Technology Insulating Glass
Low-E coatings attracting more attention

The use of ‘low emissivity’ glass, commonly referred to as low-E, is a critical component in energy
efficient windows.

The use of ‘low emissivity’ glass, commonly referred to as low-E, is a critical component in energy
efficient windows. All major glass companies and window manufacturers offer product options such as low-E, solar selective low-E, hard-coat (pyrolytic) and soft-coat (sputtered, MSVD), but what is the difference between them?

Low-E glass coatings work by reflecting or absorbing infra-red light (heat energy). The thickness of the low-E coating and the position of the lite in the insulated glass unit (#2 or #3 surface) dictate how the window will perform.

When installed on the #3 surface of an IG unit the low-E coating will primarily reflect heat from inside the room to help reduce the energy loss during the cold months, thereby reducing heating costs.

Pyrolytic low-E coatings are attracting more attention due to the strong focus on Energy Star and Green Building programs.

When installed on the #2 surface of an IG unit, the low-E coating will primarily reflect or absorb heat from the outside, thereby reducing solar gain and cooling costs during the warm months.

Pyrolytic vs. sputtered
There are two distinctly different processes used to deposit low-E coatings onto the glass surface. The pyrolytic process is done on-line during the glass manufacturing process by a chemical vapour deposition (CVD) process. The sputtered process is done off-line by a magnetron sputtering vacuum deposition (MSVD) process. Each process creates low-E coatings with different properties.

Pyrolytic low-E glass can offer several advantages over its sputtered counterpart. Since the coating is covalently bonded to the glass, pyrolytic low-E is extremely durable and can be handled, transported and stored just like clear glass.

Furthermore, pyrolytic low-E is suitable for monolithic use, making it a cost effective replacement for single-lite glazing. In addition, the passive solar properties of hard-coat low-E, as noted in the solar heat gain coefficient (SHGC) rating, allow enough solar energy to enter during the winter months to noticeably reduce heating costs.

Despite its merits, pyrolytic low-E is chiefly a niche product. The limited availability of pyrolytic coating technology and the belief of sputtered low-E as the ‘premium’ product have limited the growth, not only of pyrolytic low-E but of low-E coatings in general.

Although the energy savings and performance benefits of low emissivity coatings have been known for years, acceptance on a global scale remains limited, with low-E accounting for just 11 percent of worldwide flat glass consumption in 2003. Market penetration in regions outside North America and western Europe has been particularly slow. A glance at the worldwide low-E market reveals a sputter dominated marketplace, with sputtered low-E accounting for over 80 percent of all low-E consumption in 2003.

For years, MSVD coating technology and sputtered low-E have been the only widely available options. However, the inherent handling sensitivity and limited shelf-life of sputtered low-E render it ill-suited for transport and use in regions with developing infrastructures. Moreover, the dominant glazing in these regions is often a single lite, while sputtered low-E can only be used in a multiple lite IG unit assembly.

The higher solar heat gain coefficient of pyrolytic low-E coatings can result in significantly lower heating costs.

While the development of on-line pyrolytic coating technology represents one of the glass industry’s most significant advancements, the know-how required to successfully implement on-line coating has remained confined to a small number of players. However, that is beginning to change.

Coating trends
Recent trends show that pyrolytic low-E coatings are attracting more and more attention in both the commercial and residential glass coatings markets due to the strong focus on Energy Star and Green Building programs. This trend is largely due to research showing that low-E pyrolytic coatings, which achieve optimum year-round thermal efficiencies, can outperform many ‘high performance’ sputtered coatings in
heating dominated climates.

These low emissivity coatings reduce heat loss from the building, while at the same time allowing some passive solar energy to enter. The higher solar heat gain coefficient of pyrolytic low-E
coatings can result in significantly lower heating costs and provide a greener alternative, making pyrolytic low-E coatings ideal for the Canadian market. -end-

Article courtesy of Arkema Incorporated, a diversified chemicals manufacturer, based in Philadelphia, Pennsylvania. Technical data sourced from www.arkema-inc.com