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in the 69th issue of our heatbeat Research Newsletter we present two recent open-access articles from the International Journal of Sustainable Energy Planning and Management (Vol. 49, 2026) that approach one strategic question from two angles: how can municipalities and utilities systematically identify and quantify the local heat sources for future district heating networks? The first maps the seasonal potential of wastewater and river heat across the German federal state of Hesse; the second develops an hourly mapping methodology for industrial and tertiary waste heat, demonstrated for Milan. Lets start with an update from heatbeat.
In June, our development efforts for the heatbeat Digital Twin focused heavily on further improvements to make the software even more user-friendly. After introducing multiple selection and direct editing of pipe sections in May, we have now added multiple selection for buildings, building stations, and feed-in points. At the same time, direct editing capabilities have been significantly expanded for both these objects and the pipe sections. This has two advantages: First, workflows are now so much faster that new heating networks and expansion areas can be prepared for sizing and simulation in just a few minutes. Second, it allows inventory data for all buildings in the urban area to be kept up to date even more efficiently and comprehensively, so that data—whether for the KWP or in the day-to-day operations of heating network operators—can adapt even more easily to real-world changes.
And the new features for customizing data also enable yet another innovation: In addition to data such as nominal diameter and year of construction, additional data that is critical for determining civil engineering costs can now be entered for pipe sections. These include the location of the pipes, the surface condition, and the installation method. Based on this information, a significantly expanded cost table can be downloaded directly, allowing users to immediately evaluate the impact of changes to these project data on the costs of the heating network.
Heat pumps let district heating tap previously unused environmental sources, and wastewater and rivers are especially promising: treated wastewater stays near 12 °C year-round – well above winter river temperatures – while rivers beat ambient air on temperature and heat transfer during the heating season. Sieglar et al. deliver what large-scale studies have lacked: a combined, seasonally resolved assessment of both sources for an entire federal state, designed to feed Germany's now-mandatory municipal heat planning (Wärmeplanungsgesetz). Using standardised daily profiles for 443 of Hesse's 475 wastewater treatment plants and data for 25 rivers (~1,470 km), and the cold year 2021 for conservative results, they match supply against forecast 2045 demand at daily resolution within district-heating-suitable areas defined by a heat-density indicator.
Above 175 MWh/(ha·a), the usable potential reaches 4.9 TWh/a from wastewater and 4.5 TWh/a from river heat pumps; at the stricter 415 MWh/(ha·a) threshold it falls to 2.4 and 1.3 TWh/a. Together the two sources cover 28 % of Hesse's space-heating and hot-water demand at the 175 threshold, falling to 11 % at 415. These figures are heat-pump-bound: with a network supply of 70 °C (80 °C at -10 °C ambient temperature) the temperature lift of roughly 55–75 K drives a substantial electricity demand that the potential does not net out.
A new 1D energy-balance model captures thermal regeneration along the watercourse. On the river Nidda (five extraction points), even at full utilisation under low-flow conditions (roughly mean low-water, MLQ) the maximum cumulative cooling stayed at about -1.2 K – half of what a naive summation predicts, as the environment continuously re-warms the water. But river heat pumps faced restrictions for a median of 80 days and full interruptions for 21 days per year, in the cold-demand peak – so river heat saves fuel and electricity over the year but adds no firm capacity for the cold peak, requiring full backup. The authors therefore prioritise wastewater. The gap between the theoretical river extraction potential (111 TWh/a, 90 % of it in the Rhine and Main) and the usable 4.5 TWh/a makes the core point: value comes from the match with local demand, not the raw resource. Availability is site-specific – about three quarters of municipalities have a suitable treatment plant, only about a third a suitable river reach.
If the first study asks where natural sources lie, the second asks the same of industrial and tertiary waste heat – and adds the time dimension. Waste heat is abundant in cities but poorly mapped, so much goes unused. Menapace et al. present a replicable GIS workflow that estimates both the annual waste-heat potential at different temperature levels and its hourly profile over a typical meteorological year. Industrial sources come from company registers (activity code, employee count) crossed with a Danish process-based database and sorted into three bands (>80 °C, 60–80 °C, <60 °C); tertiary sources – supermarkets, malls, hospitals, swimming pools and ice rinks, all low-temperature (~25 °C) – are mapped from OpenStreetMap and building-height data. Annual values become hourly time series via dimensionless profiles. Data centres are not yet included.
Applied to Milan, the workflow identified 2,180 sources (1,538 industrial, 642 tertiary), 74 % of the potential at low temperature and just 13 % each at medium and high. Screening for sources within 1 km of the existing 3rd-generation network and above 1 GWh/a gave around 100 GWh/a – over 97 % low-temperature, hence requiring substantial heat-pump upgrading (a ~25 °C source raised to a high-temperature network: large lift, modest COP). The sobering result: even without demand growth, only about 13 % of that selected potential (23.9 GWh) could actually be fed in, because the waste-to-energy plant already covers the summer base load – a temporal mismatch that thermal storage could partly resolve. A 50 % demand increase lifted utilisation only to about 40 % (the waste-heat share rising from 5.4 % to about 11 %).
The lesson resonates with our own work: technical availability is not the same as usable energy. The low utilisation is shaped by Milan's specifics – a waste-to-energy-dominated 3rd-generation network – so what transfers to other utilities is the workflow, not the 13 % figure. The study also shows that the choice of reference dataset – Danish (top-down) versus Austrian MEMPHIS (bottom-up) – can substantially change the estimate. Such mapping is an initial screening tool: powerful for prioritising, but no substitute for site-specific feasibility studies.
As always, we recommend reading both articles in full – they are openly accessible. Together they confirm what we see in practice: a heat source's value is decided not by its theoretical magnitude but by how well it matches local demand in space and time – and by the temperature level that governs heat-pump efficiency and electricity demand. In our heatbeat Digital Twin we model networks together with their sources, demand profiles and operating temperatures, so that potentials such as wastewater, river and waste heat can be assessed realistically and integrated into sound designs. Together with our engineering team, we are happy to support you in planning, simulating and optimising your district heating networks.
And we have two more event announcements for you in July: First, we’d like to invite you to our next Feature Update Live Webinar on July 15, 2026. As always, you can register at https://heatbeat.de/feature-update . Among other things, we’ll be showcasing the enhancements described above for the efficient use of the Digital Twin and the new cost table. And on July 27, ENERPIPE is hosting a live seminar titled “ Expanding Heating Networks Cost-Effectively ” in Hilpoltstein. We’re excited to be participating with a presentation on the Digital Twin.
The next issue of our newsletter will be published on August 5th, 2026.