The growth in demand for Information Technology (IT) systems and the requirements to better control carbon emissions is a large challenge for data centre design. Aircooled data centres are becoming more efficient by layout and the adoption of compressor free cooling, but for higher densities, further efficiencies can be achieved with liquid (water) cooled systems, where liquid is either brought to the cabinet or is fed directly into the IT systems. This paper makes a comparison of the full energy consumption between hybrid air-cooled and direct liquid-cooled systems based on real operational systems using comparable IT components. The results based on real data demonstrate a significant level of energy reduction for a high density data centre solution that uses enclosed, immersed, direct liquid-cooled servers.