Q

Is evaporative cooling efficiency up to data center standards?

Evaporative cooling offers energy efficiency, but there are downsides to consider before choosing it over CRACs.

As energy costs rise and business computing needs change, evaporative cooling technologies are receiving more attention from data center designers.

The general design of a powered direct evaporative cooling unit hasn't changed much: A blower moves warm outside air to evaporate water from a porous material, cooling and humidifying the air.

Evaporative cooling -- also called swamp or adiabatic cooling -- uses the heat energy from warm ambient air to convert water into steam. Since heat is pulled from the incoming air, the outgoing air is cooler: about 890 BTU per pound of evaporated water (2,257 kilojoules per kg) of energy transfers.

What are the advantages and disadvantages to evaporative cooling?
Evaporative cooling efficiency is the most compelling advantage to this technique. Rather than an energy-hungry compressor used by mechanical refrigeration systems, an evaporative cooling system only needs a simple fan to move the air and a basic water pump to keep the pads wet. The components are also easier to maintain than traditional computer-room air conditioners, depending on the size and sophistication of the overall system. Evaporative cooling is environmentally friendly because the refrigerant is ordinary water rather than a chemical product, such as chlorofluorocarbons or other toxic chemicals.

The biggest disadvantage of evaporative cooling is the role of humidity -- evaporation is quite useful in climates like deserts, but can be far less effective in humid ones. At the same time, evaporative cooling requires a constant supply of water -- problematic in the dry, arid climates where it works the best. This limits evaporative cooling deployments to specific geographic areas.

Free cooling and design options

More on evaporative cooling
The Kyoto wheel
Air or water economizers

Another potential problem is the biological side effects of evaporative cooling, including algae growth and corresponding odor, pests such as mosquitos breeding in the water, and the potential for mold and mildew in duct work, which creates potential health concerns for workers.

If you're able to adopt evaporative cooling, you can increase the data center's efficiency by consolidating onto fewer servers and operating at elevated temperatures. This combination of factors makes evaporative cooling more attractive for data center use.

This was first published in July 2014

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