Quick answer: direct-to-chip dominates new AI builds and makes the highest demands on pipework purity; rear door heat exchangers are the lower-disruption bridge with the most valve positions per kW; immersion concentrates complexity in the tank and leaves the facility pipework conventional. Many sites now run more than one — which is the strongest argument for a single stainless specification across all of them.
Plenty has been written comparing the three architectures on thermodynamics. Here’s the comparison from the side we live on: what each asks of the tube, valves and fittings.
Direct-to-chip (DTC)
Coolant reaches cold plates on the processors themselves, so the Technology Cooling System is effectively an extension of the IT hardware. Pipework character: purity-led. Hygienic-grade 316L tube, controlled internal finish, orbital welds, clamp connections at CDUs, disciplined commissioning. Highest engineering bar, and the architecture behind most current demand. Scope detail: piping for direct-to-chip liquid cooling.
Rear door heat exchanger (RDHx)
A liquid-cooled coil on every rack’s rear door. Less invasive to the IT stack, and popular for lifting existing halls toward higher density. Pipework character: distribution-led. Moderate purity requirements, but lots of connection points — every door needs supply, return and isolation, so valve count and demountable joints per kW are the highest of the three. Serviceability drives the specification.
Immersion
Servers submerged in dielectric fluid; tank heat exchangers reject to a water loop. Pipework character: conventional. The exotic engineering is inside the tank (the OEM’s problem); the facility side is pressure-rated stainless at building-services scale, flanged, with per-tank isolation. Scope detail: pipework for rear door heat exchangers and immersion cooling.
Side by side
| DTC | RDHx | Immersion | |
|---|---|---|---|
| Purity demand on pipework | Highest | Moderate | Standard |
| Valve/joint count per kW | Moderate | Highest | Lowest |
| Facility loop | TCS + FWS | Distribution loop | Water loop to tanks |
| Typical tube spec | 316L hygienic | 304/316L | 304/316L pressure-rated |
| Where it’s winning | New AI builds | Retrofits, mixed halls | Niche/high-density pods |
The mixed-estate reality
New campuses increasingly deploy DTC in AI halls and RDHx elsewhere, occasionally with immersion pods. Running one stainless system across the estate — one welding procedure, one spares list, one certification format — is cheaper over the facility’s life than optimising each architecture separately. That’s a procurement decision best made once, early, and it’s exactly the conversation to have with us at design stage: liquid cooling infrastructure for data centres.
Talk to us about your project
Kevin Windsor — Product Manager, Data Centre Liquid Cooling
kw@neumo.co.uk · 01952 583 999