Calculate required CRAC unit cooling capacity for a data center's total heat load.
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.
Required cooling capacity
tons = (IT_heat_kW × (1 + room_loss%)) / 3.517, then apply safety factor
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.
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.
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.