©2019 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 61, no. 11, November 2019.
About the Author
John Peterson, P.E., is a mission critical program manager at AECOM and a member of ASHRAE TC 9.09, Mission Critical Facilities, Data Centers, Technology Spaces and Electronic Equipment.
With the expansion of cloud computing and increasing demands for online services, the number of data centers continues to grow throughout the world. As the need for energy to support these data centers rises, the need to find and use efficient cooling sources will also increase. Generating cooling on site using electricity from power plants is less efficient than planning ahead and using more localized cooling sources. To reach the energy saving goals, designers need to broaden their choices to find the most beneficial options available. Using our natural resources in a more direct way can bypass inefficient cooling steps.
The first deep lake water cooling system in the U.S. started in 2000 in Ithaca, N.Y., and serves over 70 MW of cooling. This system is presented here for lake water use. A data center in Hamina, Finland, is reviewed for using seawater. The potential efficiencies, comparisons of savings of equipment and other advantages and disadvantages are also illustrated. For data centers and other critical facilities, the additional requirement to meet higher reliability standards will also be evaluated.
Water Sources: Rivers, Lakes, Oceans
Water is the best medium for moving and rejecting heat for most cooling and heat transfer applications. Moving heat out of a data center is no different in this regard and getting water closer to the heat source improves the efficiency of the overall facility. Water can move more heat per unit (gallon or liter) than most other liquids, and is far more efficient than air systems. Because of this, chilled water is often used to pull heat from airstreams and water-cooled equipment. Water is most dense at 39.2°F (3.98°C), which is the temperature often found in deep lakes. Since about 3% of the water on earth is fresh water that we use for irrigation and consumption, alternate cooling systems should be considered that operate with salt water and other non-potable water sources to conserve this resource.
Alternate cooling systems offer several benefits including reduced consumption of potable water, reduced space for equipment, and eliminating noise and potential biohazard outbreaks that are associated with cooling towers or similar systems. Refrigerant volume is also reduced or eliminated, and there are lower needs for protection from weather degradation, vandalism, as well as protecting operating personnel from hazardous space conditions.
Rivers have long been used to support power plant and manufacturing operations. The water temperature of rivers tends to vary the most through different seasons and they are also more closely regulated upstream, downstream, and across borders.
While the surface of lakes varies with the weather and seasons, they have a more constant temperature below (Figure 1). The temperature becomes more steady with depth, as the deep water within a lake is less affected by weather, storms, and other events.
Deep ocean water, like deep lake water, has a very stable temperature year-round, and can be used for direct cooling. Even in hot, tropical locations deep ocean water can be reliable to achieve 59°F (15°C) at 1,640 ft (500 m) below the surface and about 41°F (5°C) at about 3,280 ft (1000 m).
While the temperature of surface ocean water can fluctuate seasonally, it can still be a valuable source of cooling. In hot regions such as the Middle East, surface seawater as high as 90°F (32°C) is used for condenser cooling with conventional systems. This is because even the higher temperature water is more efficient than air cooling and using potable water for evaporative cooling is not allowed due to water use restrictions.
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