DC Cooling Load Calculator — Data Center
Calculate the cooling capacity required by your data center based on IT load and target PUE. Understand what fraction of total facility power goes to cooling.
Cooling Load (kW) = IT Power × (PUE − 1)
How PUE drives cooling load
| PUE | Overhead % | Cooling for 1 MW IT |
|---|---|---|
| 1.2 | 17% | 200 kW |
| 1.5 | 33% | 500 kW |
| 2.0 | 50% | 1,000 kW |
| 3.0 | 67% | 2,000 kW |
Published: April 2026 | Author: TriVolt Editorial Team
Cooling Load and PUE
The relationship between PUE and cooling load is direct: every decimal point of PUE represents a fraction of IT power that the cooling system must remove. At PUE 1.5, 33% of total facility power goes to cooling and other overhead. At PUE 2.0, it's 50%.
This calculator answers a practical design question: given a target IT load and PUE, how many kW of cooling capacity do you need to procure?
The Formula Explained
PUE = Total Facility Power / IT Power
Total Facility Power = IT Power × PUE
Overhead (Cooling + Other) = Total − IT = IT × (PUE − 1)
Note: "cooling load" here includes all non-IT overhead — cooling, lighting, security, switchgear losses. Cooling typically dominates (60–80% of overhead).
Converting to Tons of Refrigeration
Cooling equipment is often specified in Tons of Refrigeration (TR) or BTU/hr, not kilowatts.
- 1 Ton of Refrigeration = 3.517 kW
- 1 kW = 3,412 BTU/hr
A 1 MW IT load at PUE 1.5 requires 500 kW of cooling capacity = 142 TR. Size CRAH/CRAC or chiller capacity with 20–30% headroom for redundancy and peak conditions.
Cooling Load vs. Actual Cooling Design
This calculation gives you the total overhead to reject, not the cooling system capacity. In practice, you need to size cooling for peak load, including safety factors:
- Peak load allowance: Size for 110–120% of calculated load to handle peak IT load and worst-case conditions
- Redundancy: N+1 or 2N for chiller and CRAH units in Tier II/III+ facilities
- Climate: Free cooling potential depends on wet-bulb temperature — warmer climates require more mechanical cooling hours
- Partial load efficiency: Chillers and CRAHs operate more efficiently at partial load — size appropriately, don't massively oversize
Worked Examples
Example 1 — Edge data centre, 200 kW IT, PUE 1.4:
Total facility power = 200 × 1.4 = 280 kW
Cooling overhead = 280 − 200 = 80 kW = 22.7 TR
Size CRAHs at 110% of calculated = 88 kW (25 TR) minimum.
Example 2 — Hyperscale hall, 5 MW IT, PUE 1.15:
Total facility power = 5,000 × 1.15 = 5,750 kW
Cooling overhead = 750 kW = 213 TR
At this scale, evaporative cooling or adiabatic economisers often handle the full load with near-zero mechanical refrigeration.
Free Cooling and Economisers
Mechanical refrigeration is the most energy-intensive cooling method. Modern data centres exploit ambient conditions to reduce or eliminate compressor run-time:
- Air-side economisation: Draw in cool outside air directly. Effective in northern climates (<18°C dry-bulb). Not suitable for humid tropical environments without careful psychrometric analysis.
- Water-side (indirect) economisation: Chilled water is pre-cooled through a dry cooler or cooling tower before entering the chiller. Can reduce compressor run-time by 40–70% in mild climates.
- Adiabatic cooling: Evaporative pre-cooling of the air entering a dry cooler. Trades water consumption for electricity savings. Common in hyperscale facilities in semi-arid regions.
- Rear-door heat exchangers: Row-level cooling that intercepts heat before it enters the room air stream. Particularly effective for high-density rows above 15 kW/rack.
Facilities in Dublin, Amsterdam, and northern Sweden routinely achieve PUE values of 1.05–1.15 using economisation for 80–90% of annual operating hours. A 1 MW facility shifting from PUE 1.5 to 1.2 saves approximately 300,000 kWh per year.
Common Sizing Mistakes
- Confusing IT load with nameplate power: Servers rarely draw their rated TDP simultaneously. Use measured average load (typically 40–60% of nameplate for mixed workloads) as the design basis, with a growth allowance.
- Ignoring UPS and PDU losses: UPS systems at 90–95% efficiency add 5–11% to the heat load. These losses happen inside the data hall and must be cooled.
- Sizing cooling for total nameplate: Oversized cooling systems run inefficiently at partial load. Use controls and variable-speed drives so systems modulate rather than cycle on/off.
- Single-point calculations for a phased build: Phase 1 IT load might be 20% of ultimate capacity. Size cooling infrastructure for Phase 1 while planning the path to ultimate load — oversizing chillers early wastes capital and energy.
Related Calculators
- → PUE Calculator — Calculate PUE from measured power
- → Rack Density Calculator — Cooling strategy by rack density
- → UPS Sizing Calculator — Power backup capacity
- → Cooling Load Calculator — General building cooling load
Disclaimer
This calculator derives cooling load from PUE — a useful planning estimate, not a substitute for detailed mechanical engineering design. Engage a licensed mechanical engineer for cooling system design and equipment selection.