Cooling Redundancy Calculator

Determine CRAC/CRAH units needed for N, N+1, or 2N cooling redundancy with altitude derating.

Total heat load to be removed. Approximately equal to total IT power draw plus other heat sources.
tons
Rated cooling capacity of one unit at sea level. Common: 20, 30, 50, 60, 80, 100 tons.
tons
N=no redundancy. N+1=one spare (Tier II/III). N+2=two spares. 2N=fully redundant (Tier IV). 2(N+1)=redundant+spare.
Altitude above sea level. Air density drops ~3% per 1,000 ft above 1,000 ft, reducing air-cooled capacity (ASHRAE).
ft
Additional capacity buffer. Typical 10-20% for load growth and aging.
%

Results

Altitude Derating:
Capacity reduction due to altitude.
-%
Derated Unit Capacity:
Effective capacity after altitude derating.
-tons
N Units Required (load-serving):
Minimum units to meet cooling load.
-units
Redundancy Configuration:
Redundancy scheme with actual counts.
-
Total Units to Install:
Total units including redundant spares.
-units
Total Installed Capacity:
Total derated capacity of all installed units.
-tons
Spare Capacity:
Capacity above the required cooling load.
-tons
Spare Capacity Ratio:
Spare capacity as percentage of load.
-%
Reference: ASHRAE TC 9.9 Thermal Guidelines. TIA-942 Tier classifications. Altitude derating ~3% per 1,000 ft above 1,000 ft. Tier III = N+1, Tier IV = 2N minimum.