IEA SHC, Task Solar Thermal Plants with Advance Thermal Storage Technologies for Low Energy Buildings

Status

completed

Summary

IEA SHC Task 32 "Advanced storage concepts for solar and low energy buildings" within the Implementing Agreement on Solar Heating and Cooling of the International Energy Agency was started in June 2003 and ended at the end of December 2007. It dealt with advanced heat storage for high solar fraction and other applications. Besides theoretical research on different heat storage concepts, improvements of existing storage systems and construction of new storage types was performed.

The work was structured by the following four Subtasks

Subtask A

Evaluation, analysis and dissemination of the state of the art in the field of advanced heat storage. Development of common boundary conditions for the comparison of different heat storage concepts.

Results

• Task 32 Handbook, Thermal energy storage for solar and low energy buildings
• Boundary conditions for the comparison of different heat storage technologies

Lead: Switzerland, end: 31. December 2007

Subtask B

Storage concepts based on chemical reactions and on the sorption principle:

Results

• Theoretical analysis of materials
• Simulation modules for storage concepts, seasonal simulation of storage systems within boundary conditions from Subtask A
• Prototypes of promising storage concepts

Lead: Sweden, end: 31. December 2007

Subtask C

Storage concepts based on phase change materials (PCM)

Results

• Theoretical analysis of known PCM materials
• Simulation modules for storage concepts, seasonal simulation of storage systems within boundary conditions from Subtask A
• Prototypes of promising storage concepts

Lead: Austria (Institute of Thermal Engineering, Graz University of Technology)

End: 31. December 2007

Subtask D

Storage concepts based on advanced water tanks and special devices

Results: Prototypes of promising storage concepts, Improvement of existing designs.

Lead: Germany, end: 31. December 2007

Motivation

Heat storage is one of the key problems for the use of solar thermal energy, when a high fractional savings of the conventional heat energy demand of a building should be realized. Other applications may be the introduction of heat storage material in the building walls like microencapsulated PCM plaster or in gypsum boards to increase the thermal mass and reduce the cooling load in summer or the reduction of the cycling rate and therefore emissions of boilers.

Objectives and Scope

In the here described project mainly organisational, travel and report costs as well as some scientific work fort he task like the adoption of the boundary conditions from IEA SHC Task 26 to Task 32 was financed. The research work itself was funded by two European Union projects (one on PCM slurries and one on sorption heat storage) as well as some national projects. The European Union projects ended long before the end of the task, the national projects were finished with December 2006.

Method

The different storage concepts were compared to each other using the same boundary conditions (climate, building etc.) by the way of simulations. The degree of detail in the modelling depends on the state of development of the different concepts. Water and PCM storage could be simulated in great detail and validated by laboratory measurements. Sorption and chemical storage could only be simulated as more or less lumped models from measured data and theoretical considerations.

Results

• Task 32 Handbook, Thermal energy storage for solar and low energy buildings.
• Definition of boundary conditions for different storage concepts.
• Extensive inventory of PCM Materials and storage/heat exchanger concepts.
• Detailed measurement results of water, PCM and sorption storage
• Simulation models for PCM and sorption heat storage. Validation of the models by experiments.
• Seasonal simulation of applications (solar combisystem on water and air basis, boiler cycling for conventional heating systems). The heat storage was either used short term or seasonal.
• Comparison of PCM- and sorption storage to water storage
• Unfortunately there was no significant improvement by PCM or sorption storage compared to water storage for most of the applications with the materials used so far. This can be explained on the one hand by the improvement of the storage energy content and on the other hand on the additional temperature losses during charging/discharging of the PCM and water stores. Both effects seem to level each other. For sorption storage the properties od the involved materials are very important. The materials used in Tasjk 32 could not give an advantage compared to water stores. Therefore research should focus on new materials .
• Nevertheless, two of the applications with the materials used so far look promising for deeper research:
  • sorption storage that uses the air moisture content of the exhaust air of buildings to discharge the sorption store and
  • seasonal storage using subcooled liquid PCM to avoid the heat losses during long term storage for 100 % solar fraction.
• Additionally heat pump applications based on liquid sorption are looking interesting. The development of the company Climate Well is now being introduced to the marked.
• Currently a follow up Task of IEA SHC Task 32 is in preparation (as Joint Task of the Implementing Agreements on ECES (Energy Conservation with Energy Storage) and SHC (Solar Heating and Cooling)), where new materials with better thermodynamic properties should be found. This new task, of course, will use the models and outcomes developed so far in IEA SHC Task 32.
• The results of IEA SHC Task 32 were presented in Austria at the following events:
  • Conference: Innovative Speichertechnologien, Organizer: AEE-INTEC, Tagungsort: Wirtschaftskammer Wien, 17. März 2006. All results of IEA SHC Task 32 were presented by the Operating Agent, the Subtaskleaders and selected examples
  • Meeting of Solarnet Styria at 7. February 2007
  • Meeting at Austrian Solar Thermal Platform (ASTTP) in Vienna at 3. Sept. 2007.
  • The project Modestore was additionally presented at Gleisdorf Solar 2006

Project management

Ao. Univ.-Prof. Dipl.-Ing. Dr. techn. Wolfgang Streicher

Project collaborator:
DI(FH) Dr. techn. Andreas Heinz

Company / Department:
Institut für Wärmetechnik, TU Graz

Project or cooperation partner

• DI Dagmar Jähnig, DI Dr. techn. Alexander Thür
  Firma / Institution: AEE INTEC, Gleisdorf
• Jean Christoph Hadorn
  Operating Agent Task 32, Programmleiter der Schweizer Forschungsprogramme "Solarwärme" and "Wärmespeicherung" für das Schweizer Bundesamt für Energie

Contact

Ao. Univ.-Prof. Dipl.-Ing. Dr. techn. Wolfgang Streicher
Institut für Wärmetechnik, Technische Universität Graz
Inffeldgasse 25b
A 8010 Graz
Tel.: +43 316 873-7306
Fax: +43 316 873-7305
E-Mail: w.streicher@tugraz.at