One of the delights of cheap Indian hotels is the availability of air coolers. Much more rudimentary and therefore much more cost-effective than freon-based air conditioning, air coolers are to room cooling systems what holes in the ground are to toilets: simple yet effective.
In its simplest form an air cooler is just a large box with a fan on the front face, which pulls air into the box through the other three vertical sides and pushes it out of the front. The bottom is filled with water that is pumped into the top to trickle down the three remaining vertical sides, which are normally covered in a twisted plastic matting material to give maximum surface area. It's simple: hot air is sucked into the box and passes through the trickling water, which cools it down. It works too.
The only disadvantages are the noise level (the air needs to be sucked pretty quickly to be cooled effectively) and an increase in humidity (the air blown out is pretty wet). But air-cooling has saved my life in this heat wave that's sweeping India, killing people with dehydration and sunstroke. It might be hot on the streets, but it's cool inside...
