Computer Room Air Conditioning: Work Principle, Characteristics and Technical Requirements, Benefits

Video: Computer Room Air Conditioning: Work Principle, Characteristics and Technical Requirements, Benefits

Figure 1: Computer room air conditioners.

Computer room air conditioners (CRACs), to put it simply, are air conditioners dedicated to computer rooms. Because it can not only control the temperature of the computer room, but also control the air humidity at the same time. And because of its high precision in controlling temperature and humidity, people in the industry also call it precision air conditioners for computer rooms.

Computer room air conditioners have the characteristics of high sensible heat ratio, high energy efficiency ratio, high reliability, and high precision. They are generally placed in data computer rooms, power distribution rooms, equipment rooms, etc.

1. Work Principle of Computer Room Air Conditioning

The principle of precision air conditioning is actually similar to that of ordinary air conditioning. The compressor sucks in refrigerant vapor, compresses it into high-pressure and high-temperature vapor, and then discharges it into the condenser. It releases heat to the cooling medium (water or air) in the condenser, condenses into high-pressure liquid, and is throttled into low-pressure and low-temperature refrigerant by the throttle valve. The refrigerant enters the evaporator again to absorb heat and vaporize, achieving the purpose of circulating refrigeration.

Figure 2: Working principle diagram of computer room air conditioner.

2. Characteristics and Technical Requirements of Computer Room Air Conditioning

The principle of precision air conditioning in computer rooms is similar to that of civil air conditioning, but in fact the technical requirements are stricter and more complex.
Comfort air conditioners were used in early computer rooms, so problems such as unstable operation of computer room equipment, interference in data transmission, and static electricity often occurred due to improper control of ambient temperature and humidity parameters.

Computer room precision air conditioners have the following characteristics and technical requirements:

2.1 Large Sensible Heat

Computer equipment such as hosts and peripherals, servers, switches, optical transceivers, and power support equipment such as UPS power supplies installed in the computer room will dissipate heat through heat transfer, convection, and radiation. This heat only causes the temperature rise inside the computer room and is considered sensible heat.

The heat release of a server cabinet ranges from several kilowatts to more than ten kilowatts per hour. If a blade server is installed, the heat release will be higher. The heat release of large and medium-sized computer room equipment is around 400W/m2, and data centers with higher installed density may reach more than 600W/m2. The sensible heat ratio in the computer room can be as high as 95%.

Figure 3: Structure diagram of precision air conditioner.

2.2 Small Latent Heat

There is no moisture dissipation equipment in the computer room, and latent heat mainly comes from the staff and outdoor air. Large and medium-sized computer rooms generally adopt a management model of separation of humans and machines. The enclosure structure of the computer room is well sealed. Fresh air generally enters the computer room after being pre-treated with temperature and humidity. Therefore, the latent heat in the computer room is smaller.

2.3 Large Air Volume

The heat of the equipment is transferred to the computer room through conduction and radiation. The heat is concentrated in areas with dense equipment. In order to make the temperature and humidity in each area of the computer room uniform and control it within the allowable base and fluctuation range, a large air volume is required to take away the residual heat.

2.4 Uninterrupted Operation, Year-Round Cooling

The heat dissipation of equipment in the computer room is a steady-state heat source and the equipment operates continuously throughout the year, which requires an uninterrupted air conditioning system. There are also higher requirements for the power supply of air-conditioning equipment, and the air-conditioning system that protects important computer equipment should also have a generator set as a backup power supply.

Figure 4: Centrifugal fan for computer room air conditioner.

2.5 Air Supply from Plenum Box

The air supply and return of the air conditioner in the computer room usually does not use ducts. Instead, the space under the raised floor or the upper part of the ceiling is used as a plenum box for air supply and return. The pressure-stabilizing layer formed in the plenum box can make the air supply uniform and make the static pressure equal at all points in the space.

2.6 High Cleanliness Requirements

Computer rooms have strict air cleanliness requirements. Dust, corrosive gases, etc. in the air will seriously damage the life of electronic components and cause poor contacts and short circuits. Therefore, special air conditioners for computer rooms are required to remove dust and filter the circulating air in accordance with relevant standards. In addition, fresh air should be added to the computer room to maintain positive pressure.

3. Why Can't the Computer Room Use Ordinary Air Conditioning?

The equipment in the computer room is basically microelectronics and precision equipment, which are very sensitive to temperature changes. For example, for semiconductors, for every 10°C increase in room temperature, reliability will decrease by about 25%. In addition, humidity also has a great impact on equipment in the computer room. Excessive humidity will cause water vapor to form a water film on the surface of electronic components, causing a short circuit. If the humidity is too low, it is easy to cause static electricity.

The heat release in the computer room is relatively large, and it is almost non-stop for 24 hours. The more precise the temperature, humidity, and cleanliness control during the period, the better. Such "abnormal" requirements are obviously impossible for ordinary air conditioners.

Ordinary air conditioners take into account noise reduction and energy saving, so they have low power, low air output, uneven air supply, and cannot cool fast. The filter cannot meet the hygiene indicators at the level of electronic components. To achieve constant temperature, constant humidity, constant cleanliness and long service life in the computer room, you can only use computer room precision air conditioning products.

Figure 5: Axial fan for computer room air conditioner.

4. What Are the Benefits of Using Precision Air Conditioning in Computer Rooms?

Compared with ordinary air conditioners, computer room air conditioners have the characteristics of high temperature and humidity stability, high air cleanliness, and large air supply volume. It can control the equipment to be in a constant temperature and constant humidity environment, ensuring the stable life of electronic components. This avoids a “general strike" caused by equipment heating due to high temperature, and prevents water droplets caused by excessive humidity from falling on the equipment, causing components to be burned or even causing a fire.

Secondly, precision air conditioners have a better ability to filter air impurities, and the air sent into the room is pure. It reduces the phenomenon of dust flying into components to cause short circuit, overheating and data errors.

5. Difference Between Precision Air Conditioning in Computer Rooms and Ordinary Comfort Air Conditioning

Table 1: Computer room air conditioner vs. comfort air conditioner.