Very nice set of calculations, but you missed one issue. You only accounted for heating the top 1.5 inches of concrete to 32F. It won't work that way. If the surface of the concrete is 0F, and the ground is 0F, when the heating elements kick on, they will dump just as much heat into the top 1.5 inches of concrete as they will into the 1.5 inches below the elements. Not completely true because the upper half is exposed to the air, and the lower half is attached to a very very large heat sink.
So, double the watts needed to heat the 1.5 inches of concrete and you are getting closer. -- Blue skies. Dan Rossi Carnegie Mellon University. E-Mail: d...@andrew.cmu.edu Tel: (412) 268-9081
