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RTES System Cuts Power Consumption and Prices Over a Simulated 20-Yr Interval
By Hannah Halusker, NLR
The rise of synthetic intelligence, cloud platforms, and information processing is driving a gradual improve in world information middle electrical energy consumption. Whereas operating laptop servers accounts for the most important share of information middle power use, cooling methods are available second—however a brand new examine by researchers on the Nationwide Laboratory of the Rockies (NLR), previously referred to as NREL, gives a possible answer to scale back peak power consumption.
Printed in Utilized Power earlier this yr, a techno-economic evaluation led by Hyunjun Oh, David Sickinger, and Diana Acero-Allard—researchers in NLR’s power storage and computational science teams—has demonstrated a system to chill information facilities extra effectively and cost-effectively. The strategy, known as reservoir thermal power storage (RTES), shops chilly power underground then makes use of it to chill services throughout peak-demand intervals.
What Is RTES?
RTES takes benefit of chilly out of doors air and low-cost electrical energy earlier than storing power. Each time temperatures drop—whether or not throughout colder seasons or at evening—the system makes use of tools, equivalent to dry coolers or chillers, to sit back water earlier than injecting it underground. In hotter climate, usually throughout summer time, that saved chilly water is pumped again up on demand and run by way of a warmth exchanger, the place it supplies direct cooling by absorbing warmth from a knowledge middle’s heat water return.
This warmed water is then despatched again underground into a unique, designated “scorching nicely.” It isn’t cooled instantly however as a substitute stays heat till the following recharge cycle, when chilly out of doors air and off-peak electrical energy are once more accessible to replenish the reservoir’s chilly capability. This ongoing cycle retains the system in stability and ensures dependable cooling, whereas retaining power prices low and taking stress off the grid.
RTES wells are often drilled to a depth of a few kilometer or much less—deep sufficient to succeed in groundwater—although precise depths differ with native geology. The brackish or saline aquifers that wells faucet into are naturally contained by surrounding rock layers, making them ultimate for long-term thermal power storage as a result of they’re slow-moving and chemically steady.
Examine Eventualities
Within the Utilized Power examine, the staff designed two RTES-based cooling eventualities, utilizing 4 wells drilled at a depth of 275 meters, and modeled their efficiency for information middle cooling over a 20-year interval. The examine particularly simulated a seasonal recharging cycle: discharging chilly power throughout the summer time and recharging the reservoir with chilly water in winter.
Each eventualities used dry coolers, which offer “free cooling” by transferring air over a warmth exchanger with mechanical followers—no energy-intensive compressors or refrigeration cycles are required, decreasing electrical energy use. In contrast to cooling towers, dry coolers additionally don’t devour water on-site. One of many two eventualities additionally included a warmth restoration system that captured waste warmth from the info middle to offer constructing warmth in winter.
The staff in contrast each RTES eventualities to a 3rd, management state of affairs: a traditional, non-RTES cooling system that makes use of dry coolers paired with vapor-compression chillers. Whereas chillers are typically environment friendly, their efficiency drops in the summertime as compressors should work more durable to keep up cool temperatures towards hotter out of doors situations, driving up electrical energy use. RTES avoids this difficulty as a result of it depends on saved chilly water underground, making its efficiency far much less depending on out of doors temperatures.
The important thing takeaway: By eliminating these energy-intensive refrigeration cycles, RTES was discovered to be almost seven occasions extra environment friendly than conventional chillers throughout peak summer time, with a coefficient of efficiency of 16.5 in comparison with 2.4, in line with the staff’s evaluation.
“Electrical energy consumption of conventional cooling methods is important, particularly throughout summer time, whereas the RTES system considerably lowered electrical energy consumption, yielding an revolutionary and improved methodology for information middle cooling,” stated Oh, a geothermal engineer at NLR and lead writer of the examine.
For information facilities with nonstop cooling calls for, this interprets to decrease utility prices whereas sustaining dependable, around-the-clock efficiency.
So, how a lot decrease are these utility prices? The evaluation confirmed that levelized value of cooling, a metric that measures the full value to make and ship cooling unfold out over the system’s lifetime, was reduce from $15 per megawatt-hour (MWh) with chillers to simply $5/MWh with RTES.
The examine finally demonstrated that the RTES system might reliably cool a knowledge middle over 20 years, highlighting the potential of geothermal methods for cooling along with their extra generally recognized heating functions.
The Greater Image
The U.S. Division of Power’s (DOE’s) Geothermal Applied sciences Workplace funded this examine, which is a part of a broader DOE venture with Lawrence Berkeley Nationwide Laboratory and Idaho Nationwide Laboratory to deal with power, water consumption, and prices to chill information facilities ranging in measurement and placement.
The venture targeted on a 5 megawatt (MW) high-performance computing information middle in Colorado, as described within the Utilized Power paper, in addition to a 30 MW cryptocurrency mining facility in Texas and a 70 MW hyperscale information middle in Virginia. The multilab technical report analyzes all three websites, together with water financial savings, whereas a separate publication focuses on the Texas and Virginia services.
Though this examine didn’t explicitly mannequin time-of-use electrical energy pricing or regional grid situations, ongoing NLR analysis—the Chilly Underground Thermal Power Storage (Chilly UTES) venture—builds on these findings. Taken collectively, these initiatives spotlight simply how a lot RTES can cut back electrical energy use, prices, and even water demand—findings which have helped form DOE’s Fiscal Yr 2025 analysis into RTES applied sciences.
Future analysis in and out of doors of NLR is now exploring how RTES might take even larger benefit of off-peak, lower-cost energy to function standard cooling tools at very excessive effectivity and retailer massive quantities of chilly thermal power underground for lengthy durations.
The NLR staff can also be collaborating with researchers on the College of Chicago, Princeton College, and Lawrence Berkeley Nationwide Laboratory to look at RTES alongside different water-based storage methods, equivalent to aquifer and borehole thermal power storage. This effort will assist higher understanding of which methods are finest suited to totally different regional subsurface situations.
Study extra about NLR’s power storage and geothermal analysis.
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