BY MICKEY ROSS, PRESIDENT,
ROSS WINDOW CORP
New energy efficient windows are one of the key components of any environmentally responsible "green building." Window technology has made advances in recent years. Today’s windows are loaded with features that deliver many environmental, energy efficiency, and economic benefits to building owners and tenants.
Besides being a primary consideration in the construction of new buildings, "green" windows can also be used to replace windows in existing structures. Many existing buildings have single glazed, wood or metal frame windows, that don’t close or operate properly. These windows are terribly energy inefficient and uneconomic. They secretly allow fuel cost dollars to literally fly out the window.The good news is that building owners don’t have to tolerate this robbery. Replacement with new energy efficient "green" windows is a quick, convenient, and economic option. As we head from summer into fall and winter, now is the best time to replace existing windows and become part of the "green" revolution.
Energy is transferred from the heated building interior to the exterior during the winter and during the summer heat is transferred from the exterior to the air-conditioned interior. Minimizing this year round heat transfer is the objective of energy efficient "green" windows. There are several energy efficiency aspects to windows including the frame, insulated glass material, insulated glass spacers, and the installation.
"Green" windows improve energy efficiency by controlling the forms of heat transfer. Heat or thermal heat energy can be transferred through a material in three manners. Conduction is simply the process where heat is transferred through materials touching one another. Convection is where gases or liquids circulate to transfer thermal energy. The third process is radiation. Radiation transfers heat energy at a distance through high frequency waves such as visible light, ultraviolet or microwaves. The heat transfer accomplished by greenhouses and microwave ovens are examples of radiation.
The fundamental component of any "green" window is the aluminum "thermal break" frame. Virtually all commercial buildings and residential structures over 2 or 3 stories use aluminum windows for strength, durability, and code compliance. Unfortunately aluminum is a good conductor of heat and therefore may compromise the goals of energy efficiency. Early versions of aluminum windows do in fact conduct thermal energy very readily and are not very "green." New aluminum windows have thermal break frames, which greatly reduce the conduction problem. A thermal break is a non-metallic resin or plastic material installed in the metallic window frame that physically separates the interior part of the window from the exterior part. Hence, the pathway for heat energy to be transferred or conducted through the window frame is thermally broken. Non-thermal break windows continue to be sold (thankfully in smaller and smaller numbers each year) so it is important that when specifying new or replacement windows make sure to ask for aluminum thermal break windows.
Insulated glass units consist of two or more panes of glass separated along the edges by a spacer system and elsewhere by an airspace usually between _ and 1 inch. The unit is sealed along the perimeter to prevent the movement of air in or out of the space between the glasses. This sealed airspace acts as a great insulator and dramatically improves the thermal performance of the window. The greater the insulated glass unit overall thickness the greater the insulating effect and the greater the price of the window. An insulated glass unit thickness of about 7/8 inches appears to be the optimum from a cost/benefit standpoint for most applications.
More and more types of high-performance low emissitive glazing options are now available. Commonly known as low-E, this glass coating option improves energy efficiency by controlling the radiation aspect of thermal energy transfer. Low-E glass blocks the higher angle summer sun rays from passing through and heating a building’s interior, while in winter it allows the lower angle rays of the winter sun to pass through and provide supplemental heating to the building’s interior. Several versions are now available of varying effectiveness and at various price levels. Soft coats perform better than hard coat low-E’s but cost more. Low-E glass of any type is worth the money and even if the budget is limited consider using low-E glass on at least the southern and western exposures of the building.
The air space between the glass panes in an insulated glass unit is usually filled with desiccant dried air. Inert gases can be substituted for air in this sealed space as an energy efficiency option. Inert gases are much denser than air and therefore slow the heat transfer process by reducing the amount of convection that takes place. Argon is the most common form of gas used in this application. Others such as Krypton and Xenon are more expensive and only used in special large curtain or window wall applications.
An often-overlooked energy efficiency item with insulated glass systems is the type of separator or spacer used between the glass panes along the edges. Older technology used aluminum box sections, but these conducted heat readily between the glass and the spacer. They can create unnecessary thermal stresses on and premature failures of the hermetic seal. Another drawback to these spacers is that they are a common cause of interior glass condensation in extremely cold weather. State-of-the-art window designs use "warm-edge" spacers. These systems do not have direct metal to glass contact but separate the window glass from the spacer structure with some less heat conductive material like butyl sealant or plastics. Common warm-edge spacers are the PPG "Intercept" and "SwiggleSeal." Be sure to specify a warm-edge spacer in your new construction or replacement window plans.
During installation two key items should be stressed with your window installation contractor to guarantee a "green" window. The contractor must avoid at all cost creating any thermal "short-circuits" to the aluminum window thermal break system. New windows are secured in place by metal screws and anchoring devices that if installed wrong can bridge the frame’s thermal break and create an unwanted pathway for heat to transfer from the building interior to exterior or vice-versa. Another often-overlooked installation item is the installation of appropriate insulation material between the perimeter of the new window and the building opening.
New energy efficient windows are truly a tenant and owner appreciated upgrade to any commercial or residential structure. They add value to the property and reduce energy operating costs for years to come. If selected and installed properly, "green" windows provide ongoing year round energy savings that offset the extra upfront costs. Energy efficient windows for new construction or replacement purposes make good environmental and economic sense.