01 July 2024
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District Heating feature by Ulrik Vadstrup, Regional Europe Segment Sales Manager HVACR and Torben Poulsen, Business Development Manager, Drives and Pumps, at ABB Drives
As the world strives towards a more sustainable future, district heating schemes are shifting from traditional fuel-based models to incorporate largescale heat pumps. This evolution not only represents a technological leap but also a commitment to environmental stewardship and energy efficiency. Unlike their fossil-fuelled predecessors, heat pumps offer a startling enhancement in energy efficiency, as shown by their impressive Coefficients of Performance (COP). Simply put, these systems are proficient in generating multiple units of heat for every unit of electricity consumed, drastically reducing the dependence on conventional, carbon-heavy energy sources. By tapping into renewable resources, such as excess heat, ambient air, or water sources, heat pumps can minimize the carbon footprint of district heating systems. They have the versatility necessary for meeting diverse heating requirements, from individual buildings to entire city blocks, charting the course for a more sustainable approach to urban planning and energy usage.
The impact of harmonics
However, while the increasing adoption of heat pumps is a promising development, it brings to light the infrastructural challenges of harmonics and power quality in the electrical grid. It is important to note that the widespread electrification of various aspects of society also contributes to the total harmonic distortion in the power system. The increased use of devices such as electric vehicle chargers, domestic heat pumps, LED lighting, and a variety of consumer electronics, introduces additional sources of harmonics. These devices, like variable speed drives (VSDs), have their own non-linear characteristics that cumulatively affect the quality and stability of the electrical grid. These harmonics can interfere with the stability and efficiency of the grid, potentially impacting other electrical consumers and causing broader network issues. Heat pumps, particularly large-scale installations, often employ VSDs to regulate their operation. While VSDs offer high precision in control and contribute to energy savings, their non-linear load characteristics can also introduce significant harmonic distortions into the power system.
Harmonics are electrical frequencies that can distort the fundamental waveform of the electrical supply, leading to a multitude of problems. For instance, they can cause overheating in electrical equipment, leading to premature wear and reduced lifespan. In addition, they can lead to the malfunctioning of sensitive electronic equipment, increase operational costs, and in severe cases, may result in system outages. With the grid connected to a diverse collection of residential, commercial, and industrial users, the harmonics produced by large-scale heat pumps can ripple across the network and deteriorate the power quality experienced by numerous consumers.
Furthermore, harmonics can resonate with the natural frequencies of the grid components, amplifying the distortion effects and leading to grid instability. This could result in the tripping of protection devices, loss of service, and costly damage to infrastructure. Thus, it is critical to conduct thorough harmonic analysis during the planning phase of integrating heat pumps. Techniques such as active and passive harmonic filtering, and the use of ultra-low harmonic drives, can be employed to mitigate the effects of harmonics and protect the grid infrastructure.
Collaboration is the key in project planning
Nevertheless, common mistakes are made during the conceptual stages of heat pump projects. A frequent oversight is underestimating the total harmonic distortion that will be introduced into the grid once the heat pump is operational. Planners may not fully account for the cumulative effect of the heat pump when combined with existing grid loads, leading to harmonic levels that exceed acceptable thresholds. In countries like Denmark, stringent technical regulations are in place, setting firm limits on the allowable quantity of harmonics. There is also a tendency to overlook potential grid expansions or upgrades in the vicinity, which could compound the harmonic issues in the future if not addressed during the initial design phase.
Additionally, a lack of communication between project developers, grid operators, and local authorities can result in the absence of a clear strategy to tackle harmonics. When stakeholders fail to collaborate from the outset, it often results in costly post-installation fixes. For instance, retroactively implementing harmonic filters or revising the grid infrastructure to accommodate the heat pump's electrical demands can significantly inflate project costs and timelines.
To address these challenges, project developers should prioritize communication with grid operators early on to determine harmonic standards and grid capacity. A holistic approach, factoring in the heat pump's impact on the electrical system, from generation to the point of end use, is necessary to avoid these pitfalls. Effective planning, combined with advanced ultralow harmonic technologies and proactive collaboration, is the key to maintaining grid stability while embracing the benefits of large-scale heat pumps in district heating systems. This will ensure that every watt of green electricity is put to effective use.
The cornerstone of these advanced district heating systems is the adoption of ultra-low harmonic drives, which assure the operational integrity of the heat pumps and the network they operate in. These drives mitigate the electrical disturbances and harmonics, thereby enhancing the system's efficiency and durability. While ultra-low harmonic drives present a higher initial investment, their long-term benefits are manifold. They deliver superior energy optimization, which translates into considerable cost savings over the heat pump's full lifespan.
Strategic use of technology at the design stage
Redundancy is also a critical consideration in these systems. It is common practice to install multiple pumps and compressors to ensure that the system can maintain its function even when individual components are offline for maintenance or if an unexpected failure occurs. The necessity to continue heat delivery cannot be overstated, especially during peak demand or in critical infrastructure such as hospitals or schools.
From a practical viewpoint, implementing large-scale heat pumps within a district heating network requires attention to both the load demands and the local grid's capacity. This often involves installing additional transformers and grid infrastructure to cater to the increased load, which may be measured in megawatts for larger projects. Therefore, great care must be taken to design these components to handle the maximum expected load without excessive oversizing, thereby maintaining economic viability.
Moreover, engaging with local grid operators earlier on in the planning process is essential to determine the feasibility of adding large-scale heat pumps to the region's energy mix. They can provide valuable insights into the availability of renewables, the capacity of the existing grid, and the necessary upgrades to accommodate these new energy consumers.
Conclusion
In conclusion, large-scale heat pumps signify a transition to energy-efficient district heating networks that capitalize on renewable resources and optimize power consumption. When created from renewable sources, energy becomes more and more valuable - we should use it wisely and manage it with great care.
This change, while challenging, is underpinned by detailed planning, stakeholder collaboration, and the strategic use of technology like ultra-low harmonic drives, ensuring grid stability and efficient heating.
By drawing from the wealth of experience in regions where such systems are already operational, like Scandinavia, and fully understanding the complexity involved in integrating large scale heat pumps into the grid, other regions around the world can embark on a similar transition. The collective effort in research, development, and implementation of these systems will, in turn, foster a consistent, reliable supply of sustainable heat that will benefit the environment and future generations – all while minimizing harmonic distortion in the grid.
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Case study: Esbjerg's journey to sustainable urban heating
Esbjerg, a Danish port city, has set a remarkable example in transforming its district heating system to combat climate change. The city now boasts the world's most prominent seawater heat pump system that uses CO2, which is safer for the environment, as the refrigerant. This initiative was driven by DIN Forsyning, the local utility company, aligning with their goal to stop using fossil fuels for generating heat. With the closure of the old coal-fired power plant, they have adopted an eco-friendlier approach that cuts down on the energy needed for heating by half. ABB has been a crucial player in this transformation, delivering a complete set of electrical, control, and instrumentation equipment, including efficient motors and VSDs. This technology ensures that the new heating system runs smoothly and integrates well with renewable power sources like the offshore wind turbines in the North Sea. This collaboration has set Esbjerg on a path to becoming carbon neutral by 2030. The city's experience shows how detailed planning and working together can lead to successful, sustainable heating for urban areas.
