Until recently few retailers thought about applied window film unless solar heat gain through east, south and west facing windows damaged merchandise and raised indoor temperatures to the boiling point. Truth is, advanced applied window film not only blocks solar heat but can successfully deal with numerous environmental problems in shopping centers with large amounts of glass. Applied window film offers solutions to:
- Fading of fabrics, draperies and home furnishings merchandise and store decor;
- Heat loss in cold weather;
- Reducing glare on increasingly computerized cash registers and electronic point of sale customer service systems;
- Damage from natural disasters such as windstorms, earthquakes, etc.;
- Vulnerability to forced entry
First, solar control
Too much solar heat adversely may impact shopping centers not only in the Sun Belt but also in cold climate cities like Seattle, Chicago and Boston. Even during Winter in retail establishments heat is already being generated by customers and staff, lighting and computers. Large expanses of glass (especially on southern exposures), that clearly show merchandise and shoppers inside the facility to prospective shoppers outside, can raise store temperatures and air conditioning bills. In addition to high energy cost, solar heat can lead to the following problems in shopping center retail establishments:
- Inability to use space near windows;
- Frequent use and replacement of heating and air conditioning (HVAC) equipment;
- Unproductive staff and uncomfortable patrons.
Profile of solar overheating
Only 47% of the sun's energy is seen by the eye as visible light. The other 53% of the sunâs energy adds unwanted heat, causes discomfort and fading damage in a shopping center retail establishment. A window should let in desirable energy (daylight) and block unwanted solar energy (near infrared heat) which causes overheating.
Solutions to overheating
Some shopping centers have mitigated solar exposure by replacing existing glass with expensive solar control glass though even the best solar control glass performs no better than the best applied window film. The most expensive option is to replace existing glass and window frames with a new window system designed to deal with a shopping centerâs energy performance needs and aesthetic character.
A less expensive option is to keep existing frames and replace only the glass. New glass can be selected that will be designed for the precise geographic orientation of any given building or section of a building. In either case, management may be understandably reluctant to replace existing windows or glass whose performance and appearance are generally adequate though not optimum.
A better option
More often at far less cost, the least expensive option to dramatically reduce unwanted solar heat and improve the performance of existing windows is applied window film.
Most attempts to reduce solar heat using applied window film involve the use of tinted or mirrored window films which reduce visible light and darken interiors. Most of these films are highly reflective in daylight, giving them a mirror like appearance when viewed externally. In artificial light and at night, internally they appear mirrored. These conventional films may block unwanted heat, but they also block desired visible light. In the case of retail establishments, visible light is reduced inside the store and shoppers outside cannot clearly see inside.
Shopping center retailers with dark films on their windows may have to improve lighting to compensate for the decrease in visible light transmission. This leads to higher electricity consumption. The additional use of electricity for lighting may actually increase inside temperatures requiring more air-conditioning. Increased utility costs subsequently defeat the major benefit of the film - cost savings.
The best solution to overheating - spectrally-selective clear film
Clear spectrally-selective applied window film offers the best ratio of visible light transmission to heat rejection. Spectrally-selective refers to the ability of the film to select or let in desirable daylight, while blocking out undesirable heat.
Spectrally-selective clear window film is a transparent, almost colorless polyester film coated with a clear ultra-thin spectrally-selective layer of exotic metals only a few hundred atoms thick.
The best spectrally-selective clear window film is constructed with a scratch resistant coating on one side and an adhesive coating on the other, allowing for retrofit application to existing glass.
The following table shows how different kinds of glass and applied films transmit light and heat.
*TABLE GOES HERE*
How different types of glass and applied film deal with heat & UV
With clear applied film, solar heat is significantly reduced without a noticeable reduction in the amount of daylight entering the building. With much less solar heat entering through existing glass, even retail spaces receiving direct sunlight are comfortable. Unlike dark tinted applied films, clear film possesses a clear, almost colorless appearance. From the exterior, shopping center retail establishments appear normal.
Damaging ultraviolet radiation
In addition to high levels of heat gain, conventional window glass allows high levels of UV to enter a retail establishment. Although ultraviolet energy makes up only 3% of the sun's energy, it accounts for an estimated two-thirds of fading damage to retail merchandise.
Even in winter UV through existing glass was fading fabrics and furniture in display windows of Calico Corners, a nation wide fabric retailer. ãHad we not taken quick action, we might have sustained as much as $3,000 in fading damage in one store alone,ä says Lisa Finn, property manager coordinator at Everfast, Inc., Calicoâs parent company.
Traditional "solutions" have involved the use of lined draperies and curtains, shutters, tinted or reflective glass, or dark "stick-on" window films. All of these approaches compromise windows by blocking light and impeding the ability to see through the glass. In addition, only spectrally-selective applied window film blocks up to 99% of the UV.
Heat loss in cold weather
While applied film is primarily a solar control product, it does enhance the ability of existing glass to insulate against heat loss by as much as 5 to 15%. This means some film not only blocks solar heat, but generates modest increases in overall insulation performance.
Reducing glare in the retail environment
Though clear spectrally selective window film transmits almost 40% more daylight than tinted films, compared to clear glass, it reduces light transmission by almost 20%. The installation of a clear spectrally selective window film may make expensive window treatments for glare control unnecessary.
Environmental damage and security
Shopping centers the Southeast are particularly susceptible to damage from hurricanes. In the Midwest, tornadoes are the prime weather threat. In California earthquakes are the number one environmental cause of broken windows. Applied window film will help prevent damage to property and injury by preventing or limiting flying glass shards in the event of glass breakage. Certain thicker applied window films are particularly resistant to impact and forced entry.
Shopping center management should consider the following points in selecting an applied window film:
How clear is it?
The ideal film would be totally clear, yet able to significantly block unwanted solar heat and reduce glare. Look for a 70 percent visible light transmission.
How much heat does it really block?
The manufacturer should be able to provide proven performance numbers. Look for a shading coefficient of 0.50 or lower.
Does it effectively block unwanted ultraviolet (UV) radiation?
An applied window film that blocks heat but not UV radiation will permit fading damage to merchandise and store decor. Look for applied films capable of blocking at least of 98% of UV radiation.
Does it require special care?
The best applied films require no special care. They can be cleaned just like the surface of glass.
To what kind of existing glass can it be applied?
Look for films that can be applied to windows and glass doors. Some films can be applied to single pane and insulating glass though it may affect the performance of some Low-E coatings. The highest performing applied film is always applied on the glass surface facing the interior of the building, although some manufacturers do make films for exterior applications.
What are the improper uses for applied window film?
The use of window films will increase the thermal stress on sunlit glass. There are numerous factors that will increase thermal stress such as partial shading of windows from overhangs, tightly fitting drapes, signs or decal on windows, and heating and cooling vents directed at glass. Different types of glass such as annealed versus tempered, clear versus tinted, have different solar absorption rates and will withstand different degrees of thermal stress. Professional film installers know which types of glass may be unsuited for applied window films. Tempered glass is particularly suitable while laminated glass is not.
Who applies the film?
Window film must be applied by professional window film installers who are trained in the proper installation procedures by the manufacturer of the window film. General contractors and glass contractors generally are not qualified to install applied window films. Application of applied films by unqualified and unauthorized personnel will result in voiding the manufacturerâs warranty. Look for local installers with a track record of installing nationally available films locally.
What is the price?
The price of clear applied film is a function of the degree of difficulty of the particular job. This is determined by the local applicator. Depending on the particulars of the job and the geographic area, the best clear applied window film ranges in price from approximately $9 to $12 a square foot installed. Installed prices are volume dependent, therefore on larger projects such superior performing films may be installed for less.
What is the payback?
The cost saving in preventing heat and fading damage to home electronics and other displayed merchandise can be substantial. Given a buildingâs footprint, orientation, HVAC system, and using local weather patterns, computer simulations can provide a relative payback for applied film. Given rising electricity and natural gas rates, the rate of payback is always improving ÷ averaging about four years.
What is the guarantee?
The best applied films are guaranteed not to peel, discolor, blister, bubble or demetalize for at least 10 years on a commercial installation. Look for a guarantee from the manufacturer in addition to any by the installer. There are documented cases of applied film lasting from 12 to 22 years.
Who makes it?
There are many established window film manufacturers but because of the demanding and costly manufacturing requirements only a few market spectrally-selective films.
Some real life installations of spectrally-selective window film
Both company owned and franchise properties of the following national and regional marketers use spectrally-selective window film in selected retail establishments: Hallmark Cards, Calico Corners, Kohlâs Department Stores, Blockbuster, The Gap, Esprit, McDonalds, Exxon, Race Trac and Quik Trip convenience stores.
V-Kool, Inc., Houston, TX, is a sales and marketing distribution company of V-Kool heat reflective applied films for architectural, automotive and specialized vehicular applications. V-Koolâs solar control films are manufactured by Southwall Technologies, Palo Alto, CA, whose window film technology was recognized by Popular Science as one of the 100 greatest inventions of the past millennium.
What are the benefits of applied window film?
Depending on the particular applied film:
- It reflects from 40 to 80% of the sun's heat;
- It slows heat transfer from 4 to 44%;
- It transmits up to 75% of the visible light;
- It reduces glare;
- It blocks 95 to 99% of ultraviolet radiation that can contribute to fading;
- It reduces loss of heat through the glass in the winter as much as 15%;
- It can reduce energy consumption, decreasing cooling and heating costs;
- It can make existing glass safer by making it shatter-resistant;
- It can be installed with little or no disruption to retail operations;
- It can be removed and replaced as technology advances and product performance improves. Such periodic updating of window glass is too costly.