Exchanger approach
Rate the exchanger at the actual temperatures, flow rates and fouling allowance. The fluid circuits remain separate while heat crosses the plates.
ENGINEERING EXPLAINED / WATER
The water carries the heat.
Follow the liquid, watch heat cross the metal, and change the cooling target to see when a chiller is needed.
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01 / FOLLOW THE HEAT
From the chip
to the atmosphere.
In this cold-plate, evaporative-cooling example, liquid runs through sealed channels inside the server. It does not wash over the electronics. The heat crosses a metal wall into another circuit; some tower water then evaporates into the air.
TAKE THE HEAT AWAY
The metal touches the chip.
Coolant flows through sealed channels in the cold plate. Heat conducts from the chip through the metal, then enters the moving liquid.
The illustration shows one architecture. Immersion, air cooling and dry heat rejection use different arrangements.
ILLUSTRATIVE MOTION · NOT CFD
A cooling tower is open to the atmosphere: makeup replaces evaporation, blowdown and drift. The chip coolant stays hydraulically separated. Some plants add a separate closed facility loop and another exchanger; that adds another temperature approach.
02 / CHANGE THE DESIGN POINT
When does the
chiller come back?
Lower inlet water temperatures reduce the room available for heat rejection. The threshold depends on the weather and the equipment. A 27°C target does not universally require a chiller.
Minimum supply without chiller30°C
Temperature margin+15°C
At this design pointTower can meet target
Tmin ≈ Twet-bulb + ΔTtower + ΣΔTHX
What this simple threshold assumes
This is a steady-state temperature-budget check for the illustrated water-side economizer path. Approaches are design inputs at the required load, not fixed properties of every exchanger or tower. Pump heat, pipe heat gain, fouling, controls, additional exchangers and capacity limits are omitted. Equality leaves no operating margin. A positive margin does not prove the installed equipment has enough capacity.
45°C and 27°C are comparison cases from the reel, not universal specifications for chip generations. Check the equipment supplier’s allowable coolant temperature, flow, pressure and water-quality requirements. Plate exchangers can achieve approaches around 1°C in suitable duties; that needs sufficient area and a valid rating.
03 / COUNT THE WATER ONCE
Two water footprints.
Two places it is consumed.
66
billion litres direct
Estimated US data-centre water consumption in 2023.
≈800
billion litres indirect
Water consumed through electricity generation for those facilities.
≈12×
indirect / direct
800 ÷ 66 ≈ 12.1. National totals, not a ratio for every facility.
LBNL’s 2024 report estimates consumption, not all water withdrawn. Its grid footprint uses regional electricity mixes; it is not an estimate of the data centre’s own water intake.
1,000 kWh × 4.52 L/kWh = 4,520 L
Illustration using the report’s 2023 national average indirect intensity. Local and hourly results depend on the supplying grid. Site WUE uses IT electricity in its denominator; do not divide unlike intensities to reconstruct the national ratio.
04 / THE DESIGN CHECKS
It is still a plant.
Design wet-bulb
The outdoor wet-bulb limits an evaporative tower’s cold-water temperature. Revisit the design weather and the tower approach when the cooling target changes.
Water balance
Makeup = evaporation + blowdown + drift. Water use depends on heat load, humidity, cycles of concentration and operating strategy.
Q̇evap ≈ ṁevap hfg
The reel’s ≈2,300 kJ/kg is an order-of-magnitude latent-heat value. Latent heat varies with temperature; a complete tower balance also includes sensible heat transfer and moisture conditions.
- LBNL 2024 US Data Center Energy Usage Report, pp. 39, 55–57: definitions and 2023 estimates.
- DOE: cooling water efficiency in data centres and cooling tower management.
- Alfa Laval: liquid/liquid plate exchanger approach.
- ASHRAE: emergence and expansion of liquid cooling.
Original generated equipment illustrations. Educational examples, not a vendor equipment rating.