In this paper, we investigate optimal management of a data center cooling system in coordination with ICT equipments. In recent data centers, a system manager has become able to access data in servers such as equipment temperatures, power consumption, fan rotation speeds and computational loads. The technological advance would allow one to model the cooling process more accurately and to feedback online data to control algorithms for air conditioning units, which would contribute to enhancing energy efficiency for the cooling system. In this paper, we first model the cooling process based on the above data and then formulate an optimization problem to be solved at a certain time interval to determine the reference set-point of the air conditioning units. The real-time optimization scheme is then demonstrated on a real data center cooling testbed.