CRAC Capacity
Calculate required CRAC unit cooling capacity for a data center's total heat load.
About CRAC Capacity
CRAC/CRAH cooling capacity is sized from the total heat that must be removed from the room, not just the IT load: nearly all electrical power consumed by IT equipment converts to heat, and additional heat comes from lighting, personnel, and building envelope gain. One ton of refrigeration equals 3.517 kW of heat-removal capacity, so dividing total heat load by 3.517 gives the required tonnage, and a safety factor is added on top to cover future load growth and avoid running cooling units at their absolute limit.
Formula
Required cooling capacity
tons = (IT_heat_kW × (1 + room_loss%)) / 3.517, then apply safety factor
- P_{IT}
- IT equipment heat load in kW
- r
- Room heat gain fraction
- s
- Safety factor fraction
Worked example
With the default values below, CRAC Capacity returns Recommended Cooling Capacity of 37.53. Change any input above and every figure here is recalculated in your browser.
Inputs used
- IT Heat Loadminimum 0.1 kW
- 100 kW
- Additional Room Heat Gainaccepts 0–50
- 10
- Safety Factoraccepts 0–100
- 20
Results
- Recommended Cooling Capacity
- 37.53 tons
- Calculated Requirement (no safety margin)
- 31.28 tons
- Total Heat Load (IT + room gain)
- 110.00 kW
- Total Heat Load
- 375,335 BTU/hr
Step by step
- 1Values used
- 2Required cooling capacity
- 3Recommended Cooling Capacity= 37.53 tons
- 4Calculated Requirement (no safety margin)= 31.28 tons
- 5Total Heat Load (IT + room gain)= 110.00 kW
- 6Total Heat Load= 375,335 BTU/hr
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does IT power draw equal heat load?
By the first law of thermodynamics, essentially all electrical energy consumed by IT equipment (CPUs, power supplies, fans, drives) is converted to heat with nowhere else for the energy to go — so a server drawing 500W of power load also generates approximately 500W of heat that the cooling system must remove.
What is a 'ton' of cooling capacity?
One ton of refrigeration is defined as the heat-removal rate needed to melt one ton of ice in 24 hours, equal to 3.517 kW (or 12,000 BTU/hr) of continuous heat removal — it's a legacy unit still standard in HVAC and data center cooling sizing.
Why add a safety factor on top of the calculated tonnage?
Running cooling units at exactly their calculated maximum leaves no margin for equipment additions, hot-spot variability, or degraded performance as filters and coils age — a 15-25% safety factor is standard practice to keep the system comfortably under its rated limit during normal operation.