What is the difference between upflow and downflow CRAC?

The difference between upflow and downflow CRAC units is the direction of conditioned air discharge and the way the air is distributed in the room.

Upflow CRAC

An upflow CRAC takes return air into the unit and discharges the cooled air upward. The supply air is usually delivered directly into the room or connected to a duct system above the unit.

Common features of upflow CRAC

• air is supplied upward

• often used in rooms without a raised floor

• suitable for ducted air distribution

• commonly installed in telecom rooms, control rooms, and smaller equipment rooms

Downflow CRAC

A downflow CRAC takes return air into the unit and discharges the cooled air downward. The cooled air is usually supplied into a raised floor plenum, then distributed through perforated tiles to the cold aisles or equipment areas.

Common features of downflow CRAC

• air is supplied downward

• usually used in rooms with a raised floor

• well suited for data centers with underfloor air distribution

• helps deliver cold air more directly to server racks

Main difference

So the main difference is:

• Upflow CRAC = blows cooled air upward into the room or ducts

• Downflow CRAC = blows cooled air downward into a raised floor for underfloor distribution

How to choose

• Choose upflow when there is no raised floor or when overhead ducting is preferred.

• Choose downflow when the room has a raised floor and needs underfloor air supply for server cooling.

In simple terms, the choice depends mainly on the room layout and airflow distribution design.