Report from Selected Technical Sessions
A recurring argument ran through these sessions: the test methods on which certification, energy labelling and consumer information depend were designed around steady-state operation, while the equipment they assess increasingly operates dynamically, under variable-speed control and in interaction with storage and with the grid.
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.
The limits of steady-state rating
Several papers addressed this directly. An experimental comparison of heat pump seasonal efficiency using EN 14825 alongside a dynamic load emulation approach set out the problem plainly: current standards including EN 14511-3 and EN 14825 assess performance under steady-state conditions that do not reflect real-world dynamics. A related study examined the impact of the heat pump controller on measured performance, comparing results from the EN 14825 and EN 14511 procedures against a two-mass compensation method, and found that the controller itself can materially change the outcome. That finding has uncomfortable implications: if the control logic influences the rating, then two units with identical components may be labelled differently, and a rating obtained under one method may not predict performance under another.
Work on fostering innovation in heat pump controllers through real-life testing addressed the same question from the policy side, noting that revision of the test method within the EU Energy Labelling regulation for central space heating appliances is under discussion, with the proposed change replacing stationary measurement with procedures that capture dynamic behaviour. The evaluation of reproducibility of a load-based and climate-specific test procedure using a centrally ducted cold-climate air-source heat pump, conducted as part of representativeness, repeatability and reproducibility testing, tackled the practical obstacle to any such transition: a more realistic method is only usable if different laboratories obtain comparable results from it.
Frost complicates matters further. One contribution investigated the influence of frosting on the selection of typical days for heat pump evaluation, where annual performance is extrapolated from measurements on representative days in order to reduce test time. Another examined defrost control logic for air-source heat pumps using image and cycle data, and a third assessed the impact of nozzle material and integration practices on defrost efficiency and system compliance in heat pump fans. These are unglamorous topics, but they determine whether a seasonal performance figure quoted to a consumer bears any relation to what the machine will deliver through a real winter.
Reducing the cost of certification
Certification cost is a genuine barrier to product variety, particularly for variable-speed machines and for hybrid configurations where the number of combinations to be tested multiplies quickly. Chaignon and colleagues presented model-based performance prediction of variable-speed heat pumps as a possible route to reducing certification costs, with attention to hybrid heat pumps combining a heat pump and a boiler for unrefurbished existing buildings, where the combinatorial problem is most acute. The approach raises an obvious question of confidence, and the discussion turned on how much physical testing is needed to validate a model before the model can substitute for further tests.
Analysis of the energy performance of residential inverter-driven heat pumps made the complementary point that manufacturer declarations are made under particular conditions while actual consumption depends on real operating conditions and on choices made at the design stage. Research on testing methods for refrigerant direct condensation radiation air-source heat pumps addressed a product category that existing procedures do not cover well, a reminder that standardisation lags product innovation by design.
Safety, fluids and the standards that govern them
The refrigerant transition has created a substantial standards agenda of its own. Work on the revision of ISO 817 presented an evaluation method for the self-decomposition reactivity of next-generation refrigerants, prompted by the observation that certain ethylene-based hydrofluoroolefins exhibit self-decomposition behaviour. Since ISO 817 governs refrigerant designation and safety classification, the method feeds directly into how these fluids may be applied. The Austrian survey of leak frequency, location and detection in systems up to 50 kW addressed the monitoring and safety requirements that follow from the use of flammable fluids under the F-gas Regulation and the proposed REACH restrictions.
This connects to the point made by Yosr Allouche in the opening plenary, that flammability should not be confused with safety, and that what matters is proper application, installation, standards and qualified workers. The standards sessions gave that argument technical substance: the safe deployment of hydrocarbons and other low-GWP fluids at scale rests on classification methods, charge limits, leak detection requirements and installer competence, each of which is a standardisation question rather than a research question.
Quality assurance in the field
Quality assurance extended well beyond the test laboratory. A comprehensive overview was presented of a hardware-in-the-loop testbed and testing procedure for developing district heating substations that integrate heat pumps, allowing component and control behaviour to be assessed against a simulated network before installation. The Digital Heat Pump Lab at DTU, reported in the digitalisation sessions, serves a related purpose for digital services. HPT Project 66 reported on large-scale heat pump monitoring and quality assurance in Switzerland, presented at its workshop by collaborators from OST, and a methodology for optimal high-temperature heat pump design integrating working fluid and cycle configuration selection addressed quality at the design stage for industrial machines.
The evaluation and demonstration of actual energy efficiency of heat pump systems in buildings, reported from IEA collaboration work, speaks to the underlying issue across all of this material. The credibility of heat pumps with policymakers and with consumers rests on the gap between rated and delivered performance being small and well understood. Where that gap is large, the consequences are not only technical: they feed directly into the consumer trust problem identified in the second policy forum, where participants noted that poor-quality offers damage confidence across an entire market.
The direction of travel from these sessions is reasonably clear. Test procedures are moving, slowly and with justified caution about reproducibility, from steady-state points towards load-based and dynamic methods. Modelling is being proposed as a partial substitute for physical testing, with the burden of proof still being negotiated. The refrigerant transition is generating a parallel standards workload around classification, safety and installation. And field monitoring is increasingly treated not as research but as the routine quality assurance mechanism that a mass-deployed technology requires.
All conference papers are available from the searchable HPT TCP database: https://heatpumpingtechnologies.org/publications
