guide
Cooling technology selection guide
A plain guide to choosing between air, rear-door heat exchangers, direct-to-chip liquid cooling (single and two-phase) and immersion, and to matching heat rejection, water temperature and heat reuse options to rack density, site constraints and the policy context.
Start from the IT roadmap
Rack density, the chip vendor's coolant temperature limits and refresh cycle drive the choice. Vendors place the practical limit of air cooling at roughly 30 to 50 kW per rack, which is guidance, not a standard.
Options at a glance
Air with containment suits lower densities. Rear-door heat exchangers extend air halls without changing servers. Single-phase direct-to-chip with CDUs is the mainstream route for current AI racks and still needs some air. Two-phase direct-to-chip keeps water out of the white space and has a smaller installed base. Immersion cools all components and suits warm water but needs adapted hardware and service methods.
Match the water temperature
Pick an ASHRAE W class that the IT allows. Warmer classes (W40, W45, W+) allow chiller-free operation in more climates and better heat reuse, but need tighter CDU approach temperatures.
Heat rejection and water
Dry coolers use no water but need more area and fan power in hot climates. Adiabatic and evaporative systems save energy but use water, which matters in the Gulf and in water-stressed regions. Check annual water use at your site climate.
Brownfield vs new build
In existing halls, liquid-to-air CDUs and rear doors avoid new facility pipework. New builds can design warm water loops and heat export from the start.
Policy and reporting
In Germany EnEfG section 11 sets planned energy reuse shares for new data centres of at least 10 percent from 1 July 2026, 15 percent from 1 July 2027 and 20 percent from 1 July 2028, and an amendment is proposed. EU operators above 500 kW IT report energy and water indicators each year. See the linked policy records for current status.
Product maturity
Check whether each product is prototype, announced, orderable or shipping. Ask for reference sites at similar density and climate.