What is Immersion Cooling?

Immersion cooling is an IT cooling practice by which IT components and other electronics, including complete servers, are submerged in a dielectric (electrically non-conductive) fluid that has significantly higher thermal conductivity than air (typically >1,000x the heat capacity by volume). Heat is removed from the system by circulating liquid into direct contact with hot components, then through water cooled heat exchangers.

Is Immersion Cooling a new technology?

Immersion Cooling is not new. The first reference to the specific use of dielectric fluids being used to cool “computers” is in 1966 by IBM and in 1982, Cray computing registered a patent for high density immersion cooled technology.

GRC was founded in 2009 and has had commercial deployments of its rack based Immersion Cooling systems for over 10 years. The company deployed the world’s first turnkey immersion cooled (modular) datacenter, the ICEtank, in 2013.

Asperitas was founded in 2014 and launched their first Immersed Computing^® solution in 2017, after an extensive R&D phase with an ecosystem of cutting edge partners. Asperitas is leading the Open Compute sub project on Immersion Cooling for standardisation development.

What is single-phase Immersion Cooling?

Single-phase Immersion Cooling, as the name suggests, is where the coolant stays in a single (liquid) phase, and does not evaporate. The coolant captures the heat from the immersed components and is circulated through a heat exchanger that transfers the heat to a water loop, which in turn can be cooled with an evaporative/adiabatic cooling tower, dry-cooler (radiator), or an existing chiller plant (not required, but compatible).

How is single-phase different from two-phase Immersion Cooling?

Two-phase Immersion Cooling is where the coolant is designed to evaporate (change phase from liquid to gas) at lower temperatures, boiling off when it comes in contact with hot components. The evaporated coolant vapor is then condensed back to the liquid state through the use of condenser coils, typically located at the top of a sealed rack.

There are primarily two kinds of coolants used for Immersion Cooling: Fluorocarbon-based coolants which are typically used for two-phase applications, and Hydrocarbon-based fluids which are solely used for single-phase Immersion Cooling.

What are the pros and cons of two-phase (Fluorocarbon-based) vs. single-phase (Hydrocarbon-based) Immersion Cooling?

Upfront costs: Single-phase Immersion Cooling offers dramatically lower upfront costs due to its simpler overall design, and lower coolant costs.
Energy efficiency: Both forms of Immersion Cooling offer exceptional energy efficiency (pPUE 1.01 – 1.03).
Cooling capacity: Two-phase Immersion Cooling can typically support extreme rack densities, with some providers claiming to support up to 250kW in a single rack. Some single-phase solutions also claim to support up to 200kW per rack. However, given the power density of commercially available hardware, most mainstream applications for Immersion Cooling range from 15 – 50kW per rack.
Complexity/usability: Single phase offers an inherently simpler architecture. The lack of evaporation allows for an open bath design, thereby eliminating any inhalation risks or the loss of fluid due to evaporation. The absence of a sealed rack also allows for easier access to servers and hence simpler maintenance SOPs. However, two-phase coolants (fluorocarbon) have the advantage of self-drying hardware that can make material handling easier.

How is the fluid being circulated in Immersion Cooling systems?

Single-phase immersion requires circulation of the dielectric liquids by pumps or by natural convection flow through integrated or external heat exchangers.