Deutsche Version  ACT
Thermal Storage
Liquid sorptionstorage 4.7.2016

Process characteristics absorber and regenerator
© HFT Stuttgart

Saline stores process and solar heat

Scientists at the University of Applied Sciences Stuttgart constructed

an open air run sorption heat storage, that regenerates itself by

process heat or solar thermal energy. Prototypes were developed,

consisting of regenerator, absorber and the storage. These can be used

for various cooling, heating and drying applications. By 2017, the

storage is to be ready for the market.

Project status Project completed
Type of storage Sorption (Adsorption/Absorption) Different inorganic and, if suitable, organic salt solutions are examined for their potential for energy storage
Research object Development of suitable absorption and regeneration storage units for the respective application specifications
Project duration September 2012 until June 2016

Storage systems with high energy density on one hand side avoid peak loads and on the other hand also allow a load shift over long periods of time for building heating and cooling and drying processes. For example inheat pump applications aload shift from the electrical to the thermal side is possible by means of thermo-chemical storage.

  • System sketch storage charging and discharging © HFT Stuttgart
  • Plant for the production of any air conditions © HFT Stuttgart
  • Test bench absorber © HFT STuttgart
  • Process characteristics absorber and regenerator © HFT Stuttgart

If the cooling, heating and drying processes are supported by solar thermal systems, thermal storage allows a significantly higher utilization of solar thermal energy by matching demand and production. In these cases, high energy densities are essential in order to compensate not only short-term peak loads, but also achieve long term effects. Besides the currently used water storage tanks storing just sensible heat, sorption storages offer a higher energy density, but are not yet commercially available. Sorption storages can significantly improve especially the storage problem of air driven collector systems.

Charging and discharging strategies

In this project an open air driven liquid sorption storage system is developed, which is regenerated by waste (process) heat or solar thermal energy. Demonstrators consisting of regenerator,absorber and liquid sorption storage will be developed, which can be used for various cooling, heating and drying applications and depending on the different applications enable an hourly, daily or weekly storage for thermal driving energy. For efficient energy storage, especially the charging and discharging strategies of the liquid sorption storage is one of the central research topics:

  • Development of innovative system circuits for air drying and conditioning including storage function
  • Control strategies for charging and discharging cycles for daily, weekly and monthly storage. Energy storage or a decoupling of for example solar radiation and cooling demand
  • Production of demonstrators for cooling, heating and drying applications for two different power ranges
  • Storage concept for vacuum air collectors
  • Investigation of alternative sorbents that can replace conventional liquid sorbents
  • Simulation tools for sorption units, scaling options

In additional research projects the results of the project shall be further developed to marketability and in the medium term around 2017 integrated in the product range of the project partner Wolf GmbH. Also conceivable are system solutions that allow the integration of liquid sorption storages in existing market available air driven air conditioning and heating units. Due to the new storage option for air driven collector systems, the liquid sorption storage system will significantly improve the marketing opportunities of the innovative vacuum air collectors of the company airwasol GmbH & Co. KG, which is involved as subcontractor in project.

In the first phase of the project an application analysis of liquid sorption storage systems for cooling, heating and drying applications is carried out and suitable sorbents are determined and examined. Subsequently various system concepts for the development of sorption modules will be developed for storage charging and discharging. Based on the laboratory investigated sorbents and the analysis of storage density and process characteristics, the development and design of absorption and regeneration storage modules will be done. Taking into regard the results of the performance tests of the single modules and the collector module, the complete systems for liquid sorption storage units with charging and discharging strategies for the defined application areas will be developed. Simultaneously a cost benefit analysis and economic evaluation of the complete system will be carried out.


Sub task : Concept and system development, performance analysis:
The HFT Stuttgart investigates the storage density of different liquid absorbents and materials for sorption storage system applications. By means of test benches the HFT develops optimized process characteristics for the respective application concepts with various carrier materials and distribution systems for the sorbent. Based on the study results at the HFT Stuttgart different concepts for the absorber and regenerator modules for storage loading and unloading will be elaborated and simulation models for each process will be developed. In cooperation with the project partner Wolf GmbH overall concepts of liquid sorption storage systems with charging and discharging strategies are developed. For the performance analysis, the project partner constructs sorption modules and the demonstrators of the overall systems which will be analyzed and optimized by tests in the ventilation test benches of the HFT Stuttgart.

Sub task: Planning, design and cost-effectiveness analysis:
The Company Wolf GmbH performs application analysis for liquid sorption storage systems and estimates the market potential for heating, cooling and drying applications. Furtheron project partner Wolf GmbH will support the concept development of liquid sorption storage systems and take over the construction of the, by then, sized absorber and regenerator modules as well as the complete systems. Accompanying the entire duration of the project, Wolf GmbH will carry out cost-benefit analysis of development results and the economic evaluation of the developed complete systems.

Supported by: The Federal Government on the basis of a decision by the German Bundestag


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Research funding

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