How will tomorrow’s cities be heated and cooled?

Urban areas are in a central position in curbing climate change. In Europe, buildings use nearly half of the total energy consumed and cause approximately 40 per cent of carbon emissions. A quick and large scale move towards emission-free heating of buildings requires innovative ways to use existing technologies. A shining example of this is district heating, popular especially in the Nordic countries, as it can use waste heat from data centers and industry to heat buildings.

We all want our homes to stay warm in the winter and comfortable also in the summer. If we want to curb climate change, however, we have to think about how we are heating and cooling our homes and other buildings. Climate change mitigation requires stronger link between the different energy sectors, such as buildings, transport and industry, to help them reduce carbon emissions. For instance, capturing excess heat generated by industry and data centers offers great opportunities for saving energy and cutting emissions at the same time.

Challenges of space heating in Europe

In Europe, natural gas is the primary energy source for space heating in cities. It typically relies on a collective boiler room that disperses the heat to apartments. The plus side of natural gas is that it is cheap and easy to store. However, like other fossil fuels, it is not very eco-friendly. In addition, these building-specific systems are not usually scaled for extremely low temperatures. Consequently, each apartment is supplemented with direct electric heating. This puts an added load on the electricity system.

A centralised heating system solves the problem of fluctuations in electricity consumption. Many European countries have used district heating systems for decades, but at the European level, they are overwhelmingly fired by coal or natural gas. Because district heating is not dependent on any single heat source, it would make sense to connect district heating networks to more climate-friendly heat sources.

Buildings owned by consumers, companies and communities can also become heat producers in a clean district heating network. In theory, any building that produces waste heat with clean energy could become a seller of district heat. Data centers, for instance, could cut their energy costs by selling their excess heat to the local district heating network.

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District heating – the way of the future
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Invented in the Nordic countries, district heating is a unique and efficient way to heat urban real estate. From the perspective of residents, district heating is a convenient service: a heat consumer does not have to worry about investments, maintenance, or whether there is enough heat – even in freezing temperatures. Eco-friendly heated water circulates through underground pipelines and provides heat to buildings and their service water.

A district heating network is capable of transferring heat to buildings from virtually any heat source. Even though a considerable share of district heating in Europe is still produced with natural gas and coal, several emission-free or carbon-neutral sources can be used to transfer heat to district heating networks. These sources account for a continuously growing share of production. The most significant recent changes in district heating include the transition to distributed, renewable electricity-based production forms, cogeneration of electricity and heat as a mid-term solution, and the recovery of waste heat from industry.

European detached houses are primarily heated individually using an oil- or natural gas-fired boiler or electricity, i.e. radiators and heat pumps. Installing large-scale heat pumps for entire neighbourhoods or a city instead of adopting building-specific pumps can serve multiple users through a district heating network that can direct heat to where it is needed most.

With emissions and the related costs quickly reducing, district heating will be even more competitive for customers; for individual buildings, it will be the most reliable in terms of delivery, and, for society, the most sustainable way for heating in urban areas.

Recovery of waste heat – but how?
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District heating is an ingenious space heating solution because it is not dependent on any single source of heat, and it does not even require combustion. Excess heat produced in industrial processes, in data centers and at wastewater treatment plants, for example, can be captured for emission-free heating to buildings. In advanced systems, excess heat is already recovered using heat pumps and injected into the district heating network.

The recovery and transfer of waste heat for buildings through district networks is part of climate change mitigation and the European energy transition. Using recovered excess heat means there is less need for other energy sources such as natural gas and coal. Instead, industrial-scale heat pumps that use electricity very efficiently can be used to transfer heat.

One office building is a small heat source, but once we start thinking about operations that require large amounts of electricity, the number of possible heat sources becomes enormous. For example, data centers are ideal heat sources as they consume lots of electricity and produce huge amount of heat in the process. They can sell their waste heat to a district heating network and, in doing so, reduce their operating costs. Only the district heating network is able to recycle and redistribute vast amounts of thermal energy that would otherwise be wasted.

Where can district heating be adopted?
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It has been suggested that district heating networks will play a considerable role in attaining the European Union’s targets of Secure, Clean, and Efficient Energy. However, district heating is not, at least yet, a viable option for areas with low population density. In order for the infrastructure to be efficient, it requires a high density of heat consuming buildings connected to the network.

Luckily, about 40% of the European population live in cities where these efforts need to take place. As different sectors of industry and energy become interlinked in urban areas to minimise wasted energy, in the future buildings in rural areas can increasingly be heated with clean, renewable electricity without an excessive load on the grid or, for instance, with hydrogen instead of natural gas.

Cooling buildings energy efficiently
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Electrical air conditioning equipment has become more widely adopted in Europe in the recent decades. However, they require considerable amounts of energy, placing an additional load on the electricity system. Individual air cooling units are not the best solution in urban areas because, on top of all existing electricity consumption, electrical grid capacity has to be amped up considerably to meet the demands of these types of equipment.

Even conventional water-cooling units often use considerable amounts of electricity for chilling water. A centralised solution for cooling, using renewable electricity, is an ecological and emission-free alternative.

District cooling is already the world’s ‘coolest’ way to improve the comfort level during the heat of the summer. It is a reliable way to reduce heat and humidity from buildings in urban areas. In a district cooling network, energy is redrawn to a district cooling water from the heated buildings.

Energy in the network can then either be reclaimed to bring heat to the buildings and tap water in wintertime or be cooled down with for example environmentally friendly seawater in the summertime. District cooling generates 97% less carbon emissions than cooling that is produced with traditional water-cooling units.

For example, Fortum and the Finnish city of Espoo have committed to carbon-neutral district heating in the district heating network operating in the Espoo, Kauniainen and Kirkkonummi regions in the 2020s. An intermediate goal is to phase out coal in 2025. The project is called Espoo Clean Heat.

The new generation of district heating is based on replacing fossil fuels with smart and flexible solutions that optimise the heat consumption of buildings, operate efficiently driven by artificial intelligence, and utilise multiple clean heat sources.

For example, one goal is to capture waste heat from data centers on a large scale. Just one big data centre operating on wind power electricity could cover 35 per cent of Espoo’s district heat production – without emissions.

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