I've been looking at these as well, thanks for the extra info... However
in
the true DIY spirit I was also thinking about somehow using the existing
plumbing and radiators to do the job. If you pumped very cold water around
the house would this actually generate any coolness from the radiators?

The water would have to be so cold to start off with, it would be ice!
Think of all that condensation, dripping onto your carpets too!

S.