The Advantages of Liquid Cooling

Compared to traditional air-cooling methods, liquid cooling devices either at rack level or near the racks can reduce power consumption of in-room cooling by 80-90 percent.

Shlomo Novotny is the Chief Technology Officer of Coolcentric and Vice President and Chief Technology Officer of Vette Corporation.


Data centers are an ever-growing part of our economy. The IT community is experiencing constantly increasing demands in areas such as Internet media and video, banking and finance, research, and government, just to name a few. Consequently, data centers continue to grow in both size and numbers. In addition, the performance of IT servers continues to follow Moore's law. This improves the performance per dollar spent on IT equipment, but also increases the heat density inside the data center equipment. Driven by these factors, the cost of running a data center continues to grow, even as the cost of the IT performance continues to decline.

One of the most critical sustainability issues with many data centers today is cooling. Typically, air-cooled data center operators have managed heat density issues by spreading the load and under-populating racks. This is a result of the limitations of air cooling, which creates a very costly, complex, and inefficient infrastructure. Localized, passive, low-power dissipation liquid cooling devices at either rack level or rack proximity, when compared to traditional air-cooled methods, have the capability of reducing the power consumption of in-room cooling devices by as much as 90 percent. In addition, by allowing data centers to operate with higher-density racks, rack-level liquid cooling can reduce the data center IT footprint by as much as 80 percent.

Liquid-cooling technology also permits a "pay as you go" cooling implementation, saving significant capital expenditures (CAPEX) when constructing a new data center. Present air-cooled data center construction requires an implementation from "day 1" of most of the cooling hardware for proper operation of the IT room. Localized liquid cooling is modular and would be implemented with IT expansion.

Water - an Efficient Cooling Alternative

The most energy-efficient and cost-effective way to remove the heat from the rack is by extracting the heat at the source (the rack), utilizing the airflow built in the rack through its servers and transporting the heat with liquid, which is significantly more efficient than air. Water is 3,400 times more efficient than air in removing heat. This heat extraction at the rack level could be done by a passive rear door heat exchanger (RDHx) or a side-car consisting of a liquid coil or by liquid-cooled cold plates mounted inside the servers for removal of heat from the power-dissipating components.

Alternatively, a hybrid of passive rear doors or side-cars and cold plates for high-power components inside the servers can be used. In any of these designs, one could eliminate or minimize the use of air cooling generated by the CRAC units. In addition, as much as 80 percent of the IT area could be reduced by densification utilizing liquid cooling. Furthermore, by fully populating the racks, one could obtain savings in CAPEX by eliminating excess racks and other ancillary equipment.

Free Cooling

A new trend is the introduction of air-side and water-side economizers to enable free cooling when external temperature permits. New data centers have increased their internal ambient temperature to the new American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) permitted levels, thus maximizing the number of days per year external air could be used for cooling either through direct air-side economizers or through water-side economizers.

Although air-side economizers are very efficient for energy savings, they introduce the need for extensive filtration and use of internal blowers resulting in energy consumption and contamination reliability risks. Water cooling with water-side economizers take advantage of "free-cooling" while preserving the barrier between inside air and external air.

Thus, by extracting the heat at the source, new data centers could eliminate traditional air cooling by using only liquid-circulating pumps to transport the heat to a chiller or to a water-side economizer. A few traditional units may be needed for humidity control. Water cooling permits densification of the racks and the data centers while reducing the energy consumption significantly.

Moving to More Efficient And Sustainable Operations

Data center operations have historically focused on addressing the accelerating demands of data center customers. Because of their primary focus on growth, data centers have become highly inefficient operations. Today, with other factors such as rising energy costs, limited space, and power and green initiatives, management's focus is squarely on the cost and operational inefficiencies that have been building up in data centers.

With infrastructure costs now exceeding the costs of the IT equipment itself, management must focus on gaining significant efficiencies in the data centers, which are becoming the factories of the 21st century. With cooling being a major portion of data center infrastructure costs, sizable efficiencies can be found by rethinking how data centers are cooled.

Localized liquid cooling at rack level and rack proximity eliminates one of the most inefficient elements of data center infrastructure cooling, substantially reduces energy consumption, and allows for higher rack-level compute density. In addition, liquid cooling enables cooling modularity with a "pay as you grow" investment and ensures efficient infrastructure redundancy and availability. Localized liquid cooling is no longer simply a hot-spot solution, but is now a critical component in the basis of design for new, sustainable data centers.

1. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), 1 August 2008, 2008 ASHRAE Environmental Guidelines for Datacom Equipment, available at

2. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), 2005, Datacom Equipment Power Trends and Cooling Applications.

3. Koomey, J.G., Belady, C., Patterson, M., Santos, A., Lange, K-D., 17 August 2009, Assessing Trends over Time in Performance, Costs, and Energy Use for Servers.

4. Kurkjian, C., PE, 18 May 2009, Data Center Energy Savings - by the Numbers.

5. Schmidt, R., and lyengar, M., July 2009, IBM's Rear Door Heat Exchanger and the New ASHRAE Recommended Environmental Guidelines, Proceedings of IPACK 2009 and ASME InterPACK 2009.

6. Sun Microsystems, 26 June 2008, Energy-Efficient Modular Cooling Systems, Case Study presented at the SVLG Data Center Summit.

7. United States Environmental Protection Agency, 2 August 2007, Report to Congress on Server and Data Center Efficiency, available at

Industry Perspectives is a content channel at Data Center Knowledge highlighting thought leadership in the data center arena. See our guidelines and submission process for information on participating. View previously published Industry Perspectives in our Knowledge Library.

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