Thermal Energy Storage (TES) Tanks for Data Centers: Ice, Chilled Water, and Sensible Heat

Thermal energy storage lets a data center make cooling when it is cheap or abundant - off-peak power, surplus renewables, or free-cooling hours - and use it when it is expensive. For data centers chasing PUE and demand charges, TES is one of the few storage investments with a clear operating case. This article covers the tank-based options.

For data centers, thermal energy storage (TES) is usually either a large chilled-water sensible-heat tank or an ice-storage tank, with phase-change material (PCM) a niche option. The tank stores cooling off-peak and discharges during peak; chilled-water TES is the simplest to build and integrate with a standard chilled-water plant.

The simplest TES is a large, stratified chilled-water tank. You chill water off-peak, store it, and draw it during peak. Because water's specific heat is high, the tank volume is large but the concept is robust and integrates with any chilled-water plant. The Italy Sardinia chilled process water tank (2025, 30,549 m3) is a real example of a very large coated water tank for process cooling duty.

• Stratified chilled-water tank, simplest TES.
• Integrates with any chilled-water plant.
• Large volume but robust concept.
• 30,549 m3 process tank shows the scale.

Ice storage makes ice off-peak and melts it to cool during peak. It stores far more cooling per volume than water (latent heat), so the footprint is smaller, but it needs a separate ice maker and a more complex controls sequence. It suits sites where space is tight and peak demand charges are high.

• Latent storage, smaller footprint.
• Needs ice maker and complex controls.
• Best where space is tight.
• High peak demand charges favor it.

Phase-change materials store latent heat at a fixed temperature, useful for narrow bands, but add cost and complexity. Most data center TES sticks with water or ice unless a specific temperature band makes PCM worthwhile.

• Latent heat at a fixed temperature.
• Adds cost and complexity.
• Narrow-band use cases only.
• Water or ice remain mainstream.

In a chilled-water TES, the tank is on the chilled side, charged by the chillers off-peak and discharged through the cooling coils or a plate exchanger during peak. Stratification is essential to keep charge and discharge separate. The Singapore buffer tank (2020, 3,462 m3) and Italy warm-water tank (2025, 1,200 m3) illustrate stored-water loops at different temperatures.

• Charged off-peak by chillers.
• Discharged during peak demand.
• Stratification keeps charge separate.
• Chilled side, via coils or plate exchanger.

Center Enamel supplies bolted, coated, roofed water tanks that scale to campus size for sensible-heat TES. In-house enameling and insulation options suit chilled duty; the Sardinia 30,549 m3 and Cilincing 21,088 m3 builds prove the delivery capability.

• Bolted, coated, roofed for TES.
• Insulation for chilled duty.
• Scales to campus size.
• 30,000 m3-class delivery proven.

Chilled-water sensible storage is simplest and integrates with any chilled-water plant; ice storage suits tight space and high peak charges; PCM is niche.

No. TES is large and stores hours of cooling for peak shifting; a buffer tank is small and prevents chiller short-cycling.

Large, because water storage density is low; volumes in the 10,000s of m3 are common for campus-scale TES.

It can lower energy cost and demand charges and supports free-cooling; the direct PUE effect depends on how you charge it.

On the chilled-water side, charged off-peak and discharged during peak, with stratification to keep layers separate.

Bolted coated tanks have been delivered at 20,000-30,000 m3 class, which covers campus-scale sensible-heat TES.

Thermal energy storage gives data centers a way to decouple cooling production from cooling demand, shaving peaks and riding free-cooling or off-peak power. Chilled-water sensible storage is the simplest and most integrable option, ice storage trades complexity for footprint, and PCM stays niche. The tank is a large, stratified, coated water store on the chilled side - and bolted construction scales it to campus size.

Suggested CTA: Share your peak-shaving goal and plant layout and we will size a stratified, coated TES tank and explain the charge-discharge integration.