Sunday, February 21, 2010

Global warming potentials in spray applied foams (a work in progress)

I went to a PassivHaus seminar about a year ago, and it brought up a potentially disturbing fact about polyurethane foam in particular chemistries  in residential and commercial field applied purposes.  In the old days and occasional developing countries, these spray foams used blowing agents that have absurdly high global warming potentials. 

One might ask the question:  Is it possible for your insulation to have a higher carbon footprint than you are saving with the insulation? 
[oh, and you may have noticed that I’m posting a lot about foams lately—it’s been a hot topic, that’s all.  and I’ve been doing my research, so it’s on the brain.  I’ll get off this topic soon enough]
Proper Introduction:
I heard from someone recently outside of the South Bay who actually tried to read what I’m writing here, and really couldn’t understand much, so now I feel the appropriate responsibility to explain what the bigger picture here is so that most of you can go on caring about more important things. 
SO.  We want to save energy by insulating our houses.  There are myriad (ok, maybe not quite 10,000) ways to insulate, and all sorts of materials and such.  Spray-foam is among one of the options, which is especially nice for the building scientists among us, who like having the nice draft-free walls and roofs that the foams are pretty darn good at creating. 
Spray-applied foam in the residential industry generally comes in two flavors—open cell (aka low-density water blown foam) and closed cell (aka medium-density foam). 
The open cell foam is what most houses have, and it uses water as the blowing agent, and it releases CO2 upon curing.  Pound for pound, this CO2 ultimately doesn’t amount to much, and is generally vastly worthwhile in terms of insulating value.  
The closed-cell foam is the foam in question for this post.  It is generally among the most expensive insulation, but with stellar performance: high R-value per inch, and vapor impermeability qualities.  The closed-cell foam can’t use water as a blowing agent, unlike the open-cell—it has to use a much more finely crafted and specially tuned blowing agent in order to create its wonderful matrix of  tiny unruptured air bubbles (which is how the insulation insulates, after all). 
The standard blowing agent that I’ve heard used here in the US is HFC-245fa.   It has a global warming potential of ~1000x CO2.  That means for every pound of HFC-245fa that gets released in the atmosphere, it’s worth 1000 lbs of CO2 in terms of its impact on global warming. 
I don’t have an answer yet as to whether or not closed-cell foam is a dubious application for my particular geography, but the least I can do for now is to bring up the issue and provide a research study that gives some insight, if you’re interested. 
The chart below is pilfered from a study I really, actually want to reference and support: it shows the marginal payback (for just that one extra inch of foam) for various foams with different blowing agents. 
Danny Harvey, of the University of Toronto, created the graph, and it’s located in the study:
“Net Climatic Impact of Solid Foam Insulation Produced with Halocarbon and non-Halocarbon Blowing Agents”, Building and Environment 42(8): 2860-2879, 2007.
Link to study!

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