District heating and cooling

The district heating net is a pipe network that supplies heating and hot water for connected consumers from a central power plant. It is a more efficient way to provide heat and power compared to localized boilers. District cooling is the cooling equivalent of district heating. Working in accordance to similar principles, district cooling delivers chilled water to buildings like offices and factories. Trigeneration is when electricity, heating and cooling are combined in the same plant.

Responds to the following needs

Diversification of energy sources
Cleaner energy sources
Reduced GHG emissions

Suitable for

Cities and urban areas
Densely populated areas
Residential as well as commercial buildings

Relevant CTCN Technical Assistance

Bosnia & Herzegovina: Rehabilitation and Modernization of the district heating (DH) system in the City of Banja Luka
Serbia: Modernization of the district heating system and improvements of energy efficiency of buildings in the City of Belgrade
Iran: Assistance for micro combined heat and power technology transfer, Iran

Relevant Technical Needs Assessments

Sri Lanka: Biomass residue based cogeneration combined heat and power (CHP)
Moldova: Medium term large scale Combined cycle power plants of large capacity
Argentina: Cogeneration systems based on the internal combustion engine Otto cycle (Spanish)

Technologies

A district heating plant pumps heated water to consumers where it is used for room and floor heating directly, or through a heat exchanger that transfers the heat to an internal circulation. The cold water then returns to the district heating plant which circulates endlessly in a closed pipeline. The heated supply water could also be used for domestic hot water through a heat exchanger. Some district heating systems use steam as medium for heat distribution instead of water. This is especially suitable for industrial processes which often require higher supply temperatures. A disadvantage of steam is that it has higher heat losses than water. In Sweden they are increasingly looking at using residual heat from e.g. computer server rooms for district heating. If it is too cold to be added to the district heating system they are warmed up by heat pumps. In some countries such as Denmark there is research on so called 4th generation district heating which means using a lower temperature of approximately 60-65 degrees instead of up to 80-90 which is the standard today.

For district cooling, the transition from local air conditioning units to more centralised district cooling can help to reduce peak electricity demand and increase efficiency. In winter, the source for the cooling can often be sea water, which is a cheaper resource than using electricity to run compressors for cooling. Water is then distributed to buildings and offices through existing water pipe networks, either directly or through district cooling substations.

District Heating Systems

Simple combustion (heat-only boiler station)
Combined heat and power (CHP): Cogeneration power plants produce electricity but do not waste the heat this process creates. The heat is used for district heating or other purposes, which improves the overall efficiency.
Trigeneration: A plant producing electricity, heating and cooling.

See publication: Cogeneration & Trigeneration – How to Produce Energy Efficiently

Combustion technologies

Grate firing
- Travelling grate
- Reciprocating grate
- Vibrating grate
Fluidized bed combustion (FBC)
Pressurized fluidized bed combustion (PFBC)
Circulating fluidized bed (CFB)
Chemical looping combustion (CLC): in recent years also proposed as a carbon capture technique.

Renewable energy sources

Geothermal-sourced district heating
Waste-sourced district heating
Solar thermal power
Industrial heat pumps (e.g. seawater)
Co-firing with biomass

Co-benefits of this technology

Enhancing energy security: District heating can provide significant diversity and flexibility in fuel sources, often within the same plant. This can have important security advantages. As a result, local renewable biomass is becoming increasingly important as a fuel for district heating in transition economies, particularly in the Baltic States. Latvia, for example, has reduced its dependence on imported gas and now produces over 12% of its district heating from renewables. District heating plants can often switch fuels in an emergency
Stimulating economic development: District heating has compelling economic development benefits in that greater efficiency results in a higher gross domestic product (GDP). GDP growth benefits the population as well by increasing standards of living. In some transition economies, families pay 30% or more of their take-home pay on utilities, primarily district heating. Such large expenditures for heat put a tremendous burden on families. Reducing this burden by improving the home energy efficiency would allow families to improve their standard of living. Metering is essential to allow families to benefit financially from energy efficiency improvements.
Storing renewable energy: CHP district heating is being developed in Denmark as a way to store renewable energy, particularly wind energy that exceeds instantaneous grid demand, via the use of heat pumps and thermal stores.

Product examples

[Disclaimer: Products listed here are provided by Climate Technology Network members and represent examples of products available within this technology field. The CTCN does not take responsibility for this product information and cannot guarantee its suitability in specific contexts or regions.]

Energy consumption and emission reduction in district heating systems [Ministry of Economy, Trade and Industry, Japan].
Biogas for CHP by dry fermentation [BEKON Energy Technologies]: In the absence of air and following inoculation by previously fermented material, the biological waste begins to digest, immediately resulting in the production of biogas. The biogas produced is generally utilised in combined heat and power (CHP) units for generating electricity and heat. The majority of the heat energy generated is utilised externally; for example, it may be fed into a local or district heating grid or used for drying materials.
Solar thermal energy for CHP [Villaya Microsol]: Microsol can meet some or all of the production needs of local residents, water supply, electrification of communal areas, and so forth. Microsol is based on the cogeneration principle, CHP, taking a new look at an already widespread technology; solar thermal energy.