Latent heat storage for central heating
Scientists at the Institute of Thermodynamics and Thermal Engineering at the University of Stuttgart developed with partners in the project EnErChem a thermochemical energy storage for building heating ins ingle-family and multi-family houses. EnErChem builds on the previous project "Chemical heat storage by means of reversible solid-gas reactions". A demonstration plant shows that the memory can withstand under real conditions.
|Project status||Project completed|
|Memory effect||Sorption (ad-/absorption: zeolithes)|
|Storage caracity||2-10 MWh|
|Energy storage density||> 200 kWh/m³|
|Number of cycles||1|
|Storage time||long (saisonal)|
|Charging temperature||> 130 °C|
|Discharge temperature||35 °C|
|Temperature type||low temperature|
|Project duration||December 2012 until May 2016|
Thermochemical energy storage requires knowledge from different fields of science. Material research is required to develop and optimize storage materials, enginieering research is required to develop the process design and process components. In order to meet this interdisciplinary research material scientiest and engineers are working together in this project. This makes it possible to optimize and adapt the process, the reactor desgin and the process controlling to the material characteristic such as reaction kinetic and heat of reaction. At the same time, the material research takes the boundary conditions of the process into account. The aim of the material research is not only to optimize the energy storage density of the material but also to improve the heat and mass transport during charging and discharging of the store. By this interdisciplinary research a holistic view of thermochemical energy storage becomes possible.
A high energy storage density and the technology of energy storage with almost no losses is especially important for long term storage of heat. By this, a compact storage volume and an efficient heat storage becomes possible.
However, this storage technology is at its initial phase. The objective of this project is to demonstrate the technical feasibility and the high thermal performance of thermochemical energy storage and to further promote the developemnt of this technology.
The project is a follow-up project of the joint research project CWS (FKZ 0327468B). The process design developed within the research project will now be further optimized and will then be turned in a demonstration pant.
Three areas of applications will be investigated within this research project: seasonal heat storage for solar thermal, combined heat and power (CHP) and photovoltaic (PV) systems.
Within this research project material scientist are working together with engineers. This enables the process design to be adapted to the material characteristic and vice versa. At the end of the project the following key goals shall be reached:
- a demonstration plant of a thermochemical energy store successfullytested for heating systems in single family houses
- high efficient storage materials of zeolite and salt developed and tested for thermochemical energy storage applications
Separate storage and thermal storage performance
The objective of this research project is the development and testing of a thermochemical energy storage for heating of single and multifamily buildings. The thermochemical energy store is designed as an open sorption store. Ambient air will be used as a carrier material for the heat and water vapor transport. The charging and discharging of the store takes place in an external reactor. This means that the material reservoir is separated from the reactor. By this a separation of the thermal power of the store (reactor) from the storage capacity (volume of the material reservoir) is obtained. This opens up wide range for applications as the reactor and material reservoir can be scaled independantly from each other.
As storage material new composite of zeolite and salt will be developped. The aim is to come to a compact heat storage with a high energy storage density. By this the storage volume can be significantly reduced (by a factor of three) compared to water stores. Especially for long term heat storage a compact heat storage is very important.A pilot plat of a thermochemical energy storage will be build and integrated in a heating system. This important step toward a demonstration plant will allow to gain practical experience with thermochemical energy storage under realistic operation conditions.
Three steps to the demonstration plant
This project aims to demonstrate the technical feasibility and the high thermal performance of thermochemical energy storage. For this a demonstration plant of a thermochemical energy store integrated in a building's heating system will be developed, constructed and tested.
In a first project phase the designing and dimensioning of the demonstrator takes place (first year). This includes the developement and characterizing of salt-impregnated zeolites as well as the dimensioning and construction of the components required for the thermochemical energy store.
In the second phase (2nd year) the thermochemical energy store itstelf and the interaction of the store with the conventional heating system will be tested on a hardware in the loop test rig. The focus of the testing is set on a detailled investigation of the heat and mass transport of the new storage material and the determination of the thermal perforamnce of the storage system.
In the third project phase (year 3) the demonstration plant will be set up and tested. From the demonstration plant information on the thermal performance under realisit boundary information will be gained. In addition important knowledge on installation, initial operation, operation reliablity and maintenance will be gained.
sub projcect A: The focus is set on optimizin and testing the thermochemical energy storage. A central element is development of the reactor design, the place where the heat and mass transport takes place. Numerical models are used to depict the thermal charging and discharging of the store. By this, the physical and thermal processes inside of the reactor can be analyzed. This builds the basis for a further optimization of the reactor geometry and the heat exchangers. A hardware in the loop test rig will be build to test the components of the thermochemical energy store as well as the the thermochemcial energy store as a whole. From these experiments optimization measures are defined and implemented.
Sub-project B: the focus is set on an optimization of the storage material. The objective is to gain new knowledge about the composite material of zeolite and salt, i.e. an increased understanding about the physical and chemical processes inside of the pores of the storage material. The aim is to come to an optimization of the chemical and thermal properties of the storage material specifically for the application of thermochemical energy storage.
Sub-project C: In this sub-project the heating system with thermochemical energy storage is realiized and tested. The system design for the different application (solar thermal system, CHP plan, PV system) are specified. Annual system simulation are performed to design and size of the thermochemical energy storage. A demonstration plant of the heating system with thermochemical energy storage will be build and tested under realistic boundary conditions.
Sub-project D: Production processes for an industrial production of the new storage material are developed and methods and tools for quality control are elaborated.