Seeing Clearly: Specifying Energy-Efficient Windows and Glass-Paneled Doors
- By Ellen Kollie
- August 1st, 2008
It may seem simple enough to say that you want to install energy-efficient windows and glass-paneled doors in your new construction or renovation project. And, with energy costs rising and the green movement gaining momentum, doesn’t everyone want to install high-quality products?
Alas, saying and doing are two different things, simply because there is so much to know to make an informed decision. Fear not! This article is designed to empower you with the knowledge necessary to confidently purchase the best products.
Learn the Lingo
An informed decision maker is able to use the language. Relax; we’re going for general knowledge, not fluency!
First up is framing
. Framing is the material that holds the glass in place. “It’s the structural support members; how you anchor the glass into the building,” said Josh Early, with Pittsburgh-based TRACO, which manufactures windows and doors. There are many types of frames, including curtainwall systems, as well as windows and doors.
Similarly, there are many types of framing materials. Aluminum is commonly used in higher education. It has long life, but poor energy efficiency in itself. Thermally broken aluminum frames are popular because they have a long life and greater energy efficiency than aluminum alone because they contain an insulator between the frame’s interior and exterior, thus conducting less energy.
Wood frames are known for their energy efficiency but are high maintenance. They’re commonly used in campus restoration projects. Aluminum-clad wood windows are just that, aluminum on top of wood for durability and efficiency.
Vinyl frames are energy efficient but don’t have aluminum’s life cycle. They’re not used much in campus projects. Two other framing materials are steel and Fiberglass.
The second term is glazing
. “People use this term interchangeably for a lot of different things,” said Early. “It really is the process of putting glass in a frame.”
Still, be prepared to hear people use the term glazing system
to refer to a product, like this: “A common glazing system is insulated glass where you have two panes of glass separated by air space and sealed in a frame.”
A third term is coating
, which is used in two ways. First, it refers to a product put on the glass. Reflective coatings used to be popular — they created a mirror-effect on the glass to block solar heat gain. Unfortunately, they also reduced the amount of natural daylight coming through the glass.
A common coating today is low-emissivity, also known as Low-E
, which improves energy efficiency. There are two types of Low-E coatings: hard (pyrolitic) and soft. “Because Low-E coatings, which are essentially invisible, don’t change a building’s appearance as much as reflective coatings do, reflective coatings have all but disappeared,” said Terry Zeimetz, AIA, CSI, CCPR, of Pella Windows and Doors Commercial Division, Pella, IA. Pella manufactures both windows and doors.
The second way coating
is used is to describe what aluminum frames are painted with to create architecturally pleasing colors.
A fourth term is tint
, which describes how a glass is colored, such as gray, bronze, or green. Similar to coatings, tints are designed to improve energy efficiency by blocking solar heat gain. Low-e coatings can be combined with tints. “It’s driven by thermal performance and how you try to fine tune the building’s envelope,” noted Zeimetz.