Advanced Energy Efficient Window Films
11/21/2013 1:42:32 PM by AngelaP
Window films may be an appropriate retrofit for any commercial building type, including schools, hospitals, health care facilities, offices, and commercial buildings. Only south- and west-facing windows need to be treated for “hot spot elimination,” although, for aesthetic reasons, the entire building is often retrofitted with window film to provide a consistent appearance. Energy savings benefits from use of window films are greatly reduced when:• The existing commercial building already has double-pane or tinted windows; • Cooling loads are reduced with an economizer or operable windows; and • The building is equipped with overhangs, vertical fins, awnings, or interior treatments like blinds or shades. These films are also aimed at the residential market.
Window films with low emissivity (Low-E) and high visible transmittance (VT) capability (known as Low-E/High VT) can help reduce winter heat loss in heating-dominated climates while allowing visible light to pass into the building. While their solar heat-blocking capability is slightly reduced, Low-E/High VT film replicates the performance of spectrally selective window films and represents the most desirable option in the cloudy western Washington and Oregon climate zones. While they come at a premium price, Low-E/High VT window films avoid producing a gloomy interior environment which could result in additional lighting use. High-end homeowners with attractive views often install window film to eliminate hot spots because they do not want to lose their view by closing blinds or drapes or installing reflective window films with low VT values. The Low-E/High VT films reduce eye-strain and glare, preserve views, and can save a small amount of energy.
In cooling-dominated commercial buildings, window film retrofits can reduce peak electrical demands. In residential units where air conditioning systems or heat pumps provide mechanical cooling, window film retrofits produce cooling savings. But energy savings for space cooling produced by Low-E window films are offset by the need to run the space heating equipment for more hours during the heating season to offset the loss of solar heat gain. This can result in load shifting from the cooling to the heating season. Space heating could be provided by electrical resistance heating, heat pumps, or natural gas furnaces. Supplemental wood heat is often used for residential heating. The appropriate load shape is consistent with that obtained by replacing single-pane windows with advanced windows in single-family residential units or in manufactured housing. Additional load shapes of interest include those for schools, hospitals, and small retail shops. Applicable ProCost load shapes include:---Commercial - Existing Small Office and Retail Building Envelope Measure---Residential Central Air Conditioning - Cooling Zone 3---Residential Space Heating - Baseboard Heating Zone 3---Residential Space Heating - Forced Air Furnace Heating Zone 3---Residential Space Heating - Heat Pump Heating Zone 3
Not surprisingly, the market penetration for sun control window film is highest in the cooling-dominated South and southwest regions of the United States. Window films are a mature technology with a wide range of performance values. Early versions of the films were designed for sun control and featured reflective or absorbent coatings. More recently, spectrally selective and Low-E films became available. While they command a premium price, advanced Low-E/High VT window films avoid producing a gloomy interior environment, reducing the need for additional lighting use. These window films will likely continue to improve gradually over the years.
No cost breakthroughs are anticipated. Film costs have tended to increase with inflation over the years.
Product Supply and Installation Risk:
Window films are readily available throughout the Pacific Northwest region. They are manufactured by stable, well-established firms able to scale up as needed. It is unlikely that an increase in sales volume in this region would cause a product shortage. Window films are not a “do-it-yourself” product; most local film installers are authorized dealers for one or more manufacturers. Installer training is definitely required and special procedures must be followed when installing window films. Warranties for the films are voided if installation is not performed by factory-trained and certified installers. All manufacturers offer a lifetime warranty for residential window film applications.
Window films are a retrofit technology; it does not make sense to use them on new construction that requires advanced windows. Existing residential units equipped with single-pane windows could upgrade to double-pane windows in a vinyl frame instead of undergoing a window film retrofit. Homes with double-pane windows could potentially upgrade to triple-pane windows. But, while energy savings can result, window upgrades come at a high cost. A recent study from the Pacific Northwest National Laboratory states, “…the cost effectiveness of the measure (from upgrading from a double-pane to a triple-pane window) as determined by the simple payback period, suggests that highly insulating window costs continue to make windows difficult to justify on a cost basis alone.” Window films and competing technologies such as replacement windows, storm windows, and other window treatments are mature technologies. On a cost-effectiveness basis, other technologies may or may not be competitive, but that competitive landscape is not expected to change appreciably in the foreseeable future.
The primary customer for commercial properties is the building owner and the facilities manager, although the tenant would benefit directly from heating and cooling cost reductions, and may sometimes be a direct customer. Residential decision-makers include the homeowner and landlords. Window film retrofits may be considered for single-family residences, condominiums, and townhouses.
Window films are manufactured by many companies with a wide variety of performance parameters. They are sold and installed by local distributors.
Neither commercial building owners nor homeowners have to acquire any permits to install window films. Installation is non-intrusive. Window films can be installed in one day and immediately begin to produce energy savings.
Other risks and barriers:
Some double-pane window manufacturers void their warranties when a homeowner places an “old technology” window film on their product. When an absorbent-type of film gets hot, it heats the pane it is affixed to. The inner pane of glass then expands more than the cooler exterior pane, which can create stresses on the window and result in premature seal failure. Before installing window films, ensure that window warranties are not compromised. Note that window films with high visible reflectance (VR) will look more like a mirror than a window from the inside at night. During the day, the window resembles a mirror when viewed from the outside. Some homeowners associations object to the installation of shiny or mirror-like window coatings on homes in their jurisdiction.Window films can produce glass cracking due to heat build-up if a dark absorbent film is used on non-strengthened glass that has a high solar exposure. Window films should not be retrofitted onto:• Single window panes larger than 100 square feet or double-pane windows larger than 40 square feet.• Clear glass thicker than 3/8th-inch or tinted glass thicker than ¼-inch.• Glass with a nonstandard surface, such as reflective, laminated, wired, patterned, or textured glass.• Cracked or otherwise damaged glass.• Glass in concrete, solid aluminum, or solid steel framing.Residential films are not sold on the basis of energy savings claims; instead, they are purchased to improve comfort, eliminate hot spots, preserve view, and add UV protection. The biggest barrier to the adoption of window films as an energy savings measure is their high total installed costs and extended simple paybacks.
Basis of Savings:
Energy savings benefits due to window film retrofits are expected to vary widely based on the baseline window type (single pane, double pane); performance of the film employed; local climate; building orientation; window-to-wall ratio (in each direction); the presence of shading produced by vegetation, other buildings, overhangs, fins, or awnings; building heating and cooling temperature setpoints and setbacks; use of economizers or operable windows; and the type and performance of HVAC system in use. A site-specific custom protocol would have to be developed.
Florida Solar Energy Center, “About Window Films”: http://www.fsec.ucf.edu/en/consumer/buildings/homes/windows/films.htm.Steve DeBusk, Global Energy Solutions Manager, Solutia, Inc., “A Review and Examination of EnerLogic™ Window Film Performance Claims”: http://www.enerlogicfilm.com/pdf/EnerLogic-White-Paper.pdf. Alice Rosenberg, Residential Windows Working Group, “CEE Product Overviews: Energy Efficient Fenestration Options,” Consortium for Energy Efficiency, May, 2013. Mudit Saxena, Heschong Mahone Group, Inc., “Advanced Window Film Technology Assessment-Phase 1 Report,” prepared for Pacific Gas & Electric Company, December 21, 2012: http://www.etcc-ca.com/sites/default/files/reports/ET11PGE1041%20-%20PGE%20Adv.%20Films%20ET%20Phase%201%20Tech%20Assessment%20Report_1.pdf. E-Source, “Window Film,” Business Energy Advisor, January 1, 2012. ConSol Energy and Environmental Solutions, “Energy Analysis for Window Films Applications in New and Existing Homes and Offices,” prepared for the International Window Film Association, February 7, 2012: http://www.iwfa.com/Portals/0/PDFDocs/IWFA%20Energy%20Study%20FINAL.pdf. Robert C. Bishop and Michael Shepard, E-Source Tech Memo, “New Retrofit Window Film Admits Light and Blocks Heat: Implications for Utility Rebates,” TM-92-2, September 1992. Arizona Public Service Company, “Windows and Window Treatments,” Energy Answers for Business.Efficiency Valuation Organization, “International Performance Measurement and Verification Protocol: Concepts and Options for Determining Energy and Water Savings, Volume 1,” EVO 10000-1:2012, January 2012: http://www.evo-world.org/index.php?option=com_docman&task=doc_view&gid=1543. Steve DeBusk, Global Energy Solutions Manager, Solutia, Inc., “Measuring the Savings from Energy-Control Window Film Installation Using IPMVP Options C and D”: http://www.bomaconvention.org/boma2012/CUSTOM/Case%20Study%20Solutia.pdf.Ben Larson, Ecotope, “SEEM Workshop,” October 31, 2011. Robin Mitchell, et al., Windows and Daylighting Group, Building Technologies Program, Lawrence Berkeley National Laboratory, “RESFEN5: for Calculating the Heating and Cooling Energy Use of Windows in Residential Buildings,” LBNL-40682, May 2005: http://windows.lbl.gov/software/resfen/50/RESFEN50UserManual.pdf .Robin Mitchell, et al., Windows and Daylighting Group, Building Technologies Program, Lawrence Berkeley National Laboratory, “COMFEN 4.1: Program Description: A PC Program for Calculating the Heating and Cooling Energy Use of Windows in Commercial Buildings,” October, 2012: http://windows.lbl.gov/software/comfen/4/COMFEN4.0-UserManual.pdf.
11/21/2013 1:42:32 PM by Angela Phillips