University uses lake to run its cooling system
An innovative new system which uses a lake to cool campus buildings at Cornell University uses less energy and gives off fewer pollutants than conventional systems, say university engineers.
The new $60 million lake source cooling (LSC) installation uses cold water from the depths of Cayuga Lake, and was developed to combat rising energy costs and replace the university’s conventional refrigeration system that used chlorofluorocarbons. The university expects to buy about 20 million fewer kilowatt-hours of electricity per year for cooling which, combined with the longer life-span of the system, will offset the high capital outlay, say engineers.
“People think that the cost of cooling is lower because of lake source cooling, but the cost up-front is higher,” said William Joyce, Cornell utilities engineer and director of the LSC project. “We have built something that will last 75 to 100 years, whereas conventional chillers last about 30 years. It’s a much more passive system with fewer moving parts.”
The Cornell LSC system, pumps 39.5 degree Farenheit (5°C) water from a lake depth of 250 feet (76 metres) through seven heat exchangers, where the lake water absorbs heat from a separate and sealed water supply that is circulated to campus buildings. Chilled water travels in a closed loop between the plant and the campus, two and a half miles uphill. The system uses 4,000 horsepower for 20,000 tons of cooling capacity, compared with a total of 20,000 horsepower to supply 20,000 tons of cooling used by the old system.
Although, the concept of using naturally cold, deep water for cooling systems is not new, this is the first to use a small freshwater lake. Water from the Baltic sea is being used to cool downtown businesses in Stockholm, Sweden, and an experimental system cools the Natural Energy Laboratory of Hawaii. Systems are under consideration for downtown Toronto and a research facility near Rochester, both drawing water from Lake Ontario.
Environmental impacts of the scheme have been calculated by the Cornell team, including computer modelling that shows that the amount of heat returned to the lake is equivalent to about two to four hours of sunlight per year. Rather than being stored in the lake, that heat is lost to the air, said Joyce, also pointing out that extreme care was taken during construction to avoid stirring up sediment in the lake.
Preliminary data from on-going tests for any biological effects of the system, with monitoring of nutrient and algae levels, indicates that the LSC shows no conspicuous effect on the lake, according to Robert Bland, university environmental engineer. In fact, says Bland, the water returned to the lake contains less phosphorus than was projected in the original computer model, and that amount was less than the natural variations of the southern end of the lake.
Further benefits of the system include $1.2 to $1.5 million in improvements in re-paved roads and updated utilities along the route of the pipeline through the city of Ithaca, paid for by the university in return for an easement, and the provision of a chilled-water feed to Ithaca High School, saving the school an estimated $750,000 in cooling related costs.
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