It's more down to dew point than water temperature. Very cold floors with very low humidity don't have a problem. I'm now integrating dew point calculations into my system to reduce the possibility of dew forming - summer is on the way so time for the experiments to begin.
Take a look at this thread to see what I'm doing:
http://ecorenovator.org/forum/geothe...-dewpoint.html
The aluminium radiators don't really work for cooling as there is little or no air circulation, I now turn them off during the summer. I may, at some point, incorporate a fan coil into the system in place of the radiators to see if that helps. Best solution by far though is the under floor heating/cooling.