josh ober wrote:I guess what I’m having trouble with is understanding how cob would stay cool in the heat, considering the fact that it seems it would be absorbing heat from the sun.
It does indeed absorb heat, but different materials can absorb more energy before they actually start to feel warm.
I appreciate that could be a bit hard to wrap your head around. The fundamental reason for this property is highly technical and beyond my understanding, but is explained on Wikipedia:
An example given on Wikipeida (see this table)
is that water requires about 4.5x more energy (measured in Joules) to raise its temperature by 1°C compared to an equivalent mass of concrete. So in layman's terms, concrete starts to feel warm four to five times faster than water does. This means water is the better material to use as thermal mass. Of course, water has a habit of leaking out of containers and destroying stuff. On the other hand, water can also be pumped through heat exchangers which allow you to push the heat around much faster. So there are a number of factors to consider.
Here's another useful table
showing heat capacity. Sandy clay requires about 1.6x more energy than concrete to raise the temperature.
An interesting (and counter-intuitive) detail to note is that air has a higher heat capacity than concrete. But of course, 1 tonne of air occupies a much larger volume than 1 tonne of concrete.
Finally I just want to point out that I am not a scientist or engineer, so I would love somebody who is to confirm what I have written above.