Based on the climate classification of ASHRAE 90.1 and the required operating environment conditions for data centers suggested by the ASHRAE Technical Committee TC 9.9, a dynamic building energy simulation program was used to examine the potential energy savings of the air-side free cooling technology with differential enthalpy control used in data centers in 17 climate zones. The results showed that significant free cooling potential was achieved in data centers located in mixed-humid, warm-marine, and mixed-marine climate zones. Because significant humidification is required to adjust outdoor air in climate zones with a lower dew point temperature, such as very-cold, subarctic, cool-dry, and cold-dry climate zones, the power consumed is even higher. Although the cooling degree day (CDD) and heating degree day (HDD) are key factors of climate classification and air conditioning energy consumption, they are not entirely correlated to the specific operating environment conditions of data centers. The results of this study showed that for every 2 degrees C decline in the indoor temperature of a data center, the energy saving of free cooling technology may decrease by 2.8-8.5%. The rate of decline varies in different climate zones. (C) 2013 Elsevier B.V. All rights reserved.