A Clear View
Apr 1, 2009 12:00 PM, By Kathryn Giblin
Professionally installed window film is a simple way to block solar heat and reduce energy.
A recent window-film installation at Brown University’s John D. Rockefeller, Jr. Library, Providence, R.I., had several goals: block UV light to protect against fading, maintain a cool environment and allow a clear view in and out of the library.
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.
Acceptable Use Policy blog comments powered by Disqus
