What is CRAC (Computer Room Air Conditioning) Unit |Full Form, Works, Components

Very little is known to the masses about CRAC Unit or Computer Room Air Conditioning.

However, CRAC is an important element that ensures the proper and smooth functioning of a computer system. Therefore, in this write-up, we will discuss the CRAC Unit.

Computer rooms and/ or data centers are the need of the hour. With the majority of businesses as well as individuals dependent on computers and equipment.

It is crucial to ensure maximum efficiency and consistency in the performance of the computers.

However, an important aspect of it is Computer Room Air Conditioning.

Get your hands on the meaning of CRAC alongside how it works.

Moreover, we have thrown light on the main components of a CRAC unit.

Above all, explore the difference between CRAC and CRAH. So, let’s get started.

CRAC Unit (Computer Room Air Conditioning)

What is CRAC Unit?

Also known as Computer Room Air Conditioning Unit, CRAC is a device responsible to monitor and maintain the air distribution, temperature, and humidity levels in a computer room.

With more and more equipment getting stuffed into the IT spaces, it has become crucial to ensure the maximum efficiency of every component of the infrastructure.

If the CRAC unit fails to function, it may result in downtime. This indicates that CRAC failure will lead to loss of service and cost money at times. In certain instances, it can result in the loss of customers as well.

  • With the increasing volume of equipment in computer rooms, the power draw and heat generation quickly escalate.
  • This pushes up the power consumption, heat generation, and density which demand a better approach towards computer room air conditioning.
  • Initially, computer room cooling was a minor affair.
  • Those were times when data centers required less power and generated less heat.
  • Therefore, the technicians could easily eliminate heat damage risks.
  • Pumping cold air into the room was a convenient way of bringing down the temperature.

However, simply putting cold air into the room can be an inefficient way today. Computer room equipment quickly generates hot air.

Fetching in cold air will not offer the desired cooling needed for safeguarding the equipment.

Therefore, efficient cold air distribution is needed to ensure effective heat displacement.

To ensure the best use of a CRAC unit, it is important that you run along with a long-term plan.

This should also include preventive maintenance and optimization of the precise cooling system performance.

How does a CRAC unit work?

Traditionally, an infrastructural combination of CRAC units and raised floors were used to perform data center cooling.

These units are used to pressurize the spaces beneath the floors and vent out cold air through perforated tiles into the server intakes.

Upon passing over the server component, the cold air is pushed out as a hot exhaust. The air further returns to the CRAC unit for cooling.

However, this was inefficient and lacked fine-tuned control. Although this method for good for small and low-density data centers or computer rooms, it proved to be less efficient for large ones.

Therefore, modifications were made to ensure that the modern data centers of computer rooms obtain the best results from the CRAC unit installed.

Modern data centers employ several innovative methods to ensure operating conditions. Here is how a CRAC unit functions:-

  • The racks are placed in hot and cold configurations
  • The computers and racks find positions on the raised floors with the air intakes facing opposite
  • The CRAC unit pumps cool air through the perforated tiles while the racks and computer intake it
  • They further exhaust the hot air into the hot aisle placed opposite to it
  • The CRAC units then pull the exhausted hot air further releasing it under the floor tiles to complete the cycle

Through this process, a CRAC unit handles the running of cool air throughout the system while ensuring a steady airflow in the environment.

Apart from the efficient working of CRAC units, it is crucial to monitor the air quality in the data centers or computer rooms.

This is much more than just analyzing the CRAC unit. Even the functioning of the units cannot assure that everything is fine.

Therefore, it needs to be well maintained and regularly checked for the best performance.

What are the main components of a CRAC Unit?

While understanding a computer room air conditioning unit, it is important that you know the key components such as mechanical items, refrigerants, air filters, compressors, and evaporator coils.

Mechanical items

These components are based on the CRAC unit type use. However, if the unit involves a belt, it is important to adjust its tension.

All the factory parameters and belt stretches should be properly maintained.

Over tensioning and under tensioning result, in reduced performance, if not looked after properly.

Also, it is crucial to determine the tightness of the pulley set screws and mounts.

Clean and well-maintained mechanical systems put forth better and long-lasting performance.


The refrigerant levels of the CRAC units must be at least checked once every year. If the refrigerant levels are falling, it can signify a leak.

Such defects should be immediately found and corrected. In chilled water type units, regular checks of the proportional valves should be conducted to ensure proper operation and control.

Air filters

Serving as an important maintenance task for a CRAC unit, air filters are crucial for its performance.

They should be clean as dirty ones can lead to overworking the motors alongside reducing the cooling capacity.

In case, the intensity of filters getting dirty is high, one should immediately identify the source.

Accumulation of particulates on the filters of computing hardware as well as heat sinks might result in increased internal temperature.


The compressors in any CRAC unit should be analyzed for leaks alongside the oil levels.

This owes to the fact that too much or too little oil can decrease the service life.

It is best to go with the use of manufacturer-recommended oil.

Evaporator coils

These coils are important to be maintained free of debris as well as clean.

This will ensure the smooth functioning and performance of the CRAC unit.

Electrical testing

A running CRAC unit does not indicate that everything is fine. Records such as current which different components draw should be kept for every unit.

Also, the rpm of the motor should be noted. Any changes in the trends of rpm and current indicate a developing problem.

This might require an in-depth investigation to figure out the problem.

Moreover, the power readings should always be taken after checking the firmness of the electrical components.

The wires can move due to clamp-on meters. This leads to a loose connection and results in shutting down the data center.

Therefore, the air conditioning unit’s power connections should also come under the scan and check the components.

What is the difference between CRAC and CRAH?

The primary difference between a Computer Room Air Conditioning (CRAC) and Computer Room Air Handling (CRAH) unit is as follows:-

  • A CRAC unit uses a compressor and refrigerant for cooling
  • A CRAH unit uses a control valve and chilled water for cooling purposes

Employed for cooling computers or data centers that generate an immense amount of heat, CRAC and CRAH units contribute to the difference in the performance of your computer system.


  • Similar to the air conditioning units at your homes, CRAC units have compressors built into the unit as well as the direct expansion system.
  • The cooling process is initiated when air is blown over the cooling foil which is filled with refrigerant
  • The compressor is responsible for maintaining the cool state of the refrigerant
  • The glycol mixture, water, or air eliminates excess heat from the unit
  • Usually, CRAC units offer constant volume alongside modulate on and off. However, newer models or versions have been developed having airflow variations
  • CRAC units can be placed in several manners. However, they are often installed on the opposite of the hot aisle in a data center.
  • This placement ensures that they release cool air to cool down the serves through the perforations in raised floors


  • Having a function similar to chilled water air handling units in buildings, CRAH units initiate cooling through air blowing over a cooling coil which is filled with chilled water
  • The chilled water plant or the chiller supplies the chilled water to the coil
  • CRAH units are capable of regulating fan speed to ensure a set static pressure. This ensures that the temperature and humidity levels remain stable.

CRAC units serve as an essential component for the seamless functioning of the computer rooms and/ or data centers.

Moreover, the type and size of the units vary on the size of the data centers or computer rooms.

This was all about the CRAC (Computer Room Air Conditioning) Unit.

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