Water-efficient data centers
By Winston Huff, CPD, LEED AP BD+C
Data center owners and operators have recently made great strides in energy and water efficiency. It is commonly known that data centers use significant amounts of energy, and consumers are starting to recognize the ripple effect from such energy usage. This is becoming a big public awareness issue with data centers. Consumers are concerned about the environmental or political impacts of some energy sources and understand that they have the ability to reduce their use of the energy and, as a result, decrease the harmful environmental and political impacts of certain energy sources. Thus, data centers that are good stewards of power will most likely be viewed in a positive light by the public and gain more clients.
However, did you know that data centers also use significant amounts of water as well? Data center operation is a good example of how water and energy efficiency are interlocked, but in some cases water efficiency is sacrificed to maximize energy efficiency. The following column examines how energy and water are used in data centers, organizations that are developing ways to promote water efficiency and examples of water-efficient strategies for data centers.
When new designs that use less power and water are under consideration, the team should look at data from other projects so design decisions can be based on real-world operations. Energy and water models are becoming very important when choosing the type of energy system to be used at a particular site. Benchmarking is also helpful to verify that the system will be more efficient. Unfortunately, developing a benchmarking system can be difficult.
The Green Grid (thegreengrid.org) is an organization that is taking this challenge to task and promoting energy and water efficiency in data center design and operations by developing metrics to advance energy and water effectiveness. Some of the metrics it has introduced in the past few years include power usage effectiveness, data center energy productivity, energy reuse effectiveness and data center compute efficiency. A new metric, water usage effectiveness, calculates the annual water usage of a facility (in liters) divided by the IT equipment energy used in the facility (in kilowatt-hours). Combined with the other metrics, the water usage effectiveness metric will enable data center operators to quickly assess the water, energy and carbon sustainability of their facilities, compare the results and determine whether any improvements need to be made.
The Green Grid guidelines are concerned with the amount of water that is used to generate electricity offsite, because offsite power generation can be part of a facility’s entire water footprint. Why should a facility take extra measures to reduce water usage in energy production at the data center site when the utility wastes water when electricity is initially generated? TGG suggests referring to the National Renewable Energy Laboratory report, Consumptive Water Use for U.S. Power Production (http://1.usa.gov/S022bL) to determine how much water is used in the production of power per kilowatt-hour in each state.
The U.S. Green Building Council Water Efficiency Technical Advisory Group discussed water used in offsite energy generation when developing the current LEED guidelines and the next generation of guidelines due out next year. Should this be another way for a building to obtain LEED credits? The group realized the importance of reducing water in a building and in power generation offsite. After much discussion it was decided that, at this point in time, the USGBC development guidelines should focus on water usage on-site in a building’s design and operations. Introducing complex submittals to track offsite water would be difficult when important on-site water issues still need to be addressed.
Water and energy use in data centers
Determining the right mix of energy and water-efficiency strategies is a delicate balancing act. In some cases a water-based system can be more energy efficient than a system using air, but is it really efficient to use more water to save energy?
Data centers use energy in two major ways. One is to operate the servers; the other is to move heat away from the servers. Servers operate most efficiently at a specified temperature and humidity, so, while they are operating, any excess heat produced must be removed and the proper humidity level must be maintained. The amount of power and the availability of the power are very important factors, because the power must be dependable and continuous.
Operators looking for ways to reduce water usage should first consider retro-commissioning. One common problem that can be discovered with commissioning is when computer room units and humidifiers work against each other. A computer room cooling unit removes the humidity in the air stream by cooling the air, but then the downstream humidifier adds humidity back to the same air stream. ASHRAE Technical Committee 9.9: Mission Critical Facilities, Technology Spaces and Electronic Equipment, recently recommended a reduction in the humidity levels in data centers, but many centers are reluctant to reduce these levels.
More creative options are available that use less water and energy to remove heat and maintain humidity. Green power, such as solar, wind and fuel cells, is an option to consider in power generation. These systems can reduce the amount of water used in the power generation process and can be installed on-site or offsite.
Thanks to the Internet and cloud computing, most tasks are being done in remote data centers located around the world. Because of this, data center operators can reduce energy and water usage by locating their facilities in suitable areas. For instance, a location in a cool climate can reduce the amount of cooling that is required to operate the center. In theory, a data center that can use the free, cold, dry air from outside the facility will use less power than a facility located in a region with a hot and humid climate. The cool outdoor air needs little dehumidification, so in these conditions the use of a cooling tower and the associated concerns regarding water usage can be reduced or, possibly, eliminated.
An interesting case study is the Facebook data center in Prineville, Ore. Information about the facility’s water and energy systems can be found on the Open Compute Project website (opencompute.org). The facility’s WUE has been tracked on a quarterly basis, and it is on target to achieve approximately 0.22 L/kWh for the first-year annualized calculation. Other water-efficiency strategies include a water meter to track the data center cooling water usage, reclaimed water and waterless urinals. Most of the water savings are due to the elimination of the need for a cooling tower.
The data center’s mechanical system utilizes 100 percent outside air economization with a direct evaporative cooling and humidification misting system. It differs from typical data centers because it uses outside air instead of recirculating 100 percent of the air used to cool the server room. Traditional systems use chillers and cooling towers to maintain the proper conditions. This was not required in this facility, in part because of the low temperature and humidity of the outside air.
The facility uses water in a misting system for cooling in the direct path of the supply air to the data hall. The small orifices on the spraying system require high-quality water, so the water goes through a carbon filter, softeners and reverse osmosis. Approximately 75 percent of the water that is brought into the data center cooling operation is used, while 25 percent is blown down. The next Facebook data center planned on the site will use a membrane system instead of the misting system to reduce water use even more.
Not all data centers are designed the same. Apple is in the process of building a data center in Prineville to also take advantage of the cool night air, but, unlike the Facebook facility, Apple plans on using a geothermal system to provide cooling for the building. Geothermal systems typically use less water compared to a system using a cooling tower.
Another Apple data center in Maiden, N.C., earned LEED Platinum certification. Outdoor weather conditions are much different in this location than they are in Prineville, so this facility uses a waterside economizer during the night and cool weather hours. Chilled water storage systems improve chiller efficiency by transferring 10,400 kWh of electricity consumption to off-peak hours each day. These systems allow the chillers to be turned off 75 percent of the time. The building does have a cooling tower; however, it is not used as much as a typical cooling tower system.
Google is not to be outdone in the sustainable data center competition. The company is looking into using seawater from the cold Baltic Sea in Hamina, Finland, in an old paper mill that will be converted into a data center. The cold water will be used to cool the servers, so cooling towers will not be required.
The creative minds that have designed computing systems and data center technologies have changed the way we live, socialize and work. Complicated tasks are made easier, and data is more readily available. These same creative minds may develop ways for data centers to use water and energy more efficiently. This new test bed of technology in data centers can benefit other building types and raise the bar on building water and energy efficiency.
Winston Huff, CPD, LEED AP BD+C, is a project manager, plumbing fire protection designer and sustainable coordinator with Smith Seckman Reed Consulting Engineers in Nashville, Tenn. He serves as an ASPE representative on the ICC Green Construction, Energy and Water Code Development Committee and is on the U.S. Green Building Council’s Water Efficiency Technical Advisory Group. He was the founding editor of Life Support and Biosphere Science and has served as its editor-in-chief. He also is editor of Me Green You Green (megreenyougreen.com), a LEED credit databank.