Removing heat from IT equipment has been a problem for as long as computers have existed. Liquid cooling, a new concept to many, has actually been used to cool computer equipment since the 1960s when IBM employed it for the System 360 mainframes. There were few options to cool that amount of heat at the time. Today, with decades of air cooling behind us, data centers are returning to liquid cooling, using a new generation of systems.

The introduction of complementary metal–oxide–semiconductors (CMOS) radically reduced the power consumption and, therefore, the heat generated by the semiconductors used to build computer systems. That’s how air cooling became the gold standard.

As technology progresses, modern applications, like blockchain, AI, and machine learning, are changing the landscape again. These advances bring with them heavy processing loads and increased densities, which require more powerful systems and generate more heat. This is challenging the efficiencies and cost-effectiveness of air-cooled systems — even those that have moved closer to the source like rack- and row-based cooling.                                               

Liquid Cooling 

Liquid cooling solutions take advantage of the fact that heat transfer in liquids is significantly more efficient than air. And it is no longer a niche solution. Data centers are now broadly adopting liquid cooling. According to a recent research report by Global Market Insights Inc., the data center liquid cooling market size is set to surpass $6.5 billion by 2027. And, back in 2018, an Uptime Institute survey revealed that 14% of data centers currently use some form of liquid cooling to address their needs for increased efficiency and lower operating costs.

Liquid cooling solutions are easier to maintain than air cooling, and the servers are protected from a variety of threats: dust and pollutants, corrosion-causing moisture and oxygen, and vibration-induced drive errors caused by server fans. These solutions are also easier to install and can be integrated into a data center with air-cooled racks. Immersion cooling enables a diverse density layout — with high-density racks right next to lower-density ones without stratification or the mixing of hot and cold air.

What’s more is that liquid-cooled data halls create a more comfortable working environment for employees. Reducing the number of server fans and HVAC equipment results in decreased noise levels. And, without the extreme temperature differences between hot and cold aisles, there’s a more uniform temperature throughout the white space.

Cooling solutions are never one-size-fits-all though. When considering liquid-cooled technologies, there are three options to choose from: single-phase liquid immersion, two-phase liquid immersion, and liquid to chip.

Single-Phase Liquid Immersion 

Single-phase immersion cooling uses a dielectric fluid that surrounds the servers and transfers heat by circulating through a cooling distribution unit (CDU).  The CDU then disperses the heat to a secondary fluid and returns the cooled liquid back to the server compartment.

  • Supports high rack densities.
  • 100% of the heat is removed by the coolant.
  • Average PUE of 1.02 to 1.03.
  • Cuts total data center energy use by up to 35%.

Two-Phase Immersion Cooling

Two-phase liquid immersion uses fluorocarbon-based or other volatile liquids surrounding the servers. The fluid has a low boiling point, and, when the liquid changes to gas, it captures heat from the servers to later release via water-cooled condenser coils. The coolant is then condensed by means of a heat exchanger returning the coolant to the system, where it is recycled through the system, which is well-sealed to prevent fluid loss.

  • Supports high rack densities.
  • 100% of the heat is removed by the coolant.
  • Average PUE of 1.01 to 1.02. 

Cold-Plate Cooling / Liquid-to-Chip

Liquid-to-chip, also called direct-to-chip or cold plate, runs coolant — often water — through a cold plate attached to the CPUs/GPUs inside servers, frequently using a secondary water loop on the other side of a CDU heat exchanger to carry the heat outside.

  • Supports high rack densities.
  • 60% to 70% of the heat is removed by the coolant (air cooling is used for the remaining heat load).
  • Average PUE of 1.15.  

Today’s data centers need to cut costs and reduce energy use while keeping their sensitive equipment cool, and choosing liquid cooling is an effective way to achieve these efficiencies. While the re-emergence of liquid cooling started out as an answer for high-density data centers, the benefits are no longer limited to those facilities. In fact, many of the economic benefits are realized with densities as low as 15 kW per rack. That means air cooling is becoming a legacy system, and its time is coming to an end.

Green Revolution Cooling spearhead the first annual Liquid Immersion Cooling Awareness Month. In partnership with Dell, Intel, Vertiv, and Mission Critical magazine, the initiative will increase awareness in the data center community of immersion cooling technology. Events will highlight how liquid cooling can dramatically reduce the energy consumption of today’s data centers while enabling high-density deployments. GRC and its partners will provide educational sessions with end users, server manufacturers, and other data center stakeholders to discuss the efficiency benefits and CapEx/OpEx reductions made possible with liquid immersion cooling.