Data Center Design and Low Energy, HVAC Cooling

Written by Lisa Huff

The proliferation of data brings the energy efficiency of data centers to the forefront in an effort to lower investment and operating costs, as well as their impact on the environment. Deerns Consulting Engineers has developed a three step approach to reducing the energy used to cool data centers by 80 percent while maintaining the reliability of the cooling system. The reduced system infrastructure and modularity also results in lower investment costs and increases the phasing of investment.

Step one focuses on total cost of ownership. The company uses free cooling which has resulted in up to 25 percent less cooling energy consumption in certain data centers. In Deerns model, outdoor air is drawn through a plate heat exchanger, where it absorbs heat from the IT room’s hot return air. Next it’s cooled and re-circulated through the data center. By separating the air streams, the outside air can be cooled evaporatively without influencing the humidity in the data hall and without risk of contamination from dust, smoke, pollen, and other particulates. If outdoor air temperatures rise, evaporative coolers will provide low-energy supplemental cooling without requiring refrigeration-based cooling systems. This green cooling approach optimizes the efficiency of the entire cooling system reduces a data center’s overall energy use by 25%.

Step two is to seek improvement in the efficiency of the energy that is used by storing “cooling energy”, to utilize cheap cold air or cold surface water in relation to daily or seasonal fluctuations. This has been done in a 6,500 m2 (70,000 ft2) data center for a corporate client in the Netherlands, using an aquifer to store cooling energy in winter and during the night in other seasons. Using this stored cold during warmer periods results in a reduction of the power usage efficiency (PUE) to less than 1.35 (at full load, 1.26), and a substantial reduction of the operational expenditures and indeed, the total cost of ownership.

The third step centers on an innovative and efficient way to transfer heat outside of the facility. It is referred to as the GC-DC© concept (Green Cooling for Data Centers, in collaboration with KyotoCooling© and Holland Conditioning) In the GC-DC© concept, the standard recirculation units in the computer room are replaced with compartments, which include a heat exchanger and coolers outside the computer room. Heat is expelled directly outdoors.

The direct transfer of the heat developed in the computer racks to the outdoor air, means free cooling can be used for a much greater part of the year, in temperatures up to 21°C /70°F. Beyond that, the system is aided by a compression cooling unit outside the computer room. Since the system is compartmentalized, full cooling system failures are avoided and there is no liquid cooling in the computer room. Also due to its modularity, investment costs for the cooling infrastructure can be planned in line with the growth of energy demand.

The GC-DC© concept reduces the demand for cooling energy by 80 percent when compared to a conventional system. It achieves an overall PUE of 1.15. Even in a hot climate like Phoenix, Arizona, the reduction in cooling energy is approximately 30 percent, with an overall PUE of 1.38. The GC-DC© concept is the next step in the evolution of data center cooling.

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