National University of Singapore looks to make data centers the coolest, but not the coldest with sustainable hybrid solution

The National University of Singapore (NUS) has successfully completed test-bedding for their high-efficiency hybrid cooling solution for green data centers.

The solution achieved a partial power usage effectiveness (pPUE) score of approximately 1.2 with the scope of dropping below an impressive 1.1, close to the ideal score of 1.

Google, for example, has an average PUE score of 1.11, but boasts a score as low as 1.06 using narrower boundaries.

“The power densities of servers are getting higher and higher with every new generation, so much so that air cooling will one day no longer be effective in dealing with the amount of heat generated by the chips,” said Professor PS Lee, the Programme Director of Cooling Energy Science and Technology at NUS.

The University is in discussion with data center operators to quantify the actual energy and cost saving potential of the solution by conducting comparative studies against air-cooled servers in real-world environments.

Prof. Lee added: “The system as it is, is ready for commercial deployment.  We are open to various commercialisation possibilities, such as licensing of our technology and providing consultation services on heat sink or cold plate designs.”

Professor Lee has incorporated a company known as CoolestDC Pte Ltd to enable the commercial deployment of the hybrid cooling solution.

In the testing phase, the pPUE measured was for just one rack of 20 servers with a simple control, so there is scope to drop below an impressive 1.1 after scaling up, correctly sizing equipment and using smart controls like AI.

Prof. Lee said: “With implementation of machine learning and artificial intelligence using big data, the system would be able to predict and automatically adjust to meet cooling requirements and the system capacity, based on the trend of compute load and weather conditions. This can minimize the power consumption of the cooling equipment.”

How does the National University of Singapore’s hybrid cooling solution work?

The hybrid cooling solution involves separating the cooling process based on heat dissipation of the components on the server. The high heat dissipation components such as the CPUs and GPUs are liquid-cooled using a high-performance oblique-fin heat sink, while those that dissipate low heat are air-cooled.

By operating at warmer temperatures above the ambient air temperature, the solution eliminates the need for ‘two of the most energy consuming pieces of equipment in the data center’, as a cooled water supply created via a chiller or air conditioning using a computer room air conditioning (CRAC) unit is not required.

“For air-cooled DC, given that air is inherently a lousy heat transfer medium, there is a limit on how high the inlet air temperature can go before the reliability of electronics gets affected,” said Dr Lee.

With the removal of a CRAC, raised floors and overhead plenums can be eliminated, resulting in less mechanical and electrical maintenance, the potential for lower costs and a quicker construction of a data center.

Prof. Lee added: “Our high performance liquid or two-phase cooled DC allows the inlet fluid temperature to be pushed much higher, making it viable for waste heat recovery and reuse.”

The oblique-fin heat sinks are also said to be able to provide better cooling to servers, making them more efficient, contributing to additional savings of ITE power.

The system is designed to be highly flexible to make use of existing infrastructures like hot-aisles and cooling towers and be deployed in new and brownfield data centers with minimal additional capital expenditure.

As a result of lower energy consumption PUE scores, the hybrid cooling solution could help data centers meet the Singapore Green Data Centre Standards.

Prof. Lee strongly believes the time is now for data center operators and server manufacturers to start using or getting prepared to use liquid-cooled services.

The three big wins from Professor Lee’s testing include:

  • The ‘world’s highest performance liquid cooling technology
  • A Power Usage Effectiveness score of <1.1
  • 40% server power savings and substantial performance improvement.

What’s next for NUS?

Works are underway at NUS for the next generation leakage-free, server-level cooling solution, which employs on-demand two-phase cooling based on the compute load of the servers.

Prof. Lee said: “This revolutionary solution is highly reconfigurable and can be deployed in both new and brownfield DCs.”

NUS is also looking to adopt deep reinforcement learning algorithms to provide smart control to their hybrid cooling systems. Prof. Lee hopes this will lead to optimum data center operations that balance reliability, energy consumption, carbon footprint and cost.

In another project unrelated to Prof. Lee’s projects, Keppel Data Centres is working with NUS to develop new prototypes that cool data centers and reduce their carbon footprint by harnessing cold energy released from the LNG (Liquefied Natural Gas) regasification process after entering into a partnership in 2019.