Geotimes
Technology
Lake Creates Natural Air Conditioner
Lisa M. Pinsker

On a cool spring day in Ithaca, N.Y., engineer Lanny Joyce sits at his computer to keep an eye on the system cooling the Cornell University campus 2 miles away. The system is not a usual air conditioner. Every minute, 7,000 gallons of cold water from the bottom of Cayuga Lake travel to the shoreline through an underwater and underground pipe system, cooling a separate closed water loop that goes up to campus, keeping the students and faculty cool in their final days of the semester.

A major part of construction was the deployment of more than 12,000 trench feet of piping between Cayuga Lake and the Cornell campus. Stolt Comex Seaway engineers stand on the Lake Source Cooling intake pipeline to verify the pipe position as it sinks into the lake. Concrete ballast and stiffening collars lie at 15-foot intervals on the pipe. Pusher boats on the sides moved the pipe around into position.


Joyce’s eyes beam through his oval-shaped glasses at the screen as he boasts of the energy-saving benefits of the two-year-old Lake Source Cooling (LSC) system over the old refrigeration system developed in the 1960s. Since LSC began in July of 2000, Cornell has been using 85 to 90 percent less electricity to cool the campus.

“This is it, the thing I always I love to look at: 0.084 kilowatts per ton of air conditioning. When we were running refrigeration, the total system efficiency averaged near 0.7 and on a hot day approached 1.0 kilowatts per ton,” Joyce says. “I get to look at this 85 percent reduction every day.”

Cayuga Lake sits in a glacially carved valley in central New York. At 38 miles long and 435 feet deep, it is the second largest of the six New York Finger Lakes. It is the backdrop and main player in a $57-million cooling project for Cornell.
During the summer, the lake’s surface heats up, but at 250 feet deep, the waters maintain a year-round temperature of about 39 degrees Fahrenheit. In 1994, Joyce and other Cornell staff first envisioned using Cayuga’s cool waters as a less expensive, non-CFC, renewable energy source for cooling Cornell’s campus as an alternative to the refrigeration based chilled-water system. The old system used three chilled water plants and a 4.4 million-gallon thermal storage tank to air condition Cornell with CFC refrigerants.

The Ithaca community met their idea with caution and some resistance, fearful that the project might alter the beauty and ecology of the Finger Lake. After extensive environmental assessments, the University and New York Department of Environmental Conservation approved the project in January of 1998. Since the controversial project’s operation began two years ago, LSC has come full circle — now winning praise from engineers and environmentalists alike.

This year, among its many accolades, the Cornell Utilities Department won the 2001 New York Governor’s Award for Pollution Prevention. LSC eliminates the need for about 20 million-kilowatt hours of electricity a year — enough power to serve 2,500 homes a year. Joyce says he believes the beauty of LSC lies in its simplicity.

How it works

LSC consists of two loops, one carrying water between the lake and the LSC plant on shore and one closed loop between the plant and campus. The Cornell water and lake water never mix. Once on campus, the chilled water winds around a closed loop of pipes and collects the heat removed by air conditioning in the buildings.

The heat exchange facility serves as home base for the Cornell University Lake Source Cooling Project. The project has replaced refrigeration to air condition the college campus two miles away. Photo by Lisa M. Pinsker

The onshore LSC plant pumps the 39-degree Fahrenheit lake water to a heat exchanger, where it absorbs some of the heat from the closed loop from Cornell, before the water returns to the lake. The 55-degree Fahrenheit water enters the lake at a shallow depth. “The last 100 feet of the outfall has diffusers on it — 38 nozzles that are small in diameter that direct the water and also induce lake water to mix with it, so it quickly returns to the ambient condition,” Joyce says. It turns out, Joyce adds, that the water coming out of the LSC plant is actually colder, clearer and lower in nutrients than what is already in the lake during the summer months when flow is highest. And the actual amount of heat added back into the lake is equivalent to two additional hours of sunlight each year.

The open lake loop starts at an intake pipe 250 feet below the lake surface, 10 feet above the lake bottom in water 2 miles from the plant. The intake designers, Makai Ocean Engineering, planned deployment of the piping from the surface using a controlled sink process that pumped water in at the shallow end and released air at the other.

At the beginning of design, Makai required piston coring to survey Cayuga’s sediment composition. Joyce says that it was essential to insure that the piping infrastructure would not sink into the sediments, otherwise it would have been impossible to retrieve the intake pipe. In addition to conducting formal geotechnical tests, Makai engineers placed a cinder block on the lake bottom to see how much it would sink into the sediments. Also, they dropped the block from 15 feet above the lake bottom and measured the difference in settling. An underwater, remotely operated vehicle photographed the block. Both tests revealed very minimal sinking. Later retrieval operations confirmed that the lake bottom was supporting the piping. Since the pipe deployment in fall of 1999, they’ve filmed the piping underwater three times. “The pipe is sitting in exactly the same position as original deployment,” Joyce says.

The intake features some biological adaptations. An octagon-shaped fine screen about the size of a house covers the pipe to keep fish out. The screen can come up the surface for mechanical cleaning should zebra mussels accumulate in the pipe. Also, a low-wattage light acts to deter mysids, tiny freshwater shrimp.

Getting to know the lake

Over the six years of planning and 18 months of construction, engineers had to work with biologists, geologists and limnologists to create an effective design that would not disturb the natural environment. “From the beginning the issues on the table were technical feasibility, costs, potential environmental impacts, and public acceptance,” says Liz Moran, owner of EcoLogic and principal scientist for the Lake Source Cooling project when at Stearns and Wheler,LLC. Every aspect of the lake came under close scrutiny, from temperature and nutrients to sediments and biology.

Determining the best depth for an intake pipe, for example, involved temperature profiling of the lake. Originally, the LSC team planned to put the intake at 200 feet, Joyce says, but “the temperature wiggled too much.” The intake had to be at a depth of consistently cool water. Wind blows down the lake, creating waves that slosh around like water in a bathtub. The water curls around the lake and heads up the other shore, stacking the warm water downwind, close to Ithaca, and creating rapid temperature fluctuations at depth.

“Learning the hydrodynamics of the lake was fascinating,” Moran says. Although they had 10 years of weather data from local weather groups to study heat input to the lake, before the temperature profile, they had no previous comprehensive data of the lake’s temperature structure at depth. Moran is now working on a larger project to study the lake’s entire watershed. She says the LSC data has proved invaluable to future lake studies.

The temperature structure for Cayuga Lake was just one of many new data sets that LSC motivated. To develop LSC’s Environmental Impact Statement, Moran worked closely with a committee of four Cornell scientists: a biogeochemist, a civil and environmental engineer, a fish ecologist and a limnologist, Nelson Hairston. Among the environmental impacts they looked at were the change in the lake’s phosphorus cycling.

Many scientists and people in the community were concerned that bringing phosphorus-rich bottom water to the surface would create massive algal blooms. phosphorus in Cayuga Lake comes from two sources: river runoff and wastewater treatment plants. To study this potential problem, Hairston, Moran and colleagues had to study the way water moves in the lake. It turns out that the entering phosphorus concentrations fall off quickly. Hairston says the increased phosphorus load to the surface waters from LSC is undetectable. However, to facilitate the mixing of the incoming LSC water with the ambient lake water, the engineers, on the advice of environmental investigators, decided to install the diffusers on the outfall pipe.

The Upstate Freshwater Institute monitors water conditions biweekly. Over the past two years, they have observed no unusual algal blooms on Cayuga Lake’s surface. “The constant communication between the environmental and engineering teams was absolutely essential for the project’s ultimate success,” Moran says.

A milestone

In addition to the Governor’s Award, the LSC project and team have received honors from the American Society of Civil Engineers, New York State Society of Professional Engineers, the International District Energy Association and the American Society of Heating Refrigerating and Air-Conditioning Engineers. Many longtime critics of the project, however, are still not swayed by these recent honors, according to a recent article in the Ithaca Journal. Despite the community’s sometimes lukewarm acceptance, community input and participation has resulted in a new park on the lakeshore across from the LSC plant, nearly 3,000 feet of new road and utility infrastructure in Ithaca, and a continuous walking path from campus down to the lake shore. The system also cools the local Ithaca High School.

From theLake Source Cooling heat exchange facility, engineer Lanny Joyce looks out on Cayuga Lake with pride. Photo by Lisa M. Pinsker

The project’s innovations have also opened the door for similar cooling systems. While lake- or river-source cooling has been in use since the Industrial Revolution, LSC is the first to eliminate the need for refrigeration chiller plants year-round. A couple of chillers in one plant remain on Cornell’s campus as part of a back-up system or emergency source of cooling in the summer’s hottest months, and for future peak hours as load grows on campus.

Stockholm has a similar cooling system. But that project is smaller in scope and size than LSC, says Peter Veldhuizen, a principal engineer at Gryphon International Engineering Services, the firm “of record” for LSC. He and colleagues are currently developing a system for Toronto that will use Lake Ontario for a district cooling system. They are using many of the designs from LSC. Veldhuizen says Cornell and Ithaca were fortunate to have such a large candidate lake so close-by.

Moran and Joyce walk around the LSC facilities with pride. The cool breeze coming through the plant’s grating floor from the lake water below reminds them of their success. Says Moran, “It was a rare gift to be asked to contribute ideas and expertise to such an open collaborative process that culminated in a great project with measurable environmental benefits.”

Visit Cornell's Lake Source Cooling Project Web site.


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