Thermally broken aluminum-framed systems and doors satisfy the industry’s present demand for improved efficiency, performance, and cost savings over older thermally improved products.
Thermally broken products are typically designed with a minimum of 5.3-mm of separation provided by a low conductance material with open space. Thermal breaks (or thermal barriers) consist of low thermal conductivity components that are inserted between members of higher conductivity parts to reduce or prevent the flow of unwanted thermal energy.
What are Thermal Barriers Made of?
Some thermal barriers are made of heavy-duty polyurethane resins that are built into the aluminum profiles of fully-framed storefronts, curtainwalls and entrance doors to separate the interior and exterior surfaces. These materials feature thermal conductivities that are 500 to 1,300 times lower than aluminum, which creates a thermal barrier. This break in the thermal path is necessary to prevent hot or cold air from transferring through the aluminum to the inside of the building. While originally used in colder climates, thermal barriers are equally important in warm environments to reduce heat transfer in air-conditioned buildings.
Polyurethane has low thermal conductivity, maximizing thermal efficiency in the smallest possible separation. Polyurethane systems are very strong, allowing for wider spans. Polyurethane systems are cost effective to produce and install. In addition to polyurethane systems, thermal barriers can also be manufactured in polyamide configurations. These systems feature two separate extrusions: one interior and one exterior. Its aluminum framing components are knurled and polyamide strips are inserted into the aluminum profiles. The composite extrusions are then crimped to secure the polyamide strips, thus producing a thermally broken structural composite.
Energy-Efficient Systems
When attempting to maximize energy efficiency, entrance doors are often the most problematic areas, as their basic operation results in heat loss and everyday wear of weathering components. The level of thermal performance of any door depends on multiple factors, including the type of the door, intended function and the material makeup of the door. By combining the right elements for a thermally broken door design, it can create a superior thermal barrier that enhances the overall thermal performance. Pour-and-debridge polyurethane systems and crimped-in-place plastic polyamide isolator systems are both examples of advanced engineering that allow entrance doors to effectively manage energy efficiency.
Selecting the right framing and door system that provides a true thermal break will help achieve the maximum benefits of energy savings from reduced thermal loss. Since the invention of thermal barriers in the 1970s, their pairing with commercial fenestration systems has been instrumental in saving millions of barrels of oil and other precious natural resources worldwide. As energy-efficient building design continues to play a key role in the shaping the industry at large, so will thermal barriers.
Addressing Heat Transfer
In addition to managing energy loss through aluminum system frames, it’s important to always consider the amount of heat transfer through the glass to improve performance. Glass’ ability to withstand energy transfer is called its emissivity. For example, clear glass has an approximate emissivity of 0.84, meaning it allows approximately 84 percent of energy to pass through it. To reduce the amount of energy transferred through the glass, the fenestration industry developed low-emissivity (low-E) coatings.
Once conduction (material type and design), convection (system design) and radiation (glass selection) factors are thermally improved, it’s important to address the amount of heat transfer through the edge of the glass. To manage this portion of energy loss in a given design, manufacturers have developed dual-lite insulated glass units (IGUs) that help manage unwanted energy transfer with an added warm-edge spacer.
Warm-edge spacer systems incorporate high-performance polymers and low-conductivity stainless steel to provide minimal heat transfer and maximum protection against gas leakage and moisture penetration. In addition to keeping the glass lites separated and establishing air space in the unit, the warm-edge spacer also helps ease stress induced by thermal expansion and pressure differences. It also serves as a moisture barrier that prevents water or vapor passage that would fog the unit, and ensures a gas-tight seal to prevent the loss of low-conductance gas in the air space. By creating an insulating barrier to reduce the formation of interior condensation at the edge, warm-edge spacers provide a substrate for the system’s adhesive components that create a primary and secondary sealant to deliver longevity and high performance.
Ultimately, choosing the right commercial storefront, curtainwall or entrance system that provides a true thermal break, in conjunction with the appropriate insulating glass configuration, is the best way to achieve maximum benefits of building-wide energy savings from reduced thermal loss.
Joe Schiavone, CSI, CDT, is director of sales at CR Laurence Co. Inc.-U.S. Aluminum, Los Angeles. For more information, visit www.crlaurence.com
