District Heating &
Article #136, September 2008
By Bill Cook
District Energy systems use hot water or steam to heat and cool homes and businesses within a town or community. The water circulates through an underground grid of insulated pipes, with little loss of energy. A generating plant produces the hot and cold water and pumps it into the grid. The heating plant can be configured to use woody biomass as a feedstock (chips, shreddings, pellets, etc.). Different configurations can utilize different combinations of renewable feedstocks, as well as traditional fossil fuels.
Benefits of District Heating include; 1) potential conversion to renewable energy sources, such as woody biomass, 2) energy and system efficiency, 3) energy conservation, 4) high reliability, low maintenance, 5) reduced life cycle costs, and 6) they are flexible and adaptable. Buildings on the grid do not need their own furnaces or air conditioners. New buildings have lower construction costs. Over time District Energy has been very reliable and cost competitive.
If electricity generation capacity is added, then you have a Combined Heat and Power (CHP) plant. A CHP plant uses hotter steam and higher pressure boilers. It, too, can be configured to use a variety of feedstocks, including woody biomass. CHP are common in Europe and becoming more common in the USA.
District Energy plants can serve both small and large communities. The idea is not new. Thomas Edison built a system in Philadelphia. Many systems currently exist across North America. Historically, many were abandoned over time due to inexpensive fossil fuels. With permanent price increases for fossil fuels and concerns about fossil fuel impacts on global climate change, district heating systems that run on renewable fuels have drawn a growing interest.
For communities interested in District Energy, clusters of larger buildings might first be evaluated. Schools, colleges, municipal buildings, and industrial parks might be logical choices. Once cost-savings are demonstrated, a larger number of homes may wish to be tied into the pipeline grid.
The technology for District Energy is readily available, primarily boilers and pumps. Chillers remove heat from the water for air conditioning. Air quality equipment would need to be considered and a pipeline grid engineered and constructed. An area for feedstock handling is necessary, such as room for trucks, feedstock storage, and moving feedstock into a boiler. An assessment of feedstock costs and availability is essential, especially for woody or agricultural biomass.
In the past, District Energy was used to help maintain snow-free and ice-free conditions on sidewalks and public areas, as well as for building heat. In the near future, District Energy may be an economical option to provide renewable, sustainable, and clean heat (and cooling) for business, government, and residential buildings. In some countries, a large and increasing portion of heating energy already comes from woody biomass. In Sweden, about 18 percent of their total energy consumption comes from renewable woody and agricultural feedstocks, much of that through District Energy. In the USA, biomass supplies about 3 percent of our energy consumption.
In Michigan, District Energy is employed at several universities, including Michigan State University. Detroit, Ann Arbor, and Grand Rapids each have District Energy systems as part of their infrastructure.
Across North America, a number of landmark buildings are heated and cooled from District Energy grids, such as the IDS Center in Minneapolis, several prominent facilities in Toronto, Boys Town National Hospital in Omaha, downtown St. Paul, Minnesota, the Empire State Building, and the United Nations Headquarters. Most of the North American District Energy supplies heating and cooling to commercial and government buildings. Residential use runs around 10-12 percent.
addition to renewable and economical heat, locally-grown energy plantations
can add economic activity near the heating plant. Fallow farmlands can be brought
back into production to help supply the heating plant with lower cost feedstocks.
Plantations might include species such as willow, hybrid poplar, switchgrass,
Miscanthus, or other agricultural product. As the United States slowly moves
away from its large fossil fuel appetite, District Heating from renewable feedstocks
will likely become an important component of that change.
Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at firstname.lastname@example.org or 906-786-1575.
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
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