Have a look at this from Wired magazine. It says you can save significant quantities of energy (and money) by making ice and cooling your building with that, rather than using air conditioners.

It looks like they use it in large office buildings, so I suppose it would work with blocks of flats - I wonder how small a scale it could be made to work on?

Interesting article 19tori - cool idea too (if you pardon the pun).

I read this article recently also about doing something similar on the tube

http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2007/06/05/ntube105.xml

Be interested to see if it takes off.