Typically in 2003 you would design for an average of 1.7kW with a maximum of 5kW being a possibility, however with the advent of blade servers it is not uncommon to find IT Managers looking at 25kW+ per rack in 2006. This will obviously change the design criteria of a data centre.

Our advice would always start with clearly identifying the likely maximum output from each rack (this will be available from the server manufacturer).  Once you have some maxima it is possible to identify the probable solutions.

Rack cooling in a generally air conditioned room is usually possible up to about 2kW per rack.  Underfloor air distribution methods give about 4kW per rack of cooling and forced air cooling works up to about 7kW heat load per rack.  Beyond that it would be necessary to move to more exotic technologies such as water-cooled racks.