Industrial decarbonization requires technologies that can efficiently recover waste heat, electrify process heating, and integrate renewable energy sources without compromising operational reliability. At KTH Royal Institute of Technology, researchers are contributing to this challenge through the development of an innovative compact heat exchanger within the Horizon Europe IUPS (Innovative High-Temperature Heat Pump for Flexible Industrial Systems) project. The heat exchanger design is being carried out in association with from Wroclaw University of Science and Technology.
The I-UPS project aims to develop and validate a first-of-a-kind high-temperature heat pump
capable of delivering industrial heat up to 400°C, while being integrated with thermal energy
storage and renewable electricity sources. The project seeks to unlock new opportunities for
decarbonizing industrial sectors where conventional heat pump technologies cannot currently
meet temperature requirements.
Within I-UPS, KTH researchers are developing an advanced baffle-less shell and tube compact
heat exchanger using additive manufacturing techniques and genetic algorithms to facilitate
efficient heat transfer between pressurized working gases and molten salt thermal energy storage systems. The component is specifically designed to meet the demanding operating conditions associated with high-temperature heat pump integration. Attention is given to surface roughness optimization, which enhances fluid mixing and heat transfer at the solid-fluid interface. By carefully balancing heat transfer enhancement against pressure-drop penalties, the design aims to achieve higher overall thermal efficiency and more compact heat exchanger configurations.
A heat exchanger works like a cold water pipe inside a larger pipe carrying hot fluid — the cold
absorbs heat from the hot without the two ever mixing. Conventional designs use baffles to
zigzag the flow and maximise contact time with the cold surface, but a baffle-less design
achieves the same result more effectively. This is done by twisting tubes into a spiral or using
slim support rods, resulting in the fluid swirling naturally along the full length of the exchanger,
transferring heat efficiently while reducing pressure loss, fouling and tube wear. On I-UPS, this
geometry will be optimised using genetic algorithms and additive manufacturing.
The design focuses on:
Maximizing heat transfer effectiveness.
Reducing pressure losses.
Enabling compact system integration.
Supporting high-temperature operation.
Improving overall system efficiency, flexibility and drainability.
By enhancing thermal interaction between the heat pump cycle and thermal storage, the heat
exchanger contributes directly to improved energy recovery and reduced operational costs.
A distinguishing feature of the I-UPS approach is the use of advanced optimization and manufacturing techniques. The project combines a robust numerical design optimization using genetic algorithms, and additive manufacturing (AM) using the Selecting Laser Melting (SLM) technique — specifically the ISO standard Laser based Powder Bed Fusion of Metals (PBF-LB/M) with SS 316L material. This allows for compact heat exchanger geometries that are typically difficult to achieve using conventional fabrication methods. The team responsible for the AM is from Wroclaw University of Science and Technology, Department of Advanced Manufacturing Technologies, Faculty of Mechanical Engineering.
The I-UPS heat pump, Enerin’s Stirling technology, utilizes pressurized gases such as helium, hydrogen, and nitrogen as working fluids. Unlike conventional refrigerant-based systems, the Stirling cycle offers: heat delivery at temperatures up to 400°C; no reliance on high-GWP refrigerants; high efficiency across a wide temperature range; and an excellent compatibility with waste heat recovery and renewable electricity.
To provide operational flexibility, the I-UPS system integrates ternary molten salt mixtures using technology from Kyoto Group, typically composed of nitrate-based salts commonly used in the fertilizer industry. These salts offer low melting temperatures, reducing freezing risks; high thermal stability at elevated temperatures; high energy storage density; and a low cost and wide commercial availability.
By combining the Stirling-cycle heat pumps and molten salt thermal storage technologies, IUPS is creating a flexible and efficient pathway for industrial electrification, waste heat utilization, and decarbonization with renewable energy integration.
The successful deployment of advanced heat exchanger technology can help industries:
Recover more waste heat.
Reduce fossil fuel consumption.
Increase process electrification.
Improve energy efficiency.
Lower CO₂ emissions.
Enhance operational flexibility.
Sectors such as chemicals, food processing, pulp and paper, and other energy-intensive industries stand to benefit significantly from these developments.