Different types of air distribution schemes have different impacts on the energy efficiency of cooling systems. The analysis results of this paper demonstrate that sealing an appropriate aisle (hot aisle or cold aisle) can significantly reduce the energy consumption of cooling systems in terms of the external air temperature outside data centers. Furthermore, we find that if the air temperature outside data centers is higher than the temperature at the inlet of IT equipments, sealing cold aisle outperforms sealing hot aisle. On the contrary, sealing which aisle depends on the energy efficiency ratio of the air conditioning.