[D2Grids] What is the future of heat supply in cities?

Every autumn, the heating in many houses is switched on again. In the Netherlands there is a lot of natural gas being burned in order to get it comfortably warm inside. In 2050 in the Netherlands, the supply of natural gas to the built environment will be cut off in order to achieve a more sustainable and environmentally friendly future. How are the Dutch going to heat their houses without the use of natural gas? What innovative solutions are there to warm homes in cities?

PhD student Stef Boesten researches how buildings in cities can be warmed in the future, partly within the EU-INTERRREG project D2GRIDS. The Open University of the Netherlands is an important partner in this project and is accountable for the long-term strategy and for training and education. The D2GRIDS-project includes five pilot sites in North-West Europe experimenting with innovative fifth generation district heating and cooling systems. By running pilot studies now, a great deal of experience can be gained with new techniques for heating houses before we phase out fossil fuels completely'.

Urgency of new heat supply

‘At present, in the Netherlands we mostly use natural gas from a single gas field in the Groningen province for heating homes and business premises. Since gas production from this field is now causing severe earthquakes in inhabited areas, natural gas production is being reduced at an accelerated pace until ceasing entirely by 2022. By that time the Netherlands will no longer be able to meet domestic gas needs and they will have to import natural gas from countries like the United States, Russia and, Norway. Although natural gas is the least polluting fossil fuel, this import will increase greenhouse gas emissions compared to using gas from domestic fields'. The halt of gas production in Groningen is an opportunity to look for alternative ways of heating buildings, but also geopolitical, financial and sustainability reasons are at the basis of the movement towards new heating concepts. In Europe, the heating of buildings is responsible for about 40% of energy consumption and CO2 emissions must be reduced worldwide. There are enormous benefits to be gained by working with heat networks and local systems that use sustainable heat sources. Examples include heat extraction from the subsurface (geothermal) or from surface water (hydro-thermal energy), but also from solar heat, or waste heat from a diversity of sources like waste processing, power stations and data centers'.

The subsurface as a storage place

The challenge is to store the heat somewhere to use it when needed. ‘In Beijum in Groningen this has been successfully applied since 1984. A group of houses and other buildings are connected to a heat network that is supplied by solar collectors. The heat is stored underground. In the Netherlands, the subsurface is often well suited for this purpose: for example, there are two aquiferous sandy layers, separated by clay layers which are poorly permeable to water. Drinking water is extracted from the deeper layer, but the top layer of stagnant water is ideal for storing heat. Large office buildings often already make use of subsurface heat and cold storage to heat and cool buildings.'

Sustainable and permanent solutions

Another possibility is to connect neighbourhoods to biomass power stations, such as in the Meerhoven district of Eindhoven. Houses are warmed by the heat released by burning prunings. On that scale, it is a fairly sustainable solution: prunings are burned and provide electricity and heat. The wood used for this purpose grows locally. However, the supply of biomass is not scalable: all that pruning wood has to come from somewhere. When we have to cut down forests in, for example, North America due to a lack of local supply, the solution is no longer sustainable'. Heat grids from renewable sources are a good idea, but we must strive for long-term solutions, Stef explains. A comparison can be made here with the electricity grid, where various local sources are connected to a larger network, such as solar cells and wind turbines. That's where we need to go in our heat network, local renewable heat sources can be connected to large heat networks to achieve permanent solutions.''. 

Cooling and heating

By smart design of cooling and heating, hot water can be stored, for example for use in winter. In a recently published paper Stef and his colleagues explain how fifth generation heating and cooling networks can provide cities with renewable energy. For a large part of the year, buildings, such as schools, need cooling instead of heating. The cold water they use for this purpose is warmed up when it is returned to the network. In the winter you can use this warm water for heating. This principle of exchanging heat and cold is currently being applied in the D2GRIDS pilot cases. In addition to a heating system, apartment buildings, shops and homes are also retrofitted with a cooling system. In the future, hot summers will appear more frequently, so cooling will become of increasing importance.

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Pleasant temperature

A key challenge in the research is the fact that the supplied temperature from fifth generation networks is much lower, 40-50 degrees, than the temperature that a central heating boiler reaches, 70-90 degrees. ‘That means a major change in the way people heat their homes. Underfloor heating is ideally suited to lower temperatures. However, this can be a major investment and is not always possible. In any case, it is important to insulate houses well: cavity wall insulation, double glazing and roof insulation ensure that less heat escapes and that it remains warmer in the house. Of course, it's not the intention that people should suffer from cold.’ In the project Stef examines the physical possibilities for smart heat networks and how to involve end-users. ‘Whereas in the old system they are mainly consumers of heat, in a smart heat network anyone can be both consumer and producer.'. How do you enter into a constructive dialogue with residents in order to create new heating networks? What temperature does the heat network need to have to achieve an optimal balance between heat loss, capacity and construction costs? What minimum interventions in the home are needed to make the indoor climate comfortable? How big should the (heat) pumps and storage solutions be? These are all questions to which we are currently looking for answers with the help of research at the pilot sites, so that in the future we can heat neighbourhoods and cities in a sustainable manner.

Photo credit : Martin Adams on Unsplash

Article online: https://www.ou.nl/-/toekomst-warmtevoorziening-steden