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Airflow / CRAC

Enter the heat load (kW) and the air ΔT (supply→return) and I compute the required airflow (CFM and m³/s) and the tons of refrigeration to size your CRAC/CRAH.

Thermal power to dissipate. It usually equals the electrical draw of the IT gear (watts that turn into heat).

ΔT = 12 °C = 21.6 °F

Difference between the cold supply air and the warm return air. Typically 10–14 °C in modern rooms.

Examples
redzilla.cl — crac 
 
  
 
 
Airflow
 
—
 
—
 
 
 
Airflow (SI)
 
—
 
cubic metres per second
 
 
 
Cooling
 
—
 
tons of refrigeration
 
 
  
 
 CFM —  
 
 m³/s —  
 
 Ton —  
 
 BTU/h —  
 
  
 
Calculation breakdown
 
 
  
QuantityValueFormula
   
 
 
 
 How it is calculated · airflow, m³/s and tons 
 
 1. Dry air at sea level: density
ρ = 1.2 kg/m³, specific heat cp = 1005 J/(kg·K).

 
 2. SI airflow:
Q(m³/s) = P(W) ÷ (ρ · cp · ΔT), with ΔT in K (= °C).

 
 3. To CFM: CFM = Q(m³/s) × 2118.88.
            Equivalent imperial formula: CFM = kW × 3412 ÷ (1.08 × ΔT_°F),
            with ΔT_°F = ΔT_°C × 1.8 (they agree within ±0.1 %).

 
 4. Cooling:
tons = kW ÷ 3.517 (1 TR = 3.517 kW) ·
BTU/h = kW × 3412.14.

 
 5. This airflow is the theoretical minimum for the given ΔT:
            it excludes recirculation, leakage through poorly sealed containment and CRAC headroom. Size the unit
            with margin and validate the real ΔT with probes on supply and return.

 
 
 
 
 
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