I did a search on going green in data centers and my squeaky old home internet connection delivered 9,140,000 hits in 0.56 seconds. The obvious question then should be: Is there anything new left to be said on this subject? I think the reasonable answer would be – not likely. The now-old cliché for green data centers, excluding perhaps some of the anachronistic LEED’s requirements, goes along the lines of C-suite inhabitants are interested in greening their data centers because that adds some green to the old bank account. Unfortunately, in most cases this cliché has a much weaker grasp of reality than we expect from our clichés and, while green and efficiency generally have a pretty positive correlation, green energy and greenbacks do not always have such a positive correlation. After surveying today’s conventional wisdom on strategies for going green in the data center, (spoiler alert!) I will suggest a potentially contrarian new strategy for securing both greens.

1. Pay Attention to Airflow Management

The first strategy for going green in the data center and saving some green at the same time is basically: Pay attention! Pay attention to those basic elements within the data center over which you have some control, or at least should have some control. Pay attention to airflow management. With optimized airflow management, then you can pay attention to temperature management. With effective airflow management, supply temperatures can be raised 15-20 degrees without increasing server inlet temperatures, which then establishes a good reason to pay attention to chiller and economizer management – the greenest chiller is the one that is not running and the next greenest is the one operating at the highest temperature. In addition, paying attention to airflow management makes paying attention to cooling fan energy worthwhile…and profitable. Another part of this strategy is paying attention to power conditioning and distribution. Paying attention to power distribution won’t deliver anywhere near the green dividends as paying attention to the elements of the mechanical plant, but three phase power and restricting on-line double conversion losses to out-of-spec power supply help both green initiatives.  Finally, paying attention to maintaining highest reasonable server utilization levels is a well-known and oft-discussed greening strategy. Fortunately, all these elements in the “pay attention” strategy come with systems that pay attention to them for us and they typically have ROI paybacks that can be measured in days, weeks or months instead of years. To steal a clever coinage: the greenest kW is the unused kW.

2. Utilize Renewable Energy

A second greening strategy for data centers is utilization of renewable energy, which has garnered significant media attention in the past couple years, particularly with the Google, Microsoft, Apple and Amazon investments in wind energy. This strategy will have the largest green energy impact by virtue of the most significant impact on total carbon contribution from a data center, but may not always have a similar greening impact on the old bank account. On one extreme, data centers in the far Pacific Northwest powered by hydro-electric energy at some of the lowest per kW rates in the country will have essentially immediate positive returns on investment while leaving very minimal carbon footprint. On the other extreme, we can have solar energy for data centers that may have 20 year paybacks and also dramatically extend the geographic footprint of the data center. In between those two extremes, highly publicized wind energy may have 10-14 year paybacks, which can be perplexing to a bean-counter when wind turbine equipment may have a 15-20 year anticipated life expectancy. Conversely, a data center operating off coal-powered energy for example, even with a 1.10 PUE, is going to be leaving a much larger IT equipment-driven carbon footprint.

3. Re-Use Waste Heat

A third data center greening strategy is re-use of waste heat. Deploying this strategy may not directly impact the total carbon footprint specifically of a data center, but it still results in a green effect. Whether the “customer” for that hot air is office space associated with the data center or a neighbor from an entirely different business does not, in the final analysis, lessen the impact on the total carbon footprint of the re-used heat energy. However, the greening of the bank account may or may not be the similar for an internal cost-avoidance versus any income that could be derived from selling it as an alternative to the local utility.

4. Conserve Water

A fourth strategy would be water conservation in the data center. While water conservation has started to get more industry attention in the wake of droughts in such data center hot spots as Texas and California, we do not normally think of water use as a green factor in terms associated with carbon footprint. However, I recall a meeting a few years back with the Silicon Leadership Group where one of the speakers said that the single largest use of electric energy in California was pumping water around. While the challenges of vertical topography and the distances between water sources (snowbanks) and population centers in California may not be typical to many other areas of the country, there is always going to be an energy component to water distribution. More importantly, however, even without a carbon component, the industry has recognized water as a finite resource and developed an associated metric (WUE) and it really should be part of any discussion on greening data centers. As such, therefore, an ideal green scenario would be air-to-air heat exchanger economizer cooling technology or straight airside economization where the IT load was powered by a renewable energy resource. Where such a zero-use water strategy is not practical, an alternate tactic could be deployment of a decentralized packaged wastewater treatment system that could supply a cooling tower from a building’s wastewater. While ROI paybacks for on-site wastewater treatment may extend beyond typical preferred accounting practices, they would usually be less than current captive solar and wind energy capacity payback windows. Otherwise, my advice for approaching the water resource issue is to assume nothing and don’t take your intuition to the bank. For example, direct contact liquid cooling solutions will usually consume less water than water-chilled air cooling. Likewise, evaporative cooling would seem, by definition, to be a high water-use technology, but if it is indirect evaporative cooling with an air-to-air element in freezing temperatures, then this technology will use less water than a standard cooling tower in climates where there is a sufficient number of cold dry-cooling hours. The moral of that story is: take the time to compare the different technologies under different conditions.

5. Keep it Small

A fifth strategy for greening data centers runs counter to the economies of scale value proposition of the current trend toward super-mega-data centers: Remember the old telco closet. There is actually a green strategy associated with keeping it small – environment green and wallet green. Think about a data center with no mechanical plant. If there was no mechanical plant, then suddenly that office down the hall that became available when old Bumstead finally moved his desk in next to the fridge in the breakroom is a candidate to be re-purposed as a data center. According to my granddaughter, anytime you re-purpose you are automatically being earth-friendly green! However, there is more to this story. With a direct contact liquid cooling solution that can effectively cool computer equipment with 90˚ water, the building comfort cooling return loop, which is generally going to be in the 50-60˚ range, is more than adequate for cooling and heat removal for this data center space. Likewise, if we were going to air cool this space with water chilled CRAH units, with a fully implemented containment system, 65˚F water would easily suffice, which again could be delivered by the building comfort cooling return loop. In addition to this essentially free cooling and avoidance of the capital expense for a mechanical plant, there is the added green benefit of the reduced building footprint and the eliminated carbon footprint for the additional construction activity. Furthermore, the elimination of the infrastructure investment in a mechanical plant combined with the ability to manage most data center functions remotely eliminates the economies of scale justification for extremely large data centers. Finally, in a 100 square foot office, six air-cooled server cabinets would fit and 10 liquid-cooled cabinets would fit, thereby supporting an IT load density anywhere from 200kW up to 400kW. Many businesses can easily fit within such load boundaries.

Conclusion

This green data center pie can be sliced many different ways and in nine million plus search citations, I am sure it has been sliced and diced in more ways than I care to discern. Trying to keep things simple, I’ve sliced this into five basic strategies that, for the most part, merely summarize historical and recent developments. Of the five strategies, I’d say “Pay attention” enables all the other strategies to one degree or another and “Remember the telco closet” may have offered my readers a slightly new take on an old idea. Finally, these two strategies will deliver both greens (environmental responsibility and quick payback) in straightforward, measurable fashion.