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Designing Commercial Energy Retrofit for Curtain Walls

Post Time:Dec 10,2009Classify:Industry NewsView:194

Dudley G. McFarquhar, principal, MGI McFarquhar Group Inc., Mesquite, Texas, discussed Designing Commercial Energy Retrofit for Curtain Walls at the BETEC Symposium, Dec. 10, at the Washington Convention Center.

“Curtain walls are a key area to focus on contribution and managing energy loads on buildings,” McFarquhar said. “It controls light transmission in vision areas. Key areas related to energy include glazing, gaskets, sealants, framing and shading.”

Challenges to retrofitting a curtain wall include: owner’s budget; tenant disturbance; age of the building; architectural aesthetics; site logistics (open or tight spaces for remedial access); decision on whether elements be removed/replaced; whether the remediation be extensive; and addressing tenants/employees during remediation, McFarquhar said.

The design team needs to understand the system type before starting work on retrofitting a curtain wall, McFarquhar said. “There are hidden connections. Not all systems are the same. Curtain wall design methodology, simulation tests, and water infiltration concerns need to be taken into account.”

When designing a retrofit, keep in mind building codes, industry standards, analytical mechanics and installation method, McFarquhar said. “Experience and lessons learned are important.”

There are three types of glass used in curtain walls: annealed, heat-strengthened and tempered, McFarquhar said. Composition of glazing includes: monolithic (least efficient), IG (more efficient), and laminated. “Older buildings typically have monolithic glazing in the vision area; it’s not energy efficient. IGs are widely used and effective with tint on the #2 surface to reduce UV,” he said.

If monolithic glazing can’t be replaced during retrofit, use solar films to reduce UV, McFarquhar said. “Preferably replace with IG. IGs are good options for energy efficiency. The tint is protected and offers multiple color choices.”

Gaskets are used as insulators in curtain walls. “They can crack and let in air and water. They also shrink through aging. Use pre-molded gaskets for retrofits. Use sealants (exterior/interior applied).”

Framing replacement options include siteline, depth, and type, McFarquhar said. New systems have thermal improvements and offer thermal bridge components. The rear frame is thermally isolated from the pressure cap.

Aluminum extrusions allow a lot of flexibility in adaptation systems andappendages can be added, but are challenging in existing conditions, McFarquhar said.

Use sunshades to offer aesthetic quality and shading effect on the glazing. “There is an opportunity to change the look of a building during energy efficiency upgrade,” McFarquhar said.

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