The hall is one immersion tank — forty-five kilowatts of servers standing in dielectric fluid — and one small evaporative cooling tower outside, coupled across a water pair and nothing else: no chiller, no air handler, no refrigerant. It is the arrangement the tank makers sell for data centres, drawn as two blocks so that each is what it is: the tank a liquid-cooled load fed from outside its own graph, the tower a water-serving block holding its leaving water at 32 °C. There are no rooms, on purpose: a liquid-cooled hall's IT load never reaches the room's air, so there is nothing for a room to hold.

The tank is declared, its exchanger is rated, and the fluid temperature is the answer. A tank's datasheet prints rack units and litres of fluid, never the load — that is yours — so the load is declared. What the model adds is the exchanger between the fluid and the water, rated at a point the way a coaxial condenser is, and from it the temperature the servers sit in every hour of the year against the 45 °C the servers allow. On the design day (35 °C, 25.6 °C wet bulb) the dielectric settles at 39 °C.

The tower runs on the wet bulb, and Frankfurt's is low. Holding 32 °C water needs an approach the wet bulb allows, and a German year offers it in every hour; what the tower spends is its fan, cycling at about 45 % against a load that never moves, and the loop's circulator, which runs all year and costs more than the fan: 4.8 MWh against 3.8. The whole of the cooling electricity is 2.2 % of the IT load — a partial PUE of 1.022, the number a tank maker's "PUE < 1.05" is made of, and the circulator is the half of it a datasheet never mentions. Holding 32 °C puts the dielectric at 41.9 °C, 3 K under the limit; colder water buys margin with fan hours.

What it reads on Frankfurt

IT load	45 kW declared, 394.2 MWh a year — the tank's cooling delivered, every hour
Cooling electricity	8.6 MWh — 2.2 % of the IT load, a partial PUE of 1.022: the loop circulator 4.8 MWh, the tower fan 3.8 MWh cycling at about 45 %
Dielectric	41.9 °C at the held 32 °C water — 3 K under the 45 °C limit (39 °C on the design day with the tower flat out)
Water	32 °C held by the tower on every hour of the year; no hour failed to converge

What it taught

• A liquid-cooled load is not a room. Modelling it as a hot room served by a CRAH puts the IT heat into air it never touches; the kind that fits is a load on a water loop with its own fluid-to-water exchanger.
• The load is yours and the exchanger is the maker's — and the maker does not publish it. BAC's immersion tanks print dimensions, fluid volume and pump count and no thermal figure; the rating here is an example's, and the case says so.
• A tower is a water-serving machine when a block says so: a `waterTo` coupling with a setpoint on its `waterOut`, and the controller reads its leaving water and cycles its fan to hold it.

The machines

• Immersion cooling tank on an evaporative cooler (45 kW) — open in the builder
• Baltimore Aircoil VT0-12-E cooling tower (12 tons, 53 kW) — modelled — open in the builder

Sources

• Baltimore Aircoil — COBALT immersion cooling system and CorTex tank brochures (2025): a tank paired with an evaporative, adiabatic, hybrid or dry cooler; 16–48 RU, up to 150 kW, PUE < 1.05; no per-tank thermal figure
• Baltimore Aircoil Europe — MBT immersion cooling tank engineering data: rack units, dimensions, dielectric volume, weight, pump count for eight models
• Baltimore Aircoil — VT0-12-E engineering data (Series V), the tower's own rating
• PVGIS TMY, Frankfurt

Readings of the shipped model on the building's own PVGIS typical meteorological year; engineering estimates from catalog data and published correlations. The building runs on every plan, including Free, a few times a day.