As MIT Aims to Decarbonize, Competing Ideas Focus on Thermal Energy Systems

Ditch fossil fuels in less than half the time and save half a billion dollars or more on what you would otherwise spend to decarbonize. That’s the pitch a group of students, alumni and faculty will make to administrators at the Massachusetts Institute of Technology at a campus decarbonization forum today.

The proposal, officially known as the MIT Thermal Energy Network (MITTEN), calls for an advanced heating and cooling system that uses low-temperature thermal energy from pipes connecting campus buildings.

The network would draw heat from a range of sources, including air source heat pumps, shallow boreholes drilled into the earth, waste heat that is currently vented from buildings, rooftop solar concentrators that harvest heat from sunlight and even city water mains. Water circulating through MIT’s pipe network would connect to ground source heat pumps that provide heating and cooling to individual buildings.

“The MITTEN project will cost hundreds of millions of dollars less to implement, and cost 30 percent or more less to operate,” said Herb Zien, an MIT alumnus who co-founded a company that was once the largest owner and operator of district heating and cooling systems in the United States. “It’s just going to be less expensive coming and going.”

Zien, who no longer owns the district heating company, is a volunteer member of the MIT Alumni/Student Decarbonization Team, the group behind the proposal.

The university is already considering a thermal energy system proposed by AEI, an outside consulting firm the university hired to help it come up with a plan to decarbonize—or stop burning fossil fuels on campus for heating, cooling and electricity generation—by 2050. 

AEI declined to comment, citing a non-disclosure agreement with the university. 

Separately and as part of its path toward decarbonization, MIT recently partnered with Harvard, Mass General Brigham and other Boston-area institutions to help finance the building of a solar farm in Texas and a wind farm in North Dakota that will produce clean energy. Those projects will offset fossil fuel power elsewhere, allowing MIT and other project partners to each claim a portion of the emissions reductions.

The plans by MIT’s consultant include many of the same components as the MITTEN proposal, including a pipe network linking campus buildings, heat pumps, waste heat recovery and geothermal systems.

“The overlaps are significant,” said Joe Higgins, MIT’s vice president for campus services and stewardship. It “is generally all the same concepts. It’s all the same physics.”

However, a key difference between the two proposals is that the plans by MIT’s consultant call for a central utility plant with a small number of large heat pumps to generate hot and cold water that would be moved across the campus.

Conversely, the proposal from the MIT community would circulate “ambient” temperature water, approximately 45 to 90 degrees Fahrenheit, through its pipeline network.  

In such a system, geothermal bore holes or the municipal water mains would work like a thermal battery, serving both as a source for low-temperature thermal energy and as a sink that could absorb excess heat. Hundreds of small heat pumps would then tap the ambient temperature water to provide heating and cooling at the individual buildings where it is needed.

The relatively low-temperature thermal network is similar to one that gas utility Eversource recently completed in Framingham, Mass.  

What may seem like a small difference in design could have a significant impact.

Members of the MIT Alumni/Student Decarbonization Team said they can use existing chilled-water pipes that are currently part of the university’s gas-fired district heating and cooling system for their ambient temperature network.

However, existing steam pipes currently used for district heating are too small to be repurposed to distribute hot water across the campus, according to the alumni and student group. Their plan doesn’t rely on using hot water, but the MIT consultant’s plan does.

“You would have to effectively build a whole pipe distribution network just for hot water that doesn’t exist today,” Zien said. “That costs hundreds of millions of dollars, and it will disrupt the campus for years because of all the construction.”

Zien said the cost estimate for the new pipe network is based on figures the university’s administration shared with their group. Higgins didn’t respond to a question about the cost, other than to say the university plans to release more information about the different proposals later this year.

However, Higgins said a decentralized system—the type the alumni and student group is proposing—would require far more pieces of equipment, all of which would need to be maintained.

“It would be thousands of pieces of equipment, versus a centralized approach, where we would use less than a dozen pieces of equipment,” Higgins said. “There’s a lot of operational complexity associated with that.”

Zien said the decentralized system they are proposing would use small, off-the-shelf heat pumps. He said the devices work in much the same way as refrigerators and air conditioners and offer the same high level of reliability.

“When was the last time you had a guy out to look at your refrigerator in your kitchen?” Zien asked. “Or when was the last time somebody came out to look into your air conditioner in the backyard? These are very reliable pieces of equipment, and a standard HVAC technician is able to monitor, swap them out, fix or do whatever is necessary. Whereas in the central plant, the maintenance is a big deal.”

Zien added that centralized systems are less efficient, losing between 10 to 15 percent of their thermal energy to heat loss as they distribute heat from the central plant to individual buildings.

Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory also found low-temperature thermal energy networks to be more efficient than high temperature systems in a study published in September. Part of the efficiency gains comes from the ability to balance loads between buildings, essentially using individual heat pumps to pull heat from one building while pushing it into another, depending on the buildings’ individual heating and cooling needs.

Colorado Mesa University in Grand Junction, Colorado, has saved more than $15 million in fuel costs since 2008 largely through such balancing of heating and cooling needs with a low-temperature thermal energy network, according to a U.S. Department of Energy report.

Susan Murcott, an MIT professor who is part of the MIT Alumni/Student Decarbonization Team, said she first started advocating for the thermal energy network at MIT three years ago after she started swapping fossil fuels for a ground source heat pump and solar panels to heat and cool her home.   

“A little light bulb went off in my head,” Murcott said. “If I can do this, MIT can do it. And if I can do it in 10 years, then MIT can do it in 10 years too.”

In March, the group signed an agreement with the university to develop a preliminary design for a pilot project, a decentralized thermal energy network that would provide heating and cooling to six campus buildings. Those include the university’s ice rink, a swimming pool and the student center.

The group concluded that a thermal energy network for the six buildings could be installed in two years at a cost of $10 million to $15 million, according to a report the group released in September. The report stated that a similar network could be deployed campuswide in a decade at a cost of $500 million to $750 million less than several campus decarbonization proposals prepared by MIT’s consultant.

The projected increased efficiency of the distributed system would reduce operating expenses by at least $100 million over the life of the system compared to the proposals by the consultant working for MIT, according to the report.

It “costs less to do, and it costs less to run,” said Rick Clemenzi, an MIT alumnus and co-owner of a geothermal energy network design firm who has been working with Murcott on the MIT proposal for several years.

Higgins questioned the projected cost savings in the MIT community group’s report and said the actual cost of that proposal is likely “many magnitudes higher.” 

“I just don’t want there to be an impression out there that there’s, like, some magic thing that’s 10 times cheaper and it’s faster,” Higgins said. “The reality is, it’s not.”

Higgins said MIT just completed a third-party cost assessment of the MITTEN proposal and will plan to go over the findings with the student, alumni and faculty group soon.

Jason Chen, a student member of the group, said he would like to see MIT move forward with the pilot project and provide a low-cost path to decarbonization that other universities can follow.

“We’re seen as people who innovate at the technological forefront,” said Chen, who was part of a team that won a national U.S. Department of Energy student competition last year for an earlier draft of the MIT thermal energy network proposal.

Chen said he fears MIT will pursue a more conventional centralized thermal energy system that would cost more, similar to projects Stanford and Princeton have recently completed.  

“An ideal scenario is that MIT takes leadership in saying, ‘This is a manual on how to do this for every college, and not just the elite colleges that have this money,’” Chen said.

Higgins said all options remain on the table.

“This is for the next energy era, the next 100 years,” he said. “It is very urgent, and we want to get there, but we’ve got to do this the right way.”