CRAC Capacity Calculator
Size CRAC/CRAH cooling capacity in tons of refrigeration from IT heat load, with a safety margin and room heat-gain allowance.
Inputs
IT equipment power draw ≈ heat generated (nearly all electrical power becomes heat)
Lighting, people, envelope/solar gain, and other non-IT heat sources
Margin for future growth and to avoid running cooling at 100% of calculated need
Recommended Cooling Capacity
37.53tons
Calculated Requirement (no safety margin)
31.28tons
Total Heat Load (IT + room gain)
110.00kW
Total Heat Load
375,335BTU/hr
Step by step
Values used
IT Heat Load = 100 kW; Additional Room Heat Gain = 10; Safety Factor = 20
Required cooling capacity
tons = (IT_heat_kW × (1 + room_loss%)) / 3.517, then apply safety factor
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
How it works
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
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.