NLR Evaluation Identifies Reservoir Thermal Power Storage as a Resolution for Knowledge Middle Cooling Wants

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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 enhance in world information middle electrical energy consumption. Whereas working pc servers accounts for the most important share of information middle power use, cooling programs are available in second—however a brand new examine by researchers on the Nationwide Laboratory of the Rockies (NLR), previously generally known as NREL, provides a possible resolution to cut 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 method, 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 outside air and low-cost electrical energy earlier than storing power. Every time temperatures drop—whether or not throughout colder seasons or at night time—the system makes use of gear, resembling dry coolers or chillers, to sit back water earlier than injecting it underground. In hotter climate, sometimes throughout summer season, that saved chilly water is pumped again up on demand and run by way of a warmth exchanger, the place it gives direct cooling by absorbing warmth from an information middle’s heat water return.

This warmed water is then despatched again underground into a unique, designated “scorching nicely.” It’s not cooled instantly however as an alternative stays heat till the following recharge cycle, when chilly outside air and off-peak electrical energy are once more obtainable to replenish the reservoir’s chilly capability. This ongoing cycle retains the system in steadiness 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 couple of kilometer or much less—deep sufficient to succeed in groundwater—although precise depths range with native geology. The brackish or saline aquifers that wells faucet into are naturally contained by surrounding rock layers, making them very best for long-term thermal power storage as a result of they’re slow-moving and chemically steady.

Research Eventualities

Within the Utilized Power examine, the group 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 season and recharging the reservoir with chilly water in winter.

Each eventualities used dry coolers, which offer “free cooling” by shifting 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 eat water on-site. One of many two eventualities additionally included a warmth restoration system that captured waste warmth from the information middle to offer constructing warmth in winter.

The group in contrast each RTES eventualities to a 3rd, management state of affairs: a standard, 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 take care of cool temperatures towards hotter outside circumstances, driving up electrical energy use. RTES avoids this challenge as a result of it depends on saved chilly water underground, making its efficiency far much less depending on outside 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 season, with a coefficient of efficiency of 16.5 in comparison with 2.4, in accordance with the group’s evaluation.

“Electrical energy consumption of conventional cooling programs is important, particularly throughout summer season, whereas the RTES system considerably lowered electrical energy consumption, yielding an revolutionary and improved methodology for information middle cooling,” mentioned Oh, a geothermal engineer at NLR and lead creator 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 entire value to make and ship cooling unfold out over the system’s lifetime, was reduce from $15 per megawatt-hour (MWh) with chillers to only $5/MWh with RTES.

The examine in the end demonstrated that the RTES system might reliably cool an information middle over 20 years, highlighting the potential of geothermal programs for cooling along with their extra generally identified heating purposes.

The Larger 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 challenge 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 challenge 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 circumstances, ongoing NLR analysis—the Chilly Underground Thermal Power Storage (Chilly UTES) challenge—builds on these findings. Taken collectively, these tasks spotlight simply how a lot RTES can scale 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 typical cooling gear at very excessive effectivity and retailer giant quantities of chilly thermal power underground for lengthy durations.

The NLR group can 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 programs, resembling aquifer and borehole thermal power storage. This effort will help higher understanding of which programs are greatest suited to completely different regional subsurface circumstances.

Be taught extra about NLR’s power storage and geothermal analysis.