Direct Liquid Cooling for Electronic Equipment

This report documents a demonstration of an electronic-equipment cooling system in the engineering prototype development stage that can be applied in data centers. The technology provides cooling by bringing a water-based cooling fluid into direct contact with high-heat-generating electronic components.

This direct cooling system improves overall data center energy efficiency in three ways:

• High-heat-generating electronic components are more efficiently cooled directly using water, capturing a large portion of the total electronic equipment heat generated. This captured heat reduces the load on the less-efficient air-based data center room cooling systems. The combination contributes to the overall savings.
• The power consumption of the electronic equipment internal fans is significantly reduced when equipped with this cooling system.
• The temperature of the cooling water supplied to the direct cooling system can be much higher than that commonly provided by facility chilled water loops, and therefore can be produced with lower cooling infrastructure energy consumption and possibly compressor-free cooling.

Providing opportunities for heat reuse is an additional benefit of this technology. The cooling system can be controlled to produce high return water temperatures while providing adequate component cooling.

The demonstration was conducted in a data center located at Lawrence Berkeley National Laboratory in Berkeley, California. Thirty-eight servers equipped with the liquid cooling system and instrumented for energy measurements were placed in a single rack. Two unmodified servers of the same configuration, located i n an adjacent rack, were used to provide a baseline.

The demonstration characterized the fraction of heat removed by the direct cooling technology, quantified the energy savings for a number of cooling infrastructure scenarios, and provided information that could be used to investigate heat reuse opportunities.

Thermal measurement data were used with data center energy use modeling software to estimate overall site energy use. These estimates show that an overall data center energy savings of approximately 20 percent can be expected if a center is retrofitted as specified in the models used.

Increasing the portion of heat captured by this technology is an area suggested for further development.