Data Center Infrastructure Knowledge: Server Room Air Conditioning


Data center cooling is one of the major expenditures of data center daily operation and maintenance, it is necessary to understand the cooling of the server room, through this article, you will learn: the key factor in the data center cooling system - the server room air conditioner.


I. Computer Room Air Conditioning (CRAC)

Computer Room Air Conditioner Computer Room Air Conditioner (CRAC) is a large air conditioning equipment used to transfer a large amount of heat from the data center and send a large amount of cool air back to the data center.

The main service object of the computer room air conditioner is the computer, which provides stable and reliable IDC and detects the working temperature, relative humidity and air cleanliness of the computer room, with high sensible heat ratio, high energy efficiency ratio, high reliability and high precision.

Cooling of the server room is accomplished by blowing air through the cooling coils filled with refrigerant.

In general, CRAC units are self-contained, thus allowing a single unit to fail without affecting other CRACs in the facility. self-contained units also allow capacity to be easily increased, however, CRACs lack the efficiency of scale that many large unified cooling systems have.

Therefore, data centers that use CRACs typically have higher PUEs.


II. Principle of Server Room Air Conditioning

CRAC consists of an indoor unit and an outdoor unit. The main components in the indoor unit are the electronic expansion valve, evaporator, compressor, and indoor fan; the main components in the outdoor unit are the condenser and outdoor fan.

The refrigerant temperature in the evaporator is low, the hot air from the server drawn by the indoor fan is heat exchanged with the evaporator and becomes low temperature air suitable for the entrance of the server, the refrigerant after heat absorption is discharged to the outdoor condenser through the compression of the compressor and the absorbed heat is dissipated to the environment, the refrigerant after heat dissipation flows back to the indoor unit, and after the throttling effect of the expansion valve, it becomes low temperature refrigerant and continues to absorb the hot air from the service hot air, thus completing the refrigeration cycle of CRAC.

In this cooling process, by providing electrical energy to compressors, fans and other components, the purpose of moving the heat dissipated by the server from the indoor side to the outdoor side is achieved, but this part of energy consumption makes the CRAC data center have a higher PUE value.

In addition, in order to improve the reliability of the cooling system, the N+1 or N+2 redundancy scheme is usually configured.


III. Refrigeration methods of server room air conditioning

(1) Mixed Refrigeration

The traditional mixed cooling layout with the entire room as the cooling object, resulting in a mixed flow of cold and hot airflow operation, that is, the front of the cabinet discharge of hot air can easily enter the back row of cabinets inlet, due to the mixing of cold and hot airflow, resulting in precision air conditioning refrigeration and cabinet heat exchange efficiency is reduced.

(2) vertical air supply

Vertical air supply method generally refers to the downward (upward) wind on the return (side return) wind way, generally through the air supply duct or floor static pressure box opening way to send air, vertical air supply method of air conditioning can reduce the hot and cold airflow mixing, greatly improve the efficiency of air conditioning, reduce the cost of the project, this way is an economical and practical way to send air to the server room.

(3) horizontal air supply

Horizontal air supply method generally refers to close to the cabinet, along the cabinet surface evenly level to send cold air, the cold air evenly into the cabinet, using this form of air supply can greatly shorten the heat exchange distance, improve the efficiency of air conditioning, which is more ideal for the cabinet air supply method.

Fourth, the room air conditioning considerations

However, the cooling capacity of CRAC has the potential to condense water vapor in the air into water. Therefore, data centers utilizing CRACs must install a leak detection system under the unit to detect any liquid released from the cooling method.

This is often overlooked, which is why humidity control features should also be considered.

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