The Component Stratified_Heat_Storage
The Stratified_Heat_Storage component represents a thermal storage tank whose contents are organized into several independent temperature layers. It enables the flexible exchange of energy between heat generators and consumers over time. The balancing flows are part of the optimization for intelligent use of available capacities and the development of a dynamic storage strategy. The redistribution of heat, together with the preservation of capacity for valuable high-temperature heat, increases energy quality and added value.
Component Template
The Stratified_Heat_Storage.e-ctpl component template is located in the Component template library folder Heat Supply.
Integration Into a Scheme
The following figure shows an example of how to integrate the component into a scheme (HT = high temperature, LT = low temperature).
Select the Number of charging and discharging ports independently of each other from the drop-down lists: 1 (top), 2 (top and middle), or 3 (top, middle, and bottom) for each. This allows the stratified thermal storage to be flexibly integrated into different network configurations, e.g., with solar thermal energy, heat pumps, and process waste heat.
Like the Heat Storage, the Stratified Heat Storage can be integrated into a scheme with two Operating modes, which you select once for all levels together:
How the Component Works
The Stratified Heat Storage decouples generation and consumption in terms of time and combines volatile generation from decentralized plants and renewable energies with diverse demand requirements, e.g., for hot water as well as process and heating heat, with different temperature requirements in the flow and return. Heat suppliers with different temperatures can charge the Stratified Heat Storage.
Tutorial 09 demonstrates how to use the component Stratified Heat Storage in a multi-temperature system.
In the current version, optimization as seasonal storage and structural optimization are not yet possible for this component.
Layers
The Stratified Heat Storage stores heat in different layers according to their temperature: the top layer has the highest temperature, and the bottom layer has the lowest temperature. The storage geometry and integration into the heating network are represented by the number of layers and connections. Each temperature layer can have its own pair of connection ports (pins) for charging and its own pair of connection ports (pins) for discharging. Each pair of ports is connected to an individually configurable heating circuit and has its own flow and return parameterization. This configuration of the ports allows for a dynamic charging and discharging of the individual temperature layers and thus independent change in the filling level for each individual layer. The sum of the capacities of the individual layers is limited by the specified total Storage capacity of the storable heat quantity, which you can specify as Storage capacity, Storage volume, or Storage mass. The specified temperatures are used in the model solely to convert the energy content of a layer into the volume of the layer, thereby determining the filling level of the storage. Internal heat conduction between the layers (the inevitable natural transfer of heat from the warmer to the colder layers) is not taken into account in the model. The losses relate exclusively to external heat loss.
Temperature Management
Inside the component, the individual heat circuits connected via the ports are also connected by a model, which enables multi-temperature management of the component. In addition to meeting the temperature requirements for loading and unloading each layer, demand at each level is met by means of shifting and deliberate “over-temperature utilization.”
The shifting describes the displacement of low temperature levels when the storage tank is full, but high heat potential becomes available again through generation and is economically viable to utilize. In the model, the layer with the lower energy is then reduced, and the layer with the higher energy is increased accordingly. This way, heat from cold layers downstairs is transferred to warm layers upstairs in the model. The shifting is subject to optimization and will only take place if it is economically viable.
Conversely, by utilizing over-temperature, the high-temperature layer (with the highest temperature level) can feed the two lower layers and their associated demand; and the middle layer (with the medium temperature level) can additionally discharge into the heat cycle of the lower layer (with the lowest temperature level). Over-temperature utilization actively extracts energy from the warmer storage layer to use it for the lower potentials.
The combination of shifting and over-temperature utilization, i.e., both directions cold to warm and warm to cold, enables dynamic storage strategies for flexible heat utilization.
Input Data
Default values are stored for all input values. Adjust them to the specific use case. Specify the Storage capacity, Storage mass, or Storage volume as desired.
The default storage capacity assumes that the stratified thermal storage is completely filled with the top (hot) layer.
You can specify the Charging and discharging power by Char diagrams or as Fixed parameters for maximum charging and discharging power (see following two figures).
Optionally, you can specify the Minimum part load for charging and discharging.
For Dimensioning, specify the Minimum storage-temperature, layer temperatures (outlet temperatures), Heat capacity and Density of the storage material. Specify the temperatures as time series for each layer if dynamic temperature curves are to be mapped.
For Charging and discharging behavior, specify the relative losses in percent per day, the Charging and the Discharging efficiency (default 95 %).
In addition to the Technical input data, specify the Economic input data and, if necessary, the Operational constraints.
Output Data
Technical output data for the Stratified Thermal Storage include Full load cycles and Average temperature, as well as Storage capacity, the Charging and Discharging power of the individual layers, the Filling level, and Heat content of the entire storage tank and the individual layers.
The Energy balance of charging and discharging is shown for each layer.
