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What is a CRAC Unit and its Components?

Computer Room Air Conditioning: Chapter 1


Content

Introduction to Computer Room Air Conditioning

In this module, we will learn about computer room air conditioning. We’ll also look at the difference between comfort air conditioning and computer room air conditioning. Skip to quiz!


Introduction


Computer room air conditioning deals with monitoring and maintaining temperature, humidity, and air distribution in data centers and server rooms. We usually call computer room air conditioning systems CRAC for short. It’s also known as precision air conditioning or close control air conditioning.


CRAC systems are not for comfort. Recall that comfort air conditioning is used to create comfortable temperatures for people. CRAC systems have better air filtration, higher airflow, and better humidity control mechanisms than standard air conditioning systems.


Two factors can affect the operations in data center and server rooms. They are the two H’s.


The 2 H’s that can hurt computer operations are:

  • Heat, and

  • Humidity.

Let’s discuss the importance of these factors in CRAC systems.


Sometimes our computers operate at an annoyingly slow rate or randomly shut down in the middle of important work. This could be the result of overheating. Such cases in a computer room can damage the equipment.


For example, in March 2013, a portion of Microsoft’s servers suffered from a heat spike. It caused Hotmail and Outlook.com to be offline for 16 hours.


Recall that humidity is the amount of water vapor present in air. Data centers and server rooms should be maintained between 40% and 60% RH.


Low humidity tends to result in a higher risk of static electricity buildup. It can lead to static electric discharge in a computer room. A sudden flow of electrons from one charged object to another is called static electric discharge.


In extreme humidity conditions, water vapor can condense. As data centers and server rooms are completely occupied by electronic circuits and connections, water can accumulate on them. This can corrode the equipment or can cause short circuits that could result in the loss of data or damage computer components.



Comfort vs. Precision Cooling


Air conditioners that we use in our homes or offices do not always meet computer room cooling requirements. They’re meant for creating comfortable temperatures and humidity conditions in living spaces. Computer room air conditioning systems control temperature and humidity with high precision.


HVAC systems that we use in homes or offices are turned on when required. Running them at all times puts a strain on the system, increases your electricity bill, and could damage the components. CRAC systems operate 24 hours a day, 365 days a year, unlike comfort cooling systems.


Recall that pleated media filters are the most commonly used air filters in comfort cooling applications. These are inexpensive and trap the majority of indoor air pollutants. But in CRAC systems, we use high quality air filters like HEPA to trap very small particles in the air that could damage computer room operations.


CRAC deals with monitoring and maintaining temperature, humidity, and air distribution in a server room or data center.


The 2 H’s that can hurt computer operations are:

  • Heat, and

  • Humidity.

CRACs control temperature and humidity with high precision.



 

CRAC System Components


In this module, we will look into the components of a computer room air conditioning system. Skip to quiz!


Components


The main components of a CRAC system are

  • Air filters,

  • Cooling coils,

  • EC fans,

  • Humidifiers, and

  • Dehumidifiers.

Let’s look into each of these components in detail.



Air Filter


Dust particles in the air are as harmful as heat or humidity in a computer room. Accumulation of dust particles on computer room equipment leads to equipment malfunctions. Dust particles could even lead to a fire.

All CRAC systems contain high quality air filters to clean air in a computer room. Recall that air filters trap dust particles and debris from air. We generally use HEPA filters in CRAC systems. Recall that HEPA means ‘High Efficiency Particulate Air.’


Cooling Coil


Recall that cooling coils are used to cool and dehumidify air.


The cooling coil in a CRAC system can be a:

  • Direct expansion type,

  • Chilled water type, or

  • Dual type.

In a direct expansion type CRAC, the cooling coil is also called an evaporator. Refrigerant flows through the cooling coil in this system.


A cooling coil works with other components in the refrigeration cycle to provide cooling. This type of cooling coil is found in HVAC systems like window ACs, Split ACs, etc. Let’s watch a video to recall the refrigeration cycle.


In a chilled water type CRAC, the cooling coil is connected to a chiller system. Cold water flows through the cooling coil in this system.


A chiller circulates cold water to the cooling coil of a computer room air conditioner. Recall that a chiller system is a machine that is used to produce cold water.


In some CRAC systems, both chilled water and direction expansion cooling coils are present. These systems are called dual type CRAC systems. Either one of the cooling coils works while the other is on standby, or both the cooling coils work to provide cooling.



EC Fan


Recall that commercial HVAC systems usually have belt-driven blowers with induction motors. They take up a significant amount of space in a system, which makes installation complicated.


Moreover, belt-driven blowers need replacement and maintenance due to wearing parts. In light of these factors, EC motors are a great alternative. We generally use EC motor fans in a computer room air conditioning system.


EC stands for ‘Electronically Commutated.’ We generally use EC fans in CRAC systems.


EC fans are designed to run on an AC power supply. These use permanent magnets to generate magnetic fields. They are highly efficient, produce less heat, have lower running costs, and a longer lifespan. They don’t make much noise during operation.



Optional Components


Recall that low humidity in a computer room can cause static electric discharge. Humidifiers are installed in CRAC systems to increase the amount of moisture in the air. A humidifier is an optional component in computer room air conditioning. CRAC systems may or may not have this component.


Recall that high humidity in a computer room can corrode the equipment and can cause short circuits. Dehumidifiers are installed in CRAC systems to remove water vapor in the air.


Recall that a cooling coil removes moisture from the air by condensation. Electric heaters are installed after cooling coils to increase air temperature to the desired set value. In some CRAC systems, desiccant dehumidifiers are used to decrease humidity efficiently. It’s also an optional component.


The main components of a CRAC system are:

  • Cooling coil,

  • Air filter,

  • EC blower,

  • Humidifier, and

  • Electric heaters.

Humidifiers and dehumidifiers are optional components in computer room air conditioning systems.


This guide plays a major role in air conditioning repair, understanding components of air conditioning units, understanding air conditioning service.



 

Question #1: Computer room air conditioning is also known as _____. (Select all that apply)

  1. Precision air conditioning

  2. Comfort air conditioning

  3. Close control air conditioning

  4. All the above

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Answer: Precision air conditioning

Close control air conditioning

Computer room air conditioning is also known as ‘precision air conditioning’ or ‘close control air conditioning.’


Question #2: Which of the following can affect computer operations? (Select all that apply)

  1. Heat

  2. Clean air

  3. Humidity

  4. Global warming

Scroll down for the answer...










Answer: Heat

Humidity

Both heat and humidity can affect computer operations.


Question #3: The highest quality of air filters are found in which of the following systems?

  1. Computer room air conditioning systems

  2. Residential split systems

  3. Commercial rooftop units

Scroll down for the answer...










Answer: Computer room air conditioning systems

High quality filters are used in computer room cooling to trap the dust particles effectively.


Question #4: Computer room air conditioners operate ____________.

  1. 8 hours a day

  2. 12 hours a day

  3. 16 hours a day

  4. 24 hours a day

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Answer: 24 hours a day

Computer room air conditioners operate 24 hours a day for 365 days a year continuously, unlike the comfort air conditioners.


Question #5: In a direct expansion type system, the cooling coil is also called an ________.

  1. evaporator

  2. condenser

  3. radiator

  4. cooling tower

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Answer: evaporator

In a direct expansion type system, the cooling coil is also called an evaporator.


Question #6: Which of the following component circulates cold water to the cooling coil of a computer room air conditioner?

  1. Chiller

  2. Boiler

  3. Rooftop unit

  4. Cooling tower

Scroll down for the answer...











Answer: Chiller

A chiller circulates cold water to the cooling coil of a computer room air conditioner.


Question #7: EC motors are ______ magnet motors.

  1. electric

  2. permanent

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Answer: permanent

EC motors use permanent magnets to generate magnetic fields.


Question #8: What type of fan motor is used in a computer room air conditioning system?

  1. Combustion motor

  2. Induction motor

  3. EC motor

Scroll down for the answer...










Answer: EC motor

EC fan motor is used in a computer room air conditioning system. EC stands for ‘Electronically Commutated.’

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