Task 42 / Annex 24
The Task is organised in a matrix-like structure (see diagram below) in order to maximise the interaction between materials researchers and application experts, and to increase the knowledge exchange between groups working on adjacent topics.
One axis represents materials-related activities. It is divided into groups of similar activities:
The other axis represents application-related activities, and is grouped into application categories. The categories are following the usable temperature range of thermal energy delivered by the storage systems:
Each axis corresponds to a Subtask, and each category corresponds to a Working Group. Each of the two subtasks is coordinated by one of the two Operating Agents: Andreas Hauer, Operating Agent on behalf of ECES, coordinates Subtask A on materials, and Wim van Helden, Operating Agent on behalf of SHC, coordinates Subtask B on applications. Each Working Group is coordinated by a Working Group Leader.
In addition to the Material and Application group two Working groups concerning cross-cutting issues were installed:
These working groups are dealing with questions of general interest and importance.
At the first Task/Annex meeting in February 2009 the following working group leaders were assigned:
Materials Engineering and Processing
The heart of the work is in this working group, that has the objective to study and understand compact storage materials and develop new materials with better properties, and to develop new processing technologies that enable low-cost and large scale production of these materials. This is a long-term goal, which is not expected to be achieved within the duration of the Task. The work will include the synthesis of new materials, the determination of materials characteristics, finding optimal methods for micro- and macro encapsulation of storage materials and developing novel production principles.
The first activities in this Working Group include the characterisation of compound of salt hydrates as thermochemical materials, the improvement of synthesis methods of zeolites and the use of nano-sized particles for the stimulation of crystallisation in phase change materials.
Materials Testing and Characterisation
The performance characteristics of novel thermal energy storage materials like phase-change materials or thermochemical materials often cannot be determined as straightforward as with sensible heat storage materials. In order to have proper comparison possibilities appropriate testing and characterisation procedures should be developed and assessed.
The activities in this Working Group are aimed at the development of these new procedures and include comparative testing of materials and their required methods, long-term stability determination and pre-standardisation of testing methods.
With highly sophisticated numerical models, it should be possible to find ways to optimize storage materials in combination with system components like a heat exchanger or a reactor. To this end, the existing models that describe the processes on very different length scales have to be combined. Using multiscale modelling, it is possible to make the right coupling between models on the molecular scale with models on the scale of a grain of storage material or on the scale of a reactor.
Within this working group, steps are taken towards these multiscale models for phase change materials and thermochemical materials. The group has begun to describe the state-of-the-art modelling techniques for PCM and TCM on three different length scales: micro, meso and macro.
Apparatus and Component Integration
The storage apparatus is composed of the storage material and the equipment or components necessary to charge and discharge the storage material in a controlled and optimal way. These components include heat exchangers, pumps or fans, and chemical reactors. In order to arrive at optimised apparatus configurations, work will be done on storage container and reactor design, storage apparatus design based on the selected storage material, heat transfer optimisation and apparatus and components performance assessment.
The Applications subtask has three Working Groups, divided along the typical storage temperature of a group of applications: cooling, heating and domestic hot water, and high temperature applications. Although the applications themselves place very different requirements on storage technology, the steps that must be taken are very similar for all applications. Hence, the activities within the Working Groups in this Subtask are very similar as well.
The activities serve the underlying guidance principle of the materials development within the limitations of the application. The materials development will be directed by the desired system performance. A constant assessment of performance criteria for a given application will be used to determine the chances for a given material/system combination. These criteria can come from economic, environmental, production technology or market considerations. Activities in the Application Working Groups include, amongst others, definition of application boundary conditions, definition of required thermophysical properties for each application, selection of relevant candidate materials and system technologies and performance assessment and validation.
Cross-cutting Working Groups
Theoretical Limits and System Integration are two working groups that are cross-cutting and not part of a subtask. In the first, the theoretical limits of compact thermal storage materials and systems from a physical, technical and economical viewpoint are determined. An estimate is made of the maximum possible performance to be expected from a thermal storage system in a given application, giving a set of reference points for the comparison of lab tests, field tests and commercial systems.
In the System Integration working group, the storage apparatus is considered as part of a larger thermal system. Next to the apparatus, the thermal energy supply, the control, the thermal transport components and the thermal energy user are elements of the thermal system. Methods for the design and optimisation of components and systems should be developed, together with appropriate testing methods and procedures to assess the long-term behaviour of a system.