The increasing energy consumption of data centers attracts more and more attention

much of which is consumed by the cooling system. Utilizing efficient cooling methods is the urgent need for realizing emission control targets

and the free cooling is one of these methods. The free cooling technology has three categories: airside free cooling

waterside free cooling and heat pipe free cooling. Airside free cooling is easily utilized and has good energy-saving effect

while it may affect the indoor air quality and humidity. Waterside free cooling can be modified from traditional air conditioner however its energy-saving effect is limited for additional heat transfer process. Heat pipe free cooling has no disturbance on the indoor environment and its energy-saving effect is good for utilizing phase change heat transfer. The latest advances in free cooling technology is summed up

which has the referential value for research in this field.