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