Sustainable By Design: Building Exteriors That Clean Themselves? - Facility Executive Magazine - Creating Intelligent Buildings

Titanium dioxide is being used to reduce maintenance needs,
Titanium dioxide is being used to reduce maintenance needs,

Sustainable By Design: Building Exteriors That Clean Themselves?

Sustainable By Design: Building Exteriors That Clean Themselves? - Facility Executive Magazine - Creating Intelligent Buildings

By Anne Cosgrove
Published in the May 2008 issue of
Today’s Facility Manager

Inmany cases, the aim of operating a sustainable facility intersects withthe demands of ensuring quality maintenance. For instance, the pursuitof an environmentally friendly protocol for cleaning must take intoaccount the efficiency of newly adopted products and any new proceduresthat go along with them. When considering such decisions, a facilitymanager (fm) will want to be sure the new system operates at the same,if not better, level of effectiveness and efficiency.

Building Exteriors That Clean Themselves! Shownhere is an exterior wall on a condominium in Japan. The tiles in thephoto at the right were manufactured with titanium dioxide (TiO2),while the tiles in the top photo were not. The two areas have receivedthe same maintenance, and the TiO2 treated section remains free ofvisible dirt. (Photos: Toto Hydrotect Tile)

Cleaning a building exterior, for instance, can be a time-and labor-intensive task. At its simplest, the process consumes water,detergents, and other cleaning agents. Further, the labor must bescheduled and paid for, and sometimes the process requires closing offa portion of the facility normally accessible to occupants.Additionally, the facilities staff must coordinate and schedule thisevent every time this is needed. What a boon it would be if thebuilding could clean itself!

While we are not in the realmof magically self-cleaning buildings (yet), there have beendevelopments over the past 10 years, mainly put in practice in Asia andEurope, that hold promise for reducing exterior cleaning demands.Titanium dioxide (TiO2) is a material that can be applied asa thin film to building exteriors to protect against pollutants anddebris. The compound can also be incorporated into building materialsduring the manufacturing process. Concrete, exterior tiles, tensileroof membranes, and windows are among the products currently on themarket with TiO2 technology.

The chemical make up of TiO2makes it a photocatalyst, which enables it to break down dirt thatsettles on a surface. Simply put, when a photocatalyst is exposed toultraviolet (UV) light (from the sun, for instance) in the presence ofwater vapor and oxygen, it creates a charge separation of electrons andelectron holes. The electrons disperse on the surface and react withexternal substances; this causes chemical reactions that form hydroxylradicals, which then decompose organic compounds (such as dirt andother debris) present on a surface.

The second part of thisis that the debris broken down by the photocatalytic reaction can beremoved from the surface by rainfall or rinsing. This is because thesurface becomes hydrophilic (gains the ability to gather water) afterexposure to UV light. In this state, water falling on the surfacespreads flat upon it, preventing debris from adhering to the building.

TiO2 also triggers the oxidation of airborne pollutants, including oxides of nitrogen (NOx) and volatile organic compounds (VOCs) and converts them into carbon dioxide (CO2) and water. In essence, it helps to clean the air of pollutants.

While reduced maintenance is desirable for fms, the use of TiO2 for buildings faces several barriers to widespread adoption. For one, using materials with TiO2comes at a premium. (For instance, the cost of this type of concretefrom Italcementi, an Italian manufacturer, is reported to be as high as30% to 40% more than the traditional product.)


Beyond cost, another point of discussion is the environmental impact of the byproducts of the TiO2photocatalytic process. Some argue that, while trying to minimize oneenvironmental impact through resource conservation, the presence of TiO2 may add undesirable pollutants to the air. For instance, the chemical reaction involved in photocatalysis releases CO2.The amount is negligible; however, multiplied over thousands offacilities and millions of square feet of surface area, the release ofCO2 could work against efforts to reduce greenhouse gas emissions.

An expanded look at the potential of TiO2for buildings was recently addressed in a study performed by theLawrence Berkeley National Laboratory (LBNL) in Berkeley, CA. Theproject investigated the potential of TiO2 to “clean”outdoor air through its ability to oxidize pollutants. Hashem Akbariand Paul Berdahl were the LBNL researchers for the project, and theysought to clarify the potential for reducing air pollution by focusingon measured values of catalytic activity—the rate at which air can becleaned by a given area of photocatalyst (in this case TiO2).For instance, if one square meter of a catalytic surface can clean 100cubic meters of air per day, then it has an activity of 100 meters/day.

Commenting on the potential of TiO2to combat outdoor air pollution, Berdahl said, “Prior to widespreaddeployment of passive photocatalytic air cleaning technology, largescale meteorological simulations are needed to validate deploymentstrategies.” (The report also addressed the CO2 concern previously mentioned in this article.)

Inexploring sustainability, fms often encounter strategies that remain onthe outskirts. Further research and real world installations willeventually reveal whether TiO2 holds promise for mainstream facilities.

Researchfor this article included information from the LBNL project report,which was prepared for the California Energy Commission, PublicInterest Energy Research Program. To download the report, visit (Publication #CEC-500-2007-112).

Do you have any experience with TiO2? Share your thoughts by e-mail to [email protected].

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