DWweblogo.jpg (24968 bytes)

Winter  2001


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.

Savings Potential
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.”

Market Penetration
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.



© Copyright Key Communications Inc. All rights reserved. No reproduction of any type without expressed written permission.