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District CoolingEver-Green Energy affiliate, District Cooling St. Paul, operates a large chilled water cooling system in downtown Saint Paul, Minnesota. |
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Ever-Green Energy affiliate, District Cooling St. Paul, operates a large chilled water cooling system in downtown Saint Paul, Minnesota. The non-profit company was founded in 1991. Service to its first district cooling customers began in spring 1993. Ever-Green Energy manages the operations of District Cooling. How it WorksDistrict Cooling delivers chilled water year-round through underground pipes, which are separate from District Energy's heating system pipes. The chilled water distribution system totals 70,600 feet of supply and return piping (up to 30 inches in diameter) circulating 975,000 gallons of chilled water. The water provides air conditioning with a reduced use of ozone-depleting chlorofluorocarbon (CFC) refrigerants. Chilled water is supplied by electric and low-pressure steam absorption chillers from multiple locations. In addition to chiller capacity, the system is served by two chilled water storage tanks (2.5 million gallons and 4 million gallons) that store chilled water produced at night using off-peak electricity for daytime distribution to downtown district cooling customers. Total installed capacity is almost 33,000 tons. Startup of a new cooling plant occurred in June 2003. The new facility houses two highly-efficient chillers (with room for one more) and the 4-million-gallon chilled water storage tank. The new plant further improves the efficiency and reliability of the district cooling system. Customer BaseDistrict Cooling currently serves more than 95 buildings in the downtown Saint Paul area. The customer base includes multi-family, commercial, industrial and large institutional structures. The total building area served exceeds 18.5 million square feet, or about 60 percent of downtown Saint Paul. Major district cooling customers include the Minnesota State Capitol Complex, the Warren Burger Federal Building, the City of Saint Paul, Ramsey County, the Eugene J. McCarthy Post Office, the Science Museum of Minnesota, Wells Fargo Place, Xcel Energy Center, and the world headquarters of Ecolab, Travelers and Securian. PerformanceThe district cooling system has operated reliably since operations began 15 years ago. District Cooling's reliability rating over the past five years exceeds 99.99 percent based on customer hours served. This rating includes only down time to connect new customers to a rapidly expanding system. Distribution losses are less than 1 percent. With the use of chilled-water storage, as well as advanced maintenance and operational techniques, District Cooling has been able to reduce its customers' collective peak electric demand by as much as 9,000 kilowatts. Additional system improvements, including the operation of a second chilled-water storage tank, significantly increase supply and reduce the ratio between supply and demand. Those economics result in stable rates, with increases averaging just 1.8 percent since service began. |
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