Data Center designs are changing due to the demands (thermal loading) of todays high density designs. The raised floor design with cabling running underneath along with pressurized cooling air is a 30 year old design from days when power densities were far lower. Back in the "old" days when main frames ruled the data center each unit had direct access to the cool air under the floor. In todays vertical rack system, units near the top of a rack often experiance temperatures above 100deg F. The conventional wisdom is that for every 15deg above 70deg long term reliability of electronics decreases 50%. With current rack mount servers a single rack can easily exceed 10KW of thermal load. Next generation systems are expected to exceed 25KW load on a single rack.
Simply put we are reaching a point where air cooling will no longer suffice. HP has already alerted users that future systems will need to return to chilled water for cooling (the older main frames used chilled water, many older data centers still have the chilled water plumbing in place)
