This slide deck was presented by Brittany Hanham at Passive House North Conference 2013. Outline: - North American and Passive House window rating systems - Example simulation results - What this means and things to be aware of

1. Window Standards Compared:
NFRC, ISO and Passive House Ratings
Brittany Hanam M.A.Sc., P.Eng.
September 27, 2013

2. Outline
North American and Passive
House window rating
systems
Example simulation results
What this means and things
to be aware of

3. Passive House Windows
High performance windows form an
integral part of the strategy to achieve
whole building energy targets
High solar heat gain to offset heating
energy
Low 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

4. Requirements for Passive House Windows
Component certification vs. building certification
PHI offers component certification for windows
But – windows do not need to be certified by PHI to be
used in a Passive House certified building
Passive House building
requirements for windows:
U-value < 0.80 W/m2-K (for comfort)
Solar heat gain > 0.50
recommended
Other requirements for thermal
comfort, hygiene (temperature
factor)
Overall building energy targets and
other requirements
Compliance determined via PHPP

5. Requirements for Passive House Windows
Passive House component
certification criteria for
windows
Climate specific requirements
Performance levels or
“Efficiency Classes” from A+ to
D

6. Passive House Windows – Component Certification
Criteria

7. 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

8. North American Window Products
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 glazing
Of these listings, highest SHGC is 0.33
≤ 0.8
0%
0.8 to 1.0
1% 1.0 to 1.4
10%
How are European manufacturers
achieving low U-values with triple
glazing, argon gas fill?
1.4 to 2.0
89%

9. Window Rating Standards
North America: National Fenestration Rating
Council (NFRC)
Canada: CSA A440.2 harmonized with NFRC
NFRC 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-value
EN 673 for glazing U-value
EN 410 for glazing solar heat gain (g-value)
Passive House
ISO standards with some modifications

10. Key Differences Between Window Rating Standards
Boundary conditions
(temperatures & air film
resistances)
Standard size of window
Method of accounting for edge of
glass effects
Calculation methodologies
(algorithms) for glazing unit
airspace, frame U-value
SHGC (g-factor) for whole
window or centre of glass
Treatment of sloped glazing

11. U-Value Solar Heat Gain
Exterior
Temperature
Interior
Temperatur
e
Exterior
Temperatur
e
Interior
Temperature
Solar
Radiation
NFRC -18oC 21oC 32oC 24oC 783 W/m2
ISO 0oC 20oC 30oC 25oC 500 W/m2
Passiv
e
House
Frame: -
10oC
Glazing:
20oC to -7oC
20oC 30oC
(ISO)
25oC
(ISO)
500 W/m2
(ISO)
Key Differences: Boundary Conditions
Different exterior surface temperatures
Note Passive House value for “cool-temperate” climate is
5oC, but ISO conditions are acceptable for this climate
Different solar radiation
Affects solar heat gain calculation
Different surface film coefficients

12. Key Differences: Standard Sizes
NFRC sizes depend on operator type
For example:
Fixed:
1.2 m x 1.5
m
Casement – Single:
0.6 m x 1.5 m
Tilt & Turn:
1.2 m x 1.5
m
Passive 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

13. Key Differences: Edge effects
Passive House U-Value
Uframe x Aframe
ψspacer x L glazed
perimeter
Uglazing x Aglazing
ψinstall x L window
perimeter
NFRC U-Value
Uframe x Aframe
Uedge x Aedge
2.5”
Uglazing x Aglazing
Uframe, ψspacer, Uglazing, ψinstall
entered into PHPP
Uframe, Uedge, Uglazing used
to calculate overall U-value

14. Key Differences: Algorithms
The NFRC algorithm for centre of glass U-value are
more accurate
NFRC follows ISO 15099, Passive House follows ISO
10077-2 and EN 673
Footnote in ISO 10077-2, section 6.2 (reference to EN 673):
“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.”

15. 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

16. 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 Frame
North American Fibreglass Frame
European Vinyl Frame
Showed how same product
performs under different energy
rating systems
Each window had same
glass, gas fill and spacer

17. Centre of Glazing U-Value
Triple glazing, argon gas fill, two low-e coatings
Big difference between U-values for NFRC and ISO
methods and standard temperatures
0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, W/m2-K
Gap Size, mm
NFRC, -18°C
ISO, 0°C

18. Centre of Glazing U-Value
0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, 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 coatings
Differences when only changing exterior temperature of
methodology

19. 0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, 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 coatings
Add in climate-specific temperatures for Passive House
certification…

20. Centre of Glazing U-Values
0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, 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
Examples
12.7 mm gap: NFRC U-0.72, ISO U-0.70
18 mm gap: NFRC U-0.73, ISO U-0.57

21. Centre of Glazing U-Value
0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, 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

22. 0.9
0.8
0.7
0.6
0.5
10 12 14 16 18 20
Centre of Glass U-Value, 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 ISO
NFRC optimal gap
size is approx. 13 mm
ISO optimal gap sizes
are larger, approx.18
mm

23. Centre of Glazing U-Values
Six IGU configurations were simulated
Biggest difference in U-values for larger gap sizes
Double glazing 15.875 mm gaps
Triple glazing 12.7 mm gaps
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Double -
High Solar Gain
Double -
Low Solar Gain
Triple -
High Solar Gain
Triple -
Low Solar Gain
Centre of Glass U-Value, W/m2-K
NFRC
ISO
19% 23%
0% 2%

24. NFRC frame U-values determined with actual IGU and
spacer; ISO values determined with ‘calibration panel’
of specified conductivity – lower ISO frame U-values
Also different standard material properties, e.g.
fibreglass
2.0
1.4
1.2
1.5
1.0
0.8
1.0
0.6
0.5
0.4
0.2
0.0
1.2
1.0
0.8
0.6
Fixed - Head Fixed - Sill Fixed - Jamb
0.4
Triple - 180/180
Frame U-Value, W/m2-K
Triple Glazed North American Vinyl Frame Window
NFRC
ISO
Frame U-Values
0.2
11% to 16% difference
0.0
Fixed - Head Fixed - Sill Fixed - Jamb
Triple
Frame U-Value, W/m2-K
Triple Glazed Fibreglass Frame Window
NFRC
ISO
2% to0 .40% difference
Fixed - Head Fixed - Sill Fixed - Jamb
Passive House Triple
Frame U-Value, W/m2-K
Triple Passive House European uPVC Window
NFRC
ISO
13% to 16%
difference

25. NFRC frame U-values determined with actual IGU and
spacer; ISO values determined with ‘calibration panel’
of specified conductivity – lower ISO frame U-values
Also different standard material properties, e.g.
fibreglass
2.0
1.4
1.2
1.5
1.0
0.8
1.0
0.6
0.5
0.4
0.2
0.0
Correlation
1.2
1.0
0.8
0.6
1.6
1.5
1.4
1.3
No
!
Fixed - Head Fixed - Sill Fixed - Jamb
0.4
Triple - 180/180
Frame U-Value, W/m2-K
ISO Frame U-Value
Triple Glazed North American Vinyl Frame Window
NFRC
ISO
Frame U-Values
0.2
1.2 1.3 1.4 1.5 1.6
11% to 16% difference
0.0
1.2
Fixed - Head Fixed - Sill Fixed - Jamb
Triple
Frame U-Value, W/m2-K
Triple Glazed Fibreglass Frame Window
NFRC
ISO
2% to0 .40% difference
Fixed - Head Fixed - Sill Fixed - Jamb
Passive House Triple
Frame U-Value, W/m2-K
Triple Passive House European uPVC Window
NFRC
ISO
13% to 16%
difference
NFRC Frame U-Value

26. Whole Product U-Values
ISO U-values generally lower (better) than NFRC U-values
but it depends on a lot of factors
No
No “conversion factor” between ISO and NFRC U-values
Correlation!
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.6
1.4
1.2
1.0
0.8
1.6
1.4
1.2
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Window U-Value, W/m2-K
North American Vinyl Frame Window
NFRC
ISO
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Window U-Value, W/m2-K
North American Fibreglass Frame Window
NFRC
ISO
Dbl: 0% to 15%
Dbl: 11% to
Tpl: -6% to
16%
14%
Trpl: 6% to 10%
0.0
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
Window U-Value, W/m2-K
European uPVC Frame Window
NFRC
ISO

27. Whole Product U-Values
ISO U-values generally lower (better) than NFRC U-values
but it depends on a lot of factors
1.6
1.5
No “conversion factor” between ISO and NFRC U-values
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.6
1.4
1.2
1.0
0.8
1.6
1.4
1.2
1.4
1.3
1.2
1.1
1.0
0.9
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Window U-Value, W/m2-K
North American Vinyl Frame Window
NFRC
ISO
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
Fixed Casement Fixed Casement Fixed Casement Fixed Casement
Double - High Solar Double - Low Solar Triple - High Solar Triple - Low Solar
Window U-Value, W/m2-K
North American Fibreglass Frame Window
NFRC
ISO
Double: 10% to
16%
DblT: Dbl: r0ip%le 11% t:o - 21%5% to
to 1%
Tpl: -6% to
16%
14%
Trpl: 6% to 10%
0.0
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
Window U-Value, W/m2-K
European uPVC Frame Window
NFRC
ISO
0.8
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
ISO U-Value
NFRC U-Value
No
Correlation!

28. Highest percent difference in window U-values was
18%
15%
10%
5%
0%
-5%
-10%
-15%
Percent Difference in NFRC & ISO U-Values for Triple Glazed Windows
Fixed Operable Fixed Operable
Triple - 180/180 Triple - 366/180
North American Vinyl
North American Fibreglass
European Vinyl
Whole Product U-Values
ISO rating better
NFRC rating
better

29. Solar Heat Gain Values
Centre of glass NFRC values were 1% to 8% lower than
ISO
Greater difference for low solar gain glazing
Big difference between centre of glass and whole
product values!
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Double - 180 Double - 366 Triple - 180/180 Triple - 366/180
Solar Heat Gain Coefficient
NFRC Centre of Glass
ISO Centre of Glass
NFRC Fixed SHGC
NFRC Operable SHGC
Fixed: 18% - 19% reduction
Operable: 46% - 48%
reduction

30. Summary – Biggest Difference?
Many differences, but a significant one is centre of
glass U-value calculations
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Double High Solar
NA Vinyl
Double High Solar
NA Fibreglass
Double High Solar
EU uPVC
Triple High Solar
NA Vinyl
Triple High Solar
NA Fibreglass
Triple High Solar
EU uPVC
Centre of Glass U-Value,
W/m2-K
NFRC
ISO
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Double High Solar
NA Vinyl
Double High Solar
NA Fibreglass
Double High Solar
EU uPVC
Triple High Solar
NA Vinyl
Triple High Solar
NA Fibreglass
Triple High Solar
EU uPVC
Window U-Value, W/m2-K
NFRC
ISO
Centre
of Glass
U-Values
Whole
Window
U-Values

31. Lessons Learned
Neither NFRC nor ISO system is “better”
NFRC uses more accurate algorithms, compares all
products using the same conditions
ISO 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 standards
European products will soon need to be rated to
NFRC/CSA for Canadian code compliance

32. Moving Forward…
Be aware that all window ratings are not equal
Simply 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?

33. Thank you!
bhanam@rdhbe.com
Full report will be available soon at
www.rdhbe.com