Researchers at a Fairbanks energy lab helped test the feasibility of an underground system meant to cache waste heat from Fort Wainwright’s coal power plant for later use.
And they say it would work – even in the Interior’s subarctic soils.
Robbin Garber-Slaght is a mechanical engineer and researcher at the National Renewable Energy Laboratory’s Alaska Campus in Fairbanks. She also coauthored the study, which was published in June in the journal Energy and Buildings.
Garber-Slaght said multiple questions drove the team of researchers. But here’s the big one.
“How do you take that excess heat that you have in the summer and store it in a way that you can use it in the winter? It’s free heat, how do you keep it?” she said.
The answer matters – especially in cold-climate communities, like the Fairbanks area, she said.
“We call it seasonal energy storage,” Garber-Slaght said. “And it’s a big question because we have such a high heat demand.”
Extra – or waste – heat produced in the summer can escape from energy systems and go unused. But the study analyzed a design for capturing the heat before it flees, tucking it away in an underground network referred to as Borehole Thermal Energy Storage (BTES).
And the researchers tailored the idea to a real-world setting in Interior Alaska.
Their models considered what it would look like to take extra heat the Fort Wainwright coal power plant produces during warmer months, and put it in the borehole system. The analysis then evaluated if the heat sink could meet the winter energy demand in sections of a couple buildings on base, which was nearly six times as high as their summer energy demand.
The outcome? Garber-Slaght said their design could do the job.
“We chose two buildings to start with to see if it’s feasible. And it’s feasible,” she said. “There are technically, physically feasible ways to store energy so that we can use it in the winter and have high-efficiency heating systems.”
Their design consisted of a network of 40 holes, each about a few inches wide, drilled to a depth of 300 feet. That’s where the waste heat is sent to oversummer, and the holes are connected by piping that goes back into the buildings. The design also includes a geothermal heat pump as a means of drawing heat from the reserve come winter.
The study models the 20-year performance of the system under two scenarios: one in which the boreholes were preheated for five years with hot water injections, and another with no preheating.
Both simulations worked over the whole performance period, though the preheating made the system more effective, according to the study.
Those results also aren’t restricted to old power plants and adjacent buildings, according to Garber-Slaght. She said the study demonstrates the underlying design could be viable in other energy systems that produce enough waste heat, as well.
“So it’s not limited to one design in one location,” she said.
The researchers completed the design and crunched the numbers to show technical feasibility, though their efforts didn’t include a full-blown installation.
But the research teams says the study could provide a long-term, reliable solution for dealing with the imbalanced heating and cooling loads in regions with major seasonal fluctuations in temperature.