Immersion Cooling

What Is Immersion Cooling?

Immersion cooling is an advanced liquid cooling technique used primarily in data centers and cryptocurrency mining. It involves submerging IT hardware, such as servers, GPUs, or networking equipment, directly into a thermally conductive, electrically non-conductive (dielectric) liquid. By removing the air gap between heat-generating components and the cooling medium, immersion cooling reduces thermal resistance, making it more efficient. It also eliminates the need for separate heat sinks and cooling fans.

How Does Immersion Cooling Work?

In an immersion-cooled environment, servers are placed into specialized racks, tanks, or enclosures filled with dielectric fluid. Because the fluid does not conduct electricity, it safely surrounds the bare electronic components without shorting it out the way water would.

As the IT equipment operates and generates heat, the dielectric fluid absorbs this heat directly. The thermal energy is then transferred from the fluid via a heat exchanger to a facility-level cooling loop—typically a water-based system connected to external HVAC infrastructure, such as Trane chillers, dry coolers, or cooling towers—where the heat is rejected into the atmosphere or repurposed for facility heating.

Two Methods for Immersion Cooling: Single-Phase and Two-Phase

In a single-phase immersion cooling system, the dielectric fluid remains in a liquid state throughout the entire cooling cycle.

• The process: As the fluid absorbs heat from the servers, it becomes warmer and is actively pumped (or moves via natural convection) to a coolant distribution unit (CDU) or a heat exchanger. The heat is transferred to the facility’s water loop, and the cooled dielectric fluid is circulated back into the tank.
• Key characteristics: Single-phase immersion cooling uses oil-based, synthetic, or hydrocarbon fluids. The tanks are typically unsealed or lightly sealed, making equipment access for maintenance relatively simple.

In a two-phase immersion cooling system, the dielectric fluid has a relatively low boiling point and changes its physical state from liquid to gas to remove heat.

• The process: When the submerged IT components heat up, the fluid reaches its boiling point and turns into a vapor. This vapor naturally rises to the top of the sealed tank, where it comes into contact with condenser coils chilled by the facility's water loop. Upon touching the cool coils, the vapor condenses back into a liquid and drips back down into the bath.
• Key characteristics: Two-phase immersion cooling relies on the latent heat of vaporization, which is incredibly efficient at moving heat. Because circulation happens naturally through boiling and condensation, internal pumps are typically not required.

Single-Phase vs Two-Phase Immersion Cooling

Both methods for immersion cooling are efficient, but there are differences to consider when deciding which is best for your facility:

• State change: Single-phase fluid stays a liquid; two-phase fluid continuously boils into a gas and condenses back into a liquid.
• Complexity and maintenance: Single-phase systems are generally simpler to maintain and use open-bath designs. Two-phase systems require tightly sealed tanks to prevent vapor escape and use highly specialized fluorochemical fluids.
• Cooling capacity: While both offer upgrades over air cooling, two-phase cooling is generally capable of handling the highest density loads, although single-phase is rapidly advancing to meet similar high-density demands.

Benefits of Immersion Cooling for Data Centers

Integrating immersion cooling with a facility's commercial HVAC system provides several advantages:

• Energy efficiency: By eliminating server fans, reducing the need for facility air cooling, like computer room air handlers (CRAHs), and allowing for higher facility water temperatures, immersion cooling dramatically lowers a data center's power usage effectiveness (PUE).
• High-density cooling capabilities: Immersion cooling easily handles the extreme heat loads generated by artificial intelligence (AI), machine learning, and high-performance computing (HPC) applications.
• Maximized space utilization: Because servers do not need hot/cold aisle containment or air-flow spacing, data centers can pack more compute power into a significantly smaller physical footprint.
• Increased hardware reliability: Submerging equipment isolates it from airborne contaminants, dust, moisture, and oxygen, preventing corrosion and eliminating temperature fluctuations that can degrade hardware over time.
• Sustainability and heat recovery: The warm water return temperatures generated by immersion cooling systems are ideal for integration into heat recovery systems, allowing data centers to export waste heat for district heating or other commercial applications.
• Acoustic and operational advantages: Operation is much quieter due to reduced fan usage, and there is potential for reduced maintenance costs from fewer air filters and fewer failed fans.
• Scalability and modularity: Modular immersion tanks can enable efficient phased deployment and faster installation for high-density applications, such as AI/ML clusters and HPC.