Energy-Efficient Windows Take on a Southern Charm
by Kate Offringa
The use of low-solar-gain windows in new construction in the South could save about 1 percent of total U.S. electricity usage over the next 20 years at a national electricity bill reduction of $760 million. Now that’s a charmer! This is according to a newly published paper, “Energy Savings and Pollution Prevention Benefits of Solar Heat Gain Standards in the International Energy Conservation Code” by Bill Prindle of the Alliance to Save Energy and Dariush Arasteh of Lawrence Berkeley National Laboratory.
IECC SHGC Standard
The International Energy Conservation Code (IECC) was published in 1998 by the International Code Council and was last modified in 2000. Prindle and Arasteh document the potential benefits of the IECC’s new prescriptive standard for solar heat gain control in windows. In climate zones with 3,500 or fewer heating degree days, the IECC now mandates a solar heat gain coefficient (SHGC) of 0.4 or less. The IECC requires that the SHGC value of a window be certified by the National Fenestration Rating Council. The code does allow for flexibility in meeting the SHGC standard through window products, fixed external shading or a combination of the two.
Using the RESFEN model developed by Lawrence Berkeley National Laboratory, Prindle and Arasteh simulated energy use in a typical new home in ten Southern states. The ten states in the study are those that would be most affected by the IECC SHGC standard, were they to adopt the code: South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Texas, New Mexico, Arizona and Nevada. (The energy, dollar and peak demand results of the analysis are summarized in the chart below).
Total Energy, Dollar and Demand Savings;
Annual Impacts for Each Year’s New Home Production
State Housing Starts KWh Dollars kW
South Carolina 24,467 13,261,114 $1,088,537 11,499
Georgia 67,879 31,427,977 $2,521,705 25,794
Florida 97,889 140,617,549 $10,873,021 66,565
Alabama 14,655 1,192,477 $1,192,477 7,914
Mississippi 8,671 9,295,312 $705,559 4,682
Louisiana 13,875 19,119,750 $1,491,701 5,273
Texas 99,831 88,949,421 $9,818,379 60,897
New Mexico 9,217 10,101,832 $949,535 3,595
Arizona 50,540 59,283,420 $6,994,736 32,851
Nevada 24,445 34,614,120 $2,353,565 14,667
TOTALS 411,469 407,862,972 $37,989,215 233,736
According to U.S. Census Bureau data, approximately 8 million new homes will be built in these states over the next 20 years. Prindle and Arasteh find that the savings in year 20 from meeting the IECC SHGC standard in these homes would total 8 billion kilowatt hours, $760 million in electricity bills and 4,660 megawatts of generating capacity.
“The electricity saved by the IECC would also prevent substantial amounts of air pollution and greenhouse gas emissions,” said Arasteh and Prindle. In year 20, it would prevent the emissions of 1.5 million tons of carbon equivalent and 20,000 tons of nitrogen oxides.”
According to Prindle and Arasteh, “low-solar-gain low-E windows are relatively new to these ten states, partly because the original low-E products used high-gain products more suited to heating-dominated climates.” The two cite market data indicating that market penetration of low-E windows is still below 10 percent in the South while it has reached 50 percent in the coldest parts of the country.
The Southern window market is indeed ripe for transformation.
Kate Offringa is program manager for the Efficient Windows Collaborative, a project of the Alliance To Save Energy in Washington, D.C.
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