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NFRC, ISO and Passive House RatingsWindow Standards Compared:
Brittany Hanam M.A.Sc., P.Eng.
September 27, 2013
Outline
North American and Passive House window rating systemsExample simulation resultsWhat this means and things to be aware of
High performance windows form an integral part of the strategy to achieve whole building energy targets
High solar heat gain to offset heating energyLow U-value to reduce heat loss to a point where window becomes a net gain
High performance windows provide high interior surface temperatures for thermal comfort & prevent condensation or surface mold growth
Passive House Windows
Component certification vs. building certification
PHI offers component certification for windowsBut – windows do not need to be certified by PHI to be used in a Passive House certified building
Requirements for Passive House Windows
Passive House building requirements for windows:
U-value < 0.80 W/m2-K (for comfort)Solar heat gain > 0.50 recommendedOther requirements for thermal comfort, hygiene (temperature factor)Overall building energy targets and other requirementsCompliance determined via PHPP
Passive House component certification criteria for windows
Climate specific requirementsPerformance levels or “Efficiency Classes” from A+ to D
Requirements for Passive House Windows
Passive House Windows – Component Certification Criteria
E.g. Cool-temperate climate (includes Vancouver, Montreal, Germany)
Ug ≤ 0.75
UW ≤ 0.80
UW,installed ≤ 0.85
Passive House Windows – Component Certification Criteria
≤ 0.80%
0.8 to 1.01% 1.0 to 1.4
10%
1.4 to 2.089%
What are some of the best performing windows available from North American manufacturers?From the ENERGY STAR Canada product database:
326 of 583,120 listings have U ≤ 0.8; triples have surface 6 low-e coating and/or Krypton gas fill, or quad glazingOf these listings, highest SHGC is 0.33
How are European manufacturers achieving low U-values with triple glazing, argon gas fill?
North American Window Products
North America: National Fenestration Rating Council (NFRC)
Canada: CSA A440.2 harmonized with NFRCNFRC 100 for U-value, NFRC 200 for SHGC
Europe: International Organization for Standardization (ISO)
ISO 10077-1 and 10077-2 for frame and whole window U-valueEN 673 for glazing U-valueEN 410 for glazing solar heat gain (g-value)
Passive HouseISO standards with some modifications
Window Rating Standards
Boundary conditions (temperatures & air film resistances)Standard size of window Method of accounting for edge of glass effectsCalculation methodologies (algorithms) for glazing unit airspace, frame U-valueSHGC (g-factor) for whole window or centre of glassTreatment of sloped glazing
Key Differences Between Window Rating Standards
U-Value Solar Heat Gain
Exterior Temperatu
re
Interior Temperatu
re
Exterior Temperatu
re
Interior Temperatu
re
Solar Radiatio
n
NFRC -18oC 21oC 32oC 24oC 783 W/m2
ISO 0oC 20oC 30oC 25oC 500 W/m2
Passive House
Frame: -10oC
Glazing: 20oC to -
7oC
20oC 30oC(ISO)
25oC(ISO)
500 W/m2
(ISO)
Key Differences: Boundary Conditions
Different exterior surface temperaturesNote Passive House value for “cool-temperate” climate is 5oC, but ISO conditions are acceptable for this climate
Different solar radiationAffects solar heat gain calculation
Different surface film coefficients
NFRC sizes depend on operator typeFor example:
Key Differences: Standard Sizes
Fixed:1.2 m x 1.5
m
Casement – Single:
0.6 m x 1.5 mPassive House has one standard size for fixed and operable punched windows – 1.23 m x 1.48 m
German operable windows typically Tilt & Turn – larger sizes
Tilt & Turn:1.2 m x 1.5
m
Key Differences: Edge effects
Passive House U-Value
Uframe x Aframe
Uglazing x Aglazing
ψspacer x L glazed
perimeter
ψinstall x L window
perimeter
Uframe x Aframe
Uglazing x Aglazing
Uedge x Aedge2.5”
NFRC U-Value
Uframe, ψspacer, Uglazing, ψinstall entered into PHPP
Uframe, Uedge, Uglazing used to calculate overall U-
value
The NFRC algorithm for centre of glass U-value are more accurateNFRC follows ISO 15099, Passive House follows ISO 10077-2 and EN 673
Footnote in ISO 10077-2, section 6.2 (reference to EN 673):
Key Differences: Algorithms
“NOTE The correlations for high aspect ratio cavities [in glazing] used in EN 673
and ISO 10292 tend to give low values for the equivalent thermal conductivity. More accurate correlations are given in ISO
15099.”
Key Differences: Solar Heat Gain
Passive House g-value:
Centre of glass only, does not include frame
NFRC SHGC:
Value is for whole window, lower to account for frame
How do these differences affect energy performance?
Study evaluated U-value, solar heat gain of three windows using NFRC and ISO/PHI methods
North American Vinyl FrameNorth American Fibreglass FrameEuropean Vinyl Frame
Showed how same productperforms under different energyrating systemsEach window had sameglass, gas fill and spacer
Triple glazing, argon gas fill, two low-e coatingsBig difference between U-values for NFRC and ISO methods and standard temperatures
Centre of Glazing U-Value
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
ISO, 0°C
Centre of Glazing U-Value
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
NFRC, 0°C
ISO, -18°C
ISO, 0°C
Triple glazing, argon gas fill, two low-e coatingsDifferences when only changing exterior temperature of methodology
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
NFRC, -7°C
NFRC, 0°C
NFRC, 5°C
ISO, -18°C
ISO, -7°C
ISO, 0°C
ISO, 5°C
Centre of Glazing U-Value
Triple glazing, argon gas fill, two low-e coatingsAdd in climate-specific temperatures for Passive House certification…
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
NFRC, -7°C
NFRC, 0°C
NFRC, 5°C
ISO, -18°C
ISO, -7°C
ISO, 0°C
ISO, 5°C
Examples12.7 mm gap: NFRC U-0.72, ISO U-0.7018 mm gap: NFRC U-0.73, ISO U-0.57
Centre of Glazing U-Values
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
NFRC, -7°C
NFRC, 0°C
NFRC, 5°C
ISO, -18°C
ISO, -7°C
ISO, 0°C
ISO, 5°C
Passive House centre of glazing (for window certification)
Cool-temperate U ≤ 0.75 at 0oC or 5oC
Cold U ≤ 0.55 at -3oC
Centre of Glazing U-Value
0.5
0.6
0.7
0.8
0.9
10 12 14 16 18 20
Cent
re o
f Gla
ss U
-Val
ue, W
/m2 -
K
Gap Size, mm
NFRC, -18°C
NFRC, -7°C
NFRC, 0°C
NFRC, 5°C
ISO, -18°C
ISO, -7°C
ISO, 0°C
ISO, 5°C
Centre of Glazing U-Values
Optimal gap size different for NFRC and ISONFRC optimal gap size is approx. 13 mm
ISO optimal gap sizes are larger, approx.18 mm
Six IGU configurations were simulatedBiggest difference in U-values for larger gap sizes
Double glazing 15.875 mm gapsTriple glazing 12.7 mm gaps
Centre of Glazing U-Values
0.00.20.40.60.81.01.21.41.61.8
Double -High Solar Gain
Double -Low Solar Gain
Triple -High Solar Gain
Triple -Low Solar Gain
Cent
re o
f Gla
ss U
-Val
ue, W
/m2-
K
NFRC
ISO
19% 23%
0%
2%
0.0
0.5
1.0
1.5
2.0
Fixed - Head Fixed - Sill Fixed - Jamb
Triple - 180/180
Fram
e U
-Val
ue, W
/m2 -
K
Triple Glazed North American Vinyl Frame Window
NFRC
ISO
NFRC frame U-values determined with actual IGU and spacer; ISO values determined with ‘calibration panel’ of specified conductivity – lower ISO frame U-valuesAlso different standard material properties, e.g. fibreglass
Frame U-Values
11% to 16% difference
0.00.20.40.60.81.01.21.4
Fixed - Head Fixed - Sill Fixed - Jamb
Triple
Fram
e U
-Val
ue, W
/m2 -
K
Triple Glazed Fibreglass Frame Window
NFRC
ISO
2% to 4% difference
0.00.20.40.60.81.01.2
Fixed - Head Fixed - Sill Fixed - Jamb
Passive House Triple
Fram
e U
-Val
ue, W
/m2 -
K
Triple Passive House European uPVC Window
NFRCISO
13% to 16% difference
0.0
0.5
1.0
1.5
2.0
Fixed - Head Fixed - Sill Fixed - Jamb
Triple - 180/180
Fram
e U
-Val
ue, W
/m2 -
K
Triple Glazed North American Vinyl Frame Window
NFRC
ISO
NFRC frame U-values determined with actual IGU and spacer; ISO values determined with ‘calibration panel’ of specified conductivity – lower ISO frame U-valuesAlso different standard material properties, e.g. fibreglass
Frame U-Values
11% to 16% difference
0.00.20.40.60.81.01.21.4
Fixed - Head Fixed - Sill Fixed - Jamb
Triple
Fram
e U
-Val
ue, W
/m2 -
K
Triple Glazed Fibreglass Frame Window
NFRC
ISO
2% to 4% difference
0.00.20.40.60.81.01.2
Fixed - Head Fixed - Sill Fixed - Jamb
Passive House Triple
Fram
e U
-Val
ue, W
/m2 -
K
Triple Passive House European uPVC Window
NFRCISO
13% to 16% difference
1.2
1.3
1.4
1.5
1.6
1.2 1.3 1.4 1.5 1.6
ISO
Fra
me
U-V
alue
NFRC Frame U-Value
No Correlatio
n!
No Correlatio
n!
ISO U-values generally lower (better) than NFRC U-values but it depends on a lot of factorsNo “conversion factor” between ISO and NFRC U-values
Whole Product U-Values
0.00.20.40.60.81.01.21.41.6
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
North American Vinyl Frame Window
NFRC
ISO
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
North American Fibreglass Frame Window
NFRC
ISO
Dbl: 0% to 15%
Tpl: -6% to 14%
Dbl: 11% to 16%
Trpl: 6% to 10%
0.00.20.40.60.81.01.21.41.6
Fixed Tilt & Turn Fixed Tilt & Turn Fixed Tilt & Turn Fixed Tilt & Turn
Double - High Solar Double - Low Solar PHI Triple - High Solar PHI Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
European uPVC Frame Window
NFRC
ISO
ISO U-values generally lower (better) than NFRC U-values but it depends on a lot of factorsNo “conversion factor” between ISO and NFRC U-values
Whole Product U-Values
0.00.20.40.60.81.01.21.41.6
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
North American Vinyl Frame Window
NFRC
ISO
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
North American Fibreglass Frame Window
NFRC
ISO
Double: 10% to 16%
Triple: -2% to 1%Dbl: 0% to 15%
Tpl: -6% to 14%
Dbl: 11% to 16%
Trpl: 6% to 10%
0.00.20.40.60.81.01.21.41.6
Fixed Tilt & Turn Fixed Tilt & Turn Fixed Tilt & Turn Fixed Tilt & Turn
Double - High Solar Double - Low Solar PHI Triple - High Solar PHI Triple - Low Solar
Win
dow
U-V
alue
, W/m
2 -K
European uPVC Frame Window
NFRC
ISO
0.80.91.01.11.21.31.41.51.6
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
ISO
U-V
alue
NFRC U-Value
No Correlatio
n!
-15%
-10%
-5%
0%
5%
10%
15%
Fixed Operable Fixed Operable
Triple - 180/180 Triple - 366/180
Percent Difference in NFRC & ISO U-Values for Triple Glazed Windows
North American Vinyl
North American Fibreglass
European Vinyl
Highest percent difference in window U-values was 18%
Whole Product U-Values
ISO rating better
NFRC rating better
Centre of glass NFRC values were 1% to 8% lower than ISOGreater difference for low solar gain glazingBig difference between centre of glass and whole product values!
Solar Heat Gain Values
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Double - 180 Double - 366 Triple - 180/180 Triple - 366/180
Sola
r Hea
t Gai
n Co
effici
ent
NFRC Centre of GlassISO Centre of GlassNFRC Fixed SHGCNFRC Operable SHGC
Fixed: 18% - 19% reductionOperable: 46% - 48% reduction
Many differences, but a significant one is centre of glass U-value calculations
Summary – Biggest Difference?
0.00.20.40.60.81.01.21.41.61.8
Double High SolarNA Vinyl
Double High SolarNA Fibreglass
Double High SolarEU uPVC
Triple High SolarNA Vinyl
Triple High SolarNA Fibreglass
Triple High SolarEU uPVC
Cent
re o
f Gla
ss U
-Val
ue,
W/m
2-K
NFRC
ISO
0.00.20.40.60.81.01.21.41.61.8
Double High SolarNA Vinyl
Double High SolarNA Fibreglass
Double High SolarEU uPVC
Triple High SolarNA Vinyl
Triple High SolarNA Fibreglass
Triple High SolarEU uPVC
Win
dow
U-V
alue
, W/m
2-K NFRC
ISO
Centre of
Glass U-
Values
Whole Window U-
Values
Neither NFRC nor ISO system is “better”NFRC uses more accurate algorithms, compares all products using the same conditionsISO uses more realistic climate design conditions, important for building energy modeling
Today products are optimized to perform best under the rating regimes in effect in Europe, North America
Rating regimes drive product design
Existing simulation tools have the capability to model North American products for Passive House standardsEuropean products will soon need to be rated to NFRC/CSA for Canadian code compliance
Lessons Learned
Be aware that all window ratings are not equalSimply testing to both standards will not help North American manufacturers compete with European product performance due to gap sizes
North American manufacturers consider offering larger gap sizes for Passive House projects?
North American software can be used with ISO methods
Can convert NFRC simulations
Other ideas?
Moving Forward…
Thank you!
bhanam@rdhbe.com
Full report will be available soon at www.rdhbe.com