Half of cities' energy consumption is for heating and cooling. From planning to implementation, cities are increasingly turning to modern district energy as a low carbon solution.  

As sustainable energy moves up the political agenda, low carbon solutions for heating and cooling are coming to the fore. Every year, almost 50% of the total energy consumed in Europe is used for the generation of heat for domestic or industrial purposes. Among leading institutions, there is growing consensus on what could be a big part of the solution.

The International Energy Agency recently cited co-generation and district heating as 'an essential part of strategies for greenhouse gas emissions mitigation and energy security', and last autumn the European Commission's Stress Test Communication pointed to fuel switching through district heating and cogeneration as a key measure for ensuring long-term energy security.

In a nutshell, co-generation (also known as combined heat and power or CHP) technologies allow for the simultaneous generation of heat and electricity, increasing the overall energy efficiency of the conversion process by partially recovering heat produced during electricity generation.

The heat can be used for a variety of purposes including industrial processes as well as to supply the needs of buildings. To distribute the recovered heat from the co-generation site, a district heating network (high-efficiency, insulated piping system circulating water) brings the heat to residential and commercial buildings for applications such as space heating and water heating.

Co-generation and district heating go hand-in-hand – in 2011, 79% of all district heating in OECD countries was produced by co?generation plants.

Efficiency gains here are seriously impressive. Globally, only about 36% of the energy going to thermal power plants is converted into electricity in comparison to a 58% average conversion on co?generation sites.

State?of?the?art co?generation units can reach conversion efficiencies of as much as 90%. Despite this promise, market penetration has remained stagnant over the last decade.

While some countries have achieved a high share of co?generation in electricity production (for instance, Denmark has more than 60% and Finland almost 40%), most countries have not been that successful.

Mapping the Heat

A key barrier to wider deployment is poor strategic planning for heating and cooling infrastructure. This year, as a result of the Energy Efficiency Directive (Article 14) EU member states are required to submit national to the European Commission a comprehensive assessment of the potential for the application of high efficiency co-generation and efficient district heating and cooling. 

Funded by the Intelligent Energy Europe programme, the Stratego project is supporting the development of national heating and cooling roadmaps (required by the Energy Efficiency Directive) by compiling a pan-European heat map – the European Thermal Atlas.

The heat atlas will comprise an EU28 map of 1km2 grid resolution, which for each cell (1km²) will contain the modeled heat and cooling demand, the local density of both demands, the basic geometry of DHC supply, the available waste heat resources and the potential for renewable energy sources (solar thermal, geothermal, relative accessibility of biomass).

According to Nicolas Février, who is coordinating the project, "City planners have a pivotal role in developing eco-districts where the upgrading of building stock goes hand in hand with the establishment, expansion or modernisation of district heating and cooling networks. This Atlas will allow you to rapidly check the thermal resources available in your region as well as the thermal demand".

With constancy and density of demand, cities are ideal candidates for district energy. The Nordic countries are market leaders here (or example, 98 % of Copenhagen's heating needs are met through heat networks) but in the UK, Netherlands and Belgium there are signs of market growth.  

By 2025 London aims to supply 25% of the city's energy through decentralised energy sources, like local heat networks, and has produced the London Heat Map, an interactive tool that allows users to identify thermal demand and supply in the city.

Siegfried Zoellner at ICLEI (Local governments for sustainability) said, "The many benefits of district energy make it one of the best opportunities for cities to reduce greenhouse gas emissions resulting from the heating and cooling of buildings, while at the same time improving city liveability. The ability to flexibly use a number of energy sources, including renewable and otherwise wasted energy, increases energy security, minimises environmental impact and provides affordable comfort for citizens."

Switching to renewables

Once the heat network is in place, it can use a wide range of energy sources, from fossil fuels to waste and renewable sources, such as biomass, solar and geothermal energy. Heat can be recovered from sewage, waste water and incineration. Fuel switching is not instantaneous however, averaging one to two years depending on size and capacity.

In Hungary, a beneficiary of Intelligent Energy Europe-MLEI[1] funding (EUR 285 000) City of Kecskemét is hoping to transform its natural-gas fired district heating network into a geothermal system – and aiming to attract investment of over EUR 30 million for the project.

In this area, the geothermal gradient (the temperature increase per meter of depth) is twice the global average, meaning that a 1.000 meter borehole reaches earth with a temperature of over 50°C. A number of Hungarian cities operate district heating networks that can be powered by local clean geothermal energy.

"It is a big market, and there are big opportunities," says Pál Boza who is coordinating the project.

 Above: the principle of geothermal energy.

In Europe, on average 44% of district heating runs on gas with a share of up to 80% in the countries where district heating is well-established such as Latvia, Lithuania, Slovakia, Bulgaria and Hungary.

In the Baltics and Finland, gas consumption in district heating and in combined heat and power plants typically represents around 50% of total gas consumption. There are major concerns about the vulnerability of the Baltic States to disruptions in natural gas supply from Russia.

Safeguarding against this, in Tartu (Estonia) the local district heating network is fuelled by local biomass and provides 92 % of heat demand for the city, ensuring winter warmth (and energy security) for most of its citizens.

Finland is one of the world leaders in the use of cogeneration and district heating and cooling systems – helped as it is by a climate that requires heating energy for buildings for much of the year. Here even recovered heat from sewage water is feeding into the district heating network which supplies 93 % of Helsinki's buildings with hot water.

Keeping Cool

Helsinki also has an extensive district cooling network; 80% of the district cooling comes from free or otherwise wasted energy sources, including cold seawater and absorption cooling units using the steam from the power plants. (District cooling works on broadly similar principles to district heating; cooling is provided by piping chilled water to buildings.)

Cooling also comes from the world's largest heat pump, located in a rock cave 25 metres below a park. It can produce 90 MW of district heat and 60 MW of cooling, transferring the heat to/from treated waste water or seawater as needed.

However, across Europe district cooling remains seriously underexploited with current market share as low as 2 %. The RESCUE project includes updating the European Cooling Index methodology among project activities.

Two utilities are involved (Climespace – operating an extensive district cooling network in Paris, and Helsingin Energia), along with local government association ICLEI and Swedish consultancy Capital Cooling. Commenting on the project results, Henrik Frohm from Capital Cooling said: "In particular, the workshops have been really successful in engaging with local governments. In Tartu and in Aarhus, district cooling projects are developing as direct result. Interestingly, take-up has been better in northern Europe than in the south, where there's more need for cooling."

Innovation Culture

Although cogeneration and district heating and cooling are mature technologies, there is continuing innovation in this field. The CELSIUS project, funded under the EU Smart Cities & Communities/Seventh Framework research programme (to the tune of EUR 14 million, with an additional EUR 12 million from the project partners) is working in London, Rotterdam, Genoa, Gothenburg and Cologne on twelve new demonstrator projects. Market conditions among project partners vary hugely from the mature market in Gothenburg of more than 90 % penetration, to around 2 % market share in Genoa.

In December 2014 in Gothenburg, the project achieved a world-first when a district heating connection to the ferry Stena Danica was inaugurated. Previously the Stena Danica was supplied with hot water from oil burning when she was moored. Now oil burning is replaced with hot water from the Gothenburg district heating system.

Another demonstrator project delivers waste heat from an incinerator in the Port of Rotterdam 26 kilometers to the city where it connects to the existing district heating network.

A heat hub, operational since late 2013 and located in the middle of the distribution network, acts as a distribution station and has a well-insulated buffering tank.

The capacity of the buffer is 185MWh and the discharge capacity is 30MWth. This allows for an increase in total heat delivery of the waste heat network without any additional investments in a new transport infrastructure or by means of additional heat sources.

On prospects for the European market, Jonas Cognell, program manager at the Celsius project, says: "We can see that there is some fresh movement, and new markets opening up. I think 2015 is the beginning of a breakthrough – but to see investments and decisions take place, we're probably talking about a 3-5 year timeframe."

• A high level conference focusing on the role of heating and cooling in the European energy transition will take place on 26-27 February 2015 in Brussels. 
• District Energy in Cities: Unlocking the Full Potential of Energy Efficiency and Renewable Energy

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[1]  This project development assistance facility now can be found under Horizon 2020 here.