energy efficient glazing design - institute of physics john ridealgh 30th november 2009 •...

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Energy Efficient Energy Efficient Glazing DesignGlazing Design

John Ridealgh

Off-Line Coatings Technology Group

Pilkington European Technology Centre

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• Pilkington Group Limited & NSG Group• Float Glass Manufacture• Manufacture of Large Area Coatings• Design Drivers• Thermal Design of Energy Conserving

Glazing

Talk Outline

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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

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Melting furnace

Float bath

Cooling lehr

Continuos ribbon of glass

Cross cutters

Large plate lift- off devices

Small plate lift-off devices

Raw material feed

Float Glass Manufacture - Overview

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Large Area Coating Techniques for Architectural Glass

Chemical Vapour Deposition

• Performed on the float line.

• 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

Magnetron Sputtering

• Performed in vacuum plant.

• 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

control

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GlassGlassGlass Ribbon FlowGlass Ribbon Flow

UpUp--Stream Stream ExhaustExhaust

DownDown--Stream Stream ExhaustExhaust

PrecursorPrecursor gasesgases

Outside Outside AtmosphereAtmosphere

Chemical Vapour Deposition (CVD) Coater Cross-section Diagram

CVD Coating Beam

K-glass

• Metal organic pre-cursors + Oxidant + F Dopant F:SnO2 + Waste Products

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• Generally based on SnO2 :F (Transparent conductive oxide)– K-Glass™ / Energy Advantage™

CVD Low Emissivity Coatings

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The Sputtering Process

+-ArAr+ e-

PumpsProcess Gas

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Sputter coating manufacture – schematic

Target Material

Coating Electrode

~

Semi-continuous Process

Room temperatureVacuum

Transport Rollers

More Chambers

Power Supply

Load Lock

Plasma e ee

eAr

ArAr

Atoms of material ejected by the bombardment of positive ions

Pump Pump

Gas Isolation Pump

Process Gases

Process Gases

Isolation Valve

More Chambers

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Coating manufacturing – production plant

Energy Efficient Coating Design

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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 CO2

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

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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-2k-1 (whole window), 1.2 Wm-2k-1 (centre-of-pane) – new build and replacement

• WER Band E (D for extensions) – replacement, (2010 C)– Mainland Europe – U-value 1.1 Wm-2k-1 (centre-of-pane)

• New standards that may become law– Passiv Haus – U-value <0.8, TSHT >0.5

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Design Drivers - Aesthetic

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Insulation – U-value

• One of the most important measures of glazing performance is U-value.• U-value is the rate of heat conductance per m2 of window area, per °C temperature

difference across the glazing thickness. The units are Wm-2K-1.• A low U-value means a window is more insulating.

Construction Element U-Value Wm-2K-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*

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Low-e vs Solar Control

Low-e Solar Control

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Heat flow diagram for low-E DGU

Conduction

ConvectionRadiation

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Solar & blackbody (293 K) curves

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Transmittance spectrum for 6mm float glass

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What do we need for low-E?

Kirchhoff identity: ε

= αρ

+ τ

+ α

= 1 and τ

= 0

ε

= 1 –

ρ

Need high IR reflectance for low emissivity.

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“Ideal” low-e window – cold climates

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Ideal solar control window – warm climates

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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 = Νe .e.μe where

– Ne = Number of free charge carriers (fixed for dense Ag)– μe = Mobility of charge carriers (varies with structure)– e = charge on electron

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Electrical Properties of Metals

MetalBulk Electrical Conductivity x107 (Ω.m)-1

Silver 6.8Copper 6.5

Gold 4.9Aluminium 4.0

Brass 1.6Iron 1.1

Platinum 1.0Bronze 0.7

Carbon Steel 0.4Stainless Steel 0.2

Silicon 0.5 - 0.001

ITO 0.05F:SnO2 0.02

Tables of Physical and Chemical Constants, Kaye & Laby, Longman Scientific & Technical, 1986Measured thin film values

*

*

*

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Which Metal - Spectral AbsorptionAbsorbance of Glass/10nm Metal

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

360 410 460 510 560 610 660 710

Wavelength nm

Abs

orba

nce Cu

AuAlAg

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Optical effect of silver thickness

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500 3000

Wavelength, nm

Ref

lect

ance

Thinner coatings

GlassSilver

Visible

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500 3000

Wavelength, nm

Ref

lect

ance

Thinner coatings

GlassSilver

GlassSilver

VisibleVisible

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500 3000

Wavelength, nm

Tran

smitt

ance

Thinner coatings

GlassSilver

Visible

0.0

0.2

0.4

0.6

0.8

1.0

0 500 1000 1500 2000 2500 3000

Wavelength, nm

Tran

smitt

ance

Thinner coatings

GlassSilver

GlassSilver

VisibleVisible

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A typical low-E stack• Anti-scratch

• AR layers• Barrier layer• Low-E material• Growth layer

Glass

TiO2 20nm

ZnO 5nm

Ag 10 nm

ITO 3 nm

SnO2 40 nm

TiO2 2nm

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Typical Stacks

Glass

TiO2 20nmZnO 5nmAg 12 nmITO 3 nm

SnOx 40 nmITO 3 nm

Glass

ZnO 5 nmAg 9 nm

SnOx 90 nm

Ag 9 nmITO 3 nm

SnOx 30 nm

TiO2 20nm

Low-e

Solar Control

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Typical CVD FTO Stack

Glass

SiCO 60 nm

F:SnO2 330 nm •Conductive FTO Low-e layer

•Graded Index Colour Suppression Layer

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Colour suppression for thick TCO

0

0.04

0.08

0.12

0.16

0.2

400 450 500 550 600 650 700

0

0.04

0.08

0.12

0.16

400 450 500 550 600 650 700

330 nm SnOF

Combined

a* = -20.6b* = +5.3

a* = -1.2b* = -1.0

330 nm SnOF +

60 nm SiCO

Very Green Reflection Colour

Neutral Reflection Colour

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Reflection spectra of monolithic 4 mm coated glass

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DGU Transmittance

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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-2K

Tvis %

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

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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

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Window Energy Rating

• UK has implemented WER into building regulations.• USA and Australia already have established systems, with

separate zones.

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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 leakageis 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.

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U-value (EN 673) – How good can it get?

1,4 W/(m2K) 1,1 W/(m2K) 1,0 W/(m2K) 0,7 W/(m2K) 0,5 W/(m2K)

16mm air 16mm Ar 2* 12mm Ar 2* 12mm Ar 2* 10mm Kr

Optitherm S3 = emissivity : 0.03

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U-value Revisited

Construction Element U-Value Wm-2K-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 UPVC5*

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*

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Now for something a little different…

• Vacuum glazing – NSG Spacia in production in Japan for some years.

3 mm Glass

0.2 mm Vacuum Space

•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-2K-1

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Pilkington energiKare™ Legacy

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Spacia Vacuum Glazing

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Hybrid vacuum glazing and IGU

• U-value 0.7 – 0.9 Wm-2K-1

• Total thickness 18-21 mm (about half that of triple glazing)

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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.