# Uncertain Questions?

About three hours from now, Rhett Allain and I are doing another “Uncertain Dots” Google hangout. We don’t have a real clear topic, so if you have any questions about physics, academia, blogs, etc. that you’d like to hear us answer, this would be a great time to ask them, via comments here, email, or tweeting at @rjallain or @orzelc. If you like hashtags, #UncertainDots is a good one, but longer than either of our Twitter names…

1. #1 Hal
California
February 18, 2014

I have visited several buildings which were kept remarkably cool without air conditioning (although they are situated in very hot climates): e.g., the Alhambra in Spain, the Mission in Tucson. Methods include: exploiting tendency of heat to rise, and having running water that is extremely shallow (I assume that’s to exploit evaporative cooling and the shallowness helps because it reduces the amount of water that needs to be cooled.)

But here’s my question: if we give you unlimited acccess to water (say, at the ambient temperature) is there some theoretical upper bound on how much cooling could be achieved by non-energy-consuming means like these? Can one derive from principles of thermodynamics or whatever some theorem saying hey you can’t ever get the average temperature more than X degrees cooler than the mean surrounding air unless you use some energy-consuming means like air conditioning?

Just curious…

2. #2 Eric Lund
February 18, 2014

@Hal: It seems like you are describing a swamp cooler. The usual approach is to have circulating air (such as from a fan, if you can’t get natural breezes to do it) over a reservoir of water, and the flow helps to replenish that water, while the shallowness helps you not use too much. Yes, they work on the principle that evaporating water takes heat out of the air. At least, they work in arid climates like Spain or Arizona. But I tried to rig a swamp cooler once on a humid summer evening in my house in New Hampshire (I don’t have conventional AC), and it didn’t work so well. So I would not be surprised if relative humidity is one of the variables in the relevant formula.