Calculators › Rack cooling feasibility

Rack cooling feasibility

Test a rack and facility envelope using rack power, the named liquid/residual-air heat split, qualified airflow and rear-door conditions, rack water availability, room residual capacity, and the roadmap case. Rack kW alone never selects the technology.

ScenarioNVIDIA GB300 NVL72 · 56 active / 72 installed GPUs · 1 racks · 0.14 MW IT · $9M programguide defaults (as of 2026-09)Edit the shared scenario →

Rack cooling feasibility

Current rack power (screening input)kW/rackUpper roadmap rack heat load (screening input)kW/rackHeat duty of the highest named configuration the hall must support. Connected: Vera Rubin NVL72 runs at 188 kW Max Q / 228 kW Max P (Pegatron); NVIDIA's DSX reference design plans its cabinets at 330 kW TDP, so use 330 to size reserve to that design.Heat captured to liquid% of rack heatUse the named OEM rack heat split (GB200 NVL72 ~87%, HPE 115/132 kW; GB300 NVL72 ~90%, Lenovo); do not infer it from rack kW.Future heat captured to liquid% of rack heatKeep the future split separate; default is GB300 NVL72's ~90%. Vera Rubin NVL72 compute trays are fanless and 100% liquid-cooled (NVIDIA); take the residual air for switch trays, power shelves and busbar from the OEM.Liquid path qualified at both operating points?Requires the named equipment/fluid envelope, minimum flow, pressure, CDU capacity, heat rejection and service/redundancy state at both duties.Qualified liquid-path capacitykW/rackAvailable duty at both entered operating points in the required redundancy state.Required terminal approachKUse the selected exchanger requirement; compare both terminals, never the two outlets.Air delivery/inlet envelope proven at both duties?Requires the named rack/server airflow, pressure, inlet and containment case.Rack water connection available?Includes a qualified TCS/FWS/CDU or rear-door water path.Rear-door system qualified?A rated door plus proven airflow, water conditions and room residual-heat path.Qualified door heat-capture dutykW/rackThe named rear door's rated capture at its stated water and airflow conditions. A rear-door case cannot be screened without it — the room still takes rack air heat minus this duty.Future door heat-capture dutykW/rackThe door's rated capture at the future duty's water and airflow conditions; 0 until the door is qualified there. Applies to rear-door air and to direct liquid plus rear door.Current TCS supply to rack°COne supported operating point; limit temperatures are not a design pair.Current TCS return from rack°COne supported operating point; limit temperatures are not a design pair.Current FWS supply to CDU°COne supported operating point; limit temperatures are not a design pair.Current FWS return from CDU°COne supported operating point; limit temperatures are not a design pair.Future TCS supply to rack°COne supported operating point; limit temperatures are not a design pair.Future TCS return from rack°COne supported operating point; limit temperatures are not a design pair.Future FWS supply to CDU°COne supported operating point; limit temperatures are not a design pair.Future FWS return from CDU°COne supported operating point; limit temperatures are not a design pair.Room residual-air capacitykW/rackMaximum residual rack heat the room-air system can remove in the declared redundancy case.

not established: direct liquid and residual-air paths must close at both duties; verify liquid capacity, both terminal approaches, supported fluid/flow/pressure, rack water and the air delivery/inlet envelope in the declared redundancy state

Current liquid / residual-air split121.5 / 13.5 kW

Future liquid / residual-air split205.2 / 22.8 kW

Future residual-air load22.8 kW vs 20 kW limit

Current cold / hot terminal approach5 / 5 K

Future cold / hot terminal approach5 / 5 K

At each operating point: liquid duty = rack heat × capture fraction; the air path removes the remainder. CDU cold-end approach = TCS supply to rack − FWS supply to CDU; hot-end approach = TCS return from rack − FWS return from CDU. Both must meet the selected 5 K requirement. Qualification includes the actual fluid, flows, pressure, component envelope and surviving plant capacity; positive residual air also requires proven delivery, inlet temperatures and containment. The current and future profiles are independent screening cases. No annual PUE follows from these temperatures or rack kW → Ch 5.1, Ch 5.2.

Worked decision — stated assumptions

All ledger inputs are assumed teaching values chosen to exercise this chapter’s method; they are not market quotes, OEM performance claims or operating records. Arithmetic uses the full entered precision.

Assumed inputs
Input	Value
Current rack power (screening input)	100 kW/rack
Upper roadmap rack heat load (screening input)	150 kW/rack
Heat captured to liquid	80 % of rack heat
Future heat captured to liquid	80 % of rack heat
Liquid path qualified at both operating points?	yes
Qualified liquid-path capacity	120 kW/rack
Air delivery/inlet envelope proven at both duties?	yes
Rack water connection available?	yes
Rear-door system qualified?	no
Qualified door heat-capture duty	0 kW/rack
Room residual-air capacity	30 kW/rack
Required terminal approach	5 K
Current TCS supply to rack	35 °C
Current TCS return from rack	45 °C
Current FWS supply to CDU	30 °C
Current FWS return from CDU	40 °C
Future TCS supply to rack	35 °C
Future TCS return from rack	45 °C
Future FWS supply to CDU	30 °C
Future FWS return from CDU	40 °C

Choose whether to release a 100 kW current / 150 kW future rack design. Assume 80% liquid capture in each profile: current liquid/air duties are 80/20 kW and future duties 120/30 kW. The 120 kW liquid capacity and 30 kW room capacity are assumed surviving-path ratings at the entered conditions. The Yes controls assume qualified liquid equipment, rack water and proven air delivery/inlet conditions at both duties; they are not test records. Rear-door assistance is absent.

Use the Chapter 5.1 teaching operating point at both duties: TCS 35 °C supply / 45 °C return; FWS 30 °C supply / 40 °C return. Cold-end approach = 35 − 30 = 5 K; hot-end approach = 45 − 40 = 5 K. Each meets the assumed 5 K requirement. Both heat paths pass this stated screen, with zero spare future liquid or room duty. Release equipment only after the suppliers and inlet map substantiate these assumptions.

Raise only future FWS supply to 31 °C: the cold-end approach becomes 4 K and fails; the crossover is 30 °C. Changing airflow qualification to No also leaves the design unestablished. A 200 kW future rack would require 160 kW liquid and 40 kW air, exceeding both ratings. Change the exchanger or the operating point and requalify before freezing density; no PUE is inferred.

Primary method: ASHRAE Handbook (2023), Applications ch. 20 — thermal paths and CDUs. Method and handoff: Chapter 5.1 — Thermal Fundamentals & the Density Wall.

These are transparent screening estimates, not final designs, financial advice, or project approvals. Replace every default with current project data and have the responsible project authorities validate the result. You can save, share a permalink, or export to CSV; see the full calculator suite.