How to Dissipate Excess Heat (Watts) - Understanding ΔT and CFM

Watts: The heat load that network equipment needs to dissipate. Power coming into the cabinet equals the amount of heat load produced. "Power In = Heat Load Out." Alternatively, the heat load of a cabinet can be derived by measuring the Power being delivered to the network equipment directly via a Watt meter or by measuring the current in amps and multiplying by applied voltage.

CFM: The amount of airflow that is used to dissipate the heat produced by the network equipment. It is measured in CFM or "Cubic Feet per Minute." The more CFM the greater amount of heat that is removed or dissipated. On passive systems, the amount of CFM needed at the cold aisle for the intakes is the sum of all the network equipment (servers) installed in the cabinet and equals the total amount of CFM that is exhausted. "CFM in = CFM Out"

ΔT: Delta T is the air temperature difference between the network intakes and the exhaust or the difference between the temperatures of the Cold Aisle and the Hot Aisle. It represents the amount of heat that is carried away by the airstream (CFM). It is measured in °F for the equation stated above. A ΔT between 10 F and 30 F is typical for network equipment and data centers.

• By knowing any two factors, the other can easily be obtained.
• The Cold Aisle must always provide enough CFM to the intakes of the network equipment to avoid overheating.

Graphic Representation: Watts = .316 x CFM x ΔT (°F)

Example:
9164 Watts will need 1450 CFM at 20 F ΔT: 9164 = .316 x 1450 x 20