Catalogue & Reference Guide | 6th Edition QUICK REFERENCE   Symbols | Navigation | Performance data  
GLASS PROCESSING SELECTION PERFORMANCE DESIGN GLAZING COMPLIANCE REFERENCE

R ValueR Value (Total Thermal Resistance)

The R Value is the value of thermal resistance of a building element which is the sum of the surface
resistances on each side plus each component of a building element. It is the inverse of the U Value R=1/U and is expressed as m2 °C/W.

WINDOW 5.2

Window 5.2 is a software modeling program used to determine the thermal and optical properties of glass types and windows. It was developed by Lawrence Berkeley National Laboratory (LBNL) and contains an international glass data base.

Window 5.2 supersedes the earlier Window 4.1 version which was used to calculate performance data in the 5th Edition Catalogue and Reference Guide.

As a result some performance data may vary from that listed in the 5th Edition.

NFRC 100-2001

The National Fenestration Rating Council (NFRC) sets out the environmental conditions and procedures used to determine the performance characteristics of glass.

Environmental conditions include wind speed, internal and external temperatures, solar radiation levels and heat transfer coefficients.

The following are the standard environmental conditions.
It is possible to calculate glass properties using other standard conditions or user defined conditions

W5.2 Environmental conditions

Note: The performance data listed in this publication was calculated from Window 5.2 using NFRC 100-2001 environmental conditions, where possible. In some situations the glass properties have been estimated based on similar data. Published data for some glass types may vary slightly due to the manufacturer’s spectral transmission data selected for calculation.

Other Performance Data Terminology

The following data is used in other glass publications such as those based on European Standard EN 410, and Window 5.2.

DET  Direct Energy Transmission (Tsol)
Percentage of solar radiation transmitted directly through the glass. DET + EA + ER = 100% of sun’s energy

Tuv Transmission of Ultraviolet Light
Tdw    Damage Weighted Transmission
Tdw-K   Damage Weighted Transmission NFRC
Tdw-ISO Damage Weighted Transmission ISO

EA Energy Absorption (Asol)
Percentage of solar radiation absorbed by the glass.

ER Energy Reflection (Rsol)
Percentage of solar radiation reflected by the glass.

SF Solar Factor (g)
Total energy transmitted through the glass.

SF = DET + part of EA radiated to the inside.
Same as SHGC.

swSC  Short Wave Shading Coefficient.
swSC = DET/87

lwSC  Long Wave Shading Coefficient.
lwSC = SC - swSC

RHG Relative Heat Gain.
RHG = 630(W/m2) x SC + 7.8 (°C) x U Value (summer)
Note: American Units: 1W/m2 = 0.317 BTU/(ft2.h)

RD65 Colour Rendering Index (Ra)

Ucog U Value centre of glass (cog)

U-factor – See U Value.

E – Emissivity of the surface 

CI – Condensation Index

Cog – Centre of glass

 

Sound Control

SOUND TRANSMISSION LOSSSound Transmission Loss

The average Sound Transmission Loss is useful for determining the effectiveness of glazed panels to isolate exterior noise (such as traffic) from a building. It is derived from the average of the measured transmission loss at eighteen 1/3 octave frequency bands between 100Hz and 5000Hz, or 16 bands from 125 to 4000Hz. The average STL is measured in decibels (dB), the higher the average STL figure, the more effective the glazing will be in reducing sound transmission.

SOUND TRANSMISSION LOSSSound Transmission Class

The Sound Transmission Class is useful for determining the noise reduction offered by internal building elements such as partitions and walls. It is a measure that relates the sound reduction performance against sounds which normally occur inside a building (such as voices, telephones, music etc). STC is a numerical class rating and cannot be compared with the STL. It is derived from a best fit curve comparison of a reference STC curve to the insulation curve. The higher the STC rating, the better the overall sound reduction.

 

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Symbols

Performance Data Symbols

For more detailed information click on Performance Data or go to Performance.

Visible Light Transmission
Visible Light Transmisson
Visible Light Reflectance
Visible Light Reflectance
Ultra-Violet Elimination
Ultra-Violet Elimination
Fading Reduction Coefficient
Fading Reduction Coefficient
Shading Coefficient
Shading Coefficient
Solar Heat Gain Coefficient
Solar Heat Gain Coefficient
R Value
R Value
U Value
U Value
Sound Transmission Loss
Sound Transmission Loss
Sound Transmission Class
Sound Transmission Class
Weighted Sound Reduction
Weighted Sound Reduction
Coolness Factor
Coolness Factor
Perceived Sound Reduction
Perceived Sound Reduction
Window Efficiency Rating System
Window Efficiency Rating System
   

 

Quick Reference Symbols

Look for these symbols when choosing your glass to help make your decision easier. If you are looking for particular properties in your glass selection make note of the associated icons below. Each glass type has a list of the applicable icons below it's description.

These icons should be used as a general guideline for your selection. You'll also find icons related to special manufacturing parameters including CIP Laminate, Screen Printing and Toughening.

Available Thickness
Available Thickness
Reflective Coating
Reflective Coating
Low E Coated
Low E Coated
Laminated Glass
Laminated Glass
Good Glare Control
Good Glare Control (rated VLT 70% or lower)
Good Fading Reduction
Good Fading Reduction (rated - FRC 0.5 or lower)
Good Solar Control
Good Solar Control (rated S/C 0.6
or lower)
Good Insulation
U Value
(rated - U Value 3.00 or lower)
Condensation Reducing
Condensation Reducing
Good Sounds Reduction
Good Sound Reduction (rated - PSR 40% or higher)
Fire Resistant
Fire Resistant
 
Can Be CIP Laminated
Can Be CIP Laminated
Can Be Screen Printed
Can Be Screen Printed
Can Be Toughened
Can Be Toughened
Can Have Metro Protect
Can Have Metro Protect

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Navigation

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The sixth edition of the Metro Glasstech online catalogue.

 

Product and Service Information

This online catalogue provides a complete guide to Metro GlassTech's product and service range. Every effort has been made to ensure the catalogue is as up to date and comprehensive as possible. If you need any further information, please don't hesitate to contact a Metro GlassTech representative.

Navigation

Finding your way around is easy, with clear headings on each page and a consistent layout in line with our previous catalogue. Each section has a different colour to make it clear where you are in the catalogue. For navigation, page numbers appear at the bottom of each page, along with forward and back buttons.

Reference

Each product has comprehensive relevant technical information, so we have developed a range of quick reference symbols that will assist you in selecting the most appropriate product for your application.

A full explanation for each performance data symbol can be viewed in Performance.

A glass dictionary is provided. This is a useful guide to terms and product names used in the glass industry and throughout this catalogue.

Information Boxes

INFO Information that is considered important is boxed out. Often this is information that is critical when specifying glass so it is advisable to read the info boxes carefully when you see them.

Performance Diagrams

Performance information on many glass products is shown in these performance diagrams. They are a quick way of evaluating the performance of similar glass products.

The diagrams depict a pane of glass with data relating to temperature and solar gain for both the inside and outside.

Refer to performance for comprehensive explanations of the icons used in the performance diagrams.

Example diagram

 

Product Photography

Colour ChartTo the right hand side of each performance diagram is a swatch showing a photographic sample of the glass.

These were photographed specifically for the catalogue to provide as accurate a comparison as possible. Reflective glass types have been shown with a slight reflection.

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Performance Data

Visible Light Transmission Visible Light Transmission
The percentage of visible light transmitted through the glass. VLT is measured in the 380-780nm wavelength range perpendicular to the surface. The higher the percentage the more daylight. Also known as Tv, Tvis, LT and VT.

Visible Light ReflectanceVisible Light Reflection
The percentage of visible light that is reflected by the glass surface, measured in the 380-780nm wavelength range perpendicular to the surface. The VLR can be given as the reflection from the external surface 1 or internal surface 2. The higher the percentage the more reflection. Also known as LR, VR and Rvis

Ultra-Violet EliminationUltraviolet Elimination
The percentage of ultraviolet radiation eliminated by the glass, measured over the 290-380 nm wavelength range. The higher the percentage the less UV is transmitted. This value is calculated from the percentage transmission of ultraviolet (Tuv). Therefore UV Elimination = 100 - Tuv

Fading Reduction CoefficientFading Reduction Coefficient
The ratio of fading reduction of a glass type when compared to the fading protection of 3mm clear float. The FRC of 3mm clear float is by definition 1.0 and represents the minimum fading protection offered by standard glazing. The lower the fading reduction coefficient, the better the fading protection offered.

Solar Heat Gain CoefficientSolar Heat Gain Coefficient
The measure of the total solar energy transmittance entering a building through the glazing as heat gain. It is the total heat transmission of direct solar transmission and that proportion of absorbed radiation that is re-radiated into the building from the action of heat absorbing glass. The lower the SHGC the better the glass restricts heat energy transmission. Also known as the Solar Factor (SF) or g.

Shading CoefficientShading Coefficient
The ratio of the total solar heat gain through a particular glass compared to the total solar heat gain through 3mm clear float glass. (86%) The shading coefficient of 3mm clear float is by definition 1.0 and represents a base glass performance. The lower the shading coefficient the less heat gain and thus more shading is provided by the glass. The shading coefficient is calculated as SC = SHGC / 0.86

Window Efficiency Rating SystemWindow Efficiency Rating System
The complete WERS rates the performance of windows including frames in various defined New Zealand climate zones. For this catalogue star ratings apply to centre of glass only (WERS cog) to compare glass types and a maximum rating of five stars indicates the best performance possible. Ratings in star and half star values are given, with five stars indicating the premium performance. Refer Section 12 (Page 105) for a full explanation of each star type.

U ValueU Value
The U Value is the measure of air to air heat transfer through glass due to the thermal conductance of the glazing and the difference between indoor and outdoor temperatures. It is expressed as W/m2K (Watts per m2 per 1° Kelvin) or W/ m2 °C. 1 Kelvin equals 1°C. The U value is a measure of the rate of heat gain or heat loss through the glazing due to environmental differences between outdoor and indoor air. It is measured at the centre of the glass (cog).The lower the U Value the lower the heat transfer, the better the insulation.

Coolness FactorCoolness Factor
The Coolness Factor (or luminous efficacy) is the visible light transmission divided by the shading coefficient.
CF = VLT / SC. It is a useful means of comparing different glass types in terms of the trade-off between light transmission and heat control in selecting glass. Glass types with a coolness factor of 1 transmit as much light as heat, those with a coolness factor lower than 1 transmit more heat than light and those with a coolness factor greater than 1 transmit more light than heat

R ValueR Value (Total Thermal Resistance)
The R Value is the value of thermal resistance of a building element which is the sum of the surface resistances on each side plus each component of a building element. It is the inverse of the U Value R=1/R and is expressed as m2 °C/W.

Sound Transmission LossSound Transmission Loss
The average Sound Transmission Loss is useful for determining the effectiveness of glazed panels to isolate exterior noise (e.g. traffic) from a building. It is derived from the average of the measured transmission loss at eighteen 1/3 octave frequency bands between 100Hz and 5000Hz, or 16 bands from 125 to 4000Hz. Average STL is measured in decibels (dB), the higher the average STL figure, the more effective glazing will be in reducing sound transmission.

Sound Transmission ClassSound Transmission Class
The Sound Transmission Class is useful for determining the noise reduction offered by internal building elements such as partitions and walls. It is a measure that relates the sound reduction performance against sounds which normally occur inside a building (such as voices, telephones, music etc). STC is a numerical class rating and cannot be compared with the STL. It is derived from a best fit curve comparison of a reference STC curve to the insulation curve. The higher the STC rating, the better the overall sound reduction.

Weighted Sound ReductionWeighted Sound Reduction Index
The Weighted Sound Reduction Index incorporates frequency modified correction for the human ear’s response. The RW is reported in dB and is a composite rating of sound reduction at frequencies from 100 - 5000Hz. Numerically, it is comparable to the STC values but the numbers are in dBA.

Perceived Sound ReductionPerceived Sound Reduction
The percentage by which the human ear detects a lessening in sound pressure or noise is known as the Perceived Sound Reduction. A 10dB reduction in sound pressure level is generally perceived as a halving of the original noise. Sound reduction values are ‘weighted’ and used to calculate the perceived sound reduction as a ratio relative to the RW for 3mm clear float. The dB difference in the RW value for a glass type when compared to 3mm float is calculated as a perceived sound reduction percentage. For other sound indices see Section 11.4.5 and 11.4.6

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