Wednesday, August 25, 2010

R-values and Insulated Concrete Forms in mild climates

Recently, I was contacted to try to analyze the annual performance of an insulated concrete forms in a fairly mild climate—Santa Cruz, to be specific.  

Santa Cruz is pretty mild.  The following chart shows a fairly consistent 15 degree diurnal variation (see the YELLOW bars), which ain’t much.  Life’s a beach on the beach.  By just exterior temperatures alone, we might see that substantial thermal capacitance within a wall system (as opposed to inside!) probably won’t have a chance to really heat up during the day (unless… there are caveats). 

Screen shot 2010-08-25 at 5.01.46 PM

Salesman R-values
ICF wall system purveyors tend to claim all sorts of ridiculous performance values.  Some say R-50!  Some say R-38!  Some say all sorts of stuff that doesn’t make sense.  I call them Energy Pirates (RRRRRRR!). 

Real Steady State R-values
In the least, some of these wall assemblies actually should have a decent continuous R-value, thanks to the fact that they’re reasonably monolithic, assuming you don’t start building in large thermal bridges in the form of cantilevered patios (which have long extensions of steel beams running through the thermal envelope).  This decent R-value is probably in and around R-19 (5-6 inches of EPS foam in total).  Not too shabby.  The concrete itself has a negligible R-value (0.7 per inch). 

An ICF Wall is not a light frame assembly, though.  It’s got MASS.  It’s gonna suck in heat, and let it out.  This thermal capacitance can really come in handy in certain climates.  There are electrical analogies that I can make here, but I’m still getting confused at making the analogies correctly (and intuitively).  Proponents of the ICF technology are correctly claiming some benefit here.  THERMAL MASS can have an EQUIVALENT R-VALUE. 

The question is…. how much? 

Lastly, one last chart foreshadowing conclusions—showing a psychrometric chart of the Monterey/Santa Cruz region along with evaluations of different technology performance.

Screen shot 2010-08-25 at 5.01.05 PM


Part 2:   modeling of an ICF system? 

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