ6
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000
Heating Degree Days (HDD65)
Des
ign
Tem
pera
ture
, °F
Temperature SimplificationTemperature Simplification
Heating
Cooling
IECC Climate
Zone
Heating Design
(°F)
Cooling Design
(°F)
7-8 -24 886 -14 905 -2 924 8 943 20 962 27 971 36 99
34
Envelope Heat GainEnvelope Heat Gain
0.0
0.5
1.0
1.5
2.0
2.5
2,000 2,500 3,000 3,500 4,000
Conditioned Floor Area, ft2
Tons
CZ2:1-Story CZ2: 2 Story CZ6: 1-Story CZ6: 2-Story
CoolingLoadFactors from MJ8CoolingLoadFactors from MJ8
28° 34° 40° 46°North 37 37 35 34NE 149 140 135 130East 220 219 216 213SE 172 185 196 205South 91 121 149 173SW 172 185 196 205West 220 219 216 213NW 149 140 135 130
Latitude
CLF by Orientation & LatitudeCLF by Orientation & Latitude
0
50
100
150
200
250
North East/West South
Coo
ling
Load
Fac
tor
28° 34° 40° 46°
CLF for "Typical" DistributionCLF for "Typical" Distribution
0
50
100
150
200
250
West Back South Back
Ave
rage
CLF
28° 34° 40° 46°
Understanding Design TempsUnderstanding Design Temps
y = -0.01x + 40.12
y = -0.001x + 99.870
-40
-20
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
HDD
Des
ign
Tem
p,
Common Design TemperaturesCommon Design Temperatures
88F12FBoston91F24FNorfolk92F23FAtlanta92F40FOrlando
Cooling Design Temperature
Heating Design Temperature
East Coast Cities – I-95
Range: 28F vs. 4F
35
More Design TemperaturesMore Design Temperatures
88F-10FMinneapolis94F7FKansas City98F22FDallas96F30FSan Antonio
Cooling Design Temperature
Heating Design Temperature
Central Cities –I-35
Range: 40F vs. 10F
More Design Temperatures-2More Design Temperatures-2
87F27FPortland101F33FFresno
89F7FSpokane95F12FSalt Lake City
106F32FLas Vegas108F40FPhoenix
Cooling Design Temperature
Heating Design Temperature
West Coast Cities
Range: 33F vs. 19F
Heating and Cooling Design TsHeating and Cooling Design Ts
-40
-20
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
HDD
Des
ign
Tem
p, °F
IECC Climate
Zone
Heating Design
(°F)
Cooling Design
(°F)
7-8 -24 886 -14 905 -2 924 8 943 20 962 27 971 36 99
Remember? Homes Have ChangedRemember? Homes Have Changed
49%
91%
40%
50%
60%
70%
80%
90%
100%
1973 2005
New Single Family Homes with Air Conditioning
Window solar gain is the single largest contributor to cooling loads
Source: US Census 2005
Peak Cooling for Clear GlassPeak Cooling for Clear Glass
Duct Losses
Heat Gain
Solar Gain
36
Peak Loads - 2000 ft2 HousePeak Loads - 2000 ft2 House
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.70 0.60 0.50 0.40 0.30 0.20 0.10
Clear HSLE Tinted Code MSLE LSLE Reflective
Window SHGC
Tons
DuctLossSolarGainHeatGain
Peak Loads by House SizePeak Loads by House Size
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0.70 0.60 0.50 0.40 0.30 0.20 0.10
Clear HSLE Tinted Code MSLE LSLE Reflective
Window SHGC
Tons
4,000 ft² 2,000 ft²
What's a Ton of AC Worth?What's a Ton of AC Worth?•Saving 1 ton of AC per house
– 1 ton = 12,000 Btu/hr– 13 SEER = 13,000 Btu/kWh– Using “Chris Math” – ~1 kW per house– 110 million existing homes, assume about
half have AC– ~50 million X 1 kW = 50 million kW
Roughly equal to about 100 new 500 MW coal-fired power plants…
Windows&
Comfort
(If we have time)
Windows&
Comfort
(If we have time)
Comfort = How We FeelComfort = How We Feel• Windows play a key
role in how we FEEL in a room– Too Warm?– Too Cold?
Comfort is a well understood science – and it is MEASUREABLE!
ASHRAE Standard 55
37
Comfort ReferencesComfort References Predicted Mean VotePredicted Mean Vote
The PMV model was developed by Fanger in the 1970s and is the standard method used to evaluate comfort in buildings.
7 Point Comfort Scale7 Point Comfort Scale
WarmCool
+1 +2 +3
Cold CoolSlightly
NeutralSlightly
Warm Hot
-3 -2 -1 0
PMV CalculationPMV Calculation
M = Metabolic rateL = thermal load on body
Predicted Percent DissatisfiedPredicted Percent Dissatisfied ASHRAE Comfort ProgramASHRAE Comfort Program
38
Comfort at the ThermostatComfort at the Thermostat
0%
5%
10%
15%
20%
25%
30%
35%
66°F 67°F 68°F 69°F 70°F 71°F 72°F 73°F 74°F
Thermostat Setting
Pred
icte
d Pe
rcen
t Dis
satis
fied
Window Specific InputsWindow Specific Inputs
Winter•Mean Radiant Temperature
– Window surface temperature– Window size– Proximity
Summer•Solar Impact
– Direct beam radiation– Absorbed & re-radiated (hot glass)
Glass and ComfortGlass and Comfort•A key determinant of room comfort
– Is the surface hot in the summer?– Cold in the winter?
•Good glazing can improve your comfort and save energy– Can sit and work closer to the windows– Access to natural light– May even impact thermostat settings
Efficient Windows CollaborativeEfficient Windows Collaborative
Winter ComfortWinter Comfort
0
10
20
30
40
50
60
70InsulatedWallLSLE
HSLE
Triple
Double
Single
Roo
m-S
ide
Surf
ace
Tem
pera
ture
(0F
outs
ide)
0%
10%
20%
30%
40%
Operable PatioDoor WindowWall
Pred
icte
d Pe
rcen
t Dis
satis
fied
Comfort with 52°GlassComfort with 52°Glass
25%
39
Comfort vs. Window SizeLow-E Double Pane, 70°F Thermostat, 3’ AwayComfort vs. Window SizeLow-E Double Pane, 70°F Thermostat, 3’ Away
10%
15%
20%
25%
30%
35%
40%
50 40 30 20 10 0
Outdoor Temperature, °F
Pred
icte
d Pe
rcen
t Dis
satis
fied
WindowWallPatioDoorOperable
Response to Winter ConditionsResponse to Winter Conditions
10
20
30
40
50
60
70
50 40 30 20 10 0Outdoor Temperature, °F
Roo
msi
de S
urfa
ce T
empe
ratu
re, °
F
WallQuad PaneDouble PaneSingle Pane
Comfort vs. ProximityLow-E Double Pane, 70°F Thermostat, Patio DoorComfort vs. ProximityLow-E Double Pane, 70°F Thermostat, Patio Door
10%
15%
20%
25%
30%
35%
40%
50 40 30 20 10 0
Outdoor Temperature, °F
Pred
icte
d Pe
rcen
t Dis
satis
fied 2' away
3' away4' away
Comfort vs. Glass TypePatio Door, 70°F Thermostat, 3' AwayComfort vs. Glass TypePatio Door, 70°F Thermostat, 3' Away
10%
15%
20%
25%
30%
35%
40%
50 40 30 20 10 0
Outdoor Temperature, °F
Pred
icte
d Pe
rcen
t Dis
satis
fied
Clear DoubleLow-E DoubleLow-E Triple
MRT SummaryMRT Summary
10%
20%
30%
40%
50%
Small Big Away Close Low-E ClearGlass
72°F 68°F
Window Size Proximity Glass Type Thermostat Setting
Pred
icte
d Pe
rcen
t Dis
satis
fied
Depth of DiscomfortPatio Door, 70°F ThermostatDepth of DiscomfortPatio Door, 70°F Thermostat
0
1
2
3
4
5
6
7
50°F 40°F 30°F 20°F 10°F 0°F
Outdoor Temperature
Dis
tanc
e A
way
(ft)
for 2
5% P
PD
Clear DoubleLow-E Double
40
Heating Thermostat OffsetPatio Door, 3' away, 25% max PPDHeating Thermostat OffsetPatio Door, 3' away, 25% max PPD
68
69
70
71
72
73
74
75
50°F 40°F 30°F 20°F 10°F 0°F
Outdoor Temperature
Ther
mos
tat,
Deg
rees
F Clear Double Low-E Double
Hours of Discomfort Hours of Discomfort
0
500
1000
1500
2000
2500
< 50°F < 55°F < 60°F
Hou
rs
Clear Double Low-E Double
Summer Comfort IssuesSummer Comfort Issues
Hot Glass
DirectGain
Summer ComfortSummer Comfort
75
80
85
90
95
100
105 HSLE
SingleTintDoubleTintTripleClearDoubleClearSingleClearLSLE
Roo
m-s
ide
Surf
ace
Tem
pera
ture
(90
F ou
tdoo
rs)
Summer Comfort Low-E GlassSummer Comfort Low-E Glass
0% 10% 20% 30% 40% 50% 60% 70% 80%
LSLE
MLSE
HSLE
Clear
Probability of Discomfort
Due to glass temperatureDue to solar gain
0%
10%
20%
30%
40%
50%
60%
70%
80%
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0Slightly Cool Neutral Slightly Warm
Predicted Mean Vote
Pred
icte
d Pe
rcen
t Dis
satis
fied Slightly Cool
Drops PPD from 26% to 6%
Slightly WarmIncreases PPD from 26% to 62%
Solar Offset to PMV100 btu/ft2 = +0.8 PMV PointsSolar Offset to PMV100 btu/ft2 = +0.8 PMV Points
41
Summer DiscomfortSummer Discomfort
0%
10%
20%
30%
40%
50%
60%
100 btu/ft2 200 btu/ft2 100 btu/ft2 200 btu/ft2
No Sun Partial Sun Full Sun No Sun Partial Sun Full Sun
SHGC>0.5 SHGC<0.3
Pred
icte
d Pe
rcen
t Dis
satis
fied
Discomfort in AshevilleDiscomfort in Asheville
As heville
679
24 0 0 0 0 0
766
778643
396172
521357
676
643
542
391
177
452
336
225
141
48
0
0
0
0
0
500
1,000
1,500
2,000
2,500
3,000
3,500
C lear P yro E LoĒ 179 LoĒ 272 LoĒ 366 3P Ē 179 3P Ē 272
Hours of Disco
mfort
S ummerDay
S wingS eas on
WinterDay
WinterNight
Cooling Thermostat Offset25% max PPDCooling Thermostat Offset25% max PPD
70
71
72
73
74
75
76
77
78
100 btu/ft2 200 btu/ft2
No Sun Partial Sun Full Sun
Ther
mos
tat S
ettin
g, °
F
SHGC>0.5 SHGC<0.3
Windows & Comfort SummaryWindows & Comfort Summary•Beware of trade-offs
– “They might be equal, but they’re not the same!”
•Energy models don’t capture comfort implications– T-stat setpoints
“We don’t sufficiently discredit the selection of bad windows…”
Yogi Berra Mathis
Windows Session Wrap-upWindows Session Wrap-up The Code Has ChangedThe Code Has Changed•What is the code?
42
All Together…All Together…•Least safe…•Least strong…•Least energy efficient…
…building allowed by law.
We’re not allowed to build it any crappier…
Comfort and WindowsComfort and Windows•How comfortable are you next to an
R-19 wall?– R-13? R-11?
•What about next to the windows?– Still the hottest surface in the house– Still the coolest surface in the house
•Window decisions drive the comfort conditions
Windows and Winter ComfortWindows and Winter Comfort
0
10
20
30
40
50
60
70InsulatedWallLSLE
HSLE
Triple
Double
SingleRoo
m-S
ide
Surf
ace
Tem
pera
ture
0F outside
Windows and Summer ComfortWindows and Summer Comfort
75
80
85
90
95
100
105 HSLE
SingleTintDoubleTintTripleClearDoubleClearSingleClearLSLE
Roo
m-s
ide
Surf
ace
Tem
pera
ture
90F and sunny
outside
Homes Have ChangedHomes Have Changed
49%
91%
40%
50%
60%
70%
80%
90%
100%
1973 2005
New Single Family Homes with Air Conditioning
Window solar gain is the single largest contributor to cooling loads
Source: US Census 2005
RecapRecap•Windows Matter!
– Heating, Cooling, Comfort, etc.•Key performance indices
– U-factor– SHGC– Certified, Whole Product Ratings!
•Turn on the efficiency power plant!
43
Thank you! Any Questions? Consider…Consider…•How many builders equate their
HVAC sizing decisions with their selection of windows?
•Let’s look at the Southeast
IECC Climate
Zone
Window U Wall R Ceiling R
7-8 0.35 21 496 0.35 19 495 0.35 19 384 0.40 13 383 0.65 13 302 0.75 13 301 1.20 13 30
Climate and WindowsClimate and Windows
Low U‐factor Required
Low SHGC Required
The IECC in the Southeast RegionThe IECC in the Southeast Region
Code Requirements in the Southeast RegionCode Requirements in the Southeast Region
Zone WindowU
WindowSHG
C
Ceiling Wall Foundati
on
4 0.40 ---- R38 R13 R10
3 0.65 0.40 R30 R13 R0
2 0.75 0.40 R30 R13 R0
1 1.20 0.40 R30 R13 R0
44
3 Cities in the Southeast Region3 Cities in the Southeast Region
Windows & Energyin the Southeast RegionWindows & Energyin the Southeast Region
SE Window PerformanceSE Window Performance• Compare the changes in heating and
cooling energy across 3 cities in the region as a function of SHGC or U-Factor.
• General conclusions are:– Low SHGC increase heat load but reduces solar
loads to a great extent– U-Factor has minimal impact on cooling, but does
reduce heating loads– The balance between heat and cool shifts between
zones
45
46
Let’s look at a few of these emerging technologies...
Emerging TechnologiesEmerging Technologies
Multiple glazings and films that do multiple duties.
What USED to be a passive technology is rapidly becoming active.
Old?
Frame MaterialsFrame Materials New Twists on Old MaterialsNew Twists on Old Materials
Aerogels“Foamed glass”Highly insulativeMany advancements in this area.Over R-20 per inchFragility is current weakness.Lots of research underway.
Switchable GlazingsSwitchable Glazings
47
ElectrochromicsSwitchable transmissionRange of solar controlSignificant research underwayMajor implications for utilities and peak loadsCommercial applications first
More Switches….More Switches….Liquid Crystal technologies...
... create new architectural and energy opportunities.
Transmissive State Reflective State
SPDsSuspended Particle Displays
Coming AttractionsComing Attractions•Windows that double as:
– your TV screen– your computer screen
•Windows that are integral components of:– your security system– your audio system– your water management system