Volume 50, Issue 9 - September 2015


Achieving Thermal Efficiency is No Open-and-Shut Case

When a door is constantly opening and closing, as is the case with storefront entrances, ensuring thermal efficiency can be a challenge. Add in the fact that energy codes are becoming increasingly stringent while an increase in thermal performance is also growing and you see a complicated growth pattern for commercial doors and storefronts.

Gerald Hendrick, president of U.S. Aluminum, says there has been a general trend toward thermally efficient systems that is being driven by architectural specifications.

“That takes into account new energy code requirements,” he says. “We are seeing door and entrance system specifications requiring U-values of 0.35 on average. This is coupled with requirements for medium performance glass with U-values of 0.28 - 0.29.”

In addition to thermal doors and storefronts, he adds that greatest demand for thermally efficient systems is coming from almost all institutional projects and high-end, monumental commercial buildings.

Contract glazier Bill Sullivan, executive vice president of Brin Northwestern Glass Companies and president of Heartland Glass Co. Inc., says the primary forces driving the increased use of thermal-plus storefront products are the energy codes and economics.

“In the past [in these instances] curtainwall was specified due to performance. Now, in some cases, the new thermal-plus storefront products can be used.”

Walt Lutzke, marketing coordinator at Tubelite Inc., points out that thermal performance for doors isn’t always easy to achieve.

“When the door is opened, any performance enhancements are lost. Thermal breaks and insulating glass are effective improvements during hours when the building is not in use.” He adds that vestibule entrances also reduce air infiltration during hours of operation, and that pushing the height limitations for both doors and storefront framing is a growing practice.

Know the Code

Across the country, codes have been calling for steady increases in the required performance for storefront applications, which are covered in both ASHRAE 90.1 and the commercial chapter of IECC.

According to industry codes consultant Tom Culp with Birch Point Consulting LLC, depending upon your region, here’s an idea of what you might expect in terms of thermal requirements.He adds that for entrance doors, the changes have been a little slower, “in part because they wanted to make sure the U-factors accounted for high use and ADA compliant doors, which have wider stiles and higher bottom rails.”

Zones 4-5: Low-E, thermally broken frame and one of the following:
• Argon;
• High-performance thermal break; and
• Two low-E coatings (No.2/No.4 surfaces).

Zone 6: Low-E, thermally broken frame and two of the following: 
• Argon;
• Warm-edge spacer;
• High-performance thermal break; and
• Two low-E coatings (No.2/No.4 surfaces).

Zone 7: Low-E, thermally broken frame and three of the following: 
• Argon;
• Warm-edge spacer;
• High-performance thermal break; and
• Two low-E coatings (No.2/No.4 surfaces).

Zone 8: All of the above in double glazing, or more likely a triple-glazed unit.

“Storefront designs have accommodated this with deeper/stronger members that allow for taller openings without the use of steel reinforcing,” says Lutzke. “Increased thermal performance is another trend that is being driven by new energy codes. Dual thermal breaks, high-performance glass and positioning glass to the exterior of the frame are being used to meet this demand.”

When it comes to challenges, Hendrick says one of the main ones “is keeping up with ever-evolving energy code requirements. Meeting performance ance specifications presents a moving target that can increase costs in a highly competitive market.”

Speaking of increasing costs, Lutzke points out that thermal performance enhancements to glass and framing add some cost to the overall fenestration system, “but architects and building owners are seeing the benefits, and [are] willing to invest now for a long-term return on reduced HVAC and artificial lighting expenses.”

Sullivan says there are other challenges he’s seen that have to be considered. “The biggest challenge that we have faced with thermal/storefronts is that designers push the structural capabilities of the storefront system,” he says. “We see large openings and tall openings that really should be designed using curtainwall systems, but because of cost factors they are specified using a storefront system.”

—Ellen Rogers

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