The Roman Empire was considered by many to be a society with the most technically advanced infrastructure of its time. Even today, the vestiges of the engineering in Rome are still marveled at for their ingenuity and longevity; such as the Coliseum, which was designed as the first “crowdsourced” powered data center. One of the other notable hallmarks of the Roman infrastructure, one that distinguished and shaped the Roman civilization, was the common availability of water, due to the extensive implementation of the Aqueduct system. This originated in Rome and eventually extended throughout the majority of the Roman Empire.

Now of course as we all know, the Roman Empire “blue-screened” and eventually came to an end. Without making this an arcane lesson in revisionist history, one of the factors that was presumed to be the cause of the fall of the Empire, was that Rome was known as a city with a culture of excesses that spread throughout the Empire.


Water works that outlived their makers...

So why am I discussing the Roman Empire and their presumed excesses? It is interesting to note that in looking back over 2000 years at the design criterion that the Roman engineers used to size the water distribution system, it was capable of 300 million gallons of water per day, which would equate to over 300 gallons per day per citizen (or perhaps it was in anticipation of their data centers running Windows CE VII “Caesar Edition”). This per capita water allotment was actually far more than many modern societies presently allocate. Today, in most modern societies, we take virtually unlimited water for granted, both on a personal level and for industrial uses. So, without further digression, let’s discuss the subject of “Water Usage in the Data Center”.

Water Sources
Traditionally, many data centers use water that comes primarily from municipal fresh water systems. Only recently has the increased building of many multi-megawatt “Super Sized” data centers, some approximately the size of 10 US football fields, caused the builders to seek alternate sources of water. In many instances it was because the local municipal water sources were incapable of delivering the projected requirements of these thirsty behemoths. In some cases the owner/operators wanted to be Green, in others it was a case of factoring the financial cost of water, not just power.

While the numbers vary widely with temperature, humidity, equipment type and operating conditions, a typical data center will use 20-30,000 gallons per MW per day, or 7-10 million gallons per MW per year. Of course, most of the water is not actually “consumed” it is simply the make-up water “lost” into the atmosphere as part of the evaporative cooling process in the cooling towers.

So you ask, if the water is not really consumed, and as it merely evaporates and will naturally return to the ecosystem, why is it environmentally bad, since it is not really using power? In point of fact, there is significant energy used (and a carbon footprint created), by the processing of potable water. Moreover, there is a significant amount of energy used to pump the water many miles to the data center. Of course, this is all presumably reflected in the water bill the data center pays, but it is not counted as input “energy” in anyone’s efficiency calculations.

To some local municipal or water companies it is even seen as an additional revenue and profit stream, so as long as they can supply it, it is seen as a “bonus”, not a problem. In fact Microsoft’s newest data center in Northlake, Illinois a 500,000 s/f, “state of the art” facility, required that the city expand its water processing capacity, which involved an $8 million investment to upgrade the plant. However, since Northlake saw the new data center as a potentially providing an economic benefit, the deal was approved.



...and some that didn't

Green without even 'gray' water
In an age of “Who’s Data Center is more Green”, Microsoft claims that they will have a very low PUE, projected at 1.2 or less, to compete with Google’s claim of 1.21. But in most cases, water usage is not factored in anyone’s efficiency claims, if it is mentioned at all. However, Google has long been aware of the benefits (economic and political) of using alternate water sources such as rivers, and has even begun building water recycling systems as part of their newer data centers.

In some cases, “gray” water is used in an effort to minimize the use of fresh water, but some claim that this may have some potential health risks, since some contaminates will tend to be included in the evaporative discharge. However, for data centers, this is just supposition at this point, since I am unaware of any definitive links or health studies specifically regarding the use of “gray” water in external cooling towers of data centers.

Closed loop vs. Evaporative
One of the ironic issues of a closed loop air cooled system vs. an evaporative cooling system is that they are most efficient in opposite seasons. An evaporative tower tends to remove more heat during the hot weather; while an air cooled, closed loop system, is most efficient during the cold weather. In theory a dual “hybrid” system would offer the best overall efficiency and redundancy, since each could independently support the data center, however, this alternative would increase the cost and complexity significantly. The result, a simple evaporative system is the lowest cost and therefore the most commonly used system and will continue to dominate the industry for the immediate future. However, this does not mean that water usage should be ignored in the overall evaluations when discussing or evaluating efficiency.

Paradoxically, it seems that all the “Green the Data Center” type organizations that are leading the charge to improve efficiency of the data center; most noticeably “The Green Grid”, and the “US Environmental Protection Agency”, have totally ignored water usage in their efforts to promote and measure efficiency.

Part Two:
In Part II of “Water Usage in the Roman Empire’s Data Centers” I will risk the wrath of the “Roman High Council” (a.k.a. The Green Grid) and put forth my own water usage efficiency metric to be used in conjunction with the PUE metric. I hope that the lions have been fed.

The opinions expressed in this article are those of the author and are not those of DatacenterDynamics.

Part Two will be online on Monday 19th October 2009.

Related Event: DatacenterDynamics London 10th, 11th, November 2009
Related White Paper: Green Data Center Cooling Options, Begin with Air and Water - Don Beaty PE, John Lanni PE, DLB Associates
Related Opinion: Data center efficiency and the limitation of PUE, Ian Bitterlin, Prism Power