Increasing energy costs and limited resources of available electricity are driving the data centre industry to the use of energy efficient technical equipment. Dynamic Free CoolingŪ is a control concept for data centre's air conditioning systems combining Hybrid Indirect Free Cooling Precision Air Conditioning Units, fan speed controlled drycooler and speed controlled central pumps to a highly efficient precision cooling system. All system components are centrally controlled to minimise overall energy consumption depending on the ambient temperature and the room load conditions.