Datacenter Cooling: the Importance of Secondary Circuit Heat Dissipation

The datacenter, the material hub of our digital age, is like a brain continuously at work: it processes billions of pieces of information every second and every click, every streaming video, every online transaction depends on this infrastructure. Behind it all lies a crucial challenge: Billions of calculations are performed every second, generating a huge and uninterrupted amount of heat. That’s why efficient cooling of datacenters is important.

At different times, different solutions have been set up to manage this heat: air cooling systems and water cooling systems that transfer heat to a heat transfer fluid. And this is also where the secondary circuit cooling of data centers comes in, for the disposal of heat from this same fluid through different solutions: heat exchangers, cooling towers, adiabatic coolers, dry coolers and chillers.

1. The importance of efficient cooling in data centers: an overview

Datacenters are physical facilities that house large servers, data processing machines and support equipment, running continuously around the clock. This continuous activity generates enormous amounts of heat, which must be managed effectively to ensure business continuity. Therefore, efficient cooling of datacenters is a crucial aspect to ensure optimal performance while reducing environmental impact.

The consumption associated with datacenter cooling is definitely significant: up to 40 percent of internal energy resources, according to some recent estimates. This highlights the importance of developing increasingly efficient air conditioning solutions, both functionally and economically.

The most careful organizations are trying to optimize costs and reduce environmentally harmful emissions by focusing on datacenter design based on stringent efficiency criteria, with attention to both environmental and economic sustainability.

There are different cooling systems for datacenters, each with its own advantages.

European regulations are playing an important role in driving the adoption of more efficient cooling systems.

2. Datacenter cooling: the secondary circuit

In this context, the secondary circuit of datacenter is the part of a cooling system that transfers heat from IT equipment (servers, storage, networking) to a heat transfer fluid.

Keeping the coolant at an optimal temperature is critical for several reasons.

• Preserve equipment. Inadequate cooling can damage servers, storage, and other data center components, causing high replacement costs. In fact, high temperatures can shorten the lifespan of IT equipment. Proper cooling helps protect hardware from premature failure, reducing maintenance and replacement costs.
• Energy efficiency. A well-designed and maintained system can significantly reduce data center energy consumption. In turn, the less energy used for cooling, the more is available for data processing. Environmental sustainability equals economic sustainability.
• Availability. A reliable cooling system ensures business continuity for all equipment where overheating can cause malfunctions and service interruptions.

3. Air cooling systems: advantages and limitations

Before listing the secondary circuit heat dissipation methods, let’s take a step back and learn about the technology widely used for cooling datacenters: air cooling systems. These devices use air as a means of dissipating the heat generated by IT equipment.

These are simple devices that often make a secondary circuit unnecessary.

Meanwhile, let’s look at the two options in the field: direct room cooling and in-row cooling.

3.1 Room cooling

Primary cooling fluid: air.

Secondary circuit cooling mode: not applicable (air circuit).

Description: heat is dissipated directly into the surrounding air through heat sinks, fans and dry coolers

Applications

• Datacenters with moderate heat loads.
• Cool and dry climates where outdoor air is sufficient for cooling.

Benefits

• Low installation and maintenance costs.
• No use of water.

Disadvantages

• Limited efficiency in hot climates.
• Sensitivity to environmental variations.

This approach involves using computer room air conditioning (CRAC) units to cool the entire environment.

To be evaluated:

1. the energy efficiency of this solution,
2. the mixing of hot and cold air,
3. the possible formation of hot spots.

To optimize the efficiency of room cooling, it is essential to follow ASHRAE TC 9.9 guidelines, which provide recommendations on acceptable temperatures and humidity for data centers. In addition, the use of shutter panels can prevent hot air from mixing with cold air, improving overall system efficiency.

3.2. In-row cooling

In-row cooling represents an evolution from traditional room cooling. This approach involves installing cooling units directly in the rows of server racks (i.e., the physical, closet-like structure designed to house and organize hardware devices), bringing the cooling source closer to the heat-generating IT equipment.

Benefits of in-row cooling include:

1. Increased efficiency: Row-Based air conditioning units follow short, linear paths, reducing the power needed to drive fans and increasing energy efficiency.
2. Flexibility: cooling can be tailored to the specific needs of certain rows or areas of the data center.
3. Hot spot management: in-row cooling is more effective in handling areas of high heat density, reducing the risk of equipment overheating.

Aspects to analyze.

1. Initial costs: implementing an in-row cooling system may require higher initial investment than traditional room cooling.
2. Space: in-row cooling units take up space within the rows of racks, thus may reduce the space available for IT equipment.

4. Liquid cooling

Liquid cooling is a solution for cooling the primary circuit of datacenters.

This technology takes advantage of the superior properties of liquids to dissipate heat more efficiently than other cooling systems.

The interest also comes from the increased power densities and performance required by applications in artificial intelligence, supercomputing, and other high-performance computing.

4.1. Direct liquid cooling

Primary cooling fluid: water or water + glycol

Secondary circuit cooling mode:

• Cooling tower
• Dry cooler
• Chiller

Description

Liquid passes directly through electronic components (e.g., CPU, GPU) via heat exchangers or dedicated piping.

Applications

• Data centers with high-performance equipment.
• Hybrid solutions with air cooling for secondary components.

Benefits

• Targeted cooling for critical components.
• Higher energy efficiency than air cooling.

Disadvantages

• Risk of water leakage.
• Greater complexity in maintenance.

Direct liquid cooling, also known as direct on-chip cooling, involves the use of cooling plates placed directly on the components that generate the most heat, such as CPUs and GPUs.

According to some estimates, this method can dissipate up to 70-75% of the heat produced by the equipment in the rack. The coolant, which can be water or a special fluid, circulates through these plates absorbing the heat and transporting it to an external heat exchanger.

One of the main advantages of this technology is its ability to handle very high power densities, supporting processors and GPUs with high thermal requirements. This makes it possible to significantly increase the computational density of data centers, allowing multiple servers to be housed in a small space without risk of overheating.

Let us now look at the two main forms of liquid cooling (and secondary circuit cooling modes): immersion cooling and indirect liquid cooling.

4.2. Immersion cooling

Primary cooling fluid: “dielectric fluid”.

Cooling mode of the secondary circuit:

• Plate heat exchangers,
• Secondary circuits with water or water + glycol cooled by cooling towers, dry coolers or chillers.

Description

Electronic components are immersed in a “dielectric fluid” that absorbs heat and transfers it to a secondary circuit.

Applications

• High-density computing datacenter.
• Critical applications such as scientific computing or AI.

Benefits

• Maximum thermal efficiency.
• Reduced noise and energy consumption by ventilation.
• Advanced protection from dust and moisture.

Disadvantages

• High initial cost.
• Requires fluid monitoring to maintain dielectric properties.

In immersion cooling, servers and other electronic components are fully immersed in a thermally conductive dielectric liquid. This solution eliminates the need for ventilation systems, greatly reducing noise and maintenance costs.

There are two main variants of immersion cooling:

1. Single-phase: coolant is continuously circulated and cooled to dissipate heat.
2. Two-phase: a liquid with a low boiling point is used. Heat evaporates the liquid, which then condenses and returns to the system.

Immersion cooling offers numerous advantages. Some of these: superior thermal efficiency and the ability to handle extremely high thermal loads. In addition, this technology can lead to significant energy savings by reducing energy consumption and water use compared to conventional air cooling systems.

Despite its advantages, liquid cooling also presents some challenges. Initial implementation costs can be high, especially for existing datacenters that require substantial changes to the infrastructure. In addition, the management of liquids within the datacenter requires specific expertise and adequate security measures to prevent loss and damage to equipment.

However, the long-term benefits in terms of energy efficiency, computational density and sustainability are prompting more and more datacenter operators to seriously consider adopting liquid cooling technologies. Large technology companies such as Google, Microsoft and Facebook are already experimenting with and implementing these solutions in their datacenters, demonstrating the potential of this technology for the future of the industry.

In conclusion, liquid cooling in general, and immersion cooling in particular, is emerging as a promising solution to address the growing thermal and energy challenges of modern datacenters. With the continued increase in computing power requirements and the increasing emphasis on sustainability, it is likely that this technology will play the lion’s share of the future of datacenter cooling.

4.3. Indirect liquid cooling

Primary cooling fluid: water or water + glycol

Secondary circuit cooling mode:

• Cooling towers
• Dry cooler
• Chiller

Description. Heat is transferred from electronic components to a primary refrigerant via heat exchangers.

Applications

• Medium and large data centers.
• Areas with limited water availability.

Benefits

• Greater flexibility in the use of secondary fluids.
• ossibility of using closed circuits to reduce water consumption.

Disadvantages

• Lower efficiency than direct liquid cooling.
• Higher operating costs in hot environments.

Indirect liquid cooling in datacenters is a solution that uses a fluid, usually water or a water-glycol mix, to dissipate heat generated by servers. Unlike direct cooling, in which the liquid comes into contact with IT components, in the indirect system the heat is transferred through a heat exchanger. This approach keeps devices isolated from the fluid, reducing the risk of accidental damage.

This system offers several advantages, including high energy efficiency. Separation of the fluid from IT components provides greater safety and reduces operational noise. However, indirect liquid cooling also has some critical issues. Some examples: high initial costs, more complex maintenance, and space requirements for outdoor facilities. In addition, in hot climates, efficiency may be reduced, increasing dependence on chillers.

Indirect liquid cooling is therefore a versatile and reliable choice for modern data centers, ideal for high-density applications and in settings where efficiency and security are required, provided that installation areas are not small.

5. Conclusion

Selecting the optimal cooling system for a datacenter is a complex process that requires careful evaluation of multiple factors and the involvement of specialized companies.This applies to primary circuit cooling (air, direct water, indirect water) and secondary circuit cooling (evaporative towers, adiabatic coolers, dry coolers, chillers).

As in any other area of process cooling and civil air conditioning, to make an informed decision, it is essential to consider several key aspects that influence cooling efficiency and effectiveness.