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Window film was invented to reduce temperatures in overheated buildings. Too much solar energy entering windows increased heat, making occupants uncomfortable and air conditioning more expensive to operate.

Today the management issues facing administrators extend beyond overheating and energy conservation and include dealing with stale air, moisture and mold growth, out-gassing of furniture and building components and the impact of such conditions on the productivity and well- being of building occupants. Ironically, many of the measures taken to increase energy efficiency such as “tightening” buildings to reduce both air infiltration and outflow have contributed to negative indoor environmental quality. Adding to the management challenge, sensitivity to preserving historic and community character sometimes conflicts with measures to increase energy conservation and enhance environmental standards.

The Role of Window Film
According to the California Energy Commission, 40% of a building’s cooling requirements may be from heat entering windows. As a supplement to HVAC, stopping heat at the window using window film can reduce air conditioning operating frequency and cost.

A recent window film installation at Stanford University took place at Encina Hall, a century-old administration building. Some 6,212 square feet of spectrally selective window film was applied. Spectrally selective film blocks solar heat while simultaneously transmitting natural light. Daily air conditioning (A/C) requirements to remove heat at Encina Hall prior to the film’s installation amounted to 665.57 A/C tons at an A/C cost of $66.56 per day. Daily air conditioning requirements to remove heat with the film installed are 339.44 A/C tons at an A/C cost of $33.94 per day. As a result of the film’s installation, Encina Hall now enjoys an annual savings in A/C cost of $4,891.95.

If building occupants realized there is a choice of ways to reduce heat, many might prefer using air conditioning less and window film more to keep interior temperatures comfortable and indoor air quality high. According to the Common Colds Centre, Cardiff School of Biosciences at Cardiff University in the UK, air conditioning itself may contribute to infection with common cold viruses. Anecdotal evidence suggests that air conditioning aggravates the effects of arthritis and neuritis and makes people sick due to the extreme variances between outside and inside temperatures. Note that as heat reduction becomes a shared function of HVAC and window film, benefits include both energy savings and building occupant perception of improved environmental conditions.

But saving money on air conditioning is only part of the appeal of applied window film. The propensity of carpeting and chemicals in furniture and building materials to out gas, i.e., release fumes, most of which are not healthy for building occupants, is a function of molecular motion. As the temperature increases, no matter what the source of heat, out gassing will increase.

The presence of mold has been demonstrated to be a function of moisture inside a building. Humid interiors will breed mold and the warmer those interiors become without actually reducing the amount of moisture, the more hospitable the environment for mold formation and proliferation. According to mold mitigation advice offered by the California Department of Health Services Indoor Air Quality Information Sheet, “Do not turn up the heat or use heaters in confined areas as higher temperatures increase the rate of mold growth.”

As with reducing heat to mitigate out gassing, reducing interior temperatures supportive of mold growth in humid environments need not depend entirely on HVAC systems. Less costly window film can shoulder much of the burden of interior heat reduction if that heat is caused by solar energy entering through glass in the building envelope.

If the point of window film is to reduce indoor temperatures should decision makers then opt for the window film that blocks the most heat? Unfortunately, what seems the logical implication of this endorsement of window film is not the right choice.

Types of Window Films
Tinted film blocks heat by absorption. Reflective film, that sometimes appears mirrored, reflects heat. Some of these films block heat better than others but all, to one degree or another are unable to transmit significant levels of natural light. In some cases, highly reflective window films with metalized heat-reflective coatings block as much as 85% of the visible light outside from entering the inside of a building.

Managing a building’s environment must rely on an adequate HVAC system whose ability to reduce heat is aided by the simultaneous implementation of appropriate heat-blocking window film and other relevant methods to both save energy and enhance environmental quality.

Because conventional window film blocks so much natural light it darkens building interiors often resulting in the need for additional artificial illumination that can often generate more heat. Ultimately, in many buildings this requires the use of more air conditioning which defeats the purpose of installing heat-reducing window film.

Not only does conventional window film block natural light resulting in increased artificial illumination, the denial of natural light to building occupants negatively impacts their productivity and well being. Studies conducted by the California Energy Commission, the US Department of Energy, the Rocky Mountain Institute and Rensselaer Polytechnic Institute document a relationship between low levels of natural light and less than optimum performance on the part of building occupants.

Reduced natural light is not the only problem with conventional films. Because they are tinted or reflective they change the appearance of existing glass and the external look of a building, at the University of Colorado Boulder, in determining which window film to choose, “Of major concern was the necessity that applied film be transparent and colorless so as not to change the appearance of our buildings,” explains Moe Tabrizi, campus resource energy conservation officer.

Many campus buildings experienced over-heating only through glass on the structures’ south and west sides. Using clear, spectrally selective film that did not change the appearance of existing glass, Colorado was able to install film only on windows through which over-heating occurred and not on the entire building as would have been the case using tinted or reflective film that would have changed building appearance.

No Silver Bullet
Implicit in the work of the Environmental Protection Agency’s Energy Star product rating system and the U.S. Green Building Council’s Leadership in Energy & Environmental Design (LEED) program is the contention that there is no single product solution to energy efficiency.

Decision makers responsible for a building’s environment must realize that no single program component constitutes a silver bullet. Window film can no more do the job alone than can cool roofs, super insulated walls and overburdened HVAC which historically has been expected to carry 100% of the responsibility for heat reduction.

Managing a building’s environment must rely on an adequate HVAC system whose ability to reduce heat is aided by the simultaneous implementation of appropriate heat-blocking window film and other relevant methods to both save energy and enhance environmental quality. Only when a multitude of systems function in an integrated and orchestrated approach will positive results be achieved and maintained. In such a program window film will play an increasingly important role.

Marty Watts is President and CEO of V-Kool, Inc., Houston, TX, a sales and marketing distribution company of spectrally selective applied films for architectural, automotive and specialized vehicular applications. For information, contact V-Kool, Inc., at 800.217.7046 and at www.v-kool-usa.com.

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