With the rapid development of internet and Information and communication technology (ICT), magnitude of data should be stored, managed, processed and exchanged in datacenter. So many servers are placed compactly in a limited space that heat generates in high density. It needs effective cooling system to ensure severs to operate steadily. Traditionally, air is adopted as the cooling work fluid, because air cooling system is simple to design and operate. However, since air has smaller density and specific heat than water, air cooling system consumes more energy. So water cooling systems for data center have been paid more attention by researchers. In this investigation, the energy consumption of data center cooled with air and water are compared with the cool energy transportation factor. The ratio of CETF of pump for water to CETF of fan for a small scale data center is 3.4. And it has the same characteristics with common HVAC system for buildings, which ratio of CETF of pump for water to CETF of fan is from 3~6.