Data Center Water Usage Effectiveness
Water usage effectiveness (WUE) is a measurement that attempts to quantify the relationship between the amount of water used and the amount of IT equipment energy used in kWh.
“WUE aims to create a standard by which data centers can measure their performance and improve.”
Data centers use water-cooled chiller systems or chilled water cooling towers to cool their servers. As part of this process, cold water is pumped through the data center’s cooling system. Some of this water is then returned to a cooling tower, cooled further, and recirculated through the system.
The rest of the water not directly reused in an air-cooled data center is discharged into a sewer line or surface water body, thus creating a water management problem for many data centers. This excess heat can also cause problems for nearby buildings and ecosystems.
The Water Usage Effectiveness metric attempts to fix these issues by measuring how much of the total energy required by the chiller plant goes towards directly cooling IT equipment instead of pumping, filtering, and other overhead costs related to bringing clean water into a facility using it for cooling purposes.
How to measure WUE?
The first step in the water consumption measurement of the data center is to gather water consumption information. The method can be manual or automatic.
With the manual method, the data center operators manually record the water consumption of every building component, such as the cooling tower, air conditioning, chiller, etc. These data are then entered into a data form which calculates the data center’s total water consumption.
With the automatic method, water meters are installed for each building component to monitor its water consumption. These data will then be transmitted to the PLC controller, which automatically calculates the data center’s total water consumption automatically.
Then we calculate the WUE with this formula:
WUE = Annual water consumption (in litters) / IT equipment energy usage (in kWh).
Then we will get the ratio of water usage effectiveness for a data center. For example, in a year we use 1 million liters of water per year, and consume 15 million kWh of energy in a year, then:
WUE = 1 million liters / 15 million kWh
WUE = 0.06 liters / kWh
The smaller the WUE value, the more efficient water use in the data center is, and vice versa.
In today’s increasingly resource-constrained world, measuring WUE and looking for ways to improve it further to reduce the amount of water used per unit of computing power is crucial.
Data centers use two approaches to increase cooling efficiency and reduce energy consumption:
Use of zero liquid discharge (ZLD)
The use of zero liquid discharge (ZLD) has become a standard in the industry for data center water efficiency. This system also is known as a green data center and is widely deployed for data center efficiency. The primary purpose is to reduce water usage and prevent or eliminate wastewater release into the environment. The principles of ZLD are to collect all liquid waste streams produced by IT equipment, treat the waste stream with a compatible biocide, and transport the treated stream via gravity or vacuum to a final treatment facility that will clean it before being discharged into the environment.
Reducing water usage on an individual server level
The most effective method of reducing water usage on an individual server level would be to reevaluate the type of water used to cool the system. Most data centers currently use a cooling process that utilizes chilled water, which is chilled to approximately 30-40 °F, and then pumped through a heat exchanger where it is cooled further by filtered air and filtered conditioned, and then pushed back into the data center. This water then circulates through the servers, is cooled off by the computer hardware, and then pumped back into the cooling towers. This process continues until all the heat has been removed from the chilled water, which begins to warm up and must be circulated back out of the data center.
In both cases, the goal is to reduce water usage as much as possible. This will reduce the maintenance cost and increase the ROI for the company that owns the data center.
Read more about: green data center standard
To be more efficient, many organizations have introduced waterless air-cooling systems into their data centers. Many high-tech companies are now turning to air-cooled systems instead of chillers because they are more cost-effective and reliable than chillers concerning operation and maintenance. They also have lower energy costs and can be used where chilled water is unavailable.