Codes and standards
IGMA – Filling the information vacuum
VIG appears to have the potential to assist the glass and glazing industry toward more energy-efficient windows.
By Monica Dick
The Insulating Glass Manufacturers Alliance has recently released its technical bulletin TB-2600-15 Vacuum Insulating Glass which is an informational document giving an extensive overview on the subject of vacuum insulating glass (VIG). This is one of the documents that the IGMA Emerging Technologies and Innovations Committee worked on for over a year, in which we believe readers will find an compilation of some very interesting and educational information along with data relative to VIG.
There were many contributors and experts within the IGMA membership working on this effort. The finished product has technical information that will assist those in the glass industry, as well as designers, architects, specifiers, engineers and end users of VIG, to understand the product along with the technology and science that goes into this type of insulating glass unit.
Earlier this year, a brief introduction was presented to give an outline of a few topics that will be covered as VIG becomes a viable use of glass and glazing to our industry while we continue to provide energy efficient products, and advance the use of glass. We will go over a few of the basics regarding the VIG concept first and then explain some, but not all, of the topics in the technical bulletin.
The technical bulletin begins with a brief history of the concept. A patent was issued for VIG as early as 1913 with today’s versions similar to the original concept. The VIG unit normally consists of two pieces of glass with an evacuated space between each layer, which is then sealed to keep the vacuum in the space. This principle is to virtually eliminate conductive and convective heat transmission through the cavity.
The general goal of VIG is similar to that of the conventional insulating glass units we are familiar with in that it will improve the overall insulating properties between the exterior and interior environments, lowering the U-factor of the product. The benefits of VIG are that it significantly reduces the convection and conduction within the space between the glass lites due to the vacuum in the gas space, Also, VIG units may be very thin as compared to conventional IGU’s that have a much greater space between the lites. While standard IGU depends on the increased density and inert chemical composition of the gas fill to reduce heat transmission, VIG takes exactly the opposite approach by instead leaving very few gas molecules present which dramatically reduces energy transfer between the lites.
The bulletin goes on to explain some of the differences in the VIG when compared to the typical IGU. For example the space between the two lites of glass in a VIG is typically less than one millimeter, while in a typical IGU the separation is commonly six to 13 mm. The VIG will also have an array of pillars, spacers or stanchions that maintain the void between the lites so they cannot touch under the under the vacuum that is applied in the space between the lites. These spacers are carefully engineered and placed so that the glass stresses are managed properly due to the loading from the atmospheric pressure and vacuum in the space.
There are some interesting design concepts that also allow the coupling of VIG to conventional IGU to enhance the energy efficiency of the glazing system. These “hybrid VIGs” may require special framing and supporting systems, however, it is evident that the overall results will be significant to the end user in reducing energy use and being able to take advantage of daylighting and the use of windows.
At this time VIG appears to have the potential to assist the glass and glazing industry toward more energy-efficient windows. Readers of this article are encouraged to obtain the full publication from IGMA and explore the additional information presented in the document.
Bill Lingnell has over 46 years of experience in the technical field of glass and architectural products. He holds three Masters of Science degrees in engineering: civil, mechanical and engineering science. Lingnell is the technical consultant for the Insulating Glass Manufacturers Alliance.