Airflow Supply vs Demand Calculator

Identify airflow mismatches between CRAC supply and rack demand. Rule of thumb: 1 kW IT load needs ~160 CFM.

Total racks in the zone or row being evaluated.
Average IT power per rack. Low: 3-5 kW. Medium: 5-10 kW. High: 10-25 kW.
kW
Active cooling units supplying airflow to this zone.
Airflow output of each unit. Typical 20-ton CRAC: ~8,000 CFM. 30-ton: ~12,000 CFM.
CFM
Perforated tiles in cold aisle. Enter 0 if no raised floor.
Airflow per tile. 25% open at 0.05 in w.g. = ~350 CFM. At 0.1 in w.g. = ~500 CFM.
CFM

Results

Total IT Load:-kW
Airflow Demand (IT equipment):
~160 CFM per kW at 20F temperature rise.
-CFM
CRAC Supply (total):-CFM
Tile Delivery Capacity:
Total tile airflow. If less than CRAC supply, tiles are the bottleneck.
-CFM
Effective Supply:
Actual airflow, limited by lesser of CRAC output or tile capacity.
-CFM
Supply / Demand Ratio:
Below 1.0 = deficit. 1.0-1.2 = marginal. Above 1.2 = adequate.
-
Surplus / Deficit:-CFM
Hot Spot Risk:
Risk assessment based on supply/demand ratio.
-
CFM per Rack (effective):-CFM
Reference: ASHRAE TC 9.9 Thermal Guidelines. ~160 CFM per kW at 20F (11C) delta-T. Supply/demand ratio of 1.2+ recommended.