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Glass, Glazing and Glass, Glazing and Window Energy PerformanceWindow Energy Performance

by Alex McGowan, P.Eng.by Alex McGowan, P.Eng.Levelton Consultants LimitedLevelton Consultants Limited

Victoria, British Columbia, CanadaVictoria, British Columbia, Canada

AIBC Module V “Skin Problems”AIBC Module V “Skin Problems”April 26, 2007April 26, 2007April 26, 2007April 26, 2007

Outline of PresentationOutline of Presentation

�� Physics Review Physics Review -- RadiationRadiation

�� Glazing Performance IndicesGlazing Performance Indices

�� Glazing OptionsGlazing Options�� Glazing OptionsGlazing Options

�� Implications of Glazing SelectionImplications of Glazing Selection

�� Energy RatingEnergy Rating

Physics Review: RadiationPhysics Review: Radiation

UV��VIBGYOR�� infra-red

Radiation passing through glazingRadiation passing through glazing

OUT Glazing #1 Glazing #2 I�

#1 #2 #3 #4


#1 #2 #3 #4

Radiation passing through glazingRadiation passing through glazing


#1 #2 #3 #4

Glass CharacteristicsGlass Characteristics

ε2 ε3

ρρρρ1 αααα1

ττττv

Glazing System CharacteristicsGlazing System Characteristics


U-factor = rate of heat loss per unit area per unit δT

W/m2-ºC or BTU/hr-ft2-ºF

A

B

Visible Transmittance (VT or τv) =

similar to SHGC, but in visible spectrum)

Solar Heat Gain Coefficient (SHGC) =

fraction of incident solar

that arrives at the interior

(= B/A in solar spectrum)

Glazing OptionsGlazing Options

�� reflective coatingsreflective coatings

�� lowlow--emissivity coatingsemissivity coatings

�� spectrally selective glassspectrally selective glass

�� heatheat--absorbing glassabsorbing glass�� heatheat--absorbing glassabsorbing glass

�� multiple glazingsmultiple glazings

�� gas fillsgas fills

�� heatheat--treated glasstreated glass

�� lowlow--conductivity spacersconductivity spacers

Reflective coatingsReflective coatings


#1 #2 #3 #4

(increase reflectivity of surface)

Reflective GlassReflective Glass

�� metal or metalmetal or metal--oxide oxide

�� silver, copper, gold, earthsilver, copper, gold, earth

�� high internal gainshigh internal gains

�� large cooling loadlarge cooling load

�� lower solar gainslower solar gains

�� increased comfortincreased comfort�� increased comfortincreased comfort

�� lower visible transmittancelower visible transmittance

�� dramatic façadedramatic façade

�� coating #1 = mirrorcoating #1 = mirror

�� coating #2 = tintcoating #2 = tint

�� coating #3/#4 = mistakecoating #3/#4 = mistake

Tinted GlassTinted Glass

�� colouring agents colouring agents addedadded

�� absorbs energyabsorbs energy

�� bronze, grey, green, bronze, grey, green, blueblueblueblue

�� warmer glasswarmer glass

�� breakage a concernbreakage a concern

�� edge cuts are keyedge cuts are key

�� lower visible lower visible transmittancetransmittance


#1 #2 #3 #4

LowLow--emissivity Coatingsemissivity Coatings

(Emissivity of glazing)

(Reflectivity of glazing)

LowLow--emissivity coatingsemissivity coatings


#1 #2 #3 #4

(Infrared Emissivity

of glazing)

Pyrolitic coatingsPyrolitic coatings

� metallic oxides applied during the float

� commonly called “hard” coats

� AFG Comfort E2™ (ε = 0.20) and Stopsol™

� Pilkington Energy Advantage (ε = 0.16)

� PPG Sungate 500 (ε = 0.21)� PPG Sungate 500 (ε = 0.21)

� more durable during assembly and storage

� can be heat-treated and laminated

� no need for edge deletion

� can be used monolithically (not recommended)

� reflective coatings can be on #1 surface — not recommended

Sputter coatingsSputter coatings

� bombardment of metal or metal-oxide atoms

� aka vapour deposition, or “soft” coat

� specific metal used determines performance

� AFG Comfort Ti™ (ε = 0.03 - 0.04)

� PPG Solarban 60 (ε = 0.035)

� PPG Sungate 100 (ε = 0.09)

� Cardinal Lo-e2 (ε = 0.04) or Lo-e3 (ε = 0.05)

� less durable than pyrolitic coatings

� typically lower U-factor, lower transmittance

� can be applied to any glass substrate

� some now becoming post-temperable

no low-e detected

low-e on other side of near glass

low-e on one side of far glass

all lit = low-e on contact surface

The Envelope, Please: Transmission LossesThe Envelope, Please: Transmission Losses

• U-factor is measured in W/m2-°C, or in BTU/hr-ft2°F

• R is reciprocal of U, so it’s m2-°C/W, or hr-ft2°F/BTU

• Determined by hot-box measurement (SCC accredited lab)

or computer model (FRAME/VISIO�, THERM/WI�DOW)

• Typical values:

3½” glass-fibre batt R12 (RSI 2.1) Double-glazing, clear U2.81

RRRRRSI

3½” glass-fibre batt R12 (RSI 2.1) Double-glazing, clear U2.81

Nom 2x4 stud wall R7 (RSI 1.2) Double, hard low-e on #2 U1.79

Above with 1” XPS R12.5 (RSI 2.2) Double, hard low-e on #3 U1.79

5½” glass-fibre batt R19 (RSI 3.4) Triple, hard low-e on 2/5 U1.07

Nom 2x6 stud wall R13 (RSI 2.3) Double, soft low-e on #2 U1.74

Above with 1” XPS R18.5 (RSI 3.3) Above in vinyl frame U1.87

The Envelope, Please: Solar GainsThe Envelope, Please: Solar Gains

• SHGC determined by direct measurement (�STF), or by

computer model (VISIO� in Canada, WI�DOW in the US)

• number of glazing layers

• presence of tints or coatings

• type of coating (pyrolitic or vapour-deposition)

• surface on which coating is applied (#2 or #3)

• shading (intentional, self-shading, adjacent buildings)• shading (intentional, self-shading, adjacent buildings)

• amount of glazed area and orientation

Typical values:

Single glazing 0.86 Double, hard low-e on #2 0.65

Double glazing 0.76 Double, hard low-e on #3 0.71

Triple glazing 0.69 Double, soft low-e on #2 0.42

Double reflective 0.17 Triple, soft low-e on #2 & #5 0.35

LowLow--emissivity Coatings emissivity Coatings –– triplestriples

OUT Glazing Glazing Glazing I�

#1 #2 #3

#1 #2 #3 #4 #5 #6

LowLow--emissivity Coatings emissivity Coatings –– quadsquads

OUT Glazing Glazing Glazing Glazing I�

#1 #2 #3 #4

#1 #2 #3 #4 #5 #6 #7 #8

Gas FillsGas Fills

� most common gas fill: air

� also argon, krypton, SF6

� several fill methods: timer, sniffer, batch

� lower U-factor (~5% clr; ~10% low-e)

� no effect on SHGC or visible

� problem: long-term diffusion (argon)

� problem: glass deflection

� problem: invisible

Warmer Glass = Thermal ComfortWarmer Glass = Thermal Comfort

� reduced condensation potential

� induced draft

� radiant loss� radiant loss

� asymmetric radiant loss

� �� discomfort

� So what ?

The Energy RatingThe Energy Rating

� Defined in CSA A440.2, revised in 2004

� ER = [57.76 * SHGC] - [21.9 * U] - [0.54 * L75 /Aw] + 40

= [solar gains] – [transmission losses] – [leakage losses]

Typical values (vinyl casement, insulating spacer, A3 rating):

SHGC U old ER new ERSHGC U old ER new ER

Clear double-glazed 0.55 2.44 -15 +17

Pyrolitic low-e/argon 0.52 1.73 -1.8 +30.7

Sputter low-e/argon 0.47 1.58 -2.1 +31.1

Low-e2/argon 0.30 1.52 -13.1 +23

Typical R28 wall 0.001 0.20 -4.3 +35

Energy StarEnergy StarTMTM

Energy StarEnergy StarTMTM windows windows

� Zone A (HDD < 3500): U < 2.0 (0.35) OR

ER > (17 sash, 27 no sash)

� Zone B (HDD between 3500 and 5500): U < 1.80 (0.32) OR ER > (21 sash, 31 no sash)

Zone C (HDD between 5500 and 8000): U < 1.60 (0.28) OR � Zone C (HDD between 5500 and 8000): U < 1.60 (0.28) OR ER > (25 sash, 35 no sash)

� For a list of rated windows, go to

http://oee.nrcan.gc.ca/energystar/ ORhttp://www.bchydro.com

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Glass, Glazing and Glass, Glazing and Window Energy Performance

AIBC Module V “Skin Problems”AIBC Module V “Skin Problems”April 26, 2007April 26, 2007

glass, glazing and window energy · pdf fileglass, glazing and window energy performance by...

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