Round robin tests of TES materials lead to adequate standard test procedures
The research group on Compact Thermal Energy Storage Materials of the IEA Solar Heating and Cooling Programme has taken a big step forward in developing and validating standardized thermal energy storage (TES) measurement procedures. Several round robin tests have been carried out over the past three years. During such tests, multiple laboratories examine the same material to compare results. The labs evaluated thermal properties such as thermal conductivity, thermal diffusivity, specific heat capacity, sorption enthalpy, density, and viscosity of different phase change materials (PCM) and thermochemical materials (TCM). The results will soon be published in a report titled “Standardized measurement procedures and round robin tests”, which will be available for download in the first quarter of 2025 here: https://task67.iea-shc.org/publications. The photo shows laser flash apparatus which was used to measure thermal conductivity and thermal diffusivity during the round robin tests.
Photo: Thermophysics Lab at the Austrian Institute of Technology
“The round robin tests not only harmonized participants’ measurement procedures, allowing them to compare results for the different thermophysical properties of TES materials. The tests also opened the door to discussions on the cross-cutting topic of measurement uncertainty to better understand the actual measurement accuracy and uncertainty of the collected results,” summarized Dr. Daniel Lager, Research Engineer at the Center for Energy of the AIT Austrian Institute of Technology. Lager coordinated the round robin tests in the subtask on Material Characterization and Database within IEA SHC Task 67 on Compact Thermal Energy Storage Materials.
| Measured parameter | Sample Material | Number of participating labs | Observations |
| Thermal conductivity and thermal diffusivity of liquid and solid materials | Paraffin wax CAS 8002-74-2; melting temperature 53–58 °C (PCM) | 12 labs | Different measurement methods such as laser flash, transient plane source and hot wire methods were used. With the measurement protocol and evaluation methods developed, it was possible to establish good comparability of the data across all methods. |
| Specific heat capacity of powdery materials | Strontium bromide, SrBr2 (TCM) | 6 labs | Various differential scanning calorimetry (DSC) methods were applied and some deviations were observed due to different hydration states during measurement. |
| Enthalpy change due to sorption/chemical reaction | Zeolite 13X (TCM) | 3 labs | The defined procedure and the results showed good comparability and a low standard score for the participating labs. |
| Density | Paraffin wax CAS 8002-74-2 (melting temperature 53–58 °C (PCM) | 5 labs | The density measurements in the liquid phase showed comparable results. No adaption of existing procedures was made. The density measurements in the solid phase showed that there are still strong variations and further investigations need to be conducted. |
| Viscosity | Paraffin wax CAS 8002-74-2 (melting temperature 53–58 °C (PCM) | 5 labs | Two methodologies were used to measure the viscosity at 70 °C in the liquid phase using equipment such as the controlled stress rheometer and viscometer. The data shows a reasonably low variance, so it can be stated that the measurement procedure is adequate for investigating paraffins in the molten phase. |
Table: Description of completed round robin tests within IEA SHC Task 76 carried out between 2021 and 2024. Source: Task 67
Round robin tests are an important method for improving and standardizing jointly defined test procedures. The international cooperation of research institutions within Task 67 makes it possible to agree on worldwide standards. In the Task 67 round robin tests, a total of 15 research laboratories participated from 10 different countries: Austria, Canada, Germany, France, the UK, Italy, Norway, Spain, Switzerland, and the USA (see figure below).
The Task 67 participants discussed the measurement uncertainty and deviation of results during the group meeting in April 2024 in Lucerne, Switzerland. You will find the detailed results and discussion about measurement uncertainty from the round robin tests in the report titled “Standardized measurement procedures and round robin tests”, which will be published in the first quarter 2025 here: https://task67.iea-shc.org/publications.
List of 15 research laboratories that took part in the round robin tests Source: Task 67
Websites of organizations mentioned in this news article:
IEA SHC Task 67: https://task67.iea-shc.org/
German Aerospace Center (DLR), Germany: https://www.dlr.de/en
Center for Applied Energy Research (CAE), Germany: https://cae-zerocarbon.de/
Northumbria University, United Kingdom: https://www.northumbria.ac.uk/
CanmetENERGY, Canada: https://ressources-naturelles.canada.ca/energie/bureaux-labos/canmet/centre-de-recherche-dottawa/5754
University of the Basque Country (Euskal Herriko Unibertsitatea), Spain: https://www.ehu.eus/en/en-home
CIC energiGUNE, Spain: https://cicenergigune.com/en
Universitat de Barcelona, Spain: https://web.ub.edu/en/home
SINTEF Energy, Norway: https://www.sintef.no/en/sintef-energy/
University of Birmingham, United Kingdom: https://www.birmingham.ac.uk/
Fraunhofer Institute for Solar Energy Systems ISE, Germany: https://www.ise.fraunhofer.de/
AIT Austrian Institute of Technology GmbH, Austria: https://www.ait.ac.at/en/
Lucerne University of Applied Sciences and Arts (HSLU), Switzerland: https://www.hslu.ch/en/
Universidad de Zaragoza, Spain: https://www.unizar.es/
National Research Council of Italy, CNR: https://www.cnr.it/en
