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2 R’s Won’t Make Your U

Monday, August 22nd, 2011

Article source: Engineering.Com

Architects and engineers spend a lot of time ensuring that the large buildings they design are well insulated, at least to code. But what if much of that insulation is wasted? New analysis shows that 2 R’s won’t make your U. Watch this informative video by Engineering.Com:


R value refers to the thermal resistance of a building material. The higher the R value, the more insulation the material provides. Most building designers simply provide enough insulation to meet the relevant building code or green building certification. New analysis shows that the R value of the material isn’t the only thing that affects how well a wall insulation system works. Common installation procedures can cut the effective R value in half. The culprit is thermal bridging. It’s a particular problem in the design of larger buildings that use steel and concrete studs and framing.

Steel is an excellent conductor, so any time you have steel running through the exterior curtain wall into the building, heat can follow that path either in or out of the building, essentially bypassing the insulation. This isn’t news to architects and structural engineers. What wasn’t common knowledge was how big the problem is, and how easy it is to fix.

By using sophisticated 3D thermal analysis, engineers at Morrison Hershfield working on the ASHRAE project determined that thermal bridging can result in more than double the expected heat loss. One common approach for installing insulation is with vertical Z-Girts that are in line with the steel studs. The alignment of the metal connection results in a very direct thermal bridge.

The ASHRAE study used 3D thermal modeling to follow the heat transfer across multiple types of girt connections. In addition to vertical Z Girts they modeled horizontal Z Girts, vertical and horizontal z Girts , and intermittent z Girts. As a result of this work, ASHRAE can develop new reference tables that will allow architects and engineers to truly understand the thermal performance of the buildings they design. And to improve the actual energy consumption, which is after all, the whole point.

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