A standard air cooled data center is a rare phenomenon. Generally each one is individually designed, with hundreds of different component combinations. They can also be energy hogs. Cooling system power consumption in older data centers is typically 100% or more of the IT load.

While energy efficiency has improved recently and Power Utilization Effectiveness (PUE) values - the ratio of total energy use to the IT equipment energy use - of 1.2 and better are being designed, we could be approaching the limit of air system cooling capability. While liquid cooling systems can provide further improvement, previous liquid systems have been too complex, delicate, expensive, and unreliable. This paper describes a novel cooling approach that could provide savings in energy use with lower capital cost.

In the first section of this paper we review various ways of cooling with air and demonstrate that the distance of the heat generator to the cold sink plays a large part in the total cooling energy consumption. The logical conclusion is that totally eliminating the air gap between the hot source and the cold sink is highly advantageous. Liquid, with its high heat conveyance is an effective way of achieving this.

Much work is being done in order to overcome the deficiencies of liquid cooling systems. In the second section of the paper a sampling of the design strategies being pursued is presented. A description of a "direct touch"; cooling system using pumped refrigerant will be discussed in detail. This technology was developed in part under a grant from the California Energy Commission's Public Interest Energy Research (PIER) program.

This alternative cooling system could be simpler to adopt using industry standard servers; it is robust and requires no special training to administer. Above all, it allows extensive standardization. It can reduce both energy consumption and capital expenditure by up to 50% and increase power density up to 100 times. With this technology, it becomes practical to put a small data center in a wiring closet and a petaflop computing system in a cubicle. This system is noiseless and virtually room neutral for thermal input.

Results from third party testing comparing traditional air cooling and this direct touch system are presented.