Energy layer
Cooling Load Estimator
Estimate the cooling tonnage / liquid-cooling capacity needed for a given rack density.
The engineer question
When do air-cooled racks need to switch to liquid?
Result
- Heat to remove~100% of IT power becomes heat
- 40 kW thermal
- Cooling tonnage1 RT = 3.517 kW
- 11.4 RT
- Recommended approach
- Direct-to-chip liquid (cold plate)
- Free-cooling hours / yr68% of 8,760 h
- 5,957 h
- Air cooling energy / yr
- 87.6 MWh (overhead PUE +0.25)
- Liquid cooling energy / yr
- 24.5 MWh (overhead PUE +0.07)
- Annualized cooling-energy delta vs airsavings from moving off the air baseline
- −63.1 MWh (72% less)
Recommendation
At 40 kW/rack, direct-to-chip cold plate is the mainstream 2026 answer (range ~30–80 kW). Budget a CDU per few racks and keep ~10–20% residual air for DIMMs/NICs. The liquid loop drops cooling overhead ~72% vs air in a temperate climate — the warmer your inlet target, the bigger that gap.
Assumptions
- · Tonnage uses 1 refrigeration ton = 3.517 kW thermal (ASHRAE), and assumes ~100% of IT power converts to removable heat — a deliberate worst-case; real sensible/latent split varies a few %.
- · Air→liquid thresholds are typical mid-2026 industry figures (ASHRAE TC9.9 datacom guidance, Uptime Institute / OCP cold-plate surveys, vendor CDU datasheets): air ≲15 kW, RDHx ~15–30, direct-to-chip ~30–80, immersion >80. Approximate — individual designs span ±25% around these.
- · Inlet target 27 C (ASHRAE recommended max): ~68% baseline free-cooling hours and a 1.00× chiller-energy factor vs the 27 C reference (per ASHRAE allowable envelopes + typical economizer studies). Typical, not site-measured.
- · Climate Temperate (e.g. Dublin, PNW): air cooling-overhead +0.25 PUE, liquid +0.07 PUE, 1.00× free-cooling derate. These are the cooling component of PUE only and are industry-typical rough figures (±0.05–0.10), not audited PUE.
- · Energy delta is annualized cooling energy for a single rack, holding IT load constant; it captures cooling-system overhead, not the IT power itself.
- · Excluded: capex (CDUs, manifolds, dielectric fluid, facility-water plant), water consumption (WUE) and adiabatic/evaporative make-up, redundancy (N+1/2N), pump/fan parasitics beyond the PUE overhead, humidity/contamination control, and partial-load behavior. Not a substitute for a vendor TFA or CFD study.
Worked example (default inputs)
Result
- Heat to remove~100% of IT power becomes heat
- 40 kW thermal
- Cooling tonnage1 RT = 3.517 kW
- 11.4 RT
- Recommended approach
- Direct-to-chip liquid (cold plate)
- Free-cooling hours / yr68% of 8,760 h
- 5,957 h
- Air cooling energy / yr
- 87.6 MWh (overhead PUE +0.25)
- Liquid cooling energy / yr
- 24.5 MWh (overhead PUE +0.07)
- Annualized cooling-energy delta vs airsavings from moving off the air baseline
- −63.1 MWh (72% less)
Recommendation
At 40 kW/rack, direct-to-chip cold plate is the mainstream 2026 answer (range ~30–80 kW). Budget a CDU per few racks and keep ~10–20% residual air for DIMMs/NICs. The liquid loop drops cooling overhead ~72% vs air in a temperate climate — the warmer your inlet target, the bigger that gap.
Assumptions
- · Tonnage uses 1 refrigeration ton = 3.517 kW thermal (ASHRAE), and assumes ~100% of IT power converts to removable heat — a deliberate worst-case; real sensible/latent split varies a few %.
- · Air→liquid thresholds are typical mid-2026 industry figures (ASHRAE TC9.9 datacom guidance, Uptime Institute / OCP cold-plate surveys, vendor CDU datasheets): air ≲15 kW, RDHx ~15–30, direct-to-chip ~30–80, immersion >80. Approximate — individual designs span ±25% around these.
- · Inlet target 27 C (ASHRAE recommended max): ~68% baseline free-cooling hours and a 1.00× chiller-energy factor vs the 27 C reference (per ASHRAE allowable envelopes + typical economizer studies). Typical, not site-measured.
- · Climate Temperate (e.g. Dublin, PNW): air cooling-overhead +0.25 PUE, liquid +0.07 PUE, 1.00× free-cooling derate. These are the cooling component of PUE only and are industry-typical rough figures (±0.05–0.10), not audited PUE.
- · Energy delta is annualized cooling energy for a single rack, holding IT load constant; it captures cooling-system overhead, not the IT power itself.
- · Excluded: capex (CDUs, manifolds, dielectric fluid, facility-water plant), water consumption (WUE) and adiabatic/evaporative make-up, redundancy (N+1/2N), pump/fan parasitics beyond the PUE overhead, humidity/contamination control, and partial-load behavior. Not a substitute for a vendor TFA or CFD study.
Related tools in the Energy layer
Datacenter Power Calculator
Estimate MW capacity required for an AI training or inference cluster of a given size.
Cluster Buildout Sizer
Go from a power envelope (MW) or a GPU count to the reciprocal, plus cooling tonnage and 5-yr TCO — one chained buildout view.
PUE Comparison
Compare PUE benchmarks across hyperscale operators, regions, and cooling approaches.
US Electricity Cost by Region
Per-state industrial electricity rate snapshot + 12-month trend, indexed to datacenter footprint.