Cool Runnings

09/01/2001 |

New paradigm in precision A/C technology

Too Darn Hot

IT users realize that servers can be vertically racked (dense packing) to conserve valuable floor space. The resulting power consumption and heat densities that can be created are significant. For example, the heat dissipated by a 2-foot by 2.5-foot rack can be 10kW/square foot or higher. This is the heat equivalent of one hundred 100-watt light bulbs inside a space the size of a typical home refrigerator.

With the reality of the "System-on-Chip" technology quickly approaching, the demand for precise cooling of microprocessors is rising as fast as the temperatures in today's office and data center environments. In short, computing applications are experiencing dramatic increases in power/heat density loads.

"Hot spots," caused by densely packed servers and workstations, are a prime culprit of extreme temperature swings. These circumstances create the most pressing issue currently facing engineering and facility management professionals: How to meet the ever-changing thermal requirement of computer hardware and still maintain a comfortable working environment?

It has long been recognized that significantly higher heat fluxes can be accommodated through the use of liquid cooling. Application of liquid cooling for microelectronics may be categorized as either indirect or direct.

Indirect liquid cooling is one in which the liquid does not contact the microelectronic chip, nor the substrate on which the chips are mounted. A thermal conduction path is provided from the microelectronic heat sources to a liquid-cooled cold plate attached to the module surface. Direct liquid cooling, on the other hand, is a technique where there are no physical walls separating the microelectronic chips and the surface of the substrate from the liquid coolant. This form of cooling offers the opportunity to remove heat directly from the chip with no intervening thermal conduction resistance other than that between the device heat sources and the chip surfaces in contact with the liquid.

Consequently, a tremendous amount of effort is being devoted to evaluating and developing a portfolio of products designed to deliver the best solution based on a particular application. These products are based on cooling techniques that include the Foundation Concept, where underfloor air is drawn directly into the enclosure, which protects servers, workstations, and uninterruptible power supplies (UPSs) and passes by liquid-filled coils. This technique, categorized as indirect liquid cooling, can help maximize the cooling potential of the supply air.

Considering the range of cooling technologies available today, the mandate for selecting larger-capacity air cooling units that occupy less floor space will constitute a major factor in the drive to satisfy the increasingly substantial loads still cooled by air. Reducing a cooling system's impact on floor space will continue to be a critical challenge for plant engineers in the foreseeable future.

The bottom line involves the issue of increasing the criticality of cooling systems to the site operation. Considering the fact that cooling equipment will need to be as uninterruptible as the power system itself, the continuing trend in heat/power density has numerous implications from the perspective of standby, redundancy, and operational factors where N+1 will no longer be sufficient. This, in turn, mandates the reinvigoration of current technologies in order to accommodate anticipated increases in power/heat densities.

After spending thousands, if not millions, of dollars to purchase and install sensitive electronic equipment, it should be an easy decision to properly protect it. Creating and properly installing a correct precision air-conditioning control system is more than just cutting into existing ductwork and adding vents. Thorough site analysis and proper installation will result in a custom-designed precision air-conditioning system that will provide optimum performance in cooling and protecting sensitive electronic equipment.

Dave Kelley is manager of Air Products at Liebert Corp. (, Columbus, OH, a leading manufacturer of precision air-conditioning and power protection systems.

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