Twenty-Year Payback for Embodied Carbon of Triple-Glazed Windows

Sounds like the study just looked at triple pane windows with three panes of glass and perhaps did not examine triple pane using technologies like Heat Mirror.

I am curious what our Carbon payback on granite countertops is vs laminate or other options?  or perhaps wood floors vs carpet?  Seems like we focus on those things that actually have a financial payback.

I see you do show other reasons like comfort, acoustics, operational costs, HVAC cosntruction cost savings, etc.  

I'm surprise at your statement "they don't necessarily come out ahead".  We certainly expect windows to have much much longer than 20 year life cycle, easily 50 years or longer.  So they still come out ahead even just on its own merit.

The carbon payback of any building envelope assembly is greatly dependent on climate - the greater the "delta_T", the greater the energy savings potential.  I'm surprised that this article didn't state the assumptions inherent in the study - is the 20 year payback for windows in the UK?  in Florida?  in Newfoundland?  I live in Alaska, where triple-pane has been the high-performance standard for many years, and I assume that the carbon payback is much less than 20 years when you are dealing with 14,000+ Heating Degree Days.  Making blanket statements relating to envelope energy savings undermines the importance of designing for your climate.

There seems to be a negative bias to this article right up to the end, where the many good reasons to consider triple-glazed products are finally mentioned. I think it may be confusing to many. Triple-glazed products certainly provide more efficient thermal and acoustical performance than the typical double-skin facade, for example. There are many good reasons to use triple-glazed products. It is an excellent point, however, that materials must be considered (and too often are not), and this is a good example where the additional material can have a significant impact on overall carbon footprint. Its not all about operational energy, which is rightfully the dominant focus. But as buildings and systems become increasingly efficient, embodied energy will become an increasingly larger share of the energy debt, and must be accounted for.

By the way, the graphic does not read correctly in the article, at least in my browser (chrome). You may have to follow the Circular Ecology link to the original report to view the graph correctly.

Our energy modeling on a 43,000 sf office building in the St. Louis climate showed a 5% improvement in the envelope performance of a wood framed window system as compared to a thermally broken aluminum framed system. A sensible approach can be to match or at least balance teh thermal properties of the frame and glazing system. For instance if one is using a high performance glazing system with a R-value of say 3.5 to 5 then one would wle ant a frame system that has a similar insulative value; and not a frame system something like a R-2 frame value - all other things (like infiltration rate) being equal.

I too question the durability of internally suspended film products such as Heat Mirror based on personal experience. That said however, I am an avid believer in the promise of such products as a very important tool in high performance window systems. Compared to triple glass glazing a double glazed unit with a suspended layer of Heat Mirror offers higher visible daylight transparency and essentially equal thermal performance at lighter weight. Their higher daylight transmittance allows us to accomplish the same daylight levels with smaller windows resulting in an overall higher wall insulation value.

In a recent meeting with an acoustical engineer, I was infromed that dual pane glass generally has higher STC values than triple pane glass.  This is because the tighter air space in triple pane glazing transmits vibrations more efficiently.  He said that he routinely challenges people to show him test data that supports the idea that triple pane windows have better acoustical properties, and no one ever delivers.