Thermal Continuity in Window Design08:52:00 AM on 07/07/2009
I’ve always hated drinking coffee through a lid. It’s too much like a “sippy cup”. But as I burned the skin off my upper lip this morning, I realized just how important thermal continuity is to the entire coffee mug system. Thermal continuity is important to a lot of things, just as it is with Kawneer’s new single- and double-hung window, the AA®3350 ISOPORT® Window.
You can position the thermal break in many products almost anywhere you want and get decent results. With Casement Windows for example, the ones that open and close like a door, the operable sash is nested in its frame, making it quite easy to align the thermal breaks and get good performance. Single and double hung windows, where the top sash is in a different plane than the bottom, is an entirely different story. There’s two questions here, “How do you maintain a consistent thermal break from the top to the bottom?”, and “How do you keep the thermal break in the two sashes aligned with the thermal break in the frame? “ In fancier words - How do you maintain the thermal continuity? It’s simple. It’s all in the unique thermal break design of the AA®3350.
Thermally broken aluminum windows have been around for a long time. Some use a method called “P&D” or “pour and de-bridge”. With P&D, a liquid resin is “poured” into an extruded channel, the resin quickly hardens and then the back of the channel is ripped out or “de-bridged”. This splits the aluminum extrusion into two halves joined by the thermal break. (A typical pour and de-bridge extrusion assembly is shown at left - click image to enlarge.) Other thermal products, like the AA3350, are designed with stiff plastic strips or “dog bones” clamped between two individual aluminum extrusions. This method allows much more design flexibility.
When you look at the outside frame of the AA3350, the first thing you notice is the large black plastic (actually polyamide) thermal break. (View of AA3350 polyamide thermal break used in frame jamb members shown at right - click image to enlarge.) Because this type of thermal break is not nearly as limited as P&D, we can design it large enough to maintain alignment or continuity with the thermal break in the top and bottom sash. A closer look at the unusual thermal break design where the top at bottom sash meet in the middle shows how the thermal continuity is maintained from one plane to the other. In the end, everything exposed to the weather on the outside is consistently separated from the inside.
Note how the thermal continuity is maintained between the frame and sash members .
So there… problem solved. The next time you burn your upper lip on an aluminum window look for thermal continuity. Now, I'd love to hear from you so, be sure to share your thoughts and comments.