Designing efficient data centers: Sustainable buildings, energy efficiency
Doug Bristol, PE, Electrical Engineer, Spencer Bristol, Peachtree Corners, Ga.,
Terry Cleis, PE, LEED AP, Principal, Peter Basso Associates Inc., Troy, Mich.
Scott Gatewood, PE, Project Manager/Electrical Engineer/Senior Associate, DLR Group, Omaha, Neb.
Darren Keyser, Principal, kW Mission Critical Engineering, Troy, N.Y.
Bill Kosik, PE, CEM, LEED AP, BEMP, Senior Engineer – Mission Critical, exp, Chicago
Keith Lane, PE, RCDD, NTS, LC, LEED AP BD&C, President, Lane Coburn & Associates LLC, Seattle
John Peterson, PE, PMP, CEM, LEED AP BD+C, Program Manager, AECOM, Washington, D.C.
Brandon Sedgwick, PE, Vice President, Commissioning Engineer, Hood Patterson & Dewar Inc., Atlanta
Daniel S. Voss, Mission Critical Technical Specialist, M.A. Mortenson Co., Chicago
CSE: What unusual systems or features are owners requesting to make data centers more energy efficient?
Kosik: The energy-efficient systems and features used in data centers will depend on the owner’s reliability expectations, among others. For example, a highly reliable data center that is required to be fault-tolerant has an electrical and cooling system topology that is very different than a basic redundant system topology. Focusing on the UPS system efficiency, a double-conversion UPS (used, for example, in high-reliability data centers for the banking industry) will have an efficiency that will vary between 82% and 90%. Compare this to a data center with less stringent reliability requirements (such as a supercomputing facility) and does not require UPS power for a substantial percentage of the electrical load. The overall efficiency will range from 95% to 99%. Using more efficient systems and topology will reduce energy use attributed to the UPS by 10% to 15%.
Peterson: Not necessarily new, but owners have inquired about reusing data center heat when possible. We’ve been following similar successful projects in Sweden and by university and energy labs in the U.S. to respond to these requests; however, thus far the costs have been limiting. Another method that we continually examine is how river, lake, and ocean water can provide cooling more efficiently and directly for new and legacy data centers to save not only energy but water as well.
Voss: Some owners are requesting higher voltages at the cabinets and racks for their computing equipment. The higher voltages have two advantages: First, there is less voltage loss in the distribution system; secondly, there is one less voltage conversion (transformation), which removes the inefficiencies of that conversion step.
CSE: What types of sustainable features or concerns might you encounter for a data center that you wouldn’t for other projects?
Peterson: Capturing and reusing the data center’s heat is one of the things more owners have inquired about more frequently. As the data center temperatures have increased over time, the temperatures that can be used for exchange become more viable.
Voss: In lieu of using standard open cooling towers for a chilled-water system (which evaporate thousands of gallons of water per month in the warmer months), a selected alternative choice is closed-circuit fluid coolers, which evaporate about 10% of the water evaporated by cooling towers. This saves the cost of the domestic water and keeps more water available for other uses.
CSE: What types of renewable or alternative energy systems have you recently specified to provide power in data centers? This may include photovoltaics (PVs), wind turbines, etc. Describe the challenges and solutions.
Voss: There are two main areas of renewable energy that have been integral to data centers that I have worked on. The first is hydroelectric power, which has been around for a long time, but most data center locations are not supplied by this renewable source. Second, are wind turbines mostly from a utility grid, but a couple of new sites are planning to have a local wind farm and possibly a PV farm.
Sedgwick: We frequently commission alternative energy systems for clients that are trying to offset data center power consumption with alternative generation sources, such as sun, wind, geothermal, and hydroelectric. Natural gas fuel cells are also becoming more common; clients offset natural gas consumption by purchasing biogas. We recently commissioned a large-scale microgrid control system that combines alternative energy power sources including PV, fuel cell, and battery storage with traditional diesel generation. One of the largest rooftop solar installations in the world, the 700,000-sq-ft array produces 17 mW under peak conditions—enough capacity to power up to 75% of this high-profile 2.8 million-sq-ft facility on a 175-acre campus. The facility also features a natural ventilation system designed to eliminate the need for air conditioning and heating for 9 months of the year. This unique microgrid system minimizes dependence on the utility grid and allows reliable operation while in island mode (e.g., isolated from the grid). It includes load shed, source management, special relaying and protection (due to low-fault currents), and monitoring and control of sources and loads.
Peterson: We’ve been adding photovoltaics to support all the ancillary systems of data centers—lighting, office-area power, and noncritical HVAC. The costs of these solar systems haven’t been as important as being able to point to having a renewable power source on the site. Our teams have also completed studies on the viability of other renewables on client sites including geothermal cooling, wind, and hydropower. Another cooling means is to use water from lakes and rivers as a heat sink; this has been proven to be reliable and incredibly efficient after being successfully implemented for sites throughout the world. We anticipate seeing more requests to use natural, renewable heat-sink sources to reduce capital expenditures (chillers, cooling towers, etc.) and operational expenses (cooling electrical costs, water use, chemical treatment, etc.).
CSE: What are some of the challenges or issues when designing for water use in such facilities?
Kosik: Water use in data center HVAC systems will dwarf the water use of an equally sized commercial building. Conserving water in data centers is still relatively new (10 years). Most early data centers used air-cooled DX cooling systems that did not use water for heat rejection. Many of today’s mega data centers require central chilled-water systems due to the facility size and ongoing maintenance costs. In this case, heat rejection is often accomplished using outdoor equipment that dissipates heat to the atmosphere by evaporating water, such as in an open cooling tower or evaporative cooler. It can be a catch-22 situation: reducing water use could increase energy use (which increases water use at the power-generation plant). The discussion changes based on where the data center is located. Some geographical areas have more urgent water-conservation requirements.
Voss: For water-cooled data centers that use enormous quantities of water, the challenges start when coordinating with the local municipality to determine the quantity of and flow rate of domestic water available at the data center location. In addition, many jurisdictions and designs call for a secondary source of water (usually a private well drilled for this purpose onsite). Normally, there is also a water-storage tank onsite that holds from 20,000 to 40,000 gal of water in case both water sources are not available.
Peterson: A conversation with an owner about water sounds a lot like those about energy. Using less is always better. Water use, treatment, and how it affects a data center cooling plant is often overlooked. Simply having a treatment service that routinely adjusts and updates the water quality can be a major difference in the efficiency of the cooling systems, from open loops for cooling towers to evaporation systems to closed- loop chilled-water systems.
CSE: How has the demand for energy-recovery technology influenced the design for data centers?
Voss: Energy recovery is very important, but it has not taken a strong foothold in the data centers with which I have been involved. There is a much bigger interest in lowering the PUE of the data center. The lower the PUE value (closer to 1.00) the more efficient the data center is operating, which directly translates into substantial energy-costs savings.
Kosik: Data centers present great opportunities for energy recovery. 1) Data centers have much higher supply- and return-air temperatures when compared with an office building. This creates greater opportunity for recovering energy. 2) When the computers in the data center are water-cooled, heating energy can be recovered due to the high internal temperature in the computers. Recovering high-temperature heat will make the overall system much more effective, particularly if using the heat for snow melting or space heating. Considering that a direct water-cooled computer will discharge water at 150⁰F, there are many opportunities for reclaiming the heat from the water.