01Why retrofit is structurally hard

An existing AC-native data centre is a set of physical constraints an 800 VDC upgrade has to work around. Four constraints dominate: the existing MV-to-LV substation infrastructure sized for AC distribution, the cooling plant sized for the prior rack-density profile, the real-estate footprint fixed at build time, and the operational continuity requirement that constrains what can be de-energised for how long.

Each of these translates to a specific retrofit cost. Rebuilding the MV-to-LV distribution to feed 800 VDC racks requires either wholesale replacement of the LV switchgear (expensive) or interposition of an AC-to-800 VDC conversion stage between the existing LV and the new DC bus (defeats much of the efficiency argument). Increasing rack density to the level 800 VDC economics require means the existing cooling plant is undersized. Typically by 3-5x if the retrofit is targeting 100 kW+ per rack. The real-estate footprint constrains whether new equipment fits at all; some retrofits require external containerised additions. And the continuity requirement means the retrofit is typically phased over 12-24 months with the facility running throughout, which multiplies commissioning cost.

02Retrofit capex composition

Retrofit capex is dominated by the electrical distribution rebuild, not by the rack-level equipment upgrade. Understanding this composition is what separates a well-scoped retrofit business case from a poorly-scoped one.

The counterintuitive line item is the commissioning premium. Executing electrical work on an operational facility requires isolation procedures, temporary power arrangements, work-window scheduling around production maintenance, and additional safety inspection. Vendor commissioning quotes for retrofit work typically run 30-50 percent above the equivalent greenfield quote for the same equipment scope.

03Greenfield capex composition

Greenfield capex has a categorically different composition. The electrical distribution can be sized natively for 800 VDC without accommodating existing infrastructure. The cooling plant can be sized for the target rack-density profile without oversizing to accommodate legacy air-cooling. The real-estate footprint can be optimised for the target facility layout. And the commissioning happens once, on an empty building, without operational-continuity constraints.

04Ten-year TCO comparison

The headline retrofit-vs-greenfield economics show at ten-year total cost of ownership rather than at day-one capex. Retrofit day-one capex per MW is typically 60-80 percent of greenfield day-one capex, and this appears to be the reason some operators evaluate the two on capex alone and choose retrofit. That evaluation is incomplete.

Adding opex. Energy losses from the retrofit's inherent inefficiencies (extra conversion stages, undersized cooling), maintenance premium on hybrid AC/DC operation, insurance premium on a facility that carries both architectures during phased retrofit. Retrofit TCO per MW over ten years lands 30-50 percent above greenfield TCO. The break-even is not at day one; it is roughly year 3-4 of hold, after which greenfield pulls sharply ahead.

05Break-even sensitivity: when retrofit makes sense

Three specific conditions make retrofit economically defensible: the facility is under 5 years old (so remaining useful life justifies the retrofit capital); the cooling plant is already liquid-cooling-ready (avoiding the largest single retrofit cost); the real-estate is constrained (greenfield alternative is not physically available). If all three hold, retrofit TCO can beat greenfield-plus-decommissioning. If only two hold, the case is marginal. If only one, retrofit is almost certainly the wrong choice.

06Phased retrofit: the approach that sometimes works

A phased retrofit executes the upgrade one rack cluster (or row, or hall) at a time while the rest of the facility continues to operate. The advantage is operational continuity. No full shutdown, no revenue interruption. The disadvantage is a 25-40 percent timeline premium and 15-25 percent capex premium relative to a shutdown-and-retrofit approach, plus the complexity of running two architectures side-by-side during the transition period.

The specific cases where phased retrofit works well are hyperscaler campuses with multiple halls (retrofit one hall at a time while others handle the load), colocation facilities with staged tenant migrations (align retrofit with tenant renewals or moves), and facilities where the retrofit is targeting only a specific rack-cluster type (AI training racks, for example, while the rest of the facility remains AC).

07Named case studies

Public disclosure on data centre retrofits is thin because operators have limited incentive to publicise operational disruption. The following are the retrofit cases with useful public information as of mid-2026.

08Decision framework for operators evaluating both

A defensible decision framework has three gates. Gate 1: is the facility under 5 years old? If yes, proceed. If no, greenfield unless real-estate scarcity is binding. Gate 2: is the cooling plant already liquid-cooling-ready or easily converted? If yes, proceed. If no, greenfield unless retrofit budget can absorb 40+ percent cooling capex. Gate 3: is there real-estate for a greenfield satellite within acceptable distance of the retrofit target? If yes, greenfield-plus-decommission-old. If no, retrofit becomes the default.

09The reframe for anyone evaluating now

The default assumption that retrofit is cheaper than greenfield is wrong on TCO terms even when it appears right on capex terms. Operators evaluating an 800 VDC upgrade should build the ten-year TCO model, not the day-one capex model. The retrofit case survives that scrutiny only when facility age is below 5 years and cooling plant is compatible and real-estate scarcity is binding. In the majority of evaluations, the correct answer is greenfield satellite with staged decommissioning of the legacy facility.

Part VIII moves into cooling. The co-emerging technology that determines whether the retrofit or greenfield decision even matters. Above 100 kW per rack, 800 VDC and direct-to-chip liquid cooling are not independent architecture choices.