DBDH publishes Hot Cool, but the main business is helping cities or regions in their green transition. We will help you find specific answers for a sustainable district heating solution or integrate green technology into an existing district heating system in your region – for free! Any city, or utility in the world, can call DBDH and find help for a green district heating solution suitable for their city. A similar system is often operating in Denmark, being the most advanced district heating country globally. DBDH then organizes visits to Danish reference utilities or expert delegations from Denmark to your city. For real or virtually in webinars or web meetings. DBDH is a non-profit organization - so guidance by DBDH is free of charge. Just call us. We'd love to help you district energize your city!
NO. 5 / 2026
INTERNATIONAL MAGAZINE ON DISTRICT HEATING AND COOLING
DISTRICT HEATING FROM VISION TO INFRASTRUCTURE
Sign up to receive Hot Cool
Contents
THIS EDITION'S FOCUS THEMES
6 4
Editorial CONNECTING EUROPE’S CLEAN ENERGY By Dan Jørgensen
FROM VISION TO INFRASTRUCTURE
Network Sizing: A PLANNING PHILOSOPHY, NOT JUST A TECHNICAL CALCULATION By Alexander Schou and Rune Tonell
TECHNOLOGY
10
Lessons from Albertslund Utility, Denmark: LOW-TEMPERATURE DISTRICT HEATING AS AN OPERATIONAL TOOL By Pernille Salomonsen
PROCESS HEAT
14
IMPROVING OPERATIONAL EFFICIENCY THROUGH ON-SITE CALIBRATION OF FLOW METERS By Ulrich Müller
20
BETTER DECISIONS, FASTER TRANSITION By Mathias Terp Munck, Ole Andreassen Kofoed, and Hanne Kortegaard Støchkel
24
Beyond coal: PEC BYTOM’S ROADMAP TO GREENER DISTRICT HEATING BY 2050 By Lars Gullev and Slawomir Kaminski
29
Member company profile: INGENIØR HUSE THE ENERGY SYSTEM OF THE FUTURE REQUIRES A HOLISTIC APPROACH
Cover image created with AI assistance.
DBDH Stæhr Johansens Vej 38 DK-2000 Frederiksberg Phone +45 8893 9150
Editorial team: Lars Gullev, Editor in Chief Linda Bergholt Bertelsen, Managing and Coordinating Editor Morten Jordt Duedahl, Strategy and Content Editor
Total circulation: 5.000 copies in 74 countries 10 times per year
Graphic layout Kåre Roager, kaare@68design.dk
info@dbdh.dk www.dbdh.dk
ISSN 0904 9681
NEED A DISTRICT HEATING EXPERT ?
KNOWS ONE! Reach out at dbdh.org
the Go-to-Partner for District Energy
Editorial CONNECTING EUROPE’S CLEAN ENERGY
By Dan Jørgensen, European Commissioner for Energy and Housing
Energy should provide comfort and security - not uncertainty. Yet today, too much of Europe’s heating and cooling still depends on imported fossil fuels, exposing households and businesses to volatile prices and geopolitical risks. Europe already has the clean heat resources and technologies to change this; now we must connect them through smarter, integrated heating and energy systems.
There is no denying the scale of the challenge. Heating and cooling account for around half of the European Union’s energy demand and more than a quarter of its greenhouse gas emissions. For European households, the challenge is even more pronounced: in 2023, space and water heating represented almost 78% of the final energy consumption, with most of this demand still being met by fossil fuels.
The reality is clear, but so is our response: we need cleaner heating and cooling in Europe. This is about much more than cutting emissions. It is about making energy more affordable for citizens, cities, and companies. It is about strengthening Europe’s energy security and boosting our competitiveness by making better use of local energy resources.
4
HOTCOOL no.5 2026
This potential will not disappear as our economy electrifies. On the contrary, the growth of data centers and the increasing demand for cooling will create new sources of recoverable heat. The question is how we can connect these sources with nearby demand in an economically viable and technically efficient way. Geothermal energy represents another major opportunity. It provides reliable, locally produced heat around the clock and can complement electrification and other renewable energy sources. Yet Europe still exploits only a small share of its geothermal potential. Better geological data, targeted technical assistance, risk-sharing mechanisms and improved access to finance can unlock much greater deployment across the Union. From potential to deployment The technologies that we need already exist. And in many cases, they are made in Europe. The EU is home to world- leading companies producing the technologies that make district heating and cooling systems possible, from heat pumps to smart network solutions. Therefore, by rolling out these systems, we are not only investing in cleaner energy, but also in European innovation, manufacturing, competitiveness, and jobs. The challenge now is deployment. Electricity and heating systems are still too often planned separately, even though they increasingly depend on each other. Too many projects are delayed by lengthy permitting procedures and financing constraints, as well as fragmented planning and insufficient coordination between local authorities, network operators, industry and investors. Removing these barriers is now one of Europe’s most important tasks. That is why the Commission will present a European Heating and Cooling Strategy, developed in close coordination with the Electrification Action Plan. Together, these initiatives will accelerate the deployment of clean district heating and cooling, strengthen the integration of electricity and heating systems, unlock the potential of waste heat and geothermal energy, and improve access to financing for strategic investments. They will also encourage stronger cooperation between cities, utilities, industries, and data centers, ensuring that local energy resources are used where they create the greatest value.
Delivering the clean transition of the heating and cooling sector is one of Europe’s biggest energy opportunities and a key priority for the Commission. This is where district heating and cooling come in. District heating: Connecting Europe’s energy system District heating and cooling can become a cornerstone of Europe’s clean energy transition. Unlike individual heating and cooling technology, a district heating and cooling network connects homes and businesses with different parts of the energy system. It enables the integration of clean heat sources and the recovery of waste heat. It also supports electrification, for example, by providing valuable flexibility to electricity networks. Today, around 19,000 district heating systems operate across the European Union. Together they serve around 80 million citizens through almost 200,000 km of networks and already provide around 13% of the EU’s heating supply. But this is only the tip of the iceberg – because the next generation of district heating systems can do much more. They can integrate large-scale heat pumps, geothermal energy, renewable heat, and sustainable biomass. They can also utilise recovered industrial heat and waste heat from data centers. At the same time, they can interact dynamically with the electricity system by absorbing surplus renewable electricity, reducing curtailment, and providing flexibility during periods of peak demand. This integrated approach benefits the entire energy system. Sweden already demonstrates what is possible. There, modern district heating provides flexibility equivalent to around 10 GW of peak electricity capacity. This illustrates why heat and electricity should increasingly be considered complementary energy carriers, as well as interconnected elements of local energy systems. Better integration between electricity and heating systems can reduce the need for costly grid investments while improving the resilience and efficiency of Europe’s energy infrastructure. Turning wasted heat into a valuable energy resource Europe is rich in clean heat resources. The challenge is not their availability; it is rather connecting them to where they are needed. One of the greatest opportunities is waste heat. Every day, factories, wastewater treatment plants, supermarkets and data centers release enormous amounts of usable heat into the atmosphere. Available estimates suggest that waste heat corresponds to almost 30% of total EU energy use, equivalent to nearly half of all fossil fuel consumption. Not all of this energy can be recovered in practice, but the potential remains substantial. Waste heat from industrial processes, commercial buildings and data centers could provide a stable and local source of energy for homes, businesses, and public buildings connected to heat networks. With the Energy Efficiency Roadmap, the Commission calls for waste heat recovery to cover at least 11% of EU heat demand.
Europe already has the technologies. Europe has the industrial capacity. Europe has the clean heat resources.
Now we must connect them. By doing so, we can lower energy bills, strengthen our energy security, support the European industry, and build a heating system that is cleaner, smarter, and truly made for Europe’s future.
For further information please contact: paul@steenengine.com
5
www.dbdh.dk
Network Sizing: A PLANNING PHILOSOPHY, NOT JUST A TECHNICAL CALCULATION
By Alexander Schou, Project Manager, Energy Plants and Infrastructure, COWI and Rune Tonell, Leading Project Manager, Energy Transition Advisory, COWI
6
HOTCOOL no.5 2026
All experience and empirical data point the same way: go big on transmission pipes and stay lean on distribution pipes.
The last term in the equation expresses today’s value of the cost of upgrading at a later point in time. It takes the cost of upgrading to the larger dimension (civil works plus pipe), less the scrap value of the new pipe under straight-line depreciation, weights this by the probability that the upgrade is actually needed, and discounts the result back to present value over the number of years until the upgrade would occur. The nominal pipe costs are assumed to remain unchanged throughout the entire service life. Scenario B – Sizing the backbone for the future The cost of sizing the backbone for the future C future , today, can be expressed as C future = C other(D 1 ) +C pipe(D 1 ) Future-proof sizing is the better bet whenever C future is smaller than C tight – that is, whenever: C other(D 1 ) + C pipe(D 1 ) < C other(D 0 ) + C pipe(D 0 ) + p · —---———————— other(D 1 ) pipe(D 1 ) C + C - S(t) (1 + r) t
District heating pipes are built to last 50 years or more. Over that time, almost everything behind the original sizing decision can change. Neighbourhoods grow, buildings become better insulated, the service might expand, supply temperatures might decrease, and new heat sources appear in places nobody had mapped when the first pipes went into the ground. Separate local networks may even end up being connected to share production & storage capacity and spread risk. A transmission pipe sized “correctly” for today’s conditions is, almost by definition, sized for a system that will look very different in the future. Thinking long term means accepting that some pipes get paid for before their own numbers add up – because their real value isn’t in today’s business case, but in the option they create: to densify, expand, connect, and reach better heat sources when the moment comes. Holistic Thinking Denmark’s success with district heating is usually credited to its technology, but part of the story is this: at its best, heat planning has treated whole cities as a single continuous project, with the backbone – the transmission pipes – sized for where the system is heading, not only for where it stands today.
Below, we apply this equation to a concrete example using figures from a realized COWI reference project.
A Real-World Example
Consider a 2 km transmission line, built two ways.
Scenario A uses a DN150 twin pipe – a single insulated casing carrying both the supply and return pipes – sized tightly to today’s load.
When building a new network, there are two basic options for the backbone:
Scenario B sizes the same transmission line one step larger, DN200, to match the long-term plan.
Scenario A – size it “tightly” to today’s needs and upgrade it later if needed
From a specific COWI reference project in a sub-urban area, the pipe supply cost C pipe for a DN150 is €395/m, while the remaining civil works and installation costs C other amount to €1,630/m. This shows that the cost driver is not the pipe itself; it is the excavation, soil disposal, backfilling, reinstatement, traffic management, welding, and testing. In this example, these costs constitute approximately 80% of the total transmission line costs. It should be noted that civil works and installation costs C other for a district heating pipe are highly dependent on whether the area is rural or urban. In a rural area, civil works and installation costs typically make up a much smaller share than 80%, since rural areas tend to be less congested with existing underground infrastructure, can have unpaved surfaces, and benefit from cheaper traffic management, among other factors. For the same reference project, the pipe supply cost C pipe for a DN200 is €587/m, i.e. a unit cost premium of about 49% more for a DN200, compared to the DN150. The interesting point, and the key point here, is that the remaining civil works and installation cost C other for a DN200 amounts to only €1,697/m, equivalent to an increase of just 4%.
Scenario B – size it for the long-term plan from the outset
The central question is simple: which option is cheaper over the life of the asset?
Scenario A – Sizing the backbone tightly and upgrading later if needed
In general, the cost of a pipe can be split into two parts: C pipe the cost of the pipe itself (supply, fittings, valves, joints), and C other the cost of everything else (civil works, excavation, soil disposal, backfilling, reinstatement, traffic management, welding, jointing, testing). If the utility sizes tightly now and later has to upgrade – with probability p , after t years, at discount rate r – the expected cost of sizing the backbone tightly and upgrading later if needed C tight can be expressed as: C tight = C other(D 0 ) + C pipe(D 0 ) + p · —--————————— other(D 1 ) pipe(D 1 ) C + C - S(t) (1 + r) t Where D 0 is today’s (“tight”) dimension and D 1 is the larger and upgraded dimension. S(t) = (C other(D 1 ) + C pipe(D 1 ) )· —t - L , with L being the service life of the pipe. Put simply, the entire formula tells you that you pay for the tight-dimensioned pipe now, plus a bit extra to cover the risk that you’ll have to upgrade it to a larger pipe later.
7
www.dbdh.dk
yr \ prob 20% 30% 40% 50% 60% 70% 80% 90% 100% 2 € 306,934 € 719,157 € 1,131,380 € 1,543,603 € 1,955,826 € 2,368,049 € 2,780,272 € 3,192,495 € 3,604,718 4 € 225,578 € 597,123 € 968,668 € 1,340,213 € 1,711,758 € 2,083,304 € 2,454,849 € 2,826,394 € 3,197,939 6 € 151,396 € 485,850 € 820,304 € 1,154,759 € 1,489,213 € 1,823,667 € 2,158,121 € 2,492,575 € 2,827,029 8 € 83,794 € 384,447 € 685,100 € 985,753 € 1,286,406 € 1,587,058 € 1,887,711 € 2,188,364 € 2,489,017 10 € 22,224 € 292,092 € 561,960 € 831,828 € 1,101,696 € 1,371,564 € 1,641,432 € 1,911,300 € 2,181,168 15 (€ 108,513) € 95,986 € 300,486 € 504,985 € 709,485 € 913,984 € 1,118,484 € 1,322,983 € 1,527,483 20 (€ 211,409) (€ 58,357) € 94,694 € 247,746 € 400,798 € 553,849 € 706,901 € 859,952 € 1,013,004 30 (€ 354,760) (€ 273,384) (€ 192,009) (€ 110,633) (€ 29,257) € 52,119 € 133,495 € 214,871 € 296,247 Table 1 – Expected lifetime CAPEX advantage of oversizing a 2 km backbone with 1 dimension (from DN150 to DN200), as a function of years until upgrade and probability that the upgrade is needed. Green = oversizing wins. Red = tight-sizing wins. The assumed discount rate is 3.5%, and the service life is 60 years.
The Upper Limit of the Window Of course, there is an upper limit. The example in this article illustrates the expected benefit of stepping up one pipe dimension but jumping four or five dimensions introduces a different set of problems entirely. Beyond being clearly unnecessary, available underground space also imposes a physical constraint. Finally, if the diameter is too large, low- demand periods can reduce flow velocities and cause water stagnation, increasing heat losses. On the other hand, heat loss scales with the pipe’s diameter, while the energy it carries scales with the diameter squared. So, the relative heat loss per MWh delivered actually falls as diameter grows, provided the pipe is well loaded. Oversizing only creates a heat-loss penalty while the pipe is still lightly loaded – in the early years before anticipated demand arrives. That is a transitional cost, not a permanent one. The Lower Limit of the Window Choosing too small a diameter, on the other hand, creates trouble much faster on the hydraulic side. Halving the diameter roughly quadruples the velocity. Pressure loss is hit even harder. By the Darcy–Weisbach formula, it scales roughly with the fifth power of the diameter. Go just one size too small, and pumping costs explode. This is the main reason behind the usual design limits of around 100 Pa/m and velocities under roughly 2 m/s – and why undersizing bites so quickly. Given the above, it is reasonable to assume that going up one or two dimensions does not raise OPEX – on the contrary, provided the pipe is well loaded, the relative heat loss per MWh delivered and pumping costs fall. For this reason, a CAPEX-only cost assessment, as presented in this article, should be sufficient to support a Final Investment Decision (FID). Making the Backbone Affordable Today Long-term thinking requires an investment logic that openly accepts that some pipes are paid for ahead of their local business case, because their value lies in the optionality they
This means the weighted-average extra cost of stepping up from DN150 to DN200 is only app. 13% in this case. In return, that same step-up delivers an increased capacity of app. 69% – calculated as a simple ratio between the cross-sectional areas – assuming no changes in the allowed pressure gradient or velocity of the water. Whether scenario A or B is the preferred solution financially, of course depends on the probability p that an upgrade is needed and the number of years t before it happens. For this example, T able 1 a bo ve shows the calculations. The tendency is clear: tight sizing only comes out ahead when the probability of needing more capacity is low, or when the upgrade is decades away. The table clearly shows that sizing tightly and revisiting the pipe later can easily end up being the most expensive choice – making the case for holistic planning and modest future-ready sizing clear. In addition, upgrading later means reopening a street to replace a functioning transmission line. It can disrupt supply to existing customers and delay the development, additional heat demand, or new heat source that the upgrade was meant to enable. To keep the calculation simple, these impacts are deliberately omitted. However, this does not mean every pipe should be sized for future capacity. Local distribution pipes and the connections to individual buildings are the opposite case. They are cheap and fast to install, so there is little (if any) reason to build in spare capacity up front; they can simply be extended, street by street, as new customers connect. A Practical and Technical Window The main message of this article is: “Build transmission pipes as large as reasonably possible and distribution pipes as small as practically possible”. That framing is deliberately exaggerated.
8
HOTCOOL no.5 2026
avoiding expensive constraints tomorrow. And a 69% increase in capacity might well be worth an extra investment cost of only 13%. When it comes down to it, it’s a matter of probabilities. No one knows exactly what the future holds! The graph below shows the same relative break-even pattern as Table 1 – each line is one probability level, sloping down as the upgrade horizon lengthens. If a line falls below the dashed break-even line (y = 0%), tight sizing becomes the cheaper choice. In all other cases, stepping up one dimension is the cheaper choice.
create for the system as a whole: the ability to densify, expand, connect, and reach better heat sources when the opportunity arises. None of this works if each neighbourhood connection must justify its own future-ready transmission line in isolation. It works when a city-wide heat plan treats the urban area as a single project delivered in phases, with a backbone sized to the long-term plan. As new neighbourhoods connect, they can then pay their share of the cost instead of placing the full burden on whoever happens to build first. COWI’s experience is that tight dimensioning of backbones for new district heating networks often becomes more expensive over time – not only in Denmark, but everywhere. Future-ready sizing is therefore not about overspending today; it is about
For further information please contact: Alexander Schou, axsc@cowi.com Rune Tonell, rune@cowi.com
Figure 1 - Break-even pattern. The graph uses the same underlying assumptions as in Table 1: a sub - urban project area, a weighted-average extra cost of stepping up one dimension of 13%, a service life of 60 years, and a discount rate of 3.5%.
9
www.dbdh.dk
Lessons from Albertslund Utility, Denmark: LOW-TEMPERATURE DISTRICT HEATING AS AN OPERATIONAL TOOL
10 HOTCOOL no.5 2026
By Pernille Salomonsen, Energy and Development Consultant, Albertslund Municipality
For district heating (DH) utilities planning a transition to lower temperatures, Albertslund offers a broader lesson: the benefits extend well beyond reducing heat loss. The transition can also be used to redesign the network for better day-to-day operation.
Figure 1. Over several years, Albertslund utility has lowered flow temperatures in large parts of the network and installed around 20 local shunt and substation solutions.
More than lower temperatures Low-temperature DH is often presented as an efficiency measure. When the water in the network does not have to be as hot, it loses less heat on the way to the consumer. Lower temperatures can also improve the heat pump performance and make it easier to integrate low-grade sources such as industrial surplus heat, supermarket refrigeration, data centres, wastewater, and geothermal energy. Those benefits have been an important part of the transition at Albertslund Utility. Over several years, the utility has lowered flow temperatures in large parts of the network and installed around 20 local shunt and substation solutions. The units
By combining lower temperatures with smaller hydraulic zones, local shunt and booster units, and systematic work in customer installations, Albertslund Utility has created a DH network that is easier to control, maintain, and troubleshoot, with fewer disturbances for consumers. The case is relevant far beyond Denmark because many utilities face the same question: how can an existing DH network be prepared for new heat sources and lower temperatures without compromising security of supply? Albertslund's answer is practical rather than prescriptive: start with the buildings and the data, divide the network into manageable steps, and treat low-temperature operation as an operational program, not only as a technical target.
11 www.dbdh.dk
A practical route to lower-temperature operation The Albertslund experience suggests a step-by-step approach. Start by using network data to identify the buildings and areas that determine temperature requirements. Smaller shutdowns and fewer disturbances The value of zoning becomes very clear when work is carried out on the DH network. In a traditional setup, maintenance or pipework may require shutting down a large section. In Albertslund, the zone structure often makes it possible to isolate a smaller area while keeping the rest in operation. Local units can help maintain pressure and circulation for longer, even when work is taking place elsewhere. For consumers, that means fewer noticeable interruptions. In favourable summer conditions, a short intervention may go unnoticed. For the utility, the work can be planned with more flexibility and less operational risk. Finding faults faster The same principle improves fault-finding. If there is a leak or sudden pressure loss, operators can isolate smaller areas, rebuild pressure step by step, and observe how the network responds. The search area becomes smaller, fewer consumers are affected, and the utility can shift from a broad, network- wide reaction to a structured diagnosis. In this sense, zoning is both a network design principle and a troubleshooting tool. A more resilient network DH networks depend on pumps, control systems, and electricity. A local electrical disturbance or voltage drop can therefore affect more than the immediate area around a station. Albertslund's distribution structure has helped reduce that vulnerability. A disturbance at one location does not necessarily propagate in the same way, and local shunt or booster units may help sustain conditions in parts of the network when a larger station is affected.
support temperature, pressure, and circulation closer to end- users, so the entire main network does not have to operate at the highest requirement found anywhere in the system. But the experience from Albertslund also points to something less often discussed: low-temperature DH can change how a network is operated. In Albertslund, the move towards lower temperatures has gone hand in hand with a more zoned network. That has proven valuable in day-to-day operations. Operators can respond locally instead of changing conditions for every consumer. This provides more options during normal operation, planned work, and unexpected events. Why zones matter A DH network can be compared to a road system. If all traffic depends on a few main roads, a single problem can affect a wide area. If the system has smaller, connected sections, it becomes easier to isolate a problem, redirect flow, and keep the rest of the system running. The same logic applies hydraulically. Local shunt stations support temperature and pressure closer to consumers. As a result, the main network does not always have to operate at the same high level everywhere. If one area needs a little more heat or pressure, this can often be handled locally instead of adjusting the entire network. For operators, this creates a different kind of flexibility. The network is no longer treated only as one large system controlled from a few central points. It becomes a set of smaller zones that can be managed more precisely. This does not mean creating isolated ‘islands’ with no operational relationship. The value lies in understanding the interfaces between zones: where water enters, how pressure is maintained, which valves define the zone, and how an intervention in one area affects neighbouring areas. A clear hydraulic overview is therefore essential.
Figure 2. Step-by-step route infographic illustrating Albertslund’s approach to lowering district heating temperatures.
12 HOTCOOL no.5 2026
A lesson for other district heating companies For utilities considering lower temperatures, the key message from Albertslund is to broaden the objective. Do not treat the project solely as an exercise in reducing a temperature setpoint. Use it as an opportunity to examine the network's operational architecture. Begin with the consumers and the data. Find the buildings and hydraulic conditions that define the present limit. Choose a zone where learning is possible, install the necessary monitoring, and agree in advance how success will be measured. Include heat loss, return temperature, and pumping energy, but also track interruptions, time spent locating faults, the number of consumers affected by maintenance, and the operator's ability to restore normal conditions. Then scale in stages. The right solution may include local shunts, boosters, new valves, building-level improvements, or changes in control strategy. The exact combination will vary, but the principle remains: solve local needs locally where this avoids imposing unnecessarily high conditions on the whole network. Most importantly, involve operations from the beginning. The people who run the network know where pressure is fragile, where consumer complaints arise, and which interventions are difficult. Their knowledge is essential to designing zones that work outside the hydraulic model. Low-temperature DH is therefore not only about efficiency or future heat sources. When combined with deliberate zoning and strong operational practice, it can create a network that is easier to adapt, more precise to operate and more resilient when conditions change. That is the inspiration Albertslund can offer internationally: the temperature transition can also be an operational transformation.
Distribution alone is not enough, however. Each local station introduces equipment that must be inspected, maintained, and understood. Utilities should consider backup power, safe fallback modes, remote communication, spare parts, and access during emergencies. They should also test scenarios rather than assume the system will respond as intended. What happens if a pump stops? Which valves should be operated? How quickly will pressure fall? Which consumers must be prioritised? Resilience is created through both physical design and rehearsed operational practice. Lessons from international dialogue Albertslund has hosted many visitors from utilities, municipalities and energy organisations outside Denmark. Their questions reveal that the international relevance is not limited to a particular Danish temperature level. Visitors commonly want to know how an existing system can be changed while remaining in service, how customer installations are brought into the process, how operators learn to manage several local units, and how the business case can include reliability and avoided disruption as well as reduced heat loss. One recurring experience from these visits is that the technology is usually easier to explain than the transition process. A shunt station, pump, or control valve can be shown in a diagram. The more difficult part is coordinating network data, building improvements, investment planning, communication, and operational training over several years. The visits also underline that no universal blueprint exists. Dense urban networks, smaller towns, different building standards, and different heat sources require different zone sizes and temperature paths. What can be transferred is the method: identify local constraints, create measurable zones, reduce temperatures in controlled steps, and use operational feedback to decide the next move. International guests often bring different regulatory and climatic conditions, but the core management challenge is recognisable: progress must be ambitious enough to support decarbonisation and cautious enough to preserve customer trust. More flexibility, but not less responsibility A zoned low-temperature network is not automatically simpler to operate. It may be more demanding because operators must understand how pumps, valves, controls, pressure, and local units interact. More measurement points generate more information, but also require data quality, alarm management, and clear responsibility. The gain is not that every task becomes easier. The gain is that the utility has more options. The network can be controlled more precisely, disturbances can be contained, and maintenance can be organised around smaller operational units. To realise those benefits, utilities need competent staff, documented procedures, and a culture in which operating experience feeds back into planning and design.
For further information please contact: Pernille Salomonsen, ppg@albertslund.dk
13 www.dbdh.dk
IMPROVING OPERATIONAL
EFFICIENCY THROUGH ON-SITE CALIBRATION OF FLOW METERS
By Ulrich Müller, OPTOLUTION Messtechnik GmbH
What if a 1% measurement deviation could affect a utility’s annual energy balance by more than €100,000? Laser-based on-site calibration allows district heating operators to verify large flow meters under real operating conditions - without shutting down the plant. Drawing on more than 240 field calibrations, this article shows how accurate measurement data can strengthen billing, efficiency, optimisation, and operational confidence.
14 HOTCOOL no.5 2026
Figure 1: Laser Doppler Velocimetry (LDV) system installed on an operating district-heating pipeline.
Laser-based on-site calibration enables utilities to verify the performance of installed large flow meters under real operating conditions without interrupting plant operation. By combining accredited laser metrology with practical field deployment, the method improves confidence in measurement data, supports network optimisation and delivers measurable economic benefits. Every percentage point counts. Accurate flow measurement underpins customer billing, energy balancing, efficiency calculations and regulatory reporting. As district heating (DH) networks become larger and more complex, operators increasingly depend on reliable measurement data throughout the entire service life of their assets. Many large flow meters, however, remain in operation for decades after commissioning without being recalibrated under real operating conditions. For a typical 50 MW DH metering point operating over 150 heating days per year with a heat price of €60/MWh, a measurement deviation of only 1% corresponds to an annual energy balance deviation of approximately €108,000. Reliable flow measurement is therefore not merely a metrological issue but a technical, operational and commercial requirement. Why factory calibration is not enough Factory calibration is performed under controlled laboratory conditions with well-defined flow profiles and traceable reference facilities. In service, however, pipe bends, valves, pumps, reducers, tees, and changing operating conditions frequently create asymmetric or swirling flow profiles that differ significantly from laboratory conditions. Consequently, factory calibration validates the instrument itself but cannot fully represent the performance of the complete measuring system after installation.
Conventional recalibration requires removing the meter and transporting it to an accredited laboratory. For large transmission pipelines, this often means shutdowns, bypass installations, and considerable costs. As a result, operators often postpone recalibrations or do not perform them at all. Even if performed, calibration conditions almost always differ from operational ones and therefore always introduce additional unknowns in flow meter reliability.
Advantages of laser optical on-site calibration
Bringing the calibration to the pipeline The On-Site Calibration (OSC) method reverses this concept by bringing the reference measurement system directly to the installed flow meter. The technology is based on Laser Doppler Velocimetry (LDV), which measures local flow velocity from the Doppler shift of laser light scattered by tracer particles (Figure 2). Optical access is established using a specially developed full- bore ball valve, hot tapping, and a pressure window assembly. Calibration is therefore performed while the pipeline remains fully operational, eliminating the need for service interruptions.. Measuring the real flow profile An automated traversing system moves the laser probe across the pipe diameter, recording approximately 150 local velocity Calibration without interrupting plant operation. Verification under real operating conditions. Independent of flow meter technology. Accredited according to EN ISO/IEC 17025. Applicable to DN100–DN1200. Traceable verification of the complete measuring system. Suitable for DH, district cooling and water networks.
15 www.dbdh.dk
Figure 2: LDV measuring principle and automated profile scanning
Reliable reference measurements under fluctuating conditions
measurements per profile (Figure 2). During this velocity scan, the meter-under-test values are logged at the highest possible temporal resolution. The flow meter measurement error is calculated by comparing the calculated LDV volume flow with the time-averaged volume flow of the meter. Instead of relying on a single measuring point, the OSC method captures the complete velocity distribution across the pipe cross-section. The resulting profile is used to calculate the reference volume flow while simultaneously revealing asymmetry and other hydraulic characteristics. Figure 3 shows typical measured profiles and the results graph from a calibration. The issued calibration certificate also includes information about the meter under test and the measurement conditions. Probe positioning, data acquisition and measurement sequences are fully automated after parameterisation. An optical revolver enables automatic adjustment of the measuring optics for different operating conditions, while remote monitoring allows long measurement campaigns to continue overnight without permanent operator attendance. Calibrations are typically performed at several operating points to assess meter performance across its working range. Because LDV measures velocity directly, it is independent of the measuring principle of the installed flow meter and can therefore be applied to electromagnetic, ultrasonic, orifice flow meters and other meter types.
Unlike laboratory calibrations, field measurements are performed under continuously changing operating conditions. Flow rate fluctuations caused by consumer demand or pump operation are compensated by normalising the LDV measurements with data from an independently installed ultrasonic clamp-on flow meter. This approach keeps the reference measurement independent of the flow meter under test [1]. It relies only on the proven linearity of the clamp-on instrument, which is specifically qualified for this task. Accredited measurement quality Accurate field calibration requires not only precise instrumentation but also a transparent uncertainty evaluation. The OSC method is accredited according to EN ISO/IEC 17025 [2]. To achieve the credibility and traceability required for accreditation, a wide range of uncertainties from multiple sources (see Figure 4) needed to be quantified and put together in an extensive uncertainty budget. The dominant uncertainty contribution originates from the velocity profile at the measuring location. To quantify this influence, CFD simulations were combined with high-precision LDV measurements in a publicly funded research project [3]. Mathematical analysis of the profile allows every measurement to be assigned to one of several characteristic flow classes, each associated with a realistic measurement uncertainty [4].
16 HOTCOOL no.5 2026
Figure 3: Measured profiles (profile class “slightly disturbed”) and results diagram (profile class “fully developed”)
The OSC method is also often used as a recalibration tool for flow sensors which were subsequently added as instrumentation to the grid lines. Because those flow sensors are often ultrasonic clamp-on or other comparatively easy-to- install flow meters, they often lack the needed measurement precision. An additional calibration after mounting can reduce the measurement uncertainty of these flow sensors by several percentage points. Of the 241 flow sensors calibrated to date, 45 showed measurement deviations of more than 4%, after accounting for the inherent uncertainty of the OSC method. This means approximately 19% of all inspected flow sensors show
Figure 5 shows the achievable total measurement uncertainties for each profile class. The minimum uncertainty for the “fully developed” profile class consists only of non-profile-related contributions. Practical experience More than 240 large flow meters have been calibrated in Germany, Austria, Switzerland and Australia on pipelines ranging from DN 100 to DN 1200 (Figure 6). The operating conditions of the measurements ranged from 5°C to 150°C in fluid temperature, fluid pressures ranging from 2 bar to 18 bar, and pipe sizes between DN 100 and DN 1200.
Figure 4: Main contributors to the uncertainty budget.
Figure 5: Profile classes and associated realistic expanded uncertainties (k=2).
17 www.dbdh.dk
Figure 6: Typical field applications of the OSC technology.
significant deviations from their initial test-rig calibrations (Figure 7). In addition, approximately 5 % of the submitted flow sensors could not be calibrated due to faulty measurement characteristics. At the same time, most meters showed good agreement with their original calibration, giving operators independent evidence that their installations continued to perform within specification. Benefits for utilities On-site calibration improves confidence in customer billing, energy balances, efficiency assessments and regulatory reporting. It supports network optimisation, verifies newly installed clamp-on flow meters under real operating conditions and provides traceable evidence of the performance of the complete measuring system rather than the instrument alone. Because calibration is performed without interrupting plant operation, the method minimises operational impact while maximising practical value.
Key benefits for utilities:
Higher confidence in customer billing. Reliable energy balances under real operating conditions. Reduced operational risk without plant shutdown. Traceable calibration results for audits and quality assurance. Improved efficiency through verified measurement data.
Figure 7: Results from more than 240 accredited on-site calibrations.
18 HOTCOOL no.5 2026
Conclusion Laser-based on-site calibration bridges the gap between laboratory calibration and everyday operation. By combining accredited laser metrology, automated field measurements and rigorous uncertainty evaluation, utilities can verify the accuracy of installed large flow meters under real operating conditions. As district heating systems become increasingly digital and efficiency-driven, reliable measurement data will remain a key prerequisite for sound technical, commercial and regulatory decisions.
Abbreviations FM Flow meter
LDV Laser Doppler velocimetry
OSC On-site calibration
References [1] ISO 3966:2008. Measurement of fluid flow in closed conduits – Velocity area method using Pitot static tubes. ISO Standard, 2008.
[2] EN ISO/IEC 17025:2018-03. General requirements for the competence of testing and calibration laboratories. ISO Standard, 2018-03.
[3] AGFW – Der Energieeffizienzverband für Wärme, Kälte und KWK e.V. “EnEff. Wärme – Energieeffizienz in der Fernwärme durch Vor-Ort-Kalibrierung von Durchflussmessgeräten – Kopplung von laseroptischen und numerischen Verfahren”. Joint Final Report by the Partners ILA R&D GmbH, OPTOLUTION Messtechnik GmbH, Physikalische-Technische Bundesanstalt, Technische Universität Berlin, VATTENFALL Europe Wärme AG, AGFW, Forschung und Entwicklung, Issue 46, Frankfurt/Main, 2018. [4] Müller, U.; Dues, M.; Hübert, W.; Rautenberg, C.: Improving operational efficiency of power plants through on-site calibration of flow sensors. 16th International Symposium on District Heating and Cooling, DHC2018, 9–12 September 2018, Hamburg, Germany. DOI 10.1016/j.egypro.2018.08.183
For further information please contact: Dr. Ulrich Müller, mueller@optolution.com
19 www.dbdh.dk
BETTER DECISIONS, FASTER TRANSITION
By Mathias Terp Munck and Ole Andreassen Kofoed, Artelia A/S, and Hanne Kortegaard Støchkel, DBDH
A new approach is emerging in which district heating (DH) and the process industry (PI) can both benefit from closer collaboration. To make this a reality, both sides need to make investment decisions. This is the story of the analyses and methodology behind those investment decisions.
20 HOTCOOL no.5 2026
Beyond electrification Worldwide, process industries rely heavily on natural gas and oil to generate process heat. These industries include food production, chemicals, pharmaceuticals, and other manufacturing sectors where a reliable heat supply is essential for daily operations. Reducing emissions from these sectors is often more complex than decarbonising buildings or electricity generation. Industrial processes require stable energy supplies, competitive costs, proven technologies, and an understanding of linked subprocesses. Many companies therefore focus primarily on electrification – or simply postpone addressing the issue. However, electrification is not always the most practical or cost-effective solution. In some cases, it may not even be feasible due to limitations in the local power grid. Alternative approaches are needed to accelerate emission reductions while maintaining industrial competitiveness – here DH can play a significant role. This is demonstrated by cases in operation in Europe and practical experience from Artelia’s work as a technical consultant to both industry and DH. The next step is to move from pioneering cases to a standardised methodology to support better decisions. Two current answers When an industrial company starts planning for solutions to become more sustainable, two solutions usually come up first. The first is electrification. Fossil-fuel boilers are replaced with heat pumps or electric boilers, installed on site. The company provides its own heat supply, powered by electricity. The second approach is to continue using fossil fuel locally but recover the surplus heat instead of wasting it. The surplus heat can be applied either internally or supplied to external users. This is typically low-temperature heat, but a heat pump can upgrade it to a suitable temperature level, allowing it, for example, to be utilised in a DH network to heat buildings in the surrounding urban area. New answers emerging Both approaches require the company to organise and implement the solution largely on its own. That is already an obstacle, but there are other major concerns too. For electrification, the uncertainty is future electricity prices, connection costs, and security of supply. For surplus heat recovery, the underlying problem remains if fossil fuels are still being burned on site. A third option is emerging, though still rarely seen in practice: a tailor-made mix of technologies and energy carriers, combining electricity, DH, and sometimes other solutions, matched to what each company needs. The Hot|Cool article “District Heating brings value to the process industry” lists benefits for both sides and gives examples of cases in operation across five countries. Instead of solving the challenge alone, the company can draw on the energy infrastructure already around it, such as the power grid and a DH grid. DH can supply heat to the
company, not only receive it. It becomes part of a flexible, tailored solution for that specific site. The available DH supply may not always meet the required temperature levels at a given site. However, several technologies can be applied to increase the temperature to the desired level. Although this requires additional equipment and investment, it can still be economically attractive in many cases. DH also brings something else to the table: a track record. Many DH utilities have steadily reduced the carbon content of their heat supply for years, and have a demonstrated record of continuous supply, with a low risk of failure — a quality highly valued by industrial customers. Broaden the perspective to see new solutions This is relevant for companies located near an existing DH network. But it is just as relevant when a DH system is being planned — in that case, industrial heat supply and demand should be designed into the network from the very start. Electrification and reuse of surplus heat remain valuable solutions, but they should not always be seen as the only options. In some cases, they can stand on their own; in others, they can form part of a tailor-made energy mix for industrial companies or areas. The shift in mindset is toward combined solutions that improve affordability and flexibility — and toward remembering that DH could be a key component of that mix. Seeing the whole picture An industrial production line rarely needs just one type of energy. It needs heat and electricity, at different times of the day, at different temperatures, across many connected sub- processes.
INVERTER
SOLAR CELLS (PV)
ELECTRICITY DEMAND
HEAT PUMP
ELECTRICITY GRID
HEAT DEMAND (WATER)
GAS BOILER
HEAT (WATER)
SPACE HEATING
GAS GRID
NATURAL GAS
GAS STEAM BOILER
HEAT DEMAND (STEAM)
HEAT (STEAM)
ELECTRICITY STEAM BOILER
ELECTRICITY
NATURAL GAS
ELECTRICITY
HEAT (STEAM)
SOLAR ENERGY
HEAT (WATER)
Figure 1: An example model of an industrial site’s energy system — the reference case before any integration with a DH system. Solar power, the electricity grid, and the gas grid feed a heat pump and boilers, which supply the site’s electricity demand and its water- and steam-based heat demand. The same type of model can then test alternative setups, including how district heating could supply part of this heat.
21 www.dbdh.dk
Modelling the entire process this way gives an overview that few companies have today. Instead of asking “can we replace this one boiler,” the model demonstrates and documents the combined, total need across the whole site. The model includes both the industrial site and the DH system, and Figure 1 shows an example for the industrial site alone. Behind this overview are technical specifications for every component and connection in the production process. The model can be simple or detailed, and it is built through collaboration between external engineers and technical staff at the industrial company, who provide crucial insight into internal processes. Setting up and discussing this overview alone often reveals energy efficiency gains before any new investment in supply is even considered. In Denmark, models like this are already used for business cases and planning in the DH sector, so once the industrial model is built, the combined system of industry and DH can be analysed and optimised. Comparing apples and oranges Once the total energy need is mapped, you can quantify and compare very different solutions on equal terms: economy, CO2 emissions, and other factors, such as water use. This is
perhaps the greatest value of a model-based approach — the ability to quantify impact and compare solutions directly. Figure 2 illustrates some of the solutions that can be compared this way, from the two current solutions described above to variations that integrate a DH system. Comparing solutions 1, 2, and 3 can guide which options to investigate further; comparing solutions 3 and 4 can support decisions on the speed of carbon reduction. More solutions can be added, and every one of them can, of course, be compared against the current situation – the reference case – or any other considered scenario that has been modelled. The examples in Figure 2 are simply to illustrate that many types of solutions can be analysed and compared. Solution #1 is pure electrification at the industrial site with no integration with DH. Solution #2 is selling surplus heat to the DH system at a price that can be modelled. Solution #3 replaces heat production at the industrial site with more sustainable heat from the DH system, and to keep the transition manageable for the industrial company, the existing gas boiler will run for much fewer hours but continue to operate to boost the temperature. Solution #4 takes it one step further, and the existing gas boiler
Figure 2: A model-based approach starts by modelling the reference situation, then adapting that model to represent different potential solutions — perhaps adding new production units, new energy infrastructure, or making other adjustments to the system.
22 HOTCOOL no.5 2026
Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29Powered by FlippingBook