Cogen plant, falling prices mean stable power supply at MIT

During the summer of 2001, power outages in the greater Boston area were a regular occurrence, though much less so on the MIT campus. Part of the reason for this is that the MIT cogeneration plant provides power for about 80 percent of the buildings on campus. Peter Cooper, director of utilities in the Department of Facilities, recently answered some questions about the plant and its function here at MIT.

Q: Cities and towns near Cambridge and Boston had some serious and frequent power outages over the summer. It seemed that MIT was generally not affected by those problems. Is that because our cogeneration plant provides power to so much of the campus?

A: Actually, it's that and more. The cogeneration plant serves most of the campus via a central distribution system. In addition, we have four dedicated cable circuits from NStar's Putnam Station that provide a full-capacity backup when our generator is out of service. Also, the MIT cables running within the campus are configured as loops so any building can be fed from either side of the loop. This loop configuration means that the cables are only 50 percent loaded under normal conditions; consequently we have experienced very good reliability in our MIT distribution system. In fact, the two cable outages in the past few years were due to [accidental pipe ruptures] by contractors.

I believe the reason there were so many outages on the NStar system this summer is that much load growth had occurred due to the strong economy, but they hadn't upgraded their distribution system to keep up. The record-breaking loads last summer may have exposed the weaknesses in their system.

Q: Could you briefly describe how the cogeneration plant operates and what fuels its uses?

A: The cogeneration plant, which opened six years ago, primarily uses natural gas to make electricity in a combustion turbine. The waste heat from the turbine exhaust is captured in a heat recovery steam generator. That steam is used for heating and to operate steam turbine-driven chillers for cooling. Production of both heat and power in the same process is what makes cogeneration much more efficient than producing heat and power separately.

Q: What percentage of the campus is powered by the plant?

A: Out of 130 buildings on the campus, all but 25 are on the central system.

Q: Will the plant also provide power for some or all of the major buildings that are now under construction?

A: Yes--in fact, the pipes being installed in the railroad right of way between Vassar Street and Albany Street and also near Briggs Field are for connecting these new buildings to the central plant. Two notable exceptions are the 70 Pacific St. residence and [the recently renovated] Building NW30, which will be powered by NStar, although heat and cooling for NW30 are from our plant.

Q: In July, Tech Talk announced that NStar and MIT had settled a dispute over "stranded costs" and that MIT had received a partial refund of $1.7 million. Is that the end of the case, or do you expect that MIT could receive even more of the "customer transition charges" that MIT was initially forced to pay when we began generating our own power?

A: No, the $1.7 million constituted the compromise we settled on with NStar, and that chapter is closed.

Q: At the beginning of this calendar year, MIT expected that increased energy prices would add between $7 million and $10 million to what had been budgeted for fiscal year 2001. What was the final cost overrun for our energy needs?

A: In January we were projecting about a $5 million overrun due to record-breaking gas prices. Because the winter proved less severe than anticipated, gas prices dropped substantially. By April we projected a $2.1 million overrun and that's how we closed out the year. The timing of the NStar settlement helped to cover those costs.

Q: What are the primary ways in which MIT community members can help the Institute conserve energy?

A: By shutting off lights, computers and other equipment when not in use. Closing the sashes on lab fume hoods whenever possible is very helpful; it saves the air that's been heated or cooled from being pulled into the hood and vented out the roof.

A version of this article appeared in MIT Tech Talk on November 14, 2001.

Topics: Environment and energy

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