How the DUOHEAT heat pump works
From an oil-free centrifugal compressor to a life-cycle assessment of the finished system — the engineering behind a heat pump built for industrial temperatures.
An integrated two-stage heat pump
The DUOHEAT installation is being developed as an integrated two-stage high-temperature heat pump capable of upgrading industrial waste heat to a useful temperature of up to 200 °C. Its design combines thermodynamic modelling, advanced component development, experimental testing and intelligent control in one coordinated research programme.
From cycle modelling to system architecture
The development process begins with mathematical modelling of several two-stage heat-pump configurations. Both single-fluid and dual-fluid cycles are considered, including pure substances and mixtures operating under subcritical and supercritical conditions.
The thermodynamic properties of the working fluids are evaluated using the REFPROP database and compared with data available in scientific literature. The aim is to identify combinations of working fluids and operating parameters that can achieve a temperature lift of approximately 100 K while maintaining high efficiency, low environmental impact and acceptable investment costs.
The optimisation is therefore not based on a single performance indicator. Instead, it considers several criteria simultaneously, including:
- coefficient of performance and internal efficiency,
- environmental indicators,
- investment and operating costs,
- expected component performance,
- and the practical limitations of valves, piping and other commercially available equipment.
The selected cycle architecture will define the design conditions for the compressors and heat exchangers. It will also provide a common framework for integrating the results obtained by all research teams involved in the project.
Building and integrating the demonstrator
Once the main cycle configuration has been selected, the system will move from numerical models to physical construction. External contractors will manufacture and assemble the installation according to the engineering documentation prepared during the first stage of the project.
The completed demonstrator will undergo leakage tests, component inspections and a structured commissioning process. The performance of individual components and of the complete heat-pump system will then be compared with the original mathematical models.
This comparison is especially important because it allows the models to be improved iteratively. Experimental data will be used to describe not only steady operating points, but also start-up, shutdown, transient and emergency conditions.
The installation will bring together:
- the two-stage thermodynamic cycle,
- high-speed oil-free centrifugal compression,
- high-temperature heat exchangers,
- electric drives and power electronics,
- measurement and control systems,
- and advanced diagnostic tools.
Intelligent operation under changing conditions
Industrial heat sources rarely remain constant. Their temperature, flow rate and heat demand may vary over time. For this reason, the DUOHEAT system will be tested under changing source and sink conditions and at different compressor rotational speeds.
The final control strategy will use validated thermodynamic and component models to optimise the operation of the complete installation automatically. Long-duration tests of at least 150 hours of continuous operation are planned to assess system stability, reliability and energy performance.
Experimental measurements, numerical simulations and artificial-intelligence models will be combined into a single knowledge base. This will support real-time monitoring, fault detection, performance prediction and future optimisation of the system.
A life-cycle assessment will also be carried out. It will include greenhouse-gas emissions, energy consumption, raw-material use and other environmental impacts. This will make it possible to evaluate the technology not only in terms of thermodynamic efficiency, but also from the broader perspective of sustainable industrial development.
By integrating high-performance components with advanced control and diagnostics, the DUOHEAT installation is intended to become a practical platform for the electrification of high-temperature industrial processes.