August 27, 2020

Cup of Joe Second Law of Thermodynamics

In order: 1. 2. 3. 0. Hmmm.

In an isolated system, a process can occur only if it increases the total entropy of the system. Yeah, ok.

  • Heat flows from warm too cold. Why? Because. Of the second law.
  • Moisture moves from warm to cold. Why? Because.
  • Moisture moves from more to less. Why? Because.
  • Air moves from a higher pressure to a lower pressure. Why? Because.

All because of the second law of thermodynamics.

For architects, engineers and construction professionals, we are primarily concerned about moisture. Moisture moves from warm to cold and from more to less. Most of the time, those are in the same direction. In real life, water vapor condenses on the cold spot in an assembly. Sometimes though, moisture moving from warm to cold is in a different direction from more to less. In that case, more to less wins.

Buildings where this scenario is common are special use facilities. Indoor swimming pools, hospitals, and museums. Oh, and indoor grow rooms. But unless you are dealing with special use, worry about warm too cold. Moisture ends up on the cold spot.

So where do I put my vapor barrier? Why can't I use vinyl wall coverings? What about epoxy and oil-based paints? What if I want to hang art of a wall? Why do cabinets come without a backside?

Watch and learn!

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