Strategies for Re-Using Data Center Heat Energy and Their Impact on PUE (Both Real and Perceived)
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Is it possible to recycle some data center energy to achieve a PUE less than 1.00? The simple answer is no. However, over the years, such claims have been made and are invariably followed by wise nods, knowing winks, and comments such as, "Well, somebody doesn't understand PUE basic math." While striving for a PUE of less than 1.00 undoubtedly gets us into the realm of physics-defying fantasy, that does not however mean there is no value in recycling the heat energy produced by our ICT equipment. After all, we have already recognized the great value in actually increasing PUE by dramatically reducing the divisor of our PUE equation through virtualization, turning off comatose servers, migrating from Windows to Linux, etc. The PUE rock showing above the water level may be bigger, but the sea level itself is lower (hence, the ongoing discussion for new and improved metrics). Such is the case with looking for ways to perform useful work with the thermal energy produced by ICT equipment. While we may not give ourselves a bragging-rights PUE decimal fraction, perhaps we can improve our organization's bottom line and contribute positively to the planet's health. This session will explore five strategies for re-using data center heat energy while discussing their impacts on PUE, the bottom line, and the environment. Key takeaways: - Learn about the different strategies that are available to re-use (recycle) heat energy produced by ICT equipment. - Understand the relationship between recycling data center heat energy and resultant impacts on PUE. - Learn about the benefits of recycling data center heat energy for your organization's bottom line and the environment.
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Strategies for Re-Using Data Center Heat Energy and Their Impact on PUE (Both Real and Perceived)
- 1. Strategies for Re-Using Data Center Heat Energy and Their Impact on PUE (Both Real and Perceived)
- 2. datacenterworld.com | #datacenterworld Information Classification: General Speaker Background • Thought leader and recognized expert on data center optimization with over 25 years of experience • Certified US Department of Energy Data Center Energy Practitioner (DCEP) HVAC and IT Specialist • Presented on various topics around the world: • How IT Decisions Impact Facilities: The Benefit of Mutual Understanding • Designing, Deploying and Managing Efficient Data Centers • Myths of Data Center Containment • Understanding the Science Behind Data Center Airflow Management • Data Center Cooling Efficiency: Understanding the Science of the 4 Delta T’s Lars Strong, P.E. Senior Engineer and Company Science Officer, Upsite Technologies
- 3. datacenterworld.com | #datacenterworld Information Classification: General Agenda • What is your experience? • Understanding Power Usage Effectiveness (PUE) • What is PUE? • PUE Levels of Measurement • How Airflow Management Relates to PUE • Can You Achieve a PUE of Less Than 1.00? • The 4 Delta Ts • Strategies for Data Center Heat Energy Re-Use • Ship the Hot Air Next Door • Tap the Chilled Water Loop • Hot Water Cooling • Relationship Between Recycling Data Center Heat Energy and PUE • Questions
- 4. datacenterworld.com | #datacenterworld Information Classification: General Interactive • Do you operate a data center? • Are you re-using heat? • How is it going? • Do you know of a heat re-use project? • Are you considering / planning on re-using heat?
- 6. datacenterworld.com | #datacenterworld Information Classification: General Introduction to PUE • PUE / DCiE originally from The Green Grid, now falls under ISO/IEC JCT1 SC39 WG1 and is defined by an international ISO standard – ISO/IEC 30134-2 • This is the *only* definition of PUE and figures measured or reported in any other way are not true PUE • ISO is an independent, non-governmental membership organization and the world's largest developer of voluntary International Standards • Members are the national standards bodies of the 163 member countries around the world. Based in Geneva, Switzerland • ISO works alongside International Electrotechnical Commission (IEC), in the development of emerging international data centre standards • ISO/IEC JCT1 SC39 WG1 are responsible for the development of the ISO/IEC 30134 series of standards (data centre resource efficiency KPIs) • All ISO standards are designed to dovetail so the format for the 30134 series will be similar and relate to familiar standards series such as ISO 9000, ISO 27000, ISO 50000 and ISO 14000 etc.
- 7. datacenterworld.com | #datacenterworld Information Classification: General What is PUE? • PUE is defined as the ratio of total facilities energy to IT equipment energy • (Total Facility Power) / (IT Equipment Power) = PUE • Total facility energy is defined as the energy dedicated solely to the data center • The energy measured at the utility meter of a dedicated data center facility or at the meter for a data center or data room in a mixed-use facility • The IT equipment energy is defined as the energy consumed by equipment that is used to manage, process, store, or route data within the compute space • IT equipment energy includes the energy associated with all of the IT equipment (compute, storage, and network equipment) along with supplemental equipment (KVM switches, monitors, and workstations/laptops used to monitor or otherwise control the data center) • Total facility energy includes all IT equipment energy as described in the bullet above plus everything that supports the IT equipment using energy
- 8. datacenterworld.com | #datacenterworld Information Classification: General PUE Levels of Measurement Chart • Regardless of how the measurements are taken it is always worth remembering that PUE is not an overall energy efficiency metric • PUE merely measures the overhead that the building puts on the IT load it hosts • True energy efficiency requires a focus on the IT load power consumption and reduction too • Ironically reducing the power consumed by the IT load and thereby reducing the total kW hours used can actually increase the PUE • This is one of the reasons that PUE is not a true energy efficiency metric
- 9. datacenterworld.com | #datacenterworld Information Classification: General PUE Levels of Measurement Chart • There is a direct relationship between airflow management and PUE – the better the airflow management, the better the PUE • Mechanical cooling + fan cooling is 35% of total load and 73% of non-IT load Total Load IT Load PUE = = 1.92
- 10. datacenterworld.com | #datacenterworld Information Classification: General Partial PUE (pPUE) • While PUE includes all energy-using components within a facility, pPUE includes all energy-using components within a boundary/zone • A boundary/zone can be a physical designation such as a container, room, modular pod, or building • It also can be a logical boundary such as equipment owned by a department or a customer, owned versus leased equipment, or any other boundary that makes sense for the management of the assets • (Total energy inside the boundary) / (Total IT equipment energy inside the boundary) = pPUE
- 11. datacenterworld.com | #datacenterworld Information Classification: General Can you Achieve a PUE of Less than 1.00? • For a few years now, there have been many claims that achieving a PUE of less than 1.00 was possible by recycling some data center energy • These claims usually derive from either obtaining off-grid electricity or producing some energy from the IT ΔT that is used to perform some other task • Neither of these cases change the basic math of total power into the data center divided by IT consumed power = 1 or higher, unless the IT thermal output were converted to energy to provide a portion of the energy required to operate our IT equipment, thereby subtracting that portion from total consumption • This result of IT equipment energy use exceeding total data center energy use gets us a PUE less than 1.00, and also gets us into the realm of physics-defying fantasy • However, while achieving a PUE of less than 1.00 is simply not possible, that does not mean that efforts in mining heat energy produced by IT equipment hold no value, there can be a real and positive ecological impact
- 12. datacenterworld.com | #datacenterworld Information Classification: General Can you Achieve a PUE of Less than 1.00? – Yes PUE = 1.0
- 13. datacenterworld.com | #datacenterworld Information Classification: General Can you Achieve a PUE of Less than 1.00? – Yes PUE > 1.0
- 14. datacenterworld.com | #datacenterworld Information Classification: General Can you Achieve a PUE of Less than 1.00? ISO/IEC 30134 Information Technology – Data Centres – Key Performance Indicators • ISO/IEC 30134-1:2018 — Part 1: Overview and general requirements • ISO/IEC 30134-2:2018 — Part 2: Power usage effectiveness (PUE) • ISO/IEC 30134-3:2018 — Part 3: Renewable energy factor (REF) • ISO/IEC 30134-4:2017 — Part 4: IT Equipment Energy Efficiency for servers (ITEEsv) • ISO/IEC 30134-5:2017 — Part 5: IT Equipment Utilization for servers (ITEUsv) • ISO/IEC 30134-6:2021 — Part 6: Energy Reuse Factor (ERF) • ISO/IEC 30134-7 — Part 7: Cooling Efficiency Ratio (CER) • ISO/IEC 30134-8:2022 — Part 8: Carbon Usage Effectiveness (CUE) • ISO/IEC 30134-9:2022 — Part 9: Water Usage Effectiveness (WUE)
- 15. Strategies for Data Center Heat Energy Re-Use
- 16. datacenterworld.com | #datacenterworld Information Classification: General Strategies We’ll Be Looking At • While a PUE of less than 1.00 cannot be an achievable goal, we can still improve our organization’s bottom line and contribute positively to the planet’s health in other ways • To help us measure and report this reliably since we cannot have a PUE of less than 1 there is another metric in the ISO/IEC 30134 series to help us do this: • ISO/IEC 30134-6 - Energy Reuse Factor (ERF) • There a few strategies we’ll look at in the subsequent slides: • Ship the Hot Air Next Door • Tap the Chilled Water Loop • Hot Water Cooling • Something to consider though is that the technology to recover the otherwise wasted heat is available to us now and has been for some time • The real difficulty is finding a customer or use for what is typically relatively low-grade heat which doesn’t transport well • The effective use of ‘waste’ heat requires collaboration with potentially interested parties at the early planning stage
- 17. datacenterworld.com | #datacenterworld Information Classification: General Ship the Hot Air Next Door • Shipping the hot air next door, on the surface, may seem like the simplest and most straightforward application of data center waste heat re-use, but unfortunately it can get complicated pretty quickly when we try to compensate for it’s being what we call low grade heat energy • Data center return air has been used to heat adjacent office spaces, auditoriums, and even a greenhouse
- 18. datacenterworld.com | #datacenterworld Information Classification: General Ship the Hot Air Next Door • In general, there are a few obstacles with this strategy: • Working waste air is typically going to be in the 80˚ to 95˚F range, which prevents it from being particularly useful except when it can be applied to comfort temperature range applications in close proximity to the data center • The requirement for proximity is another obstacle, as hot air does not travel well • Another obstacle is that anyone looking for squeezing out more energy efficiencies after reaching their PUE goal, has most assuredly already implemented some form of free cooling and has fine-tuned their infrastructure • The dilemma is that when our free cooling temperatures are the lowest during that cold time of the year and our associated waste air temperatures are the lowest, that is exactly when our customer (internal or external) is going to be looking to us for the most heat • Conversely, during the summer, when we are cranking out hot return air, our customer may be looking for some heat relief
- 19. datacenterworld.com | #datacenterworld Information Classification: General Ship the Hot Air Next Door • Yandex, a large Russian data center operator with facilities around the world • In their data center in Mantsala, hot waste air is piped through heat pumps and air-to-liquid heat exchangers to produce 90˚ to 115˚F water that then requires a short lift to 130˚ to 140˚F, which is useable for local district heating • This particular site has been operational for several years and has reduced the carbon emissions of the city by 40% and reduced local consumers’ heating prices by 12% • Similar strategies have been deployed by Facebook in Denmark and numerous facilities in Sweden, including a Digiplex evaporative air-to-air economizer retrofit project in Stockholm projected to provide heating for 10,000 homes • Cooling, on the other hand, can be accomplished by using absorption chillers to convert the heat to cooling, though it can be a stretch to get good performance from an absorption chiller with the air temperatures we typically see
- 20. datacenterworld.com | #datacenterworld Information Classification: General The Four Delta Ts (ΔT) 1. Though IT equipment 2. IT equipment exhaust to cooling unit 3. Through cooling unit 4. Cooling unit supply to IT equipment intake
- 21. datacenterworld.com | #datacenterworld Information Classification: General The Four Delta Ts (ΔT) • In most data centers the greatest loss of efficiency is having a low temperature of air returning to the cooling units • The goal is to always have the highest possible return air temperature to cooling units
- 22. datacenterworld.com | #datacenterworld Information Classification: General Tap the Chilled Water Loop • Chilled water loop may occasionally be somewhat of a misnomer • We may tap it on the supply side (chilled) or on the return side (warm, or at least less chilled) • In an example from the University of Syracuse, part of that water loop can be downright hot • In a recent example in the UK this technique has been used to heat a public swimming pool with more similar projects to follow
- 23. datacenterworld.com | #datacenterworld Information Classification: General Tap the Chilled Water Loop • The turbines produced 585˚F exhaust air which was put to work in two separate operations in the chiller room: • Provide input to absorption chillers with capacity to provide cooling to the data center as well as supply the air conditioning chilled water loop for a large office building nearby • Provide the heat to an air-to-liquid heat exchanger to deliver heat to that same office building during the winter
- 24. datacenterworld.com | #datacenterworld Information Classification: General Tap the Chilled Water Loop • A more current, easier-to-diagram and still-operating example of productive loop-tapping can be demonstrated in the Westin-Amazon cooperative project in Seattle • In this neatly symbiotic relationship, the Amazon campus is essentially an economizer and condenser for the Westin Carrier Hotel and the Westin’s thirty four floors of data center essentially comprise a private utility providing heating energy to the Amazon campus • In this case, Amazon taps the return water loop from the Westin’s data center cooling and the Westin taps the return water loop from Amazon’s heating
- 25. datacenterworld.com | #datacenterworld Information Classification: General Tap the Chilled Water Loop • AAmazon should save around 80 million kW hours of electricity over the first twenty five years, roughly equivalent to eliminating carbon emissions of sixty five million pounds of coal • Saves water from tower evaporation loss and saves operating expense of running cooling towers • Estimated $985,000 annual savings for five million square feet of office space • This is also being done by at North in Sweden by connecting directly to an adjacent district heating system to provide winter heating to residential homes
- 26. datacenterworld.com | #datacenterworld Information Classification: General Hot Water Cooling • The third category of data center heat energy re-use is hot water cooling, which can benefit either of the first two categories, but is particularly beneficial with data center liquid cooling • As previously mentioned, if data center waste air is being used to facilitate generator starters, raising supply air from 65˚F or 70˚F up to 78-80˚F will produce a return air temperature high enough to eliminate block heaters • In the Westin-Amazon project, a good airflow containment execution could allow the data center water supply to the utility heat exchanger to be increased enough to reduce the heat recovery plant lift by 28% • Neither of these cases utilize cooling with warm or hot water, but even moving the needle these small steps can produce significant benefits • When we start working with hot water, we get higher grade waste heat energy and water is easier to move around than air
- 27. datacenterworld.com | #datacenterworld Information Classification: General Hot Water Cooling • The IBM proof-of-concept data center at the Zurich Research Laboratory took advantage of innovations in direct contact liquid cooling whereby hot water was pumped through copper microchannels attached to computer chips • Findings included: • 140˚F supply water maintained chip temperatures around 176˚F, safely below the recommended 185˚F maximum • Hot water cooling resulted in a post-process “return” temperature of 149˚F • In addition to providing heat for an adjacent lab, the absorption chiller provided 49kW of cooling capacity at about 70˚F
- 28. datacenterworld.com | #datacenterworld Information Classification: General Hot Water Cooling • Around the same time that the IBM proof-of-concept hot water liquid cooling experiment was being implemented in Switzerland, eBay was experimenting with warm water cooling in Phoenix in the well-publicized Mercury Project • The Mercury Project involved one part of the data center cooled by chilled water loop connected to chillers and then a second data center using condenser return water from the first data center up to 87˚F to supply rack-mounted rear door heat exchangers • Obviously, temperatures exceeded ASHRAE recommended server inlet air temperatures, but remained within the Class A2 allowable range
- 29. Summary
- 30. datacenterworld.com | #datacenterworld Information Classification: General Key Takeaways • Lack of demand for heat energy produced by data centers, particularly in the United States, can be a show-stopper or at least a significant complication • Heat energy is not quite as transportable as electric energy, so a customer/consumer of heat energy in close proximity to the data center is critical • In northern Europe there is a built-in infrastructure in district heating networks with on-line demand for heat energy • The Westin/Amazon project is such a perfect model because the Amazon office buildings effectively represent the equivalent of a local heating district “customer”
- 31. Thank you! Questions? Lars Strong Upsite Technologies lds@upsite.com 505.798.0208
Editor's Notes
- The IT load is measured at the output of the UPS equipment and can be read from the UPS front panel, through a meter on the UPS output, or, in cases of multiple UPS modules, through a single meter on the common UPS output bus Facility load is measured from the utility service entrance that feeds all of the electrical and mechanical equipment used to power, cool, and condition the data center Measurement period is either weekly or monthly The IT load is measured at the output of the PDUs within the data center and can typically be read from the PDU front panel The facility load is measured from the utility service entrance that feeds all of the electrical and mechanical equipment used to power, cool, and condition the data center Measurement period is daily/hourly at the same time The IT load is measured at each individual piece of IT equipment within the data center, either by metered rack PDUs that monitor at the strip or receptacle level or by the IT device itself The incoming energy is measured from the utility service entrance that feeds all of the electrical and mechanical equipment used to power, cool, and condition the data center Measurement period is every 15 minutes or less
- It should be noted that a PUE calculation uses the IT energy as the denominator in a fraction and is thus undefined if the IT energy in a zone is zero. Since the reason for a pPUE calculation is to provide a metric of the efficiency of delivering energy and cooling to IT equipment, pPUE has no meaning for a zone that contains no IT equipment. Such a zone would more appropriately be accounted for as overhead.
- There is great value in actually increasing PUE by dramatically reducing the divisor of our PUE equation through virtualization, turning off comatose servers, migrating from Windows to Linux, etc. The PUE rock showing above the water level may be bigger, but the sea level itself is lower (hence, the ongoing discussion for new and improved metrics) Such is the case with looking for ways to perform useful work with the thermal energy produced by the work performed by our IT equipment
- I’ll be starting today with the most straightforward – the Notre Dame practice of exploiting the elevated temperature of the data center return air to do some useful work – in this case maintaining an operational greenhouse temperature at the South Bend Greenhouse and Botanical Gardens through the sometimes brutal northern Indiana winter. We call this strategy, “Ship the hot air next door.”
- In both these cases, however, there are ways to take advantage of our data center waste heat that may require adding to our facilities engineering tool kit. Heat pumps and absorption chillers may help us bridge the gap from low grade heat energy to at least somewhat useful grade energy. In both cases, heating or cooling, the folks who are using this design approach typically start with transferring the heat from air to water.
- Meanwhile, why is it that my good examples all seem to come from Northern Europe, at least in this section on shipping the hot air next door? The cooler ambient temperatures, providing access to much larger blocks of free cooling time, have attracted data center companies serious about energy efficiency and pursuing carbon emission reduction and neutral goals. More importantly, however, is probably the prevalence of district heating. For my American readers who may not be familiar with the term, we are merely talking about a heating and cooling district where all the homes or buildings are connected to a single heating and cooling source, versus having individual boilers or furnaces. Each district will either buy heating and cooling from some other supplier (utility) or have its own production facility. The opportunity for the data center is to become that source, profitably, at a lower cost than either the existing vendor or captive facility. The scale of this opportunity can be illustrated by the fact that data centers now account for over 10% of Sweden’s municipal heating supply. Taking it one step further, Finland actively markets itself as a great place to locate your data center because of the income opportunities associated with selling to these heating district networks. In addition, in many public utility jurisdictions, if you are going to sell this energy to your neighbor, you may need to get yourself registered as a utility. So does that mean that localities and regions that are limited in implementation of heating district networks are relegated to heating greenhouses, generator heater blocks, internal office spaces and perhaps melting some snow on the sidewalk between the parking lot and front door, none of which will likely have a separate profitability line on the company 10K report? While shipping the hot air next door may not be a profit center, it can still deliver an internal benefit and some of these payback periods can still be relatively short. However, there are still significant opportunities associated with chilled water loops and various iterations of liquid cooling.
- The second category of data center energy recapture I will call “tapping the loop”, i.e. the chilled water loop. The figure to the right provides a simplified overview of the University of Syracuse’s data center and supporting electrical and mechanical infrastructure
- This example had several unique and innovative features for a decade-old deployment and actually represented a proof-of-concept collaboration between the university and IBM. First, primary power was generated on site by a roomful of natural gas-powered turbines The electrical grid connection was purely as a back up to the back, i.e., there was N+2 turbine redundancy and then there was a propane reserve back-up to the liquid natural gas source and then full UPS battery back-up, charged by the turbine output The connection to the electrical grid was intended for use only after the upstream four levels had either failed or been exhausted Roger Schmidt, IBM Scientist Emeritus who was the IBM Technical Lead on this project, informed me that after ten years the turbines had worn out and the cost of electricity was so low that the university has since converted this data center over to a traditional chiller and cooling tower mechanical infrastructure. Nevertheless, this facility had a good run and provided impetus for explorations in the benefits of loop tapping.
- - The figure here dramatically over-simplifies what they accomplished with this project, but it illustrates the basic building blocks into which all the detailed engineering is applied.
- - The basic elements of this installation are not particularly innovative and have been employed in other places (data center as well as industrial) around the world over the years. Heat produced by the data center is captured on cooling coils and removed by water that is pumped through a heat exchanger under the street between the two sets of structures. Water passing through the other side of the heat exchanger has its temperature raised, but not raised high enough to be effective in providing comfort heating. Heat pumps with a coefficient of performance around 4 increase the temperature of the water to 120˚-130˚F, thereby economically generating a viable heat source for all the buildings of the Amazon campus. Boilers are in place in case the data centers do not produce adequate heat but, according to Jeff Sloan, McKinstry engineer who orchestrated this project, Amazon typically consumes only a small portion of the data center waste heat and the boilers have rarely operated since everything got up and operational. Once the heat is removed from the water to provide comfort heating in the office buildings and the associated biosphere dome, the return water from Amazon cools the data across the street.
- - Post-process return air of 149˚F was an adequate grade heat energy for both building heating and cooling through an absorption chiller, without requiring a boost from heat pumps
- It was within this operation that Dean Nelson and his team came up with a business mission-based data center efficiency metric tying data center costs to customer sales transactions, thereby giving form to that illusive tipping point between data center efficiency and effectiveness. In this case, the “customer” was internal and the waste heat was not used as a heat energy source but as a cooling source. The Project Mercury model does, in fact, offer a vision for low risk warm water cooling that could be available to many data centers without having to transition all the way to some form of direct contact liquid cooling. For example, data centers using rear door heat exchangers can operate with supply temperatures north of 65˚F, which easily exceeds the return temperature of a building comfort cooling return water loop. Tapping into the return water is essentially free cooling and then during the time of year when the building AC might not be running continuously (or at all, my friends in Minnesota), the rear door heat exchangers can be supplied through a free cooling heat exchanger economizer. The same principle applies to direct contact liquid cooling, which should be essentially free to operate in any facility with any meaningful-size comfort cooling load.