November 22, 2023

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

ForewordHello everyone, I'm Mr. Lin, system solution of main side of data center cold plate liquid cooling system, let's take a look at knowledge points together! Text#1. Primary side system based on cold plate liquid cooling scheme

According to different water temperature requirements at liquid-cooled secondary side end, liquid-cooled primary side cooling source can use mechanical cooling system and natural cooling system.

The mechanical refrigeration system includes an air-cooled water system and a water-cooled water system, which can provide medium temperature chilled water with a temperature of 12-18°C; free cooling uses cooling capacity of outdoor unit. air when outside weather conditions permit. Instead of mechanical cooling, a free cooling system can be implemented using open cooling towers, closed cooling towers, and dry coolers that can provide cooling water above 30°C.

The type of cooling source for liquid cooled primary side must be determined in conjunction with water temperature requirements at secondary side end and site environment.

1.1 Mechanical cooling system • Air-cooled water cooling system

Air-cooled chilled water system is a chilled water preparation method, which mainly consists of air-cooled chillers, chilled water pump and accessories, and liquid refrigerant is evaporated directly into evaporator coil for cooling chilled water outside coil by absorbing heat and cooling it to a liquid state using air cooling.

The air-cooled water-cooled system does not require a special machine room and installation of cooling towers and pump rooms. The initial cost is low, operation is convenient and does not require professional maintenance. There is no water cooling system, which saves water and reduces maintenance costs.

However, air-cooled chillers are usually installed outdoors, and operating and maintenance conditions are relatively harsh. Maintainability and reliability are not as good as water-cooled chillers, and air-cooled chillers have poor cooling effect and poor running efficiency in summer.

• Water-cooled water cooling system

A water cooling system is a method of preparing chilled water. It mainly consists of water-cooled chillers, chilled water pump, cooling water pump, cooling tower and auxiliary devices. refrigerant in evaporator plate Evaporate directlyinside pipe to absorb heat and cool chilled water outside coil, and cool it to a liquid state with water cooling.

The advantages of water-cooled water cooling system are low power consumption, good cooling effect throughout year, high reliability and long service life. However, it requires a special engine room, cooling tower, cooling water pump, chilled water pump and other equipment. The initial investment is relatively large, and circulating water is required. Water consumption is large, and unit casing and refrigeration units need to be maintained. air-cooled, its maintenance cost is relatively high.

1.2 Free Cooling System • Open Cooling Tower

The open cooling tower sprays circulating cooling water directly onto cooling tower fill, and at same time, fan directs airflow into cooling tower to evaporate and cool circulating water by heat and mass transfer between outside air and cooling water. After cooling, circulating water exits at bottom parts of cooling tower (see figure). In an open cooling tower, heat and mass transfer takes place between circulating cooling water and outside air.

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

Scheme of open cooling tower

• Closed cooling tower

The Closed Cooling Tower is a device that places a tubular heat exchanger inside cooling tower and removes heat to atmosphere by exchanging heat between outside air, atomized water, and circulating cooling water in tube (see figure) .

The closed cooling tower has two systems of internal circulation and external circulation. The internal circulation is connected with equipment to be cooled, forming a closed system that removes heat of system to cooling tower, that is, internal circulation water passes through heat exchange plate. The pipe gives off heat to atmosphere, external circulation consists from circulating spray pump, water distribution system, water collection pan and piping. The external circulating water does not contact internal circulating water, but only absorbs internal circulating water through a heat exchanger in cooling tower, after which heat of circulating water is dissipated by direct contact with air.

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

Scheme of a closed cooling tower

The water quality in closed cooling tower is good, cooled heat exchanger is not scaleable and has a long service life. This has obvious advantages in cases where quality of external environment is poor and quality of circulating water is unsatisfactory. high; cost is high, floor area is large, and weight is heavy.

• Dry cooler

A dry cooler is a dry cooler. There is no water consumption during operation. It cools liquid in tube by passing liquid inside tube and natural wind outside tube, lowering temperature of liquid in tube to achieve purpose of cooling (see figure). Ethylene glycol solution is usually used as a secondary coolant in a dry cooler, and concentration of solution must be chosen according to extreme temperatures at site in winter.

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

Dry cooler diagram

The dry cooler does not have a compressor, overall power consumption is low, service life of unit is long, and initial investment is lower than air-cooled cold water system and water-cooled cold water system. , but it is usually installed outdoors, working environment is relatively harsh, and it is hot in summer. In poorer areas, it is necessary to set up a water spray cooling system or a wet curtain system to improve heat transfer, resulting in an increase in floor space.

1.3 Application scenarios of main side of system

In a liquid cooling system with a cold plate, the heat generating device does not directly contact liquid, but dissipates heat through direct contact with liquid-filled cooling plate, or heat is transferred to cold plate by heat-conducting component, then heat is removed liquid circulation inside cold plate.

Because heat-generating components such as server chips do not need to be in direct contact with liquid, this method requires fewer changes to existing server chip components and auxiliary components, and is more convenient to operate. It has become most mature and widely used. liquid cooling plan.

The secondary side is relatively stable and configurable through Coolant Distribution Unit (CDU) and subsequent system architecture. The primary side may consider different usage conditions and combination scenarios. According to cooling method, it is mainly divided into mechanical cooling and natural cooling, and combined with household situation, it is divided as follows:

Table reference liquid supply temperature on primary and secondary sides

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

The cooling source on primary side consists of various components. Determine if water temperature needs to be lowered according to local outdoor temperature (including dry/wet bulb temperature) and fluid temperature at inlet of liquid cooling system. server; in addition, supply water temperature should be higher than room dew point. The temperature should be about 2°C~3°C higher to prevent condensation (see table).

• Option 1: chiller + cooling tower (open + plate change)

In high temperature and high humidity areas, ambient temperature requirements of computer room are high, and direct use of closed cooling towers/dry coolers cannot directly meet cooling requirements, and an auxiliary mechanical refrigeration device is required. ; The cold source usually uses combined cooling of chillers + cooling towers. This design has high adaptability and high efficiency, but consumes a lot of water, so it is not suitable for water scarce areas.

Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

Scheme of cooling tower + water-cooled chiller + plate change system

The system is divided into two modes depending on change in outside temperature:

  • Mode 1: low outdoor temperature, no need to turn on chiller, and only cooling tower + plate replacement can meet cooling requirement.
  • Mode 2: The cooling tower leaving water temperature is higher than required by CDU, and mechanical cooling is required in addition to cooling, forming a combination of tower and chiller.
  • • Second option: air-cooled chillers

    The air-cooled chiller integrates condenser, water pump, compressor and other components, and is usually equipped with a dry cooler (free cooling source module), which has a high degree of integration (see figure); however, latent heat of evaporation of water cannot be used, and energy efficiency of system is low, suitable for small system environments and water scarce areas.

    Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

    Air-cooled chiller diagram

    The use mode is same as Scenario 1 and also has two modes:

  • Mode 1: low outdoor temperature, no need to turn on cooling machine, and only natural cold source module can meet cooling requirement.
  • Mode 2: The natural cooling source module cannot meet temperature requirements of CDU, and mechanical cooling is required for additional cooling, so an air-cooled chiller is directly used.
  • • Third option: liquid/dry cooler

    When local temperatures are low throughout year, a closed cooling tower/dry cooler can be used for direct cooling (see figure ) without mechanical cooling throughout year.

    Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

    Closed Cooling Tower/Dry Cooler Fluid Cooling System Schematic

    The system is also divided into two modes:

  • Mode 1: dry mode, no need for water evaporation to dissipate heat.
  • Mode 2: wet mode, system must remove heat by latent heat of vaporization of sprayed water, and closed cooling tower at this time is same as open cooling tower. The dry cooler is first cooled through wet film at air inlet and then performs secondary cooling.
  • • Option four: open cooling tower

    The cooling mode of an open cooling tower is exactly same as that of a closed cooling tower (see figure), except that water path of open cooling tower is connected to atmosphere and water quality is poor.

    Primary Side System Solution of Data Center Cold Plate Liquid Cooling System

    Open cooling tower cooling scheme

    The above diagram considers requirements of liquid cooling side as main factor (see table). During actual operation of machine room with liquid cooling of cold plate, liquid cooling system often still needs to be equipped with a small number of air conditioners to meet heat dissipation requirements of non-liquid cooling components in server.

    Table Proposed scheme for a cold source on primary side

    Primary Side System Solution of Data Center Cold Plate Liquid Cooling System
No. 2. Overview of liquid cooling system with a secondary side cold plate

    The secondary side fluid circuit refers to design from CDU to rack, which connects to IT equipment through coolant supply and return manifold, and then returns to CDU through manifold.

    The heat from secondary side refrigeration circuit is transferred to primary side refrigeration circuit through plate heat exchanger of cooling distribution unit and finally vented to atmosphere or recovered for reuse.

    As power density of IT equipment increases, more efficient cooling methods are required to meet growing demand for computing power.

    Compared to traditional air cooling, liquid cooling provides more efficient cooling. The transition time to liquid cooling depends on many different factors, including cooling performance requirements, power configuration, PUE requirements, IT hardware density, cooling costs, and future IT hardware performance requirements and deployment strategies.

    Additionally, total cost of ownership must consider need to renovate existing facilities or rebuild a new computer room in data center.

    The direct reason for adopting liquid cooling is that traditional air cooling solution can no longer meet heat dissipation requirements of IT equipment, so a new solution is needed to improve cooling capacity.

    There is no general guidance on when and at what power level liquid cooling is required for high-power components such as CPUs and GPUs.

    However, it should be noted that in addition to cost analysis, some design features of liquid cooling solution also need to be taken into account, for example, all wetted materials in cooling circuit are compatible with coolant used and maintain a long service life. - reliability period, coolant used cannot be mixed with any other coolant, etc.

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