High Density Colocation UK
High density colocation places specialist demands on data centre facilities. This guide covers the power, cooling and infrastructure requirements for deployments above 20 kW per rack in UK facilities.
Defining high density
Standard colocation facilities are typically designed for rack deployments in the 5 to 15 kW range. This covers the vast majority of traditional enterprise server deployments and remains the market norm. High density begins where standard air cooling and standard power distribution start to struggle, generally above 15 to 20 kW per rack.
The growth of GPU computing, high-performance computing and dense storage deployments has pushed the definition of high density upward. What was considered exceptional five years ago (30 kW per rack) is now routine for AI workloads. Some AI deployments reach 60 to 80 kW per rack or above, requiring purpose-built infrastructure.
Cooling technologies at high density
In-row cooling: Cooling units placed within the row of racks, cooling air as it is pulled from the hot aisle and pushed back into the cold aisle. Effective at densities up to approximately 20 to 30 kW per rack, depending on facility design.
Rear-door heat exchangers (RDHx): A water-cooled door attached to the rear of a rack. Hot air from the servers passes through the door and is cooled before re-entering the room. Requires chilled water infrastructure to the rack row. Effective at densities up to approximately 30 to 50 kW per rack.
Direct-to-chip cooling: Liquid cooling plates attached directly to the CPU and GPU processors, removing heat at the source rather than from the room air. Requires facility coolant distribution infrastructure to each rack and hardware compatibility. Supports densities of 50 kW per rack and above.
Liquid immersion: Hardware submerged in a dielectric fluid that absorbs and dissipates heat. Very high density capability but requires specialist hardware compatibility and significant operational expertise. Not yet widely available in UK commercial colocation facilities.
Power distribution at high density
High density deployments require higher-rated power feeds than standard racks. A rack drawing 30 kW at 240V single-phase requires approximately 125A. In practice, operators provision dual A+B feeds per rack at 32A or 63A per phase (3-phase), with PDUs rated to match. The facility's busbar and UPS infrastructure must support the aggregate load of adjacent high-density racks without relying on diversity assumptions that do not apply to GPU workloads.
What to verify before committing
When a UK facility claims to offer high-density colocation, verify: the maximum sustainable power density per rack (not the theoretical maximum, which can be overstated), the cooling technology available at your target density, whether liquid cooling requires a minimum commitment or additional infrastructure lead time, the power feed specification per rack, and whether adjacent racks can simultaneously draw their contracted maximum without degrading the thermal performance of your deployment.
Frequently asked questions
What is considered high density in colocation?
The threshold varies, but most industry practitioners define high density colocation as deployments above 15 to 20 kW per rack. Standard colocation facilities are typically designed for 5 to 15 kW per rack. Above 20 kW, specialist cooling and power infrastructure is generally needed.
What are the UK options for high density colocation?
UK facilities with verified high-density capability include major campus operators in London and the South East, along with a growing number of specialist high-density facilities in regional markets. Availability of liquid cooling specifically is more limited; it is worth confirming exact capability, not just general high-density claims.
Is high density colocation more expensive?
Yes. High density colocation commands a premium over standard density, reflecting the additional infrastructure investment in cooling and power distribution. The premium varies by facility and cooling technology, but expect to pay 20 to 50 percent more per kW than equivalent standard density space in the same facility.
Can I mix high density and standard density racks?
Yes, in most facilities. Operators typically have high-density zones or can accommodate a mix of standard and high-density racks in the same cage, with appropriate cooling and power provisioning for each. Discuss your mix of requirements with the facility during the sales process.
Planning a high-density deployment?
Use the AI Readiness Checker to assess your cooling and power requirements, or contact Cagelab for help identifying UK facilities with verified high-density capability.