A modular approach to high efficiency hybrid rack cooling

28Apr

posted by: Alan Vincent, Foremost Electronics

Content streaming, online banking, cloud computing, sophisticated smart phone apps and eCommerce are just a few examples of applications that are fuelling data processing and traffic demand in data centres throughout the world. Emerging technologies, such as Artificial Intelligence (AI), telemedicine, machine learning, autonomous (driverless) vehicles and other real time modelling applications will accelerate demand further.

The International Data Corp. (IDC) predicts that by 2025 we will generate 175 Zettabytes of data annually. Forecasts suggest that the total electricity demand of information and communications technology will accelerate exponentially in the 2020s, and data centres will continue to grow in their share of power consumption (Nature, 13 Sept. 2018 Vol 561). Inside the data centre, High Performance Computing servers are energy intensive and densely configured, producing more heat in smaller spaces.

Power Density Trends

Power density – the amount of electricity used by servers and storage in a given rack – has been monitored since the early 2000s. Surveys from the Uptime Institute tracked steady rates of 3 to 5 kW per rack for many years. Then, in 2018, they reported a jump to 6 to 7 kW averages, with 40 percent of respondents reporting over 20 kW per rack power densities (Uptime Institute 8th Annual Global Data Centre Survey).

Heat Management Options

Increased heat densities of IT Equipment (ITE) in high performance data centres continues to drive the need for more efficient and effective cooling technologies. Traditional air cooling is not a sustainable solution in these settings. While liquid cooling offers far greater efficiencies than air cooling, many liquid cooling options require large capital expenditures, are difficult to integrate with existing infrastructure, and present complications when upgrades or added capacity are needed.

The available cooling choices are:
• Air-cooled, direct.
• Liquid-cooled - indirect water-cooled.
• Hybrid - direct-and-indirect water-cooled.

The Way Forward

A modular approach to maximising liquid cooling efficiencies incorporating direct-contact liquid cooling and advanced rack level integrated cooling solutions.

To understand the full advantage of the hybrid cooling system, first we must note that a typical server houses a variety of hardware. A few of those components, including the CPU, GPU, memory, power supply, and some older hard drives, consume the most energy and create the most heat. Many other components such as switches, routers, and network hardware, consume only small amounts of energy and generate small amounts of heat.

To remove all of the rack heat with direct-contact liquid cooling is complex and expensive requiring a configuration in which every heat source in the rack – large or small – has a separate coldplate and connection to the chilled coolant system.

In the hybrid system, the highest energy consuming components are selectively cooled with direct-contact liquid cooling, and the balance of the rack is cooled with air cooling via a Rear Door Cooler (RDC).
For the direct-contact liquid cooling, low-profile coldplates are placed directly on high-heat-generating components; conditioned coolant is circulated through micro channels in the plates, sometimes in series, to provide concentrated cooling directly to the components.

A Coolant Distribution Unit (CDU) is mounted in the bottom of the rack and includes a liquid-to-liquid heat exchanger, pump and control system. It constantly monitors pressures, flow, and filtration of the unit. A rack manifold manages liquid distribution between the CDU and any number of coldplate loops. The manifold puts architecture in place to accommodate additional direct-contact liquid cooling in the future without additional facility plumbing requirements.

Managing the major heat-producing components with direct-contact liquid cooling can often achieve 70 to 80% of the cooling requirement. The balance of the heat load – the remaining 20 to 30% – is the sum of the many low-heat-producing components. This remaining heat is air cooled with a self-contained Rear Door Cooler (RDC) unit mounted to the back of the rack and utilising an integrated air-to-water heat exchanger.

The RDC unit is an active solution with fans that pull the warm air out of the rack, through a rear door cooler – an air-to-water heat exchanger. An integrated differential pressure sensor is used to control the air flow to the required cooling needs and thus minimize the energy consumption of the unit. A water control kit allows water flow regulation according to the current heat load.

Integrated Hybrid Cooling

The rack-level Hybrid Liquid Cooling System presents a unique entry point to achieving much higher efficiencies of liquid cooling as well as built-in components that provide flexibility and scalability for attaining additional efficiencies long term.

Foremost Electronics in collaboration with nVent Schroff can supply all the elements of a rack level Hybrid Liquid Cooling System (HLCS) including direct-to-chip liquid cooling and liquid-assist RackChiller rear door air cooling panels.

More information here: www.4most.co.uk.