CRAC Unit vs CRAH Unit | What’s the difference?

November 16, 2022 |

The difference between a CRAC Unit System and a CRAH Unit System is how the heat is transferred and then removed/ejected from the system. A CRAC Unit transfers the heat from the system and ejects by only using the Refrigerant Cycle, whereas a CRAH Unit utilizes Chilled Water, the Refrigerant Cycle, and Condenser Water.

Below we compare and provide a high-level comparison table between the two with graphics to visually explain the fundamentals of the different systems.

To read more detail on the different types of unit see the following articles: CRAC Unit and CRAH Unit

Component Comparision Table

COMPONENTCRAC UNITCRAH UNIT
Unit frameXX
Panels [sides, bottom, and top] X X
Sound attenuation X X
Access doors X X
Inspection Windows X X
Base frames X X
Filters X X
Supply air plenum X X
Supply air grilleX* X*
Return air plenum X X
Return air grilleX*X*
Fan Section X X
Fan Motors X X
Fans X X
Fan Guards X X
Vibration isolators XX
Humidifier X* X*
Water supply and pipework [for humidifier] X* X*
Reheat coil X* X*
Dx Cooling coil X
Water Cooling coilX
Condensate drip tray X X
Condensate pipework X X
Condensate pump X* X*
Control panel X X
Control wiring X X
Temperature sensorsX X
Humidity sensors X X
Network switch X* X*
Control/expansion valveX
Refrigerant pipework X
Refrigerant [R407A] X X**
Chilled water pipeworkX
Isolation valvesX
Commissioning station/PICVX
StrainersX
Pipework temperature gaugesX
Pipework pressure gaugesX
Compressor X
Dx Condenser unit [external] X
Condenser fans X
Condenser coils X
Chilled water pumpsX
Water-cooled chillerX
Condenser water pipeworkX
Condenser water pumps X
Cooling towerX
Air-cooled chiller [if no condenser water]X***

*usually would be an ‘option’ | **the refrigerant noted within the CRAH Unit System is found within the chiller and what allows the heat from the chilled water system to be moved to the condenser water system before being ejected at the cooling towers | ***On some occasions the chiller used will be ‘air-cooled’ , removing the need for the condenser water equipment.

CRAC Dx System Pipework Diagram

The following diagram details a ‘typical’ system layout for a CRAC Unit Dx System.

It can be seen that the cooling process is managed and created by the condenser unit via the refrigeration process.

The condenser will be installed and located externally.

CRAH Water Cooled Chiller Pipework Diagram

The following diagram details a ‘typical’ system layout for a CRAH Water-Cooled Chiller System.

It can be seen that the cooling process is managed and created by the water-cooled chiller, which is used like a heat exchanger using the refrigeration process to transfer the heat from the chilled water system to the condenser water system, where the cooling towers will reject it to the atmosphere.

The chillers will be installed internally, and cooling towers externally.

CRAH Air Cooled Chiller Pipework Diagram

The following diagram details a ‘typical’ system layout for a CRAH Air-Cooled Chiller System.

It can be seen that the cooling process is managed and created by the air-cooled chiller via the refrigeration process.

The air-cooled chiller will be installed and located externally.


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