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Rice University team finds economical way to recycle data center heat into power

A team of Rice University researchers has found a way to convert data center waste into clean power using rooftop solar collectors. Photo courtesy Rice University.

As data centers expand, their energy demands rise as well. Researchers at Rice University have discovered a way to capture low-temperature waste heat from data centers and convert it back into usable power.

The team has introduced a novel solar thermal-boosted organic Rankine cycle (ORC)—a power system that uses a safe working fluid to make electricity from heat. The design incorporates low-cost rooftop flat-plate solar collectors, which warm the data center’s coolant stream before it enters the ORC. The findings, published in Solar Energy, show that the additional “solar bump” helps surpass the technical roadblocks with data center waste, which has typically been too cool to generate power on its own.

The research was supported by the Alliance for Sustainable Energy LLC, the National Renewable Energy Laboratory and the U.S. Department of Energy.

“There’s an invisible river of warm air flowing out of data centers,” Laura Schaefer, the Burton J. and Ann M. McMurtry Chair of Mechanical Engineering at Rice and co-author of the paper, said in a news release. “Our question was: Can we nudge that heat to a slightly higher temperature with sunlight and convert a lot more of it into electricity? The answer is yes, and it’s economically compelling.”

Traditionally, electric heat pumps have been used to raise temperatures before recovery, but the benefits were limited because the pumps consumed significant extra power.

Kashif Liaqat, a graduate student in mechanical engineering at Rice, and Schaefer achieved a "temperature lift” by using solar energy to create thermoeconomic models. They modeled affordable, low-profile rooftop solar collectors that fed into an ORC and tied into a liquid-cooling loop. The collectors were validated against industry tools and tested at some of America’s largest data center hubs in Ashburn, Virginia, and Los Angeles, which provided varying climate challenges.

The system recovered 60 percent to 80 percent more electricity annually from the same waste heat, with a 60 percent boost in Ashburn and an 80 percent boost in Los Angeles, according to Rice. It also achieved over 8 percent higher ORC efficiency during peak hours, and an increase in annual average efficiency. The approach also lowered the cost of electricity from the recovered power by 5.5 percent in Ashburn and by 16.5 percent in Los Angeles.

“What the industry considers a weakness becomes a strength once you add solar,” Liaqat said in a news release. “That’s great news for modern data centers.”

Next up, the team will look to pilot its hybrid system in operational sites and explore thermal storage, which the researchers hope could bank solar heat during the day to assist with energy recovery efforts at night.

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A View From HETI

Ching-Wu Chu, a professor of physics at the University of Houston and founding director and chief scientist at Texas Center for Superconductivity. Photo courtesy of UH

University of Houston researchers have set a new benchmark in the field of superconductivity.

Researchers from the UH physics department and the Texas Center for Superconductivity (TcSUH) have broken the transition temperature record for superconductivity at ambient pressure. The accomplishment could lead to more efficient ways to generate, transmit and store energy, which researchers believe could improve power grids, medical technologies and energy systems by enabling electricity to flow without resistance, according to a release from UH.

To break the record, UH researchers achieved a transition temperature 151 Kelvin, which is the highest ever recorded at ambient pressure since the discovery of superconductivity in 1911.

The transition temperature represents the point just before a material becomes superconducting, where electricity can flow through it without resistance. Scientists have been working for decades to push transition temperature closer to room temperature, which would make superconducting technologies more practical and affordable.

Currently, most superconductors must be cooled to extremely low temperatures, making them more expensive and difficult to operate.

UH physicists Ching-Wu Chu and Liangzi Deng published the research in the Proceedings of the National Academy of Sciences earlier this month. It was funded by Intellectual Ventures and the state of Texas via TcSUH and other foundations. Chu, founding director and chief scientist at TcSUH, previously made the breakthrough discovery that the material YBCO reaches superconductivity at minus 93 K in 1987. This helped begin a global competition to develop high-temperature superconductors.

“Transmitting electricity in the grid loses about 8% of the electricity,” Chu, who’s also a professor of physics at UH and the paper’s senior author, said in a news release. “If we conserve that energy, that’s billions of dollars of savings and it also saves us lots of effort and reduces environmental impacts.”

Chu and his team used a technique known as pressure quenching, which has been adapted from techniques used to create diamonds. With pressure quenching, researchers first apply intense pressure to the material to enhance its superconducting properties and raise its transition temperature.

Next, researchers are targeting ambient-pressure, room-temperature superconductivity of around 300 K. In a companion PNAS paper, Chu and Deng point to pressure quenching as a promising approach to help bridge the gap between current results and that goal.

“Room-temperature superconductivity has been seen as a ‘holy grail’ by scientists for over a century,” Rohit Prasankumar, director of superconductivity research at Intellectual Ventures, said in the release. “The UH team’s result shows that this goal is closer than ever before. However, the distance between the new record set in this study and room temperature is still about 140 C. Closing this gap will require concerted, intentional efforts by the broader scientific community, including materials scientists, chemists, and engineers, as well as physicists.”

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