District or urban heating: what it is, how it works, and its benefits

What is district heating?

Urban or district heating centralises the heat energy production systems for whole neighbourhoods or even cities. These networks are used to regulate temperature and provide hot water for buildings and detached houses.

One typical (and famous) example of district heating systems working is the steam that comes from underground in the streets of New York, and which appears so often in films and TV series. It comes from the urban heating networks, systems whose oldest versions date back to ancient Rome, which offer many benefits and are a very interesting solution for enabling the energy transition in towns and cities.

District heating: a sustainable option

Urban heating systems are an alternative to optimise the sustainable development and growth of cities. As explained in the United Nations Environmental Programme (UNEP), heating, cooling and hot water account for 60% of the energy demand in buildings. In most of these, the energy comes from fossil fuels, which contribute to climate change when they are burned.

Cities are also home to more than half of the world’s population, they consume more than two thirds of its energy and represent more than 70% of the carbon dioxide emissions (CO₂, one of the main greenhouse gases that are causing climate change).

Creating integrated urban systems that encourage circularity and the use of renewable energy is fundamental to drive the energy transition and advance towards a system that is carbon-free, clean, and sustainable.

How the urban heating system works

District heating systems consist of three main elements: the power plant, the distribution network, and the substations in the buildings.

• The power plant is the same for the whole system. It is where the water (or a different fluid) is heated and pumped out into the distribution system.

• When it enters the distribution network, the energy is carried through heat insulated pipes to prevent heat being lost on the way.
• Finally, it reaches the substations in the buildings , where it is distributed to regulate temperature and provide hot water for homes, offices, and factories.

What source of energy makes all this possible? The fact is that these systems have used all kinds of options in the past, from fossil fuels to renewable energy in different energy vectors. Today, in order to reduce their environmental impact, the choice is renewable energy sources like solar, geothermal or biomass.

The benefits of district heating systems

The main benefit of these networks is that operating on a large scale, makes them more efficient in terms of the resources required. It is also true that there are many other benefits when compared with individual systems:

• They use less energy: operating on a large scale makes them more efficient.
• They are cheaper: as a result, the cost for individual users is lower.
• They are more sustainable: being more efficient, they emit less pollution and greenhouse gases. Besides, by working with clean energy, these emissions can be completely eliminated.
• They make buildings safer: the absence of separate boilers reduces the risk of explosions or gas leaks.

It is important to remember that energy generation is shared, but each user controls the temperature regulation in their own home. Billing is also individual, which is another benefit for the users.

Where are district heating systems used?

Although New York is one of the best-known places where district heating systems are used, they are in use in many cities around the world. The initiative District Energy in Cities, promoted by the UNEP to extend urban central heating systems to the greatest possible number of places, names 45·'champion cities' around the world.

In 2015, these cities had already installed more than 36 gigawatts (GW) capacity for urban heating (enough to supply around 3.6 million homes) and 6 GW capacity for urban cooling (which could be used by around 600 thousand homes). These systems contain at least 12 kilometres of connections.

Which cities are these? They include Aberdeen (United Kingdom), Amsterdam (Netherlands), Anshan (China), Bergen (Norway), Botosani (Romania), Brest (France) and Doha (Qatar).

The pioneering project of district heating in Spain was the power plant of the Ciudad Universitaria de Madrid. It was set up in 1932 and is still working. Today, one of the most important projects is that of Soria. This city in Castile and Leon uses biomass to transport temperature regulation and hot water to 8 thousand homes and 30 buildings for non-residential use.

One of the most interesting features of this network is that it uses biomass from the forests of the region, which has a long and important tradition of forestry. Giving this material a new use is one way of encouraging the circular economy, forest maintenance, and the creation of local jobs.

Urban heating in the future

The first urban heating networks that we know of date back to ancient Rome, specifically the 4th century BC. At that time, large cauldrons were used to heat water that was then distributed to private homes, thermal baths and other buildings.

Today, the future of district heating looks very different from those early methods, at least in technical terms. They are also increasingly unlike the systems that provided picturesque steam for series and cinema filmed in New York in the last few decades.

The future of these temperature regulation systems is dominated by more sustainable solutions that rely on renewable energy and optimisation to ensure that both private homes and cities in general can contribute towards making a cleaner and more sustainable world.