Smart cooling strategies help data centers maintain 7x24 uptime, maximize energy efficiency, control overhead costs, and meet sustainability goals.
To reap these benefits, data center designers use what is often referred to as “free cooling.” It’s a method of cooling a building without using air conditioning when ambient temperatures are low enough. This reduces wear and tear on compressors and can save electricity. As with most things so named, though, it’s a misnomer — nothing is free.
Power is still needed to run pumps and fans that keep water and air moving in any environment, and thus it’s not technically “free.” But, used wisely, this method can contribute greatly to reducing a facility's electrical expenses and carbon footprint.
The system used to achieve free cooling is known as an economizer. Air-side economizers exist and are not unheard of in data centers. However, water-side economizers are more common.
When outside air temperatures are low enough to cool the loads within the data center or provide a portion of the required cooling, economizing can relieve some of the energy use of the mechanical compressors. There are different methods by which this can be accomplished, depending upon the type of chiller utilized and how the system is piped. But typically, three-way valves allow water, or a water/glycol mix, to be pumped from the air handler in the interior of the data center, carrying heat with it to an additional heat exchanger coil that is mounted in-line with the outdoor condenser.
The heat exchanger releases heat to the outside, chilled water is pumped back into the building, and the process begins anew. ASHRAE recommends using integral economizers to capture some cooling capability from lower ambient temperatures while the mechanical compressors handle the remaining load.
What’s the Best Choice for a Data Center?
There’s no “one size fits all” approach for cooling a data center, which is why consulting with an expert is crucial. Cooling experts consider the footprint of the building and property, the climate it’s in, and the IT load to design a system that best addresses the customer’s needs.
Water-cooled chillers offer greater energy savings than air-cooled chillers, but they are more complex; more costly to install; and they lose some water to drift, blowdown, and evaporation. In areas with low wet-bulb ambient temperatures, such as Phoenix, it’s easy to evaporate water in a cooling tower. In warm, dry climates, it’s common to have an outdoor temperature of 110°F. But, because the wet-bulb temperature is only 65°, the air temperature returning to the data center can be a cool, 70° without using refrigeration.
The heat from the white space is captured and removed from the chiller through a cooling tower, dry (air) cooler, or a combination of both — typically called an evaporative fluid cooler. If a conventional cooling tower or an evaporative fluid cooler is used, there will be water consumption due to evaporation. For an air-cooled chiller, the heat is removed in a closed-loop heat exchanger, and no water is consumed.
The U.S. Environmental Protection Agency (EPA) predicts that by 2024, 40 U.S. states will experience water shortages. Forward-thinking data centers are looking to use water efficiently, even more so if they're located in areas already drought-prone. In these circumstances, data centers can use air-cooled chillers with a closed-loop waterside economizer.
Air-cooled chillers are an increasingly popular choice for colocation managers who appreciate modular flexibility. The cooling system can be easily expanded in modules to meet clients’ varied needs, unlike water-cooled chillers that require additional plumbing, maintenance, and floor space. However, when it comes to buildings that lack roof space or land, water-cooled chillers are the better option.
Good, Better, or Best?
It’s a mistake to treat a chiller as a commodity. A more efficient cooling system saves energy costs on operational profit and loss statements and helps meet sustainability goals. There are other benefits, often unconsidered, by those buying on price alone.
Using less power could mean saving money on other capital expenditures, such as generators, electrical cabling, and switchgear. That could make a more efficient piece of equipment that is much more cost-effective over the system’s life cycle and potentially provide more usable power for the IT equipment.
With greater cooling efficiency, the chiller plant size can be reduced, translating in power to support more IT capacity — critical for data centers promising high levels of redundancy.
Ford Data Center
The Ford Motor Co. transformed its Dearborn, Michigan, campus to a modern, high-tech facility to foster innovation. Key considerations for its large Tier III data center were to reduce its energy consumption and carbon dioxide emissions.
Ford required HVAC systems that could adhere to special tolerances and guarantee chiller capacities were selected to maximize uptime and lower the total cost of ownership. Six 670-ton centrifugal chillers were installed to handle the cooling needs of the data center. To further increase efficiency, when outdoor temperatures are cold, an integrated economizer option provides up to 45% of chiller capacity without running the compressor.
Historic Mill Redevelopment
When Cape Augusta Digital Properties (CADP) redeveloped the historic Sibley Textile Mill in Augusta, Georgia, into a 10-MW data center, it took advantage of its unique location. The data center is powered by the same water source for much of its cooling, the Augusta Canal. CADP selected chillers that allow the plant to operate at a 20° temperature differential with a 55° chilled water loop.
The system is a great use case for economization and unique for the facility’s southern geographic area. The CADP's economizer runs without mechanical cooling for much of the year, helping the data center achieve a PUE that ranges from 1.13 to 1.15.
Studies by the U.S. Department of Energy show the average PUE for data centers is 1.8, but organizations focusing on efficiency typically achieve PUE values of 1.2 or less.
Strategy + Selection = Maximum Investment
Optimizing energy use is a balancing act. Even though the chiller compressor doesn’t start when the economizer is in use, it doesn't automatically result in savings. The system could be wasting electricity for the amount of chilled water produced this way by blowing more air through the conditioned space than needed. This consumes more energy, which means the pumps and fans could be working much harder to provide proper cooling.
The combined energy impact of running the chiller compressor could be less than working just one component, especially with all the advancements in compressor technologies. Today’s variable-speed compressors operate efficiently at lower temperatures, with equipment-saving features, such as refrigerant management and oil mitigation.
Weigh the benefits of the “better” or “best” options. Selecting equipment that offers economization 364 days of the year still leaves one peak day for which it's unavailable. Therefore, the entire infrastructure must be designed to handle the cooling loads of that one peak day, negating many of the benefits of installing a more efficient cooling system.
Expert cooling designers can make informed decisions about which strategy is ideal for a facility to meet its CapEx, OpEx, and sustainability goals.