Do You Know the Hydro-Footprint Of Your Data Center?

Ron Vokoun, DBIA, LEED AP BD+C, leads the Mission Critical Market for JE Dunn Construction’s western region. Ron is a 25-year veteran of the construction industry with a focus on mission critical facilities and sustainability. Ron was previously Director of Mission Critical for Gray Construction and also served in leadership roles with Qwest Communications and Aerie Networks. Harold Simmons, Director of Strategy and Mission Critical Solutions for United Metal Products, co-authored this article. See more on Harold below.

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In my last column, Water Consciousness Continues in the Data Center, cooling technologies that are proven to reduce the consumption of water were discussed. I also outlined issues surrounding the availability and potential alternative sources of water for data center cooling. Clearly, there are ways to make data center water usage more sustainable. In this column, let’s discuss the complex relationship between water and energy use in the data center.

WUE and PUE

The Green Grid has been at the forefront of the data center energy efficiency movement and is again leading the way in monitoring the use of water in data centers. The Water Usage Effectiveness (WUE) established a Key Performance Indicator (KPI) metric to measure the amount of water used in a data center.

WUE

Water Usage Effectiveness (WUE) is a metric to evaluate water use and it is being promoted by the Green Grid.

The complexity in the relationship between water and energy use can be illustrated by comparing WUE and PUE in a particular data center. If your focus is purely on reducing on-site water use, you can use air-cooled chillers and have a great WUE. However, there may be a premium paid in the form of higher energy usage compared to a technology such as evaporative cooling depending on your location, thereby elevating your PUE.

An aspect of water use that is often ignored is the amount of water used in the production of the power that is used in the data center, which leads us to the discussion of hydro-footprint.

Hydro-Footprint

Depending on the location of your data center, the production of power can be quite water intensive. The National Renewable Energy Laboratory (NREL) performed a study titled Consumptive Water Use for U.S. Power Production (PDF) that analyzed the amount of water used in the production of power in each state. Illustrating the impact of water used in the production of power, let's continue, using the data from my last column.

According to the NREL study, power produced in the state of Arizona, on average, uses 7.85 gallons of water per kilowatt-hour. The table below illustrates the annual power use for a 36,000 CFM cooling unit using four different technologies. (Assumptions for both charts: DC located in Phoenix, based on ASHRAE recommended humidity range, based on inlet supply temperature to servers at 80-degrees F, water and power consumption is for 36,000 CFM unit, data is representative and does not apply to all brands, and data provided by United Metal Products.)

AnnualizedPowerConsumption

Click to enlarge graphic.

The table below shows the amount of water used annually for cooling for the four different technologies, as well as the amount of water used in the production of the power used in their operation giving the total hydro-footprint of each unit.

WaterConsumption

Click to enlarge graphic.

As you can see, although the air-cooled chiller uses the least amount of water in cooling operations, it’s higher power use yields a higher overall hydro-footprint than Options 1 & 2. This exercise highlights the need to look at water use more holistically and include the water used in the production of power.

The Green Grid’s WUE metric also has the ability to take this into consideration by adding the water used during the production of the power used by the cooling equipment to the annual site water usage.

WUE-source

WUE Source calculation.

Whichever metric you use, it will help you weigh the options for both power and water consumption and make an informed decision. By tracking your data centers’ efficiency in consuming water and energy, you take a huge step toward creating a more operationally sustainable data center environment.

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Co-author Harold Simmons is Director of Strategy and Mission Critical Solutions for United Metal Products and Chil-Pak.

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