[Greenbuilding] dynamic benefit of massive systems

[nick pine]

Alan Abrams <alan at abramsdesignbuild.com> wrote:

> I came across a claim that a 12" thick AAC block wall achieves R-22 (more than double the rated per unit R-value of the material itself) in the Washington, DC climate... I am skeptical of the claim mentioned above, and would not want to count on it for the not unusual three weeks of late January when the daytime temp never gets out of the 20's... am I alone?

No. This works best when the outdoor highs and lows are less than and greater than 68 F...

On a day with average exterior temp T, a 68 F concrete
house with 2" R10 Styrofoam walls will lose or gain about |68-T|/R10 Btu/h.
With min and max temps Tmin and Tmax, a frame house in the same location
with walls with an equivalent R-value might lose (68-Tmin)/R all night and 
gain (Tmax-68)/R all day, with an equivalent R-value of 5(Tmax-Tmin)/|68-T|.

Here is a list of US locations and equivalent R-values, based on NREL data:

location          month       Tmin   T       Tmax    equivalent R-value

Philadelphia      June        61.8   71.8    81.7    26.2
Phoenix, AZ       April       55.3   69.9    84.5    76.8
Flagstaff         July        50.5   66.3    81.9    92.3
Prescott          June        49.9   67.2    84.5    216.3
Albuquerque       September   55.2   68.6    81.9    222.5
San Diego         October     60.9   67.7    74.6    228.3
Houston           April       58.1   68.3    78.4    338.3
Ely, NV           July        48.0   67.5    87.0    390.0
Colorado Springs  August      55.2   68.3    81.3    435.0
Las Vegas         October     54.3   68.3    82.1    463.3
Elkins, WV        August      56.2   67.8    79.3    577.5
Bakersfield       October     54.8   67.8    80.7    647.5
Rock Springs, WY  July        52.8   68.0    83.1    infinite!

Nick
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