Replacement Windows – The Role of Low-E Coatings in Energy Efficiency
If your utility bills are high, it may be economically beneficial for you to replace your old windows with energy efficient windows. Several factors contribute to the energy efficiency of a window. Let’s take a closer look at the role of low emittance coatings. Learn more in this video.
A low-emittance (low-e) coating is a microscopically thin metallic or metallic oxide material applied in multiple layers to a window that is virtually invisible and helps to suppress radiant heat flow. A typical low-e coating is transparent to visible light and short-wave infrared radiation but reflective of long-wave infrared radiation.
In double-paned windows, heat radiates from a warm pane of glass to a cooler pain. If one glass surface is coated with a low-e material, and that surface is positioned to face the gap between the glass panes, a significant part of the radiant heat transfer will be blocked. This in turn lowers the total heat flow through the window. Different types of low-e coatings have been designed to allow for high, moderate or low solar gain.
High solar gain low-e glass is the best choice for buildings located in heating-dominated climate areas and is also ideal for passive solar design projects. Conversely, low solar gain low-e glass is the preferred choice for buildings located in cooling-dominated climate areas. High solar gain glass performs better in the winter, while low solar gain glass performs better in the summer. For homes located in climates where both heating and cooling are required, depending on the house design and operation, similar annual energy costs may be achieved with low-e coatings with high, moderate or low solar gains.
Some low solar gain low-e coatings have been developed which lower solar gains to an even higher level; however, this effect is achieved by reducing light transmittal, which gives the glass a slightly tinted appearance. Such coatings should only be used where cooling is important and where a tinted effect is desired.
