District Energy (also called district heating and district cooling) refers to generating any combination of electricity, steam, heating, or cooling at a central plant and then distributing that energy to a network of nearby buildings. As a result, individual buildings connected to the network avoid the need to install and maintain their own boilers, furnaces, chillers, or air conditioners, saving on capital and maintenance costs. Many district energy schemes use combined heat and power, recycling the thermal energy left over from electricity generation for heating or cooling. District energy is an efficient, reliable, and cost-effective option for any cluster or network of buildings.
District energy networks are very common in dense downtown areas and at colleges and universities. They are also often found at medical campuses, military bases, office parks, convention centers, sports arenas, airports, sustainable housing developments, or other clusters of buildings.
Who uses district energy?
District energy systems have been operating in the US for over 100 years and currently serve more than 4.3 billion sq ft of building space, including landmark buildings like the US Capitol and Supreme Court, the Empire State Building, the Mayo Clinic and Harvard Medical School.
Sometimes all of the buildings in a district energy network are commonly owned, as at a university or medical campus; in other cases each building is privately owned, as in a downtown area. The number of customer buildings served by a typical district energy system may range from as few as three or four in a new project under development to as many as 1,800 (as with Con Edison Steam Business Unit in Manhattan, the largest district steam system in the world).
Mature steam systems in U.S. cities like Philadelphia, Indianapolis, Boston or Denver serve between 200 and 400 customer buildings. Larger and established combination district heating and district cooling systems such as those in Hartford, Minneapolis, and Omaha generally serve between 65 and 150 customer buildings on heating and between 50 and 125 customer buildings on cooling. In most cases, the urban district energy system typically serves over 50% of the Class A commercial office space in the central business district and in many cases, market share exceeds 85%.
District energy systems are the preferred method of heating and cooling at most major college and university campuses. In the U.S. hundreds of campus energy systems provide highly reliable and scalable energy supply. Many U.S. universities are adding or increasing their ability to generate electricity on campus and are recycling heat from power generation to heat buildings and drive steam chillers for campus air conditioning.
Why district energy?
District energy is reliable, cost-effective, and efficient. In addition to the many inherent benefits of combined heat and power and other forms of onsite energy or recycled energy, district energy has the additional efficiency advantage of aggregating the electrical, heating, and cooling loads of multiple nearby buildings. A central plant serving steady, even loads is more efficient than individual building heating and cooling systems that have to ramp up or down to meet the buildingâ€™s needs. For instance, on the cooling side, the design for stand-alone chiller plants typically call for installation of between 30 % and 100% more cooling capacity than what is required from a district energy provider.
Aggregating the energy requirements of dozens or even hundreds of different buildings also allows the district energy system to employ industrial-grade equipment designed to utilize multiple fuels and employ technologies that would otherwise simply not be economically or technically feasible for individual buildings, such as deep lake water cooling, direct geothermal, or waste wood combustion. This fuel flexibility creates a market advantage for district energy systems and establishes the district energy system as an asset for community energy planning. Additionally, the availability of district energy service reduces the capital cost of developing an office building by cutting the boiler and chiller plant capital cost from the project, and frees up valuable space within the customer buildings.