by Judy Li
As part of a special National Geographic series on energy issues, Christina Nunez published an interesting piece about district energy, the distribution of thermal energy through a network of underground pipes to heat and cool a group of buildings, and how it is being harnessed for sustainable energy development. District energy is widely used and has a long history; many cities around the world have extensive subterranean systems built decades ago.
Now, there is new interest in district energy as a way for cities to reduce emissions and boost energy efficiency. Traditionally attached to coal- or oil-fired power plants, old systems are being renovated to deliver steam generated by cleaner fuels and recovered waste heat from power plants. Also, systems are being expanded or built in a number of countries. A United Nations Environmental Programme report from last year showed that 45 “champion cities” have cut primary energy use 30 to 50 percent by recycling waste heat for district energy.
For businesses, it is cheaper for them to tap into the municipal system than to maintain their own machines for heat. Many universities and hospitals are investing in similar systems as part of their emergency micro grids. In the US, old steam systems have been prone to leaks and explosions but proper upgrades and maintenance can prevent them. Some places have chosen to convert to hot water systems, which are safer and more reliable than steam systems.
Taxes on carbon pollution and tax credits for combined heat and power systems have helped to promote district energy. Relative to European countries, it has been slow to develop in North America where it is mostly driven by private investment. The US Department of Energy is supporting more district energy with a technical assistant program and possible loan guarantees.