An R9 Window -- Hypothetical Design
PHIUS Senior Scientist Graham Wright undertook the following hypothetical design exercise to demonstrate how a window could be designed and constructed to meet PHIUS' performance recommendations for climate Zone 8. The goals of the exercise were to achieve the following levels of performance:
- An R9 whole-window installed (including accounting for some installation thermal bridge coefficient)
- Solar heat gain coefficient (SHGC) ≥ 0.5 at center of glass without the use of any cost-prohibitive technologies
- The glass is set deep into the frame in order to isolate the conductive part of the assembly in the middle of the window.
- The glass is surrounded by insulation on both sides, with more insulation used on the outboard side of the assembly.
- The outboard edge of the frame is articulated to lengthen the heat loss pathway and provide structure.
- The design exercise demonstrates that achieving the desired level of performance is not overly difficult and could be accomplished with off-the-shelf materials and components.
- While performing the design exercise it took several attempts to get the glazing right; the starting parameters used were a 4-pane Cardinal catalog unit with Argon measuring 2 inches thick overall. Although this assembly barely met the requirements of climate Zone 8, the frame was easier to nail down and we got it right on the first try.
- Although the resulting frame is a bit thick, aesthetically it does not appear to be too oversized or impractical.
- Achieving the same levels of performance with an operable window would be more difficult.