What is District Heating?

  • A district heating plant is often a combined heat and power plant (CHP). By co-producing heat and power in the same process, the heat that would otherwise be wasted in electricity production is utilized. This leaves tremendous energy savings of up to 30%.

    In essence, any energy source can be used in a district heating system. Renewables such as biomass, solar energy and waste are becoming increasingly applied in district heating utilities either completely or as a complement to traditional fossil fuels. District heating is in other words ready for today's clean energy sources as well as those of the future.

     

  • How does District Heating work?

    Through a district heating network, the heat producing plant pumps heated supply water to consumers where it is used as room-/floor-heating and to generate domestic hot water. The domestic hot water gets heated in a heat exchanger in which the heated supply water transfers its heat to the water coming out of the taps.

    For room heating, the supply water might be used directly. Alternatively, a heat exchanger could also transfer the heat to an internal circulation. The supply water – which is now cold because the heat has been transferred to domestic hot water and room heating – then returns to the district heating plant. The district heating supply water circulates endlessly in a closed pipeline.

    Some district heating systems use steam as medium for heat distribution instead of water. This is to achieve higher supply temperatures, which are often necessary for industrial processes. A disadvantage of steam is that it has higher heat losses than water.

    Environmentally Friendly & Energy-Efficient Heating Supply 

    Due to simultaneous production of heat and electricity in combined heat and power plants, district heating is very energy-efficient. By implementing renewable energy sources and utilizing waste heat generated by industry the environmental gain by district heating is further evident. This kind of energy utilization is beneficial for both environment and society in general.

    Compared to individual heating systems the district heating plants are better at reducing emissions of hazardous compounds since they have more advanced pollution control equipment and through their more controlled conditions when generating heat. Furthermore, district heating is very convenient for consumers - who hardly notice how their radiators and tap water is heated in their everyday.

    District Heating Enables a Green Future

    District Heating is not only compatible with renewable energy sources of today; With an established district heating network, future energy sources can also be utilized centrally and distributed to consumers through existing district heating pipes.
    Add to that supreme efficiency and ability to utilize waste heat from electricity production and you have a system that is potentially the cornerstone of the future energy supply.

    Renewable Energy – Substituting Fossil Fuels with Sustainable Alternatives  
    In pace with increasing environmental concerns, renewables have become a key issue. The flexibility of district heating allows for substitution to environmentally friendly alternatives. 

    Renewable energy is energy generated by natural resources and includes geothermal energy, biomass, wind energy, water energy, solar energy etc.

    It is greenhouse-neutral. This means that it does not increase the concentration of greenhouse gases (e.g. CO2, methane, nitrous oxide and CFC) in the atmosphere.

    These alternative renewable energy sources are compatible with district heating either directly or indirectly. Energy sources which are usually utilized in electricity generation such as water and wind energy are rarely used in district heating systems, but the majority of renewables are used to a high degree in district heating. 

    District Heating in Denmark

    In Denmark most district heating plants are combined heat and power plants that distribute the heat made from the surplus heat generated by the production of electricity. An example is the Sønderborg Kraftvarmeværk (CHP) in Southern Denmark, which burns waste to generate heat and electricity.

    The Danish District heating system is the result of visionary thinking and long term planning. During the oil crises in the 70s the foundation of today's district heating system was built based on a strong demand to save energy.

    Heat planning has been the central driver for the successful implementation of district heating. Gradual replacement of natural gas and oil supply to district heating along with other initiatives such as incentives for insulation of buildings and a switch to renewable power production has put Denmark in the front seat of energy savings. 

    Combined Heat and Power (CHP)
    A large part of the CO2 savings and reduced energy consumption in Denmark are owed to co-production of heat and power. A traditional power plant only converts approximately 40% of the total energy input to electricity while 60% is wasted to the surroundings as heat. In a combined heat and power plant, 50% of energy input will be converted to heat and distributed to consumers in a district heating network. Thus, energy waste is reduced from 60% to 10%!

    While fossil fuels have been the dominant fuel in both CHP's and pure heat plants in the 70s and 80s, there is a strong tendency towards the use of renewable energy sources. While wind energy has been the predominant renewable method for producing electricity, geothermal heating, biomass and solar energy are employed in the production of heat or in the combined production of the two.

    Geothermic Heating
    In 1984 the first geothermic heating installation was built in Thisted as a pilot project for research - since then the plant has been expanded and today we also have a geothermic installation in Copenhagen and more are planned in other parts of Denmark.

    Biomass
    In Denmark we have CHP plants in many cities that burn straw or wood to generate heat and electricity. Often they are supplemented by co-firing of gas or coal, but in some cases biomass is the sole energy source.

    Waste is the primary type of biomass used in Denmark, and in many cities waste is used for heat and electricity generation. Furthermore, incinerating the waste reduces the demand for landfills vastly.

    Solar Energy
    Around the country, solar thermal systems have been installed as supplements to existing district heating utilities. The world's largest solar heating system, which covers almost 20,000 m2 is situated in Marstal on the island Ærø. The solar collectors make sure that 600 households are solely heated by solar energy all year. It includes seasonal storage of solar heat in a soil deposit.

    We export District Heating
    The district heating sector and the CHPs in Denmark have managed to maintain stable energy consumption for years – and even a decreasing consumption during times of economic growth. This has made an impression on both politicians, district heating plants and district heating sectors across the world. And with this in mind it is safe to say that Denmark is a world leader in district heating. Danish district heating technology is an important export, a fact that also benefits the Danish economy! 

    The Danish District Heating History by "DBDH" More about Danish District Heating by the "Danish District Heating Association" More about Danish District Heating by the "Danish Energy Agency"
  • District Energy Documentary

    This documentary introduces you to the concept of district energy, how it works and its merits for contributing to the security of energy supply, multi fuel flexibility and energy efficiency. The film presents several cases that show how energy - which would otherwise have been wasted - is utilized and turned into effective heating of buildings and homes.

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