When no heat hits the fan

Liquid immersion cooling is an emerging and promising cooling technology, and a potential alternative to air cooling in data centers.

"Space is always a scarce resource, and immersion cooling makes for extremely compact datacenters", says Odd Roar Schmidt, Project Director R&D at Eltek. Behind him, immersed in in a tank of blue liquid, is a power module operating under somewhat counterintuitive conditions.

What is liquid immersion cooling?

Liquid immersion cooling involves immersing electronic equipment in an electrically insulated, fluorinated inert fluid that absorbs the heat generated by the equipment. The technology is an alternative to traditional air cooling, as well as water cooling. It comes with one particularly significant promise: to reduce space requirements in the data center by as much as 70%.

As long as the waste heat is taken care of, it eliminates the need for voluminous air cooling infrastructure such as fans and airducts. If the waste heat cannot be handled, a fan is required. The liquid is not corrosive or incompatible with electricity, like water. Liquid immersion cooling paves the way for ultra-dense data centers, but also has drawbacks to be considered.

The liquid used in immersion cooling is non-conductive and non-corrosive – either mineral oil or engineered liquids – in which servers and even entire systems can be directly immersed. This can be done without damaging the equipment or altering the electromagnetic characteristics of sensitive electronic circuits.

In so-called two-phase liquid cooling, the liquid has a much lower boiling point than water and other potential cooling liquids. Heat from the equipment boils the liquid, creating vapor that carries the heat away to be recollected against a chilled coil or condenser.

By far the most attractive advantage is the compactness it allows for.

Odd Roar Schmidt, Project Director R&D

A compact and quiet revolution

Liquid immersion cooling has several important benefits.

"By far the most attractive advantage is the compactness it allows for", says Odd Roar Schmidt. "There are no risk of hotspots that so often can be a problem in air-cooled sites. Eliminating the need for fans and air ducts, liquid immersions saves considerable space in the data center and removes the noise from the fans as well as adjusting the air temperature to a comfortable level" Schmidt explains.

At the system, module and component levels, too, the design can be much more compact with direct immersion cooling than with air cooling, as there is no space and intricate planning needed for air passage.

Yet another benefit is the reduced electricity bill associated with air cooling and conditioning. In addition, liquid immersion does away with the noise and vibration caused by the fans. The waste heat can also be sold and distributed into district heating networks, which makes it even more attractive in economic terms.

Revolutions come at a cost

Despite obvious advantages, immersion cooling is still not adopted as a mainstream cooling technology. The greatest obstacle is perhaps the cost and complexity associated with a move from traditional cooling to a new cooling infrastructure and concept. There are many differences between the two, and issues include what to do with running and well-functioning data centers in view of the cost and complexity of retrofitting and servicing immersed equipment. It is harder to retrofit and service liquid immersed systems than traditional systems.

There is always the question of how to handle spills, as well as the need to put in place procedures for storage and waste handling of used liquid. Therefore, it seems that demand for liquid immersion will remain low and only pick up in due course when new compact data centers take center stage in data center development.

On the technical side, there is also still a big issue related to contamination of the liquid, and the potential effects of this on the equipment, and potentially, harm to people. This problem is prominent even with enclosed liquid baths.

Another issue is the sheer weight of the liquid – any consideration to build liquid cooling installations should include a structural analysis of the building and floor holding it.

Eltek and immersion cooling

Liquid immersion cooling is a viable alternative for greenfield, ultra-compact data center installations. Eltek has already, in cooperation with the supplier of cooling liquid and customers, developed and supplied the market with a Flatpack 2 rectifier for immersion cooling. The Flatpack 2 for immersion cooling is available as a standard product through Eltek’s sales channels.

Jun 25, 2019
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