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Many data center operators, as they take steps to ensure competitiveness in a challenging market, are examining new approaches to data center cooling technology. The current heat-exchange methods for cooling data centers are inherently inefficient when it comes to meeting the requirements imposed by today's dense, high-speed computing equipment. They can also lead to considerable expenses.

By implementing a solution that aligns with a range of business initiatives ' including cost-effective operation, optimization of energy efficiencies, reduced management complexity and the need to meet green computing initiatives ' data center operators can address these challenges and extend their competitive advantage.

Conventional Cooling
It can be wasteful using room air as a heat-exchange medium and by mixing hot and cold air you can limit cabinet, frame and rack density -- you can't effectively cool high heat density equipment placed close together.

Current conventional heat removal systems include:

  • Computer room air conditioners (CRAC). Large air handlers that blow cold air through under-floor ducts and plenums in a raised-floor environment up into a "cold" aisle, where the air intake of the server equipment is pointed. In this model the exhaust sides are pointed towards a "hot" aisle where the heated air is pulled by the CRAC units.
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  • Aisle containment solutions. These trap cold or hot air so they can concentrate air streams and increase efficiency, but they still rely on air as the heat transfer medium.
  • Chilled water systems. Chilled water systems bring chilled water into the data center to perform the heat exchange, with water acting as the heat-transfer medium. These increase efficiency by using water, which is a far better conductor of heat than air.

    In row or overhead systems. These systems pull hot exhaust air into the dedicated duct systems where heat exchangers remove the heat.
Phase Change of Two-Phase Cooling
A more cost-effective and efficient solution for maximizing heat transfer and enabling higher heat density equipment frames can be accomplished using properly positioned phase change or two-phase pumped refrigerant cooling methods. Pumping low pressure, oil-free, refrigerant through micro-channel heat exchangers can provide up to 90 percent less energy consumption for the primary cooling loop within the room. 
A refrigerant-based system can also be deployed to cool existing computing equipment in existing IT cabinets without extensive and expensive changes to the present data-center infrastructure. The primary benefits of such a solution include reduced energy requirements, optimized utilization of data center space and lower OPEX and CAPEX. It is also 11-to-40 times more efficient than conventional computer room conditioning CRAC systems.

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This method of precision cooling places a coil directly at the exhaust of the server equipment. This is connected to a manifold system that circulates refrigerant in the primary loop in a multi loop system. The exhaust air from the server equipment passes through this coil. The heat is extracted using a phase change of the refrigerant from liquid to gas (heat is absorbed from the server exhaust). The refrigerant then travels through the manifold system to a heat exchanger in the pumping unit where the heat is transferred to the building heat sink and ultimately exhausted into the atmosphere.
The coil is mounted in a structure that incorporates two low power auxiliary fans to insure sufficient airflow through the coil and prevent heat build up at the coil's input side. Figure 3 shows a photograph of the heat exchanger installed in a cabinet with the upper unit extended, providing access to the rear of the server and the lower unit in the normal closed position during system operation. 

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This active airflow design compensates for the varying distance between the exhaust point of the server and the input side of the coil, insuring maximum airflow in multiple configurations and multiple cabinet designs. It is a method that maximizes the cooling effectiveness and provides an efficient means of removing the heat from the data center. 

The effectiveness of the system allows the data center operator to reclaim space in existing cabinets and rows to maximize density within the existing footprint. Secondary benefits include reduced internal server temperatures and reduced noise throughout data center due to server fans operating at slower speeds because of the efficiency of the method of cooling. Better still, intake and exhaust aisle temperatures are close to balanced resulting from the systems efficiency. 

There are numerous methods and systems to cool data centers but the efficiency provided by the phase change heat exchange method provides energy efficiency benefits beyond the capability of conventional air handling methods.