The construction of domestic data centers is in full swing. Do you know the technological development of data center cooling? Let's take a look together!

       In the early days of the data center, there was no dedicated precision air conditioner, and there was no uniform standard. Only civilian high-power air conditioners were used. This type of air conditioner is mainly designed for people and is not suitable for use in the environment of the data center. In contrast, in constant temperature, constant humidity, dust removal and other environments, it cannot meet the requirements. Of course, there are too many restrictions in the early stage of development, and I have to use it.

In the 1970s, the emergence of precision air conditioners dedicated to computer rooms can effectively guarantee the constant temperature and humidity environment of the data center. In terms of dust removal, the fresh air system and positive pressure dust removal in the computer room are used to meet the requirements of the data center to maintain a moderately constant level, good air cleanliness, and remote monitoring.

    After 2000, with the rapid development of the Internet, the transmission of information became more frequent, and the amount of data and calculations generated increased. People put forward higher requirements for the high availability of precision air conditioning systems. In the design, Availability, green energy saving, and dynamic cooling have become the new main development directions.

       In the 1960s, water cooling began to be applied to mainframe computers and high-performance personal computers. In the early days, because the heat load of the data center was lower, the cost of air cooling was lower than that of water cooling, so air cooling was mainly used at that time. However, with the continuous increase of equipment and the denser servers, it is found that air cooling can no longer meet the requirements, and water cooling has gradually entered the stage, because in terms of heat conduction, water is more effective than air. According to calculations, when used for cooling, the efficiency of water is 3500 times that of air. As a result, IBM researchers developed direct radiation cooling technology, which is a new breakthrough in water cooling technology. In a closed system, water is directly sprayed onto the chip backplane, and then the moisture that absorbs the heat of the chip is sucked dry. The system uses as many as 50,000 nozzles and a complex tree-like loop structure system. About ten years ago, people found that the water-cooling pipes were directly connected to the server through the rack, and worked together with the water-cooling copper seat on the processor radiator. This method has better heat dissipation efficiency than before, and later, because Water-cooling features low energy consumption and high efficiency, and has gradually become the main cooling method for computer rooms.

       Regardless of whether it is air-cooled or water-cooled, people are always unsatisfied with the technical requirements. In order to make the data center safer and more green and energy-saving, in order to cope with the future big data era, the high-density demand of the data center, a kind of A new refrigeration technology emerged at the historic moment, that is, the immersion liquid cooling technology that directly immerses the server into the insulating liquid to run.

  Although the cost of this technology is high, the prospect of development is still very impressive. In recent years, the construction of domestic data centers is in full swing, and data centers are developing towards large and ultra-large, and liquid cooling will give full play to its technical advantages.

The general structure of the liquid cooling system: the outdoor side includes the cooling tower, the primary side pipe network, and the primary side coolant; the indoor side includes the CDU, liquid cooling cabinets, ICT equipment, the secondary side pipe network, and the secondary side coolant.

Immersion liquid cooling is divided into single-phase liquid cooling and phase change liquid cooling according to whether the working fluid undergoes phase change.
 

At present, air cooling technology is one of the most mature and widely used cooling solutions in data centers. It achieves heat exchange through the alternating arrangement of cold/hot air passages. The hot air generated by the racks is cooled by the cold air generated by the computer room air conditioner (CRAC) or the computer room air handling unit (CRAH), and the cold air is delivered to the cold air channel between the racks through the underground vents. Among them, CRAC uses refrigerant as medium for cooling, while CRAH uses water-air heat exchanger to cool water. In a typical air-cooled data center, all server racks are arranged in rows. The air cooled by the CRAH or CRAC unit enters the data center room through the underground ventilation duct, diffuses through the servers, absorbs the heat generated by the server, enters the hot air duct, and returns to the CRAH or CRAC unit. Therefore, air cooling technology cools all the electronic components in the server rack at the same time.

Air-cooled technology has the disadvantages of low density and relatively low heat dissipation capacity. This is especially evident for high-performance computing (HPC) applications. In addition, air-cooled technology has the following disadvantages: 1) Hot spots. Due to the lack of a proper air flow control system, the heat generated by the server equipment and the cold air exchange heat unevenly, easily forming localized hot spots between and inside the server racks. Therefore, to adequately eliminate these hot spots, the data center needs to be overcooled, adding additional energy consumption. 2) Mechanical energy consumption. During the cooling process, a large part of the electric energy is used to drive the fans and pumps, so as to realize the circulation of air and water. 3) Environmental compatibility. In order to maintain the stable operation of the data center, systems using air-cooled technology usually need to run uninterrupted all year round. Therefore, even in winter, when the outdoor temperature is low, it is necessary to maintain the cooling cycle of the data center, which is not conducive to energy saving. 4) It takes up a lot of space. To be cooled effectively, data centers typically require a large amount of space for air conditioners and server racks.