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In every data centre, thousands of processors are working regularly, and this generates data and a huge amount of heat. Managing this heat is one of the most important challenges in maintaining a functional IT environment. Standard office air conditioning is insufficient and will lack the power, efficiency, and reliability necessary. Before explaining CRAC vs CRAH, it is important to know about precision air conditioning.
As you might know, this precision air conditioning is a specialised field of cooling designed to maintain a stable environment for sensitive electronics 24 hours a day, 365 days a year. Within this field, you will see two main acronyms: CRAC and CRAH.
Even though Computer Room Air Conditioners (CRAC) and Computer Room Air Handlers (CRAH) sound similar, operate on different principles. Understanding the CRAC vs CRAH is important for designing an effective and efficient data centre cooling strategy.
The CRAC Unit
A Computer Room Air Conditioner, or CRAC unit, is a self-contained system. It works much like a refrigerator or a standard residential air conditioner, just on a much larger scale. The main mechanism is a direct expansion (DX) refrigeration cycle.
Inside the CRAC unit is a closed loop containing a refrigerant gas as well as its own compressor. The process is straightforward. The unit pulls in hot air from the data centre, passes it over a cold coil filled with the refrigerant, and then pushes the newly chilled air back into the room. During this process, the refrigerant absorbs the heat and turns into a gas. And this gas is then sent to a compressor where it is pressurised and cooled, ready to start the cycle again.
Because the compressor is an integral part of the unit, a CRAC system is a complete, all-in-one cooling solution.
The CRAH Unit
A Computer Room Air Handler, or CRAH unit, takes a different approach. It does not create cold air on its own. Instead, it functions more like the radiator in your car, using a cool liquid to remove heat. A CRAH is part of a larger system that includes a central chiller plant, which is usually located elsewhere in the building or on the roof.
This central chiller produces a continuous supply of chilled water, which is piped to the CRAH units within the data centre. The CRAH simply consists of a cooling coil and fans. It draws in the hot air from the data centre, passes it over the coil filled with chilled water, and distributes the resulting cold air. The water, now warmed from absorbing the heat, is piped back to the central chiller to be cooled again.
A CRAH unit is an air handling unit that depends on an external source for its cooling capacity.
CRAC vs CRAH
The choice between these two technologies hinges on operational differences. And please note that this impacts everything from energy consumption to the scale of the facility they are best suited for.
| Feature | CRAC Unit | CRAH Unit |
| Cooling Method | Direct Expansion (DX) with refrigerant | Chilled water from a central plant |
| Main Components | Internal compressor | Cooling coil and fans (no compressor) |
| Energy Efficiency | Generally less efficient, especially at scale | Highly efficient for large data centres |
| Ideal Scale | Small to medium-sized data centres | Large, enterprise-scale data centres |
| Installation | Simpler, as it is a self-contained unit | More complex, requires extensive piping |
| Upfront Cost | Lower per-unit cost | Higher initial system cost (including chiller) |
Applications for CRAC and CRAH
After understanding CRAC vs CRAH, you need to find which unit is right for the facility. That decision should be taken depending on your scale, existing infrastructure, as well as long-term efficiency goals.
Why Choose a CRAC Unit?
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- Ideal choice for small to medium-sized server rooms or data centres.
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- Its self-contained nature makes it easier and faster to deploy.
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- The lower upfront cost per unit is attractive for smaller projects.
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- The perfect solution for facilities that do not have an existing central chiller plant.
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- Where CRAC unit installation would be impractical or too expensive.
Why Choose a CRAH Unit?
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- This is ideal in large, enterprise-scale data centres.
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- While the initial investment in the unit and the supporting chiller infrastructure is higher, the long-term operational savings are important.
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- Chilled water systems are more energy-efficient when cooling large spaces. This can lead to a much lower Power Usage Effectiveness (PUE) rating as well as reduced electricity costs.
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- For any organisation focused on building a large, high-density, and highly efficient data centre, a CRAH system is the standard.
Conclusion
The choice between a CRAC and CRAH system is a main decision in data centre design. Making the right one requires a thorough analysis of heat load, growth plans, as well as long-term operational budget.
At BTLME, our team of experienced engineers can provide a complete assessment of needs, and this will help suggest a precision air conditioning solution that is perfect for your facility. We work with world-class manufacturers to provide reliable, high-performance CRAC and CRAH systems. BTLME also offer expert installation and long-term maintenance support.
Frequently Asked Questions (FAQs)
Close control unit is the general industry term for any air conditioner designed to control the temperature and humidity within a tight tolerance. This is very essential for protecting sensitive electronic equipment. Both CRAC and CRAH units are types of close control units.
Yes, CRAC and CRAH units can be used in the same data centre. This is very common in large facilities. A data centre might use a CRAH system for the main server hall where the heat density is high. And they might use smaller, independent CRAC units for less demanding areas like networking rooms or electrical rooms where a chilled water loop may not be necessary.