Rant: Home Depot Duct Tape

I quick one this evening, just for the sake of generating content and developing good habits.

I was at the Home Depot a month ago buying supplies for a small HVAC project.  In the midst of looking for proper adhesives and binding substrates for some flexduct and associated boots, I could almost NOT find the appropriate code-approved tape and mastic and webbing and ties.  Sheesh, it was a battle.  Nearly all the tape they had in the aisle was not code approved and probably would have lastly a hot minute on that cold duct (or vice-versa). 

After 5 minutes of careful examination, I find it at the bottom right corner of an array of shiny foil nothing tapes. 

Disappointment reigned.  While code-approved tape probably have more to do with fire=rating than actual adhesive performance, nevertheless, complying with code should not be so hard.  Having ductwork that won’t leak in 1 year wouldn’t be so bad.

On the bright side, as long as folks keep using hat crap, I’ll have more of a retrofit marketing plan

There are a wealth of reports and studies about this, but for the n00b: http://www.lbl.gov/Science-Articles/Archive/duct-tape-HVAC.html

Embodied Carbon Footprinting Literature Review

A quick table and chart

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Study	Description	Location	Square Footage	Projected Life of Home	Total Embodied CO2 (kg)	Embodied kg CO2/sq. ft.	Operational CO2--50 yr (kg)	Operational kg CO2/sq. ft.-yr
U. Mich[1]	Standard Home	Michigan	2450	50	81,795	33.39	931,486	7.60
U. Mich	Energy Efficient Home	Michigan	2450	50	79,992	32.65	294,463	2.40
CORRIM[2]	Home-Steel Structure	Minneapolis	2062	75	37,047	17.97	1,300,000	8.41
CORRIM	Home-Wood Structure	Minneapolis	2062	75	46,826	22.71	1,300,000	8.41
CORRIM	Home-Concrete structure	Atlanta	2153	75	21,367	9.92	762,500	4.72
CORRIM	Home-Wood structure	Atlanta	2153	75	28,004	13.01	762,500	4.72
Australia[3]	Median	Australia	1773	50	84,900	47.87	507,000	5.72
Australia	Max (Embodied)	Australia	3444	50	164,700	47.82	899,000	5.22
Australia	Min (Embodied)	Australia	980	50	56,800	57.99	238,100	4.86

 

[1] Blanchard, Steven, and Peter Reppe. Life Cycle Analysis of a Residential Home in Michigan. Report (University of Michigan. Center for Sustainable Systems), no. CSS98-05. Ann Arbor, Mich: Center for Sustainable Systems, University of Michigan, 1998. Internet resource.

[2] Life Cycle Environmental Performance of Renewable Materials in the Context of Residential Building Construction: Phase I Interim Research Report. Seattle, WA: Consortium for Research on Renewable Industrial Materials (CORRIM, 2002. Print.)

[3]Pullen, Stephen F. "Energy Used in the Construction and Operation of Houses." Architectural Science Review. 43.2 (2000): 87. Print. This study analyzes 25 homes of all ages and assemblies around Adelaide, Australia. Maxima, minima, and average results were calculated directly from the data provided in the paper.

Insulated Concrete Forms part 2

Oak Ridge to the Rescue!!

So, last time we spoke, I was trying to work through the actual performance (equivalent R-value) of an insulated mass wall, within a mild coastal climate.  In this post, I will review the one tool that I found which might give some insight, but less than ideal.

As it turns out, most energy modeling software that isn’t TRANSYS or EnergyPlus just doesn’t really like thermal capacitance.  They model heat as ‘BTU’s in—BTU’s out’ which for the purposes of most energy modeling, is quite sufficient.  In  other words, it doesn’t really respect the 2nd law of thermodynamics.   However with massive wall systems, all the heat slushing in and out results in some fairly tricky dynamics.  Keeping track of the temperature of the mass can be important in some designs, and is definitely important when it comes to comfort. 

The traditional energy modeling software don’t really mess with this level of detail because it’s tricky and is essentially a finite element model. 

Oak Ridge Thermal Mass Calculator:

Google that and you’ll find a nice software tool circa 2000.  There aren’t too many options within the tool, so I chose a 3000 square foot 2-story ranch house with R-19 continuous steady state insulation (the EPS on the outside/inside of the wall).  The tool calculates an assortment of equivalent R-values based on the location of the insulation with respect to the mass—inside, outside, or in the middle.  It then gives us charts like the following, which shows:

ICF 2-story residence in Phoenix (R-19 steady state R-value):  R-31 equivalent

The ICF performance is on the right side, labeled as “ICI,” or ‘insulation-concrete-insulation’

ICF 2-story residence in Seattle (R-19 steady state R-value):  R-26 equivalent

You can see that the equivalent R-value of the wall in a temperate, cloudy environment, such as Seattles, is substantially less than the performance in Phoenix.  R-26 ain’t too shabby, however, as far as overall wall performances are concerned.  

Conclusions:
The heavy thermal mass wall system works well, and the ICF is a good product, assuming one can contend with its adaptations in building style.  The walls tend to have superior air-tightness relative to light frame assemblies due to the requisite attention to details and the monolithic nature of the wall assembly. 
HOWEVER

Achieving R-26 in a light frame is not hard.  Just put some rigid foam on the interior or exterior, dude.

Also, if you noticed on those charts that the interior mass wall universally worked the best.  Take note of that!  Interior mass is where the mass should be, exposed, naked for all the interior world to see.  And, of course, if you want some passive solar benefit, you could also put your mass where the sun does shine!  ;)

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). 

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.

 

Part 2:   modeling of an ICF system?