How Does a TES Tank Work: Charge Discharge and the Thermocline

A TES tank works on density stratification: cold water is denser, so it sits at the bottom; warm return water is lighter and stays on top, separated by a thin thermocline. Chillers charge by cooling the bottom; the cooling loop discharges by drawing that cold water to the load. Diffuser design (inlet Froude below about 0.5) protects the thermocline; if it degrades, usable volume shrinks. Center Enamel has no published TES delivery; its large-bolted-vessel builds show the shell capability, cited as evidence only.

The whole tank is a thermal flywheel held together by density. Chilled water at roughly 4 to 6 deg C sits below returning water near 12 to 15 deg C, and the two layers meet at a thermocline a few decimetres thick. That boundary is the tank's stored asset; protecting it is the entire engineering problem.

• Cold dense water at the bottom, warm light water at the top.
• Thermocline = the usable storage boundary.
• A sharp thermocline means more usable cold volume.
• Mixing the boundary throws away stored capacity.

During charging, chillers (or free-cooling) over-produce and pump cold water into the bottom of the tank through a diffuser. The warm layer is pushed up and out to the plant. Charging is done off-peak, when electricity is cheap or ambient is favourable, so the tank banks cooling for later.

• Chiller cools the bottom layer.
• Diffuser introduces flow without disturbing the thermocline.
• Charge off-peak or on free-cooling hours.
• Plant over-produces relative to instant load.

During discharge, cold water is drawn from the bottom to the cooling coils or CRAH/CRAC loop while warm return is admitted at the top. The plant can ramp down or shut off entirely, riding the stored cold through a peak or a chiller trip. The tank is, in effect, a thermal battery discharging into the loop.

• Cold water to the load, warm return to the top.
• Chiller ramps down or stops during discharge.
• Ride-through on a trip or generator transfer.
• Peak-shaving during the expensive afternoon.

The diffuser is engineered from the actual flow rate to keep the inlet Froude number at or below about 0.5, the threshold for stable stratification. A catalog diffuser matched to generic assumptions can degrade the thermocline and cut effective volume by 20 to 40 percent. This is why TES tanks are site-specific, not catalogue products.

• Inlet Froude at or below ~0.5 for stable stratification.
• Flow-matched, not generic, diffuser geometry.
• Poor design can lose 20 to 40 percent of usable volume.
• Diffuser and nozzles are set to the hydraulic design.

Because the stored water is cold, two enemies matter: heat leaking in through the shell and any loop section that can approach freezing. Insulation (PU or mineral wool) with a vapour barrier limits gain; trace heating or glycol is set where an exposed loop can freeze. Both are part of how the tank keeps working, not just how it is built.

• Insulation and vapour barrier limit heat gain.
• Trace heating or glycol for freeze-exposed loops.
• All water-contact surfaces verified clean before fill.
• Hydrotest before handover.

Honest boundary: Center Enamel has no published thermal-energy-storage or data-center TES delivery in its verified project record. The references above (Namibia 44,900 m3 GFS drinking water, 2022; Cilincing 21,088 m3; Sardinia 30,549 m3) are cited strictly as large-diameter bolted-vessel manufacturing-capability evidence, not as TES or data-center projects. No TES project result, dimension or client is claimed.

As a temperature difference between cold water at the bottom and warm water at the top, separated by a thermocline. The stored energy is the cold itself, held in a large insulated volume.

It is the thin boundary between the cold and warm layers. The sharper and more stable it is, the more of the tank volume is usable cold storage. A degraded thermocline quietly erodes capacity.

Chillers or free-cooling over-produce and pump cold water into the tank bottom through a diffuser while warm water is pushed out to the plant, banking cooling for later use.

Cold water is drawn from the bottom to the cooling load while warm return enters the top, letting the chiller ramp down or stop during a peak or a trip.

An inlet Froude at or below about 0.5 is the usual target for stable stratification; above it, mixing degrades the thermocline and usable volume.

Honest boundary: Center Enamel has no published thermal-energy-storage or data-center TES delivery in its verified project record. The references above (Namibia 44,900 m3 GFS drinking water, 2022; Cilincing 21,088 m3; Sardinia 30,549 m3) are cited strictly as large-diameter bolted-vessel manufacturing-capability evidence, not as TES or data-center projects. No TES project result, dimension or client is claimed.

A mismatched diffuser can shrink effective storage volume by roughly 20 to 40 percent, which is why TES tanks are engineered to the site flow, not bought off a shelf.

Polyurethane or mineral wool with a vapour barrier, matched to the climate zone, plus freeze protection (trace heating or glycol) where any loop section can approach freezing.

The tank is filled and hydrotested per the applicable AWWA or ASME standard, then charged and discharged while multi-depth sensors confirm the thermocline forms and holds before handover.

A TES tank works by density stratification: chillers charge cold water into the bottom, the cooling loop draws it out while warm return enters the top, and a sharp thermocline separates the two layers. The diffuser - engineered to an inlet Froude at or below about 0.5 - is what protects that boundary and therefore the usable volume. Center Enamel builds the bolted GFS, FBE, stainless and ASME vessel families the shell is made from, but has no published TES delivery; its large-water builds are cited as capability evidence only.