Glass, Glazing and Window Energy Performance by Alex McGowan, P.Eng. Levelton Consultants Limited Victoria, British Columbia, Canada AIBC Module V Skin Problems April 26, 2007
Outline of Presentation Physics Review - Radiation Glazing Performance Indices Glazing Options Implications of Glazing Selection Energy Rating
Physics Review: Radiation UV VIBGYOR infra-red
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Radiation passing through glazing OUT Glazing #1 Glazing #2 I #1 #2 #3 #4
Glass Characteristics OUT Glazing #1 Glazing #2 I #1 #2 #3 #4 ε 2 ε 3 ρ1 α 1 τ v
Glazing System Characteristics OUT Glazing #1 Glazing #2 I U-factor = rate of heat loss per unit area per unit δt W/m 2 -ºC or BTU/hr-ft 2 -ºF A Solar Heat Gain Coefficient (SHGC) = fraction of incident solar that arrives at the interior (= B/A in solar spectrum) B Visible Transmittance (VT or τ v ) = similar to SHGC, but in visible spectrum)
Glazing Options reflective coatings low-emissivity coatings spectrally selective glass heat-absorbing absorbing glass multiple glazings gas fills heat-treated treated glass low-conductivity spacers
Reflective coatings OUT Glazing #1 Glazing #2 I #1 #2 #3 #4 (increase reflectivity of surface)
Reflective Glass metal or metal-oxide silver, copper, gold, earth high internal gains large cooling load lower solar gains increased comfort lower visible transmittance dramatic façade coating #1 = mirror coating #2 = tint coating #3/#4 = mistake
Tinted Glass colouring agents added absorbs energy bronze, grey, green, blue warmer glass breakage a concern edge cuts are key lower visible transmittance
Low-emissivity Coatings OUT Glazing #1 Glazing #2 I #1 #2 #3 #4 (Emissivity of glazing) (Reflectivity of glazing)
Low-emissivity coatings OUT Glazing #1 Glazing #2 I #1 #2 #3 #4 (Infrared Emissivity of glazing)
Pyrolitic 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) 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 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-e 2 (ε = 0.04) or Lo-e 3 (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 Losses U-factor is measured in W/m 2 - C, or in BTU/hr-ft 2 F R is reciprocal of U, so it s m 2 - C/W, or hr-ft 2 F/BTU Determined by hot-box measurement RSI (SCC Raccredited lab) or computer model (FRAME/VISIO, THERM/WI DOW) Typical values: 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 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) 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
Low-emissivity Coatings triples OUT Glazing Glazing Glazing I #1 #2 #3 #1 #2 #3 #4 #5 #6
Low-emissivity Coatings triples OUT Glazing Glazing Glazing I #1 #2 #3 #1 #2 #3 #4 #5 #6
Low-emissivity Coatings triples OUT Glazing Glazing Glazing I #1 #2 #3 #1 #2 #3 #4 #5 #6
Low-emissivity Coatings quads OUT Glazing Glazing Glazing Glazing I #1 #2 #3 #4 #1 #2 #3 #4 #5 #6 #7 #8
Gas Fills most common gas fill: air also argon, krypton, SF 6 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 Comfort reduced condensation potential induced draft radiant loss asymmetric radiant loss discomfort So what?
The 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 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-e 2 /argon 0.30 1.52-13.1 +23 Typical R28 wall 0.001 0.20-4.3 +35
Energy Star TM
Energy Star TM 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 ER > (25 sash, 35 no sash) For a list of rated windows, go to http://oee.nrcan.gc.ca/energystar/ OR http://www.bchydro.com
Questions Comments Concerns Glass, Glazing and Window Energy Performance AIBC Module V Skin Problems April 26, 2007