Glass technologies to improve sustainable performanceBob Schrock

Architectural ServicesPPG Architectural Coatings Mobile: 513-543-2555

E-Mail: bob.schrock@ppg.com

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UV3%

VISIBLE44%

INFRARED53%

SPECTRAL DISTRIBUTION OF SOLAR ENERGY

AT THE SURFACE OF THE EARTH

Short-Wave Solar Energy Spectrum

The Solar Energy Spectrum & Glass Performance Measures

Ideal Glass

Ideal Glass

Allow as much visible light as possible

Keep out Infrared Energy, especially Short Wavelength

How Low-e Coatings Impact Glass Performance

Coated Glass Terms

Visible Light Transmittance (VLT): A measure of how much light passes through a window. VLTs range from 0 (no light) to 1 (all light).

Solar Heat Gain Coefficient (SHGC): The fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits.

NOTE: Shading Coefficient is a similar measure to SHGC and not used interchangeably. SHGC is 86% of Shading Coefficient. Clarify which measure is being used.

U-Value: A rating given to a window based on how much heat loss it allows. U-values generally range from 0.2 (very little heat loss) to 1.2 (high heat loss).

Visible light, SHGC and U factors are optimized by low e coatings

How Low-e Coatings Impact Glass Performance

Types of Coated Glass

Non Low-e Glass: Tinted glass or reflective coating provide some degree of energy management

Passive Low-e: Mostly pyrolytic, hard coat coatings that have lower performing SHGC and therefore allow free heat in the winter

Solar Control Low-e: Mostly MSVD Magnetron Sputter Vacuum Deposition, soft coats. These are the highest performing low e coatings. They have low SHGC to keep solar energy out, have high visible light to let light in, and reflect heat back into the interior space.

Bill and Melinda Gates FoundationArchitect: NBBJ

How Low-e Coatings Impact Glass Performance

Performance Glazing

Reflective Coating:

Solar reflective coatings

Block direct solar heat transmission

Provides enhanced design aesthetics

Can be used with tints

May reduce visible light

SHGC down to .23 in clear

Reflective properties

Interior

Exterior

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Reflective Glass

Ideal Glass

Reflective MSVD

“Reflective Glass

Passive Low-e: Pyrolytic Coatings

Hard coat:. Coating is applied to molten glass and becomes integral with the glass. Very durable, can be uses as monolithic pane

Passive glass: Allows higher levels of solar energy through the glass to take advantage of winter warming. Provides some U factor to reduce heat loss through the glass

Range of performance:

Visible Light Transmittance (VLT) – 54%-74%

Winter Night U-Value – .33-.37

Solar Heat Gain Coefficient (SHGC) – .45-.66

Light to Solar Gain (LSG) – 1.09-1.25

Performance Glazing

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Passive Low-E Coatings

Pyrolytic Coatings

“Moderate” Glazing

Ideal Glass

“Passive Solar” Low-E Coatings

Solar Control Low-e: MSVD Coating Process

Also called“soft coat”, must be sealed in an IGU

Superior solar control, SHGC down to .27 in clear

Good U factor performance to reduce heat loss

High visible light with low reflectance is possible

Total thickness of low-e coating – 150 nanometers

Applied in layers. Double and Triple Silver Low e

Performance Glazing

150 nm

zinc stannate

silver

zinc stannate

titaniumzinc oxide

zinc oxide

silver

zinc stannate

titanium dioxide

titaniumzinc oxide

zinc oxide

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Double Layer

Solar Control Low e Glazing

Ideal Glass

“Solar Control” Low-E Coatings

Triple layer

U-Values

Improving U-Values

Reduces heat loss through the fenestration

Optimize gas cavity, ½” optimal size for air filled units

Using noble gas. Argon or Krypton improves16% and 27% respectively.

Apply low-e coatings to 2nd as well as 4th surface

Low thermal transmitting spacers, Warm Edge

Triple-glazing

U- Values

Improving U-Values

Triple Glazing

More energy efficient

Thermal insulation benefit

Acoustic performance

Higher cost

Framing considerations, glass thickness, weight etc.

Benefits of Low-e Glass

Benefits of energy efficient glass:

Low infrared heat gain

High visible natural light transmittance.

Less artificial lighting

Reduction of long wave heat gain/loss

Increased comfort/productivity

Results:

Overall reduction in energy usageLow-e, ½” airspace, ¼” clear VLT SHGC U-Value LSG

Pyrolytic 54% – 74%

0.45 – 0.66 0.33 – 0.37 1.09 – 1.25

Double-Silver MSVD(High VLT/Low Reflectance)

53% – 70%

0.28 – 0.39 0.29 – 0.29 1.76 – 1.98

Triple-Silver MSVD(High VLT/Low Reflectance)

61% - 64% 0.27 – 0.30 0.28 – 0.29 2.17 – 2.37

Other methods for Reducing Heat Gain

• Darker glass or tints

• Overhangs

• Exterior Shading Devices

• Interior shading devices

• Ceramic frit

• Tinted laminate

• Dynamic Glass

Many of these options also reduce visible light. Some still need low e coatings

Methods for Reducing Heat Gain

Dynamic Glass technology

Thermochromic materials for use in variable tinting windows can adapt to changing sunlight intensity to reduce heat load in buildings

Electrochromic Switchable technology using voltage to switch between is between a clear and transparent tinted state with no degradation in view,

Photochromic materials change their transparency in response to UV light intensity. Not commercially available

Gasochromic gas is introduced into the cavity Exposure to oxygen returns the window to its original transparent state.

Polymer Dispersed Liquid Crystal thin layer of liquid crystals is between two transparent electrical conductors. Also called Liquid Crystal Device.

Suspended Particle Device electrically controlled film utilizes a thin, liquid-like layer in which numerous microscopic particles are suspended

Methods for Reducing Heat Gain

Darkening glass activated by heat, Thermochromic

As the sun heats the glass the special coating darkens, then as the sun moves away the glass cools and returns to clear

Dynamic Glass

• Minimize SHGC

• Maximize daylighting

• Reduce glare, fading and noise

• Increase safety

• Still requires a low e coating

The middle glass does not have the heat activated coating

Electric current is applied to a special coating to control the level of tinting in stages from clear (60% VLT) down to 1%

It takes less than a 60 watt bulb to control 2,000 sq ft of glass

It can be automatically or manually controlled. Can be controlled in zones or individually.

The coating can perform as low e glass with SHGC around .41 for clear down to .09 for full tint. U factor needs to be considered.

Dynamic Glass

Darkening glass activated by electric current, Electrochromic

• Darkening glass activated by light, photochromic

As light (UV) hits the glass the special coating darkens,

like Transitions lenses in sunglasses

Dynamic Glass

Darkening glass, electric activated Suspended Particle Dispersion SPD

Electrically controlled film

Microscopic particles are suspended in thin, liquid-like layer

In unpowered state the particles are randomly oriented and partially block sunlight transmission and view.

When electric field to be applied to the dispersed particle film, the particles align and raise the transmittance

Polymer Dispersed Liquid Crystal and Liquid Crystal Device are similar technology.

Dynamic Glass

Many innovative solutions to managing energy and daylighting in commercial buildings