Report from Selected Technical Sessions
Industrial applications formed the largest single block of the Vienna programme. The most significant development was one of emphasis rather than of temperature record: high-temperature heat pumps are now being reported from operating industrial plants, and the research effort has shifted correspondingly from demonstrating capability to solving integration.
Each section is based on a report contributed by the organiser or session chair and has been edited by the HPT Magazine editor for length and consistency.
From pre-screening to installed plant
Report contributed by Benjamin Zühlsdorf, Danish Technological Institute
Session HTH1 laid out the logic of cost-optimal integration as a progression. Because temperature lift and equipment sizing dictate both capital and operating cost, the defining challenge is the balance between integration cost and thermodynamic efficiency. Kaida established an accessible baseline with a method to estimate standard heat pump coefficient of performance within plus or minus 10 percent using only external process temperatures and logarithmic mean temperature lift. Babaei and colleagues extended this with a Carnot-based pre-screening method combining pinch-based profiles with a genetic algorithm, navigating the non-convex design space to identify the optimal trade-off between efficiency and total annual cost in seconds.
Thermodynamic targets must then become physical systems. Schlosser and colleagues introduced a technology-matching framework using generic energy demand models for common unit operations such as drying, sterilisation and separation, to match process temperature and load profiles with suitable configurations, refrigerants and cycle designs. Walden and colleagues addressed the limits of static matching by bringing time-resolved process data into the design stage, demonstrating that thermal storage buffers on both source and sink sides stabilise operation and absorb fluctuation. Sizing these buffers with a two-stage optimisation model achieved a 27.4 percent reduction in operating expenditure in an automotive paint shop case study. Jende and colleagues closed the loop with insights from active EU initiatives including SOLINDARITY and EEETHOS, scaling reversed Brayton and cascade steam-generating units to capacities up to 1 MW thermal in operating pulp and paper, food and ceramics plants.
Steam, and the industries that run on it
Steam generation was the centre of gravity. Papers addressed the conceptual design and integration of steam-generating units into high-temperature heat pumps, the combined pathway of high-temperature heat pumps and steam compressors for decarbonising chemical industry processes, and the optimal design of an industrial steam heat pump for paper drying. Several contributions reported on R718 systems, using water as the working fluid, including performance assessment and geometric design of a steam compressor within the GEOSYN project and dynamic performance evaluation of the resulting machine.
Pulp and paper recurred more than any other sector. Contributions covered technical, economic and environmental analysis of integrating a high-temperature heat pump coupled with mechanical vapour recompression into steam generation, the dynamic simulation of heat pump integration in paper drying to overcome system complexity, heat recovery with a steam compressor in superheated steam drying, the design of a heat upgrade system for a paper factory, and first operational experience of a steam-generating Type II absorption heat pump in a paper mill. The absorption heat transformer case is instructive: it upgrades roughly half of its driving heat to a higher temperature with almost negligible electricity consumption, an option that changes the economics wherever a large waste heat stream and a modest electricity price ratio coincide.
Drying more broadly was treated as a target in its own right. One overview analysed current drying processes and the energy reduction potential available through heat pumps, noting that industrial drying accounts for roughly 10 to 25 percent of total industrial energy consumption across sectors including food, chemicals, paper and textiles. A separate paper surveyed realised case studies of heat pumps in industrial drying, and another reported a mechanical vapour recompression system supplying 150 degree Celsius steam to an industrial drying process at a major production site.
Scale, replication and novel cycles
Session HTH13 showed the scale now being reached. Rizzi presented two large industrial cases, one in a steel plant where waste heat from an electric arc furnace cooling circuit is upgraded for district heating, and one in a paper mill where a large heat pump combined with mechanical vapour recompression produces process steam at around 170 degrees Celsius and 5 bar. That combination of temperature and pressure moves heat pumps into duty traditionally reserved for fossil steam systems. Parra Ruiz presented the 150 degree Celsius MVR drying case and underlined that performance depends strongly on vapour handling, control, buffering and matching the machine to the process.
Replication was treated seriously rather than assumed. An analysis of industrial decarbonisation with cascade heat pump systems assessed the replication potential across Austrian industry, building on pilot plants including the AHEAD project. Work on modularisation and upscaling of high-temperature heat pumps addressed the manufacturing question that follows: if every installation is bespoke, the sector cannot scale at the rate targets require. A high-temperature application study in the ceramic sector examined one of the hard-to-abate industries where economics depend on both private investment and public support.
Session HTH5 covered the novel cycles still expanding the technical boundary. Drews presented control strategies for constant supply temperature of a high-temperature Brayton heat pump, addressing the practical problem that Brayton cycles, though well suited to drying and preheating with their large temperature glides, are harder to hold at stable supply temperature than subcritical vapour compression systems. That the session gave space to control rather than cycle novelty is itself a sign of maturing. Chen presented a high-temperature tri-phase thermochemical heat pump for industrial process heating, reporting an efficiency improvement of nearly 20 percent for the test rig, and illustrating that alternative concepts may still offer substantial gains. Comparative assessments of mechanical vapour compression against Joule and Brayton configurations mapped where each belongs. Multi-stage rotary liquid-piston compression was presented as a further route to high temperature lift.
The overall picture from the industrial sessions is consistent with the conclusion of the HPT Project 68 workshop. The supplier landscape and the number of demonstration cases are growing rapidly, the equipment exists across a widening temperature range, and the decisive factor for performance and for decarbonisation impact is now the quality of process integration. The barriers most often reported are the availability of reliable process data, the readiness of existing distribution systems, the share of project cost taken by integration work, and the organisational task of aligning end-users, suppliers, integrators, grid operators and permitting authorities early enough to matter.
All conference papers are available from the searchable HPT TCP database: https://heatpumpingtechnologies.org/publications
