With the rapid explosion of information technology (IT), data centres have been expanding in terms of scale and capacity worldwide. As a result, a huge increase in energy consumption in data centres has become an obvious problem. The heat dissipated by large servers and IT equipment is reaching levels that make it difficult to cool these systems in data centres. This paper has studied a specific set of field measurements from a data centre in Chongqing in order to research its particular operational thermal environment and energy consumption. Detailed measurements including electronic equipment inlet/outlet air temperatures, air volume of perforated tiles and computer room air conditioning (CRAC) units, power consumption of IT equipment, CRAC units as well as lighting system, were gathered. In addition to these measurements, metrics play a significant role in theoretical analysis about its operation effect, which include Power Usage Effectiveness (PUE) and heating, ventilation and air conditioning (HVAC) Effectiveness Index. The PUE value was 1.62 suggesting there are further improvements in energy efficiency, compared with the highly efficient data centres, while 23% of the HVAC Effectiveness Index denotes HVAC system running well. The database indicated that there were no over-hot points while further improvements in poor airflow and serious over-cold points were needed. It was also found that maintaining the hot aisle/cold aisle was a simple and efficient way of improving rack cooling effectiveness as well as providing good separation between the supply and return air pathways.