Typical Types of Data Center Cooling Systems

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First, mechanical air-cooled refrigeration

Before 2005, in the initial stage of network business development, the computing power scale of the data center was still relatively small, and the data center mainly used mechanical air-cooled air conditioners for cooling. The basic operating principle of this type of air conditioner is the same as that of a household air conditioner, mainly through the mechanical work of the compressor to change the state of the refrigerant to cool.

1. The compressor compresses the gaseous refrigerant into a high temperature and high pressure state.

2. When the high-temperature and high-pressure gaseous refrigerant passes through the condenser, because the ambient temperature is lower than the boiling point of the refrigerant, it condenses into a liquid state and releases heat to the environment at the same time.

3. The liquid refrigerant coming out of the condenser passes through the expansion valve to throttle and reduce pressure, and then enters the evaporator.

4. After entering the evaporator, because the ambient temperature is higher than the boiling point of the refrigerant, the liquid refrigerant evaporates into a gaseous state, and at the same time absorbs heat from the environment for cooling purposes.

The above process is cyclical, utilizing the principle of condensation heat release and evaporation heat absorption during the gaseous and liquid state conversion process of the refrigerant.

When the mechanical air-cooled air conditioner is actually installed and deployed, the condenser is usually deployed outdoors for heat dissipation, and the evaporator, expansion valve, and compressor are deployed indoors to cool the equipment.

Each unit of the mechanical air-cooled air conditioner is relatively independently controlled and operated, and the installation and maintenance are relatively simple. At the same time, the cooling efficiency is relatively low, and the outdoor unit will occupy a large space.

Second, chilled water refrigeration

From 2005 to 2015, with the explosion of Internet and mobile Internet services, the computing power of data centers increased, and chilled water systems began to be gradually applied. The chilled water system is based on the mechanical air-cooled refrigeration cycle, and the cooling water cycle and the chilled water cycle are superimposed to achieve refrigeration.

1. Refrigerant cycle: Same as mechanical air-cooled refrigeration, cooling at the evaporator generates cooling capacity, and heating at the condenser generates heat.

2. Chilled water circulation: The water in the water pump drives the pipeline to exchange heat with the evaporator to obtain chilled water, which carries the cooling capacity to the air handling unit.

3. Air circulation: The air handling unit exchanges heat with chilled water to obtain cold air, which is then sent to the room to achieve the purpose of cooling.

4. Cooling water cycle: The water in the pump drives the pipeline to exchange heat with the condenser to obtain cooling water, which carries heat to the cooling tower, and the heat is released through the cooling tower.

When the chilled water air conditioning system is actually installed and deployed, the compressor, condenser, evaporator, expansion valve, etc. are usually integrated and deployed in the building for cooling, and the cooling tower is deployed on the roof to dissipate heat.

The chilled water system has a larger cooling capacity, higher energy efficiency and stability, and provides centralized cooling for multiple terminals. At the same time, due to the large number of water pipes, a large number of welding operations are required during installation and deployment.

Third, indirect evaporative refrigeration

From 2005 to 2015, with the explosion of Internet and mobile Internet services, the computing power scale of the data center further increased, and the indirect evaporative refrigeration system began to be gradually applied. Indirect evaporative cooling uses a non-direct contact heat exchanger to exchange heat between the external natural cold air and the hot return air of the data center. The principle is shown in the figure below.

1. External natural air (secondary air) enters from the bottom, passes through the heat exchanger, and exits from the top.

2. The air in the data center (primary air) enters the air from the horizontal, and exchanges heat with the secondary air through the heat exchanger to achieve the purpose of cooling.

The indirect evaporative cooling air conditioner integrates multiple working modes and provides different cooling levels.

dry mode

When the secondary air temperature is low, it can directly exchange heat with the primary air to achieve refrigeration.

wet mode

When the temperature of the secondary air is high, the secondary air is humidified by spraying water to evaporate the secondary air and cool down, and then exchange heat with the primary air to achieve refrigeration.

blend mode

On the basis of dry mode and wet mode, a traditional mechanical air cooling system is added as an auxiliary cooling method.

When the indirect evaporative cooling air conditioner is actually installed and deployed, it is usually deployed on the side or top of the data center.

Indirect evaporative refrigeration combines natural cold source refrigeration and evaporative refrigeration technology to increase natural cooling time and further improve refrigeration efficiency. At the same time, products based on indirect evaporative refrigeration are gradually prefabricated and modularized, making installation and deployment more convenient.

Fourth, liquid cooling

When it comes to liquid cooling, do you think of the practices of companies such as Google and Microsoft directly placing data centers in the sea or in mountain caves, or DIY cool liquid-cooled chassis. After 2020, the continuous growth of computing power in the data center has caused the heat dissipation of the traditional air cooling method to approach the bottleneck, and the liquid cooling technology with higher heat dissipation efficiency has gradually emerged.

There are usually three ways of liquid cooling:

Cold plate liquid cooling

The heat of the heating device is indirectly transferred to the cooling liquid in the circulation pipeline through the liquid cold plate, and the heat is taken away.

Immersion liquid cooling

The cooling liquid is directly used as the heat transfer medium, and the heating element is completely “bubbled” in the cooling liquid and exchanges heat through direct contact.

Spray liquid cooling

Dissipate heat from heat-generating components by spraying coolant.

When the liquid-cooled refrigeration system is actually installed and deployed, the cooling tower is usually deployed outdoors, and the CDU (Cooling Distribution Unit) and liquid cooling devices in the cabinet are deployed indoors, and the cooling capacity is supplemented by air-cooled air conditioners.

Liquid cooling technology benefits from the higher specific heat capacity of liquid than gas, which has higher heat dissipation efficiency. Liquid-cooled refrigeration uses liquid instead of traditional air to dissipate heat, and directly cools high-heat-generating devices such as CPUs efficiently. The liquid cooling system only needs a small amount of energy-consuming components such as water pumps, and the energy-saving effect is remarkable.

Comparison of Centralized Cooling Modes