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Window Film Boosts Indoor Air Quality

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Spectrally selective window film not only allows natural light in and keeps heat out, it also indirectly improves indoor air quality.


Marty Watts


Today’s indoor building management challenge includes dealing with high indoor temperatures; stale, under-ventilated and circulated air; moisture and mold growth; out-gassing from furniture and building components; and the impact of such conditions on the productivity and health of building occupants.

Stanford Univ.’s Encina Hall saves $4,892 annually after installing spectrally selective window film.

Sick-building syndrome not only threatens building occupants, it can result in litigation that threatens the bottom line of employers and building owners. Ironically, many of the measures taken to increase energy efficiency, such as “tightening” buildings to reduce air infiltration and outflow, have degraded building air quality.

Building managers must understand how light and heat that pass through existing glass can affect a building’s environment. Knowing how glass performs will make clear the role of window film in mitigating the ability of glass to have a negative impact on the indoor environment.

According to the California Energy Commission, Sacramento, 30% of a building’s cooling requirement results from heat entering through existing windows. Yet, reducing heat in a building is usually considered to be an exclusive HVAC function. However, the HVAC system can be supplemented. Stopping heat at the window by using heat-blocking window film can not only reduce air-conditioning operating frequency and cost, but can also placate many building occupants who believe “conditioned” air is less desirable than non-conditioned air.

For example, at Stanford (CA) Univ. Encina Hall, about 6,212 sq. ft. of spectrally selective window film was installed. This film blocks solar heat while simultaneously transmitting natural light. As a result of the film’s installation, Encina Hall now enjoys an annual air-conditioning cost savings of $4,892.

Some building occupants might prefer using air conditioning less and window film more for two reasons-to keep interior temperatures comfortable and to reduce illness.

The Common Colds Centre, Cardiff School of Biosciences at Cardiff University, Cardiff, Wales, United Kingdom, has found that air conditioning may contribute to infection with common cold viruses. “The lining of the nose is covered with a thin layer of mucus that protects against infection. Since air conditioners extract moisture from the air, they may cause some drying of the protective mucous blanket in the nose and predispose to infection. The cold air may also help viruses establish a hold in the nose as they reproduce better in a cold nose,” according to the Centre’s website.

Heat and indoor air quality
Increased heat increases the motion of molecules, amplifying the effects of outgassing. Outgassing is the propensity of carpeting, furniture glue, and various chemicals in building materials to release fumes that are not healthy for building occupants to breathe.

The presence of mold has been demonstrated to be a function of indoor moisture levels. 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 Dept. of Health Services Indoor Air Quality Information Sheet, June 2004, “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 outgassing, reducing interior temperatures supportive of mold growth in humid environments need not depend entirely on HVAC systems and the necessity to subject building occupants to prolonged “conditioned” air. Less costly and more benign 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.

Unfortunately, many conventional window films block so much natural light they darken building interiors, often resulting in the need for additional artificial illumination that can often generate more heat. 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 has a negative effect on productivity and well being, according to studies conducted by the California Energy Commission and the U.S. Dept. of Energy. Fortunately, spectrally selective film blocks significant amounts of solar heat entering a building without reducing desired levels of natural light.

The quality of the indoor air and the overall environment depends on selecting furnishings and building components with low outgassing properties and on preventing the formation of condensation and humidity in sufficient amounts to cause mold growth. Most significantly, a strategy to manage a building’s environment must rely on an adequate HVAC system, with the ability to reduce heat aided by implementing appropriate heat-blocking window film and other relevant methods, to 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.