A Clear View

April 1, 2009
Professionally installed window film is a simple way to block solar heat and reduce energy.

From around the corner to around the nation, schools and universities are looking to reduce their energy bills. Some are concerned about fuel costs and the impact on their operating budgets; others are motivated by the desire to reduce their carbon footprints and their impacts on the environment.

Professionally installed window film can play a key role in energy savings — some estimate that window film can produce energy savings up to 30 percent. Conducting an energy analysis enables education administrators to determine where window film can yield the most substantial results. Choosing the right kind of window film and the right professional to install it can make classrooms more comfortable and reduce air-conditioning usage.

The reason window film saves energy is that it blocks solar heat, keeping a room more uniformly cool. In classroom buildings, the effect that window film has on overall energy consumption and interior comfort levels can be significant.

Analyze energy use

Schools trying to determine the best areas for energy conservation can receive assistance from energy service companies, utilities companies and certified energy consultants, as well as solar, glazing and window film experts, certified through local building associations, and national groups such as the European Window Film Association and Glass and Glazing Federation.

Many of these experts use a modeling program. They conduct analyses on trouble areas, such as office spaces with uncontrollable hot spots, entry areas with large atrium windows, or other areas with large windows or glass doors.

When considering an energy audit, look for sophisticated programs that take into account:

  • Shape and size of a building or campus, including number of stories and occupants.

  • Orientation of the building.

  • Number of windows, type of glass and shade provided by awnings or trees.

  • Statistical weather data.

  • Building construction: materials used for walls, floors and roof.

  • Heating and cooling system, including power and efficiency.

  • Location of vents and thermostats, as well as the thermostat settings.

Comprehensive modeling programs that include these factors will quantify energy savings and comfort improvements more accurately throughout a building.

Several choices of window film are available. Facility managers should consider criteria such as safety, glare benefits or overall energy saving benefits before deciding which window films to buy.

How glass works

A comprehensive understanding of how glass works — and the process of heat transfer — can help schools and universities understand how window film works. There are three types of heat transfer: radiation, conduction and convection.

Solar energy (also called solar radiation) comes in through a window and is converted to heat when it strikes people or objects. If you block the transfer of solar energy, you keep it from turning into heat. Window film interrupts the transfer of energy by reflecting the majority of energy back outside the window (and absorbing the remainder).

Through an untreated window, solar energy can take one of three paths: it can be transmitted, absorbed or reflected.

Some radiation is transmitted through a window. The percentage of transmitted radiation is equal to UV light + visible light + near infrared rays. Absorption is the solar energy that is soaked up into the window, and some light is reflected back to its source.

Understanding these three principles of glass is critical, as is knowing which type of windows are in the building. Some window films work primarily by reflecting solar energy; others work primarily by absorbing solar rays. If the wrong film is applied to certain low-e windows, for example, it can be forced to absorb too much solar energy, causing it to crack.

Blocking light from entering a building also can be accomplished through interior window treatments and awnings. However, they mainly reduce glare, and are inefficient at blocking infrared and ultraviolet energy. Heat pockets, fading and other problems still exist. Window film offers a solution that reduces energy consumption and rejects UV radiation.

For many campuses, glare also is a concern. Films with lower visible light transmission (VLT) are better for glare control and privacy; higher VLTs offer more natural light. When selecting a film, administrators may want a consultant to walk them through these priorities so they can choose the film best suited to the conditions.

Most professionally installed window films with a shading coefficient of 0.50 or lower can help reduce the interior temperature in a facility. These slight changes in temperature can bring a reduction of up to a 25 percent in cooling costs. Because it takes considerable energy to remove heat from a room, window film can reduce the load on air-conditioning systems.

Choosing the right film

With many options for window film on the market, how can schools and universities identify the right ones? Consider outside endorsements from energy-focused organizations, such as the Clinton Climate Initiative. Also factor in the depth and longevity of the brand, the manufacturing capabilities and the extent of the dealer network.

If choosing a high-quality spectrally selective film (which blocks more infrared energy than visible light), schools should understand the technical differences of the two different types of film: ceramic and heat-repelling (HR) films. Ceramic films function primarily by utilizing microscopic grains to absorb nearly all infrared radiation (NIR) from the sun. This has the effect of capturing the energy from the sun into the coating on the film, which when applied directly on glass, retains the energy and therefore reduces heat gain into the building. A byproduct of absorbing solar energy in the film is that it raises the temperature of the glass, which under the wrong circumstances, can lead to window seal failures and glass breakage.

HR films use multiple thin layers of metal and metal oxides to reflect near infrared radiation away from building windows. Because HR films function primarily by reflecting — rather than absorbing — NIR radiation, HR films have lower absorption values, and there is less risk of seal failure or glass breakage when applied to windows. HR films prevent the solar heat from entering glass.

Manufacturing modern solar-control window film is a complex process involving high-quality raw materials and advanced technologies. If the application of window film is part of an institution's environmental initiatives, it should look for a manufacturer whose commitments to environmental standards matches its own. Ask about recycling and reclaiming programs, find out about waste disposal and verify that environmental sustainability is more than a fad by ensuring a long-term organizational commitment.

Read the "Evaluating window film installers" sidebar for more information.

Giblin is vice president of marketing of Bekaert Specialty Films LLC, San Diego, Calif., which develops, manufactures and distributes specialty films for use as solar control, safety films and for industrial applications. She can be reached at [email protected].


Percentage of potential energy savings when using window film.

Evaluating window film installers

Window film installers have become a sophisticated group of technical and marketing experts — they must be as educated on energy savings as they are on window safety, as knowledgeable about building codes as they are about HVAC systems.

As window film has advanced, so too has the education of the manufacturers. Look for installers who can consult with you on your building needs. During a consultation with a window film professional, plan to cover your concerns and goals, and review energy consumption and your expectations for realizing a return on investment. Walk through critical hot spots and surrounding areas to gain a better understanding of the modifications window film can bring about.

Finally, consider using this checklist for verifying whether an installer is credible:

  • What are the installer's accreditations?

  • How long has the installer worked with this window film manufacturer?

  • Who do you call with questions: the installer or the manufacturer?

  • Is the warranty provided on the whole window or just the glass panes?

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