Excess heat, often a byproduct of industrial processes, is an untapped energy resource with enormous potential. In the context of global sustainability and energy efficiency efforts, district heating systems supported by digitization can play a key role in the energy transition.
Is excess heat an untapped energy source in the world?
Harnessing Excess Heat: Excess heat, often regarded as wasted energy, is an inevitable byproduct of most industrial and commercial processes. This industrial waste heat results from operations such as manufacturing, energy production, chemical production, and various treatment processes. In these industries, energy is either converted or used to perform specific tasks, but not all of the energy is utilized. A significant portion of it escapes as waste heat, serving no productive purpose. Today, industries ranging from factories to data centers, supermarkets, metro systems, and wastewater treatment facilities all produce substantial amounts of excess heat.
To fully understand the concept of excess heat, it is necessary to refer to the laws of thermodynamics. According to the second law of thermodynamics, for example, when energy is converted through a heat engine, waste heat is inevitably produced. This principle highlights that no energy conversion process can ever achieve perfect efficiency, with a portion of the energy being released as heat in the process.
Excess Heat in Industrial Processes
Various industrial activities generate large quantities of waste heat. For instance, cooling systems or exhaust mechanisms often release this excess heat into the environment without any productive purpose. Despite being considered “waste,” this heat still holds a significant amount of energy that could be harnessed. As industries increasingly recognize the potential value in this waste heat, many have turned to waste heat recovery systems. These systems capture and repurpose the heat to enhance energy efficiency, reduce operational costs, and lower their carbon footprint.
The Need for Energy Efficiency and Waste Heat Utilization
As global awareness of climate change intensifies, achieving net-zero emissions has become an urgent priority. However, even with skyrocketing energy prices following geopolitical tensions like the Russia-Ukraine conflict, and the ongoing uncertainty surrounding energy supply, we are far from achieving the average annual efficiency improvement of 4%. In the European Union alone, excess heat represents approximately 2.86 TWh/year, nearly corresponding to the EU’s total energy demand for heat and hot water in residential and commercial buildings.[1] This highlights the vast, untapped potential of waste heat that could be harnessed for a variety of purposes.
Reutilizing Waste Heat with Advanced Technologies
The good news is that this wasted energy is far from being useless. A range of established technologies, such as heat pumps and steam compressors, can be employed to recover and redistribute excess heat.
For example, waste heat can be used to provide warm water or heat to factories or, through district energy systems, supply energy to neighboring homes, such as those connected to a wastewater treatment facility.
Heat pumps, which are electrically powered devices capable of transferring heat from one location to another, are particularly effective in this regard. These systems can be applied in a variety of settings. For instance, they can capture heat from the exhaust of industrial furnaces or from the heated water in data center cooling systems and then redirect this heat to the heating systems of nearby buildings. This technology has great potential not only in current applications but also in future energy systems. As we move toward more sustainable energy solutions, Power-to-X technologies — facilities capable of generating large amounts of excess heat — will become more widespread. This heat can be effectively harnessed, particularly when it is low in temperature, through the use of heat pumps.
A Vision for the Future
The ability to capture and utilize excess heat on a large scale offers immense opportunities for improving energy efficiency and achieving sustainability goals. Heat pumps, district energy systems, and waste heat recovery technologies are integral to the transition toward a low-carbon future. By tapping into the potential of this previously discarded energy, industries and communities alike can significantly reduce their reliance on traditional, more energy-intensive systems. This approach not only helps reduce carbon emissions but also contributes to the economic and environmental sustainability of the energy sector.
In conclusion, while excess heat has historically been viewed as a waste product, it holds the key to a more efficient and sustainable energy future. With the aid of advanced technologies such as heat pumps and steam compressors, this waste heat can be redirected and repurposed, helping to address some of the most pressing challenges of our time. The combination of these technologies, alongside the growing emphasis on digitalization and energy optimization, could revolutionize the way we think about energy:
- production,
- distribution,
- consumption.
District heating system
District heating is a network of insulated pipes that transports heat from a central energy source to provide space heating and hot water to buildings connected to the system. The most advanced form of district heating, known as 4th Generation District Heating (4DHC), operates at lower temperatures, resulting in reduced heat loss through the pipes, improved energy efficiency, and the ability to incorporate a wider range of heat sources.[4]
One of the key advantages of district heating is its ability to integrate multiple locally available, renewable, and low-carbon heat sources. This decentralization ensures that the system is not dependent on a single heat source, offering a more reliable, continuous, and cost-effective service. Furthermore, district heating systems can recover and repurpose waste heat generated from processes such as electricity production or industrial activities, using this surplus heat to warm homes and businesses within the area. [2]
The most widely cited example of district heating is Copenhagen, where 98% of the city’s buildings are served by district heating networks.
District heating plays a significant role in meeting heating demands across Europe, with over 10,000 networks in operation. Collectively, these networks account for approximately 8% of the total heat demand across the continent.[4] However, the impact of district heating is even more pronounced in certain regions. In Eastern and Northern European countries, including Latvia, Denmark, Poland, and Sweden, district heating systems supply energy to more than 60% of the population. These countries have embraced district heating due to its efficiency, ability to integrate renewable energy sources, and potential for reducing carbon emissions, making it a key element in their efforts to decarbonize the heating sector. The widespread use of district heating in these regions highlights its effectiveness as a solution for sustainable and reliable energy distribution.
District heating in history
Throughout history, it is well-documented that during the Roman era, geothermal hot springs were used to heat homes, baths, and greenhouses. One of the earliest planned geothermal heating projects can be traced to the 14th century in the village of Chaudes-Aigues in Cantal, France, where geothermal water was distributed through wooden pipes. Remarkably, this system is still operational today. The first official commercial district heating system, however, was introduced in 1877 in New York by engineer Birdsill Holly. Within just three years, the system had expanded to cover 5 kilometers, including heating for factories. Today, New York still boasts the largest district heating system in the United States, providing heat for residential buildings, restaurant kitchens, laundromats, and even absorption cooling systems.
In 1903, Copenhagen, Denmark, established its first waste-to-energy plant, producing steam that was then used for district heating, marking a significant development in the use of renewable energy for urban heating solutions.[3]
On December 1, 1903, the waste-to-energy plant in Copenhagen began operation, generating heat in the form of steam. This heat was then utilized to supply energy to several newly constructed buildings, including a hospital, a municipal building, an orphanage, and a home for the poor. This innovative use of waste-derived steam for district heating marked an important step in the integration of sustainable energy solutions in urban infrastructure.[3]
Trends in District Energy
The district energy sector is currently experiencing a major transformation, influenced by several key trends that are reshaping the way energy is sourced, distributed, and consumed. These developments reflect a broader shift toward sustainability, energy security, and efficiency in response to both global challenges and technological advancements.
1) The Shift from Single-Source to Multi-Source Systems
One of the most significant trends in the district energy sector is the move from single source to multi-source energy systems. This change has been accelerated by the need for energy security, particularly in the wake of geopolitical crises such as the conflict in Ukraine. These events have highlighted the risks of relying on a single energy source, such as gas imports from Russia, making energy independence a critical priority for many countries. Multi-source systems now incorporate a diverse mix of energy solutions, including:
- renewable energy,
- energy digitalization,
- improved energy efficiency,
- ensuring more resilient and sustainable energy supply chains.
2) The Decarbonization Shift
The second trend driving change in district energy is the global shift towards decarbonization. As countries and industries work to meet their climate targets and reduce carbon emissions, the district energy sector is undergoing a significant transformation. This shift is leading to the widespread adoption of low-carbon technologies and increased integration of renewable energy sources within district heating systems. Decarbonization is not just a policy goal but a key driver of:
- innovation and investment in the energy sector,
- prompting new developments in energy production,
- distribution,
- consumption.
3) Electrification of the Heating Sector
The third major trend involves the electrification of the heating sector, which plays a crucial role in enabling the reuse of waste heat. This transition is essential for increasing the efficiency of district heating systems, as it allows for the integration of waste heat from industrial processes, data centers, and other sources. A critical condition for achieving this is the reduction of temperature in the district heating grid. By lowering the operating temperature, district systems can more effectively capture and utilize waste heat, contributing to overall energy savings and supporting the broader goal of reducing carbon emissions.
These three trends—moving to multi-source systems, driving decarbonization, and electrifying the heating sector — are not only transforming district energy systems but also reflecting a broader shift in global energy strategies. As countries strive to secure a sustainable, resilient, and low-carbon energy future, the evolution of district energy is proving to be an essential component of this transition. The ability to harness waste heat, integrate renewable energy, and improve energy efficiency will be key to achieving the energy goals of the future.
The Role of Digitalization in Optimizing District Energy Systems
As district energy systems become increasingly complex, the need for end-to-end optimization has never been more critical. Manual optimization of individual network segments is not only inefficient but often impractical. This raises an important question: what are the tangible benefits of digitalization in this context?
Benefits of Digitalization in the District Energy Sector
Digitalization is pivotal in addressing the current challenges facing the energy sector, including the shortage of skilled workforce, the diversification of heat planning, and the complexities of network design. District energy systems, which are essential for decarbonizing the heating and cooling sectors, require advanced solutions to effectively integrate renewable energy and waste heat sources. To enable this transition, a fundamental prerequisite is the seamless connectivity of all relevant data — encompassing demand distribution, energy production, weather forecasts, and other critical parameters. By collecting and analyzing this data, valuable insights can be unlocked, enabling the application of advanced technologies like machine learning to enhance operational efficiency.
As production systems become more complex and renewable energy sources exhibit increased rigidity, digitalization offers the flexibility needed to maintain smooth operations. Modern district energy systems are far more sophisticated than their predecessors, now integrating diverse renewable energy sources, waste heat recovery systems, and large-scale heat pumps. These systems often incorporate numerous smaller sources — five or more — into the network, increasing operational complexity. In this environment, digitalization and advanced machine learning play a crucial role in managing these complexities effectively.
Optimizing Heat Storage and Enhancing System Efficiency
District energy systems also hold significant potential for sector coupling, particularly through the efficient use of heat storage. For example, surplus green electricity can be efficiently converted into warm water, thus reducing waste and optimizing energy use. Furthermore, digitalization plays a vital role in the design, optimization, and expansion of energy networks, particularly by enabling real-time adjustments to temperature and pressure. This capability facilitates the seamless integration of renewable and waste heat sources, while simultaneously lowering network temperatures. Lower temperatures reduce heat losses, improving system efficiency and enhancing the coefficient of performance (COP).
Machine learning-driven network technologies can leverage historical load profiles, demand data, and weather conditions to determine the optimal balance between temperature and flow at any given moment. For individual buildings, artificial intelligence (AI) can assess energy characteristics and determine the most efficient secondary supply temperature, based on both internal and external conditions. This results in improved occupant comfort and optimized energy efficiency, reducing overall demand and operational costs.
Facilitating Load Flexibility for Renewables Integration
Another significant advantage of digitalization is its ability to provide load flexibility, which is essential for the integration of renewable energy and waste heat sources. By incorporating load flexibility into both production and distribution processes, energy usage can be optimized by utilizing buildings as thermal storage. This capability allows for load shifting, which helps to mitigate energy peaks during high-demand periods, such as in the morning. By balancing demand more efficiently, digitalization enables a more responsive and resilient energy system, supporting the wider integration of renewable energy sources and reducing reliance on non-renewable backup systems.
In conclusion, digitalization is at the heart of the transformation taking place within the district energy sector. Through advanced data connectivity, machine learning, and real-time optimization, digital technologies enhance operational efficiency, improve system flexibility, and enable the integration of renewable and waste heat sources. As energy systems continue to evolve, digitalization will be essential in unlocking new efficiencies, optimizing energy use, and supporting the transition to a sustainable, low-carbon future.
Źródła
[1] https://www.whyenergyefficiency.com/solutions/allsolutions/the-worlds-largest-
untapped-energy-source-excess-heat P8
[2] https://guidetodistrictheating.eu/about/what-is-district-heating/
[3] https://kojenturk.org/tr/bolgesel-isitma-nedir-7
[4] https://vb.nweurope.eu/media/11053/case-to-energy-consumers_web.pdf P7
Autor: MSc. Eng. FATİH KARACA
09.01. 2025, Warsaw
