Energy Efficient Glazing Design John Ridealgh Off-Line Coatings Technology Group Pilkington European Technology Centre 2 John Ridealgh 30th November 2009
Talk Outline Pilkington Group Limited & NSG Group Float Glass Manufacture Manufacture of Large Area Coatings Design Drivers Thermal Design of Energy Conserving Glazing 3 John Ridealgh 30th November 2009
NSG Group Pilkington a member of NSG Group from June 2006 Equal largest flat glass producer Main business areas; Building Products, Automotive Products, Speciality Glass Sales c. 5.7 billion 31,500 employees worldwide Manufacturing operations in 29 countries Sales in 130+ countries Annual R&D spend c. 81 million 4 John Ridealgh 30th November 2009
Float Glass Manufacture - Overview Cooling lehr Continuos ribbon of glass Cross cutters Large plate liftoff devices Small plate lift-off devices Float bath Melting furnace Raw material feed 5 John Ridealgh 30th November 2009
Large Area Coating Techniques for Architectural Glass Chemical Vapour Deposition Magnetron Sputtering Performed on the float line. Performed in vacuum plant. Chemical Vapour Deposition Beams are inserted into the tin bath atmosphere above the glass, or in the lehr gap. Deposition temperature is above 600 C uses process heat. Non-metallic materials, mostly oxides Hard, well adhered, crystalline High deposition rate May be directly fed on conveyors from the float line or in a different factory. Room temperature deposition requiring electrical power. Metals, Oxides, Nitrides Very good thickness control Very good stoichiometry control Very good composition 6 John Ridealgh 30th November 2009 control
CVD Coating Beam Precursor gases Up-Stream Exhaust Down-Stream Exhaust Glass Outside Atmosphere Glass Ribbon Flow Chemical Vapour Deposition (CVD) Coater Cross-section Diagram K-glass Metal organic pre-cursors + Oxidant + F Dopant F:SnO 2 + Waste Products 7 John Ridealgh 30th November 2009
CVD Low Emissivity Coatings Generally based on SnO 2 :F (Transparent conductive oxide) K-Glass / Energy Advantage 8 John Ridealgh 30th November 2009
The Sputtering Process - + Process Gas Ar + e - Pumps 9 John Ridealgh 30th November 2009
Sputter coating manufacture schematic Power Supply Process Gases ~ Process Gases Pump Isolation Valve Vacuum Atoms of material ejected by the bombardment of positive ions Plasma e e Coating Electrode Ar e Ar e Ar Room temperature Target Material Pump Load Lock More Chambers Transport Rollers Semi-continuous Process Gas Isolation Pump More Chambers 10 John Ridealgh 30th November 2009
Coating manufacturing production plant 11 John Ridealgh 30th November 2009
Energy Efficient Coating Design
Design Drivers Environmental 40-50% European Energy Usage is associated with Buildings This is mainly heating, lighting and cooling. The EU Energy Commissioner has prioritised energy efficiency of buildings Target 20% reduction in energy consumption by 2020 (c.f. 2005). For 2010 all new build dwellings in the UK must have a 25% drop in CO 2 emission w.r.t. 2006 new build. Full energy saving potential of fitting low-e coatings in all new and replacement glazing is 27% by 2020 Expect doubling of air-conditioning in buildings by 2020 1ºC cooling uses double energy of 1 C heating 16-18 million tonnes of CO2 could be saved each year by installation of solar control glazing in existing and new business premises 13 John Ridealgh 30th November 2009
Design Drivers Legal Legislation is in place to improve energy efficiency of buildings UK - Building Regulations Part L Approved Documents TER (Target carbon dioxide Emissions Rating) calculating emissions for whole house all new builds Longstop U-value 2.2 Wm -2 k -1 (whole window), 1.2 Wm -2 k -1 (centre-of-pane) new build and replacement WER Band E (D for extensions) replacement, (2010 C) Mainland Europe U-value 1.1 Wm -2 k -1 (centre-of-pane) New standards that may become law Passiv Haus U-value <0.8, TSHT >0.5 14 John Ridealgh 30th November 2009
Design Drivers - Aesthetic 15 John Ridealgh 30th November 2009
Insulation U-value One of the most important measures of glazing performance is U-value. U-value is the rate of heat conductance per m 2 of window area, per C temperature difference across the glazing thickness. The units are Wm -2 K -1. A low U-value means a window is more insulating. Construction Element U-Value Wm -2 K -1 Outer Wall 0.35-0.7 Ground Floor 0.25-0.7 Insulated Roof 0.25-0.35 Solid Timber External Door 2.2-3.3 Single Glazed Window UPVC 5 * Source: The Building Regulations 2000 Approved Document L1A (2006 Addition) & Calcs * 16 John Ridealgh 30th November 2009
Low-e vs Solar Control Low-e Solar Control 17 John Ridealgh 30th November 2009
Heat flow diagram for low-e DGU Radiation Convection Conduction 18 John Ridealgh 30th November 2009
Solar & blackbody (293 K) curves 19 John Ridealgh 30th November 2009
Transmittance spectrum for 6mm float glass 20 John Ridealgh 30th November 2009
What do we need for low-e? Kirchhoff identity: ε = α ρ + τ + α = 1 and τ = 0 ε = 1 ρ Need high IR reflectance for low emissivity. 21 John Ridealgh 30th November 2009
Ideal low-e window cold climates 22 John Ridealgh 30th November 2009
Ideal solar control window warm climates 23 John Ridealgh 30th November 2009
What do we need for low-e materials? Need high IR reflectance for low emissivity. Reflectance and conductivity both depend on the number of free charge carriers and their mobility. The most reflective metals are the most conductive, so we can use conductivity to select low-e materials. Conductivity σ = Ν e.e.μ e where N e = Number of free charge carriers (fixed for dense Ag) μ e = Mobility of charge carriers (varies with structure) e = charge on electron 24 John Ridealgh 30th November 2009
Electrical Properties of Metals Bulk Electrical Metal Conductivity x10 7 (Ω.m) -1 Silver 6.8 Copper 6.5 Gold 4.9 Aluminium 4.0 Brass 1.6 Iron 1.1 Platinum 1.0 Bronze 0.7 Carbon Steel 0.4 Stainless Steel 0.2 Silicon 0.5-0.001 * * ITO 0.05 F:SnO 2 0.02 Tables of Physical and Chemical Constants, Kaye & Laby, Longman Scientific & Technical, 1986 * Measured thin film values 25 John Ridealgh 30th November 2009
Which Metal - Spectral Absorption Absorbance of Glass/10nm Metal 1 0.9 0.8 0.7 Absorbance 0.6 0.5 0.4 Cu Au Al Ag 0.3 0.2 0.1 0 360 410 460 510 560 610 660 710 Wavelength nm 26 John Ridealgh 30th November 2009
Optical effect of silver thickness Visible Visible 1.0 1.0 R e f le c ta n c e 0.8 0.6 0.4 0.2 Thinner coatings Silver Glass T ran sm ittan ce 0.8 0.6 0.4 0.2 Thinner coatings Silver Glass 0.0 0.0 0 500 1000 1500 2000 2500 3000 0 500 1000 1500 2000 2500 3000 Wavelength, nm Wavelength, nm 27 John Ridealgh 30th November 2009
A typical low-e stack TiO 2 2nm Anti-scratch SnO 2 40 nm ITO 3 nm Ag 10 nm ZnO 5nm AR layers Barrier layer Low-E material Growth layer TiO 2 20nm Glass 28 John Ridealgh 30th November 2009
Typical Stacks Low-e SnO x 40 nm ITO 3 nm Ag 12 nm ZnO 5nm TiO 2 20nm Glass Solar Control SnO x 30 nm ITO 3 nm Ag 9 nm SnO x 90 nm ITO 3 nm Ag 9 nm ZnO 5 nm TiO 2 20nm Glass 29 John Ridealgh 30th November 2009
Typical CVD FTO Stack F:SnO 2 330 nm Conductive FTO Low-e layer SiCO 60 nm Graded Index Colour Suppression Layer Glass 30 John Ridealgh 30th November 2009
Colour suppression for thick TCO 0.2 0.16 0.12 330 nm SnOF a* = -20.6 b* = +5.3 0.08 0.04 Very Green Reflection Colour 0 400 450 500 550 600 650 700 0.16 0.12 0.08 0.04 Neutral Reflection Colour 330 nm SnOF + 60 nm SiCO Combined 0 400 450 500 550 600 650 700 a* = -1.2 b* = -1.0 31 John Ridealgh 30th November 2009
Reflection spectra of monolithic 4 mm coated glass 32 John Ridealgh 30th November 2009
DGU Transmittance 33 John Ridealgh 30th November 2009
Thermal & Optical Properties of DGUs U-values of various glazing configurations. DGU (Double Glazing Unit) construction 4mm glass/16 mm cavity with 90% Ar fill /4 mm glass. Calculations to EN410/673 Glazing Warm pane normal emissivity U-value Wm -2 K T vis % TSHT % Selectivity Single Glazed 4 mm Glass 0.89 5.8 90 85 1.1 Uncoated 4 mm Glass DGU 0.89 2.6 81 75 1.1 Pyrolytic low-e DGU 0.15 1.5 75 72 1 Single Silver low-e DGU 0.03 1.1 80 63 1.3 Solar Control Double Silver DGU 0.02 1.1 68 36 1.9 34 John Ridealgh 30th November 2009
Window Energy Ratings Offer an easy method of comparing window energy performance. Takes into account more than U-value U-value TSHT Air Leakage Frame design Can be tailored to climate zone Different countries have different calculations but same scale 35 John Ridealgh 30th November 2009
Window Energy Rating UK has implemented WER into building regulations. USA and Australia already have established systems, with separate zones. 36 John Ridealgh 30th November 2009
Windows Energy Ratings UK Results For the UK climate, K-glass is as energy efficient as Ag based coatings for low-e applications. This is because it has a higher passive solar gain (TSHT/g-value). In these examples, Window 1 has a frame U value of 1.8, the frame factor is 20% and the heat loss rate due to air leakage is 0.03 W/m2/K. Window 2 has a frame U value of 1.9, a frame factor of 25% and air leakage 0.03. 37 John Ridealgh 30th November 2009
U-value (EN 673) How good can it get? Optitherm S3 = emissivity : 0.03 16mm air 16mm Ar 2* 12mm Ar 2* 12mm Ar 2* 10mm Kr 1,4 W/(m 2 K) 1,1 W/(m 2 K) 1,0 W/(m 2 K) 0,7 W/(m 2 K) 0,5 W/(m 2 K) 38 John Ridealgh 30th November 2009
U-value Revisited Construction Element U-Value Wm -2 K -1 Outer Wall 0.35-0.7 Ground Floor 0.25-0.7 Insulated Roof 0.25-0.35 Solid Timber External Door 2.2-3.3 Single Glazed Window UPVC 5 * Double Glazed Ag Low-e Window 1.1 * Triple Glazed Ag Low-e Window 1.0-0.5 * Source: The Building Regulations 2000 Approved Document L1A (2006 Addition) & Calcs * 39 John Ridealgh 30th November 2009
Now for something a little different Vacuum glazing NSG Spacia in production in Japan for some years. Very thin profile ~6 mm total Separator pillars 0.5 mm diameter, 20 mm spacing Glass solder seals 10 year lifetime guarantee U-value 1.3-1.5 Wm -2 K -1 3 mm Glass 0.2 mm Vacuum Space 40 John Ridealgh 30th November 2009
Pilkington energikare Legacy 41 John Ridealgh 30th November 2009
Spacia Vacuum Glazing 42 John Ridealgh 30th November 2009
Hybrid vacuum glazing and IGU U-value 0.7 0.9 Wm -2 K -1 Total thickness 18-21 mm (about half that of triple glazing) 43 John Ridealgh 30th November 2009
Summary We ve followed energy efficient glazing through from glass manufacture to coating design and manufacture. The insulation efficiency of glazing can be dramatically improved by the addition of coatings. They can reach a similar level to other building components or beyond. Low-e DGUs transmit as much light as uncoated glass DGUs, but are twice as insulating Solar control selectivity is near theoretical maximum. Must balance emissivity against passive solar heating to obtain the optimum performance for a given climatic zone. Energy efficient glazing can play a very positive role in reducing energy loss from buildings whilst allowing innovative aesthetic designs. 44 John Ridealgh 30th November 2009