District heating – an advanced driver of the green transition

Few people outside the industry would have believed a couple of years ago that district heating is being talked about today as a solution for the future. However, district heating networks play an important role in the green transition, as they enable new, emission-free methods of heat production, such as the utilization of waste heat. Moreover, in the heat recovery of green hydrogen projects, they are irreplaceable.

The term “district heating” has an old ring to it. It is thought of as a municipal service that had to be developed in Finland’s cold conditions to enable the effective distribution of heat even to remote areas. Within the last year, however, the term has resurfaced in connection with the energy crisis and green projects: district heating is suddenly seen as a significant enabler of the green transition.

The district heating network is largely a Nordic solution. District heating has also been used in Central and Eastern Europe but not in such an advanced way as in Finland, where it has a long history. According to Statistics Finland, district heating was the most popular heating solution in Finland in 2020.

District heat production also in transition

In 2020, more than a fifth of Finland’s district heating was produced using forest fuels, and the figure was expected to increase.¹ At that time, the energy crisis was not yet in sight, and some of the fuel was procured from Russia. Now Russian imports have ended, and a shortage in the supply of energy wood is looming. This has accelerated, among other things, investments in electric boilers, which are currently mainly made by larger operators in the district heating sector.

Of course, wood chips will continue to be used in heating centers and current power plants, but large district heating companies in particular are struggling with the challenge of how heat production will be implemented in the future. Also in smaller district heating networks, various heat recovery solutions are already being implemented, and the introduction of electric boilers is being explored.

Electricity can help make heat production greener, as long as the electricity itself is produced using renewable energy, such as wind power. Today, the use of electric boilers still relies on cheap hours: their use is limited to times when cheap spot market electricity is available.

Hydrogen economy is coming – with the help of district heating networks

The ongoing sector integration can be seen, for example, in the merger of the electricity and heat sectors. At its most advanced, it means the heat recovery of green hydrogen projects: the hydrogen plant operates on wind power, and the waste heat is used to heat cities.

Elomatic’s project development company Green North Energy also has similar plans. The waste heat from the Naantali plant under development is to be used in Turku’s district heating network. The amounts of energy generated by hydrogen plants are usually huge. Finding a use for all the waste heat in summer, when less heating is needed, can even be a problem for the energy company.

One seventh of Finland’s district heating already comes from waste heat²

In addition to hydrogen plants, waste heat is generated in industrial processes, data centers and various refrigeration devices. If a factory is able to utilize the heat itself, it is usually the best option. Otherwise, waste heat is collected in the district heating network and transferred to where there is a sufficient demand for heat.

Since the start of the energy crisis, energy companies have become increasingly interested in waste heat. The growing interest can also be seen in our Elomatic consulting group. We are commissioned to explore the possibilities of utilizing different sites for district heating networks and clarifying what type of power they can receive.

Utilizing waste heat always requires detailed assessments. It is not always possible due to technical or commercial limitations, for example.

Waste heat even from waste water

New sources of waste heat are constantly being researched, and one subject of interest is treated wastewater. A good example of this is the recovery of waste heat at the Pått wastewater treatment plant built by Vaasan Sähkö: the heat from the plant is directed to the district heating network, where it is sufficient for the needs of almost 2000 detached houses.³ 

Especially if operations involve a lot of energy consumption and there are large amounts of waste heat in the buildings, it is usually profitable to recover the heat. For example, it might make sense to build a two-way solution in connection with the energy renovation of a large spa if it is located close to a district heating network.

Heat storage also needed

Renewable energy sources are cyclical by nature. When using them, heat storage is needed to enable heat to be produced when it is most profitable and used when it is needed. The district heating network is itself a form of short-term storage. To enable the use of it as storage capacity, measurement technology and digitization are needed.

One possible solution is the combination of an electric boiler and storage. In addition, very large-scale storage facilities are under development. For example, Vantaa Energy is planning the world’s largest seasonal heat storage under Ring Road III.

Towards low-temperature networks

New energy production methods, such as waste heat recovery, typically produce slightly cooler water than traditional technologies. In the future, district heating networks will be built largely as low-temperature networks in which the temperature of the circulating water is lower, as the name suggests. To be precise, the rating has been dropped from the previous 115 degrees Celsius to 90 degrees Celsius. These lower temperature levels can be used in networks outside of the coldest periods of frost and the heating season, and on a case-by-case basis throughout the year.

The challenge in this is the long transition period, as the renewal time of current networks is 60 to 80 or even 100 years. Current networks are designed for a larger temperature range, so the narrowing of the temperature range caused by the drop in supply temperature and the resulting increase in flow cause a limitation to the network’s transmission capacity.

A drop in the temperature level nevertheless improves the energy efficiency of networks, as heat losses remain lower than in traditional district heating networks. In addition, a low-temperature network enables heat pump energies to be taken into the network, meaning that the temperature level is more favorable for transfer.

Clear advantages for district heating customers

With the help of district heating, entire cities can switch to green heating at once without the need for local companies and residents to acquire new heat production equipment. Digitization will enable even more in the future, such as demand flexibility that will let consumers limit their own heat intake if there is a need to reduce heat consumption.

From our consultants’ point of view, things get more complicated as heat production becomes more diverse. Managing energy production will be even more challenging when heat production units and heat storage are added here and there along the grid. However, the network still has to operate on the customer’s terms: demand and supply must meet.

References

1 Vaasan Sähkö 2021 Kaukolämpö on tulevaisuuden lämmitysratkaisu | Vaasan Sähkö (vaasansahko.fi)

2 Finnish Energy, Kaukolämpötilasto 2021 https://energia.fi/files/7487/Kaukolampotilasto_2021.pdf, page 4

3 Elomatic 2022 Vaasan Sähkö has commissioned Elomatic to design and project manage a future heat pump plant – Elomatic