Insulating Glass
In order to reduce heat gain or loss through glass, two or more
lites may be sealed together to create an insulating glass (IG)
unit.
The majority of
insulating glass units consist of two lites of glass enclosing a
hermetically sealed air space. The lites are held apart by a spacer
around the entire perimeter. The spacer contains a
moisture-adsorbent material called desiccant that serves to keep the
enclosed air free of visible moisture. The entire perimeter of the
assembly is sealed.
The most commonly
used edge construction contains a metallic spacer of roll-formed
aluminum, stainless steel, coated steel or galvanized steel. It is
sealed with a single seal of polysulfide, polyurethane or hot-melt
butyl, or with a dual seal consisting of a primary seal of
polyisobutylene and a secondary seal of silicone, polysulfide or
polyurethane. The corners of the metallic spacer may be square-cut
and joined with a metal, plastic or nylon corner key, may be
miter-cut and brazed, welded or soldered, or may be bent. Recent
years have seen the introduction of warm edge technology products as
spacer materials. These products include extruded butyl materials,
foam rubber based materials, formed plastics and metal strip based
products, many with desiccant included as a component.
Improvements in edge
of insulating glass U-values as a result of warm-edge technologies
play a vital role in meeting overall window performance requirements
for state adopted residential fenestration codes.
Thermal performance
of insulating glass units is enhanced by using solar control
substrates and coated glass (low-emissivity or reflective), coated
polyester suspended films, insulating gases (such as argon, krypton
or xenon) and warm edge technology products. Initial heating and
cooling equipment costs and ongoing operating costs are reduced.
Insulating glass
units also offer benefits by reducing sound transmission. Laminated
glass constructions and sulfur hexafluoride (SF6) gas filling
further enhance the sound reduction characteristics of the
insulating glass unit.
Industry product
classification, performance requirements and testing procedures for
insulating glass units are defined in the following ASTM
International documents:
E 773 Standard
Test Method Accelerated Weathering of Sealed Insulating Glass
Units
E 774 Standard Specification for Sealed Insulating Glass Units
E 2188 Standard Test Method for Insulating Glass Unit
Performance
E 2189 Standard Test Method for Testing Resistance to
Fogging in Insulating Glass Units
E 2190 Standard Specification for Insulating Glass Unit
Performance and Evaluation
Most insulating glass
fabricators voluntarily participate in insulating glass
certification programs. The purpose of the certification programs is
to assure the user that the purchased product is a faithful replica
of one that has passed certain prescribed tests. Therefore,
participants in a certification program must complete the following
requirements: 1) submit specimens of their production product to
independent testing laboratories for the prescribed tests; and 2)
agree to periodic, unannounced inspections of their regular
production by an independent agency to ensure that actual production
employs the same materials and techniques as the tested specimen.
The Insulating
Division of the Glass Association of North America (GANA) and the
Insulating Glass Manufacturers Alliance (IGMA) promote the highest
standards in insulating glass unit production, testing,
certification and business ethics through their memberships. The
industry establishes voluntary quality standards and collects
statistical and other non-proprietary information related to field
performance of insulating glass for dissemination to manufacturers
and consumers.
Note: The GANA
Glazing Manual (Section II - Fabricated Architectural Glass
Products) should be consulted for additional detailed information on
insulating glass design considerations, material compatibility and
glazing guidelines prior to specifying and using insulating glass
constructions.
The above information is from the
GANA Glazing Manual, 2004 Edition - the most frequently
referenced resource in the architectural glass and glazing industry.
The Glazing Manual is an excellent addition to any technical
library.
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