(JBED) - Summer 2006 - The Whole Building Design Guide

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eaders are encouraged to follow the reference listed for further background. COMFORT VS. CODE: A REAL WORLD EXAMPLE In 2003, the Building America program supported the development of a Habitat for Humanity duplex in the Chicago area. This structure used envelope improvements, which included low solar gain low-E windows, to achieve an energy performance that is 37 per cent better than the model energy code. The windows used in this project can be represented by the line labeled as ‘Quad’ pane in Figure 1. The winter design temperature in Chicago is about 0°F; reading up the quad pane line we see that the glass temperature will be approximately 55°F at this design condition. Assuming this is adequate comfort—we can now compare the comfort implications from alternative energy strategies. The same energy performance can be accomplished using ordinary double pane windows along with a high efficiency furnace. The metrics listed below suggest, however, that these two structures are very different. 1. Peak cooling loads increase by 18 per cent. This creates an extra burden for the electrical utility to generate sufficient electricity reliability during hot weather periods. 2. Carbon emissions increase by 12 per cent. The Midwest uses mostly coal for electric generation. 3. There will be 989 hours in the winter when the double pane glass is colder than the 55°F benchmark for the original low solar gain low-E. 4. There will be 260 hours in the summer where, despite the presence of air-conditioning, more than 30 per cent of the occupants will be dissatisfied. This compares to 0 hours with the low solar gain low-E glass. 5. The house with double pane windows is at risk for solar overheat 760 hours during the swing season. This is not an energy consumption measure, but indicates the level of involvement needed by the home owner either through operation of drapes/blinds or opening of the windows to vent excess heat. All told this “equivalent” structure will be outside the comfort 38 Journal of Building Enclosure Design TABLE 1: EQUAL COMFORT FOR CHICAGO HOUSE Low Solar Gain Double Pane Single Pane Low-E Clear Clear Winter Thermostat Setting 70°F 72°F 73°F Summer Thermostat Setting 78°F 74°F 73°F Energy Increase vs. — 26% 50% Low Solar Gain Low E boundaries for 32 per cent of the hours in a year. Compare this to less than 10 per cent of the hours for the base case of low solar gain windows. The folly of the equipment for envelope trade-offs can be extended all the way to single pane windows. The combination of a high efficiency furnace plus a high efficiency air-conditioner gets the single pane windows back to an equal energy score, but the building space is now uncomfortable for 50 per cent of the hours in the year! Faced with uncomfortable windows a homeowner can chose to: 1. Tough it out; 2. Move away from the window; 3. Leave the room; 4. Add or remove clothing layers; 5. Close the drapes and/or open the window; and 6. Turn the thermostat setting to “comfort”. Table 1 shows that in spite of paper “equivalence”, homeowners could drive an energy increase approaching 50 per cent with a simple vote of the thermostat adjustment. CONCLUSIONS In comparison to most elements in the building envelope, windows are “first responders” to weather changes. Inefficient windows will be cold in the winter and hot in the summer. The general populace would expect an energy efficient house to be comfortable year round. If, as envelope designers, we allow paper trade-offs that fail the consumer comfort expectations, we’ve failed our professional responsibilities. More importantly these paper savings, given over to the control of a homeowner, could destroy any semblance of a national energy policy and lead to dramatic cost overruns and supply disruptions. REFERENCES 1. ASHRAE 2005 Handbook of Fundamentals, Chapter 8; and Standard 55-2004. http://www.ashrae.org 2. LBNL research paper available through ASHRAE via URL: http://resourcecenter.ashrae.org/store/ashrae/newstore.cgiite mid=7354&view=item&page=1&loginid=8813121&priority=none&words=window %20comfort&method=and& 3. NFRC comfort research: www.nfrc.org/documents/ UCBThermalComfortFinalReportFeb72006.pdf 4. Building America Habitat for Humanity duplex: www.eere.energy. gov/buildings/building_america/cfm/project.cfm/project=EEBA%202003%20HfH%20Duplex/state=IL/full=Illinois/city=Chicago ■
By Valerie L. Block and Tammy Amos, DuPont Glass Laminating Solutions, Wilmington, DE PROTECTION AGAINST TERRORIST ATTACKS IS now a common theme in the design of government and commercial properties. Americans witnessed terrorism firsthand in 1995 with the bombing of the Alfred P. Murrah Federal Building in Oklahoma City that resulted in the deaths of 168 men, women and children. Three years later, two United States embassies in East Africa were the targets of terrorist attacks that left 224 people dead and many more injured. These two events, and others like it that have occurred around the world, have led to a heightened awareness of the need for greater security in both government and commercial buildings. DIFFERENCES IN GLASS BREAKAGE MAKE A DIFFERENCE Annealed glass is made by floating molten glass over a bath of molten tin in a furnace. The glass ribbon is gradually cooled to room temperature through an annealing process that also removes residual stresses that may have formed during manufacturing. While there are many beneficial uses of annealed glass in buildings, after an explosion, annealed glass breaks into long, jagged shards that can cause serious injuries. Tempered glass is a safety glazing material, according to the Consumer Product Safety standard 16 CFR 1201. Tempered glass is made by reheating annealed glass in a furnace to approximately 1150 °F, which is then rapidly cooled by flowing air uniformly onto both surfaces. The cooling process locks the outer portion of the glass in a state of compression and the central core in tension. Although tempered glass is considerably stronger than annealed glass, it is not retained in its frame when breakage occurs. Instead the glass breaks into a myriad of relatively small pieces of glass. Laminated glass is often specified in windows, doors and façades needing blast protection because it provides impact safety. The interlayer used to bond two or more pieces of glass together provides glass retention after a bomb has been exploded, and in doing so, minimizes the chance of flying glass injuries to building occupants or passersby. In addition, this glass retention feature helps maintain the integrity of the building envelope against further vandalism after a terrorist attack has occurred. IMPACT RESISTANCE AND ENERGY SAVINGS Glass retention is desirable in glazing installed in seismic regions, as well as in residential and commercial fenestration intended for use in hurricane-prone areas. Impact resistant glazing in properly designed frames keeps a home or building intact during a severe weather event, protecting occupants and the structure itself from collapse and interior water damage. Window and curtain wall companies have applied the knowledge gained from impact testing of hurricane products to the development of products that offer bomb blast protection. Laminated glass not only contributes to the overall performance of the window by its ability to remain integral in its frame if breakage should occur, but it can also deliver acoustical benefits in terms of reducing outside noise. From an energy savings point of view, laminated glass can be made with high performance glass and/or coatings that result in a high visible light transmittance and low solar heat gain coefficient. While architects may specify laminated glass for security, the cost justification can often be measured in terms of energy savings expressed through lower utility bills. APPLICABLE STANDARDS AND TESTS ASTM F1642 Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loading (available at www.astm.org) provides testing information for the glazing or fenestration system in either a shock tube or open-air environment. The Feature Laminated Glass, Providing Security against Terrorist Attacks Windows in the Wilkie D. Ferguson, Jr. Federal Courthouse, Miami, Florida were made with laminated glass to provide both hurricane impact and bomb blast protection. Historic renovation included blast resistant windows at the National Courts, Washington, D.C. Photo courtesy of Masonry Arts. standard also includes criteria for the classification of fragmentation. Currently, a specification to accompany the test method is under development. The ISC Security Design Criteria adopted by U.S. General Services Administration in 2001 requires a balanced design of window systems to four specified levels. At the minimum level, any glazing is acceptable. At the medium level and high levels, the preferred glazing systems include tempered glass with security film on the interior surface and attached to the frame, laminated glass, or blast curtains. Monolithic annealed, heat strengthened and wired glasses are unacceptable glazing products. Specifications for windows, skylights and glazed doors are provided in the U.S. Department of Defense Unified Facilities Criteria (UFC) Minimum Anti-terrorism Standards for Buildings. The UFC criteria Summer 2006 39
Page 1: JBED Summer 2006 Journal of Buildin
Page 6: Message from NIBS David A. Harris,
Page 10 and 11: Feature Dynamic, Integrated Façade
Page 12 and 13: 1. COMMERCIALLY AVAILABLE SOLUTIONS
Page 14 and 15: procure them for the final building
Page 16 and 17: obstruction and/or daylight reflect
Page 19 and 20: Feature All That Glass Is there an
Page 21 and 22: façade at the street corner. It is
Page 23 and 24: cess to the perimeter, concrete str
Page 26 and 27: Feature Architectural Glazing for S
Page 28 and 29: could consist of lites that have di
Page 30: esidents. Another concern from the
Page 33 and 34: from the California Central Valley
Page 37: Feature Window Comfort & Energy Cod
Page 41 and 42: Feature How Does Fenestration Fit I
Page 43: Council (ICC), one might expect tha
Page 46 and 47: Industry Update By James C. Benney,
Page 48 and 49: BEC Corner HOUSTON-BEC By Andy MacP
Page 50: Buyer’s Guide AIR BARRIERS Dupont

(JBED) - Summer 2006 - The Whole Building Design Guide

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