Latent Heat Storage

Integration Into a Scheme

Note the Special Features of Thermic Storages.

How the Component Works

The Latent Heat Storage stores heat in a phase change medium. This Phase change material is liquid when hot and solid when cold. Unlike other storage systems, the charging and discharging capacity is not limited by a maximum capacity specification; instead, the maximum capacities are determined by the material data and temperature conditions or optionally by specifying a characteristic curve. Internally, a distinction is made between three phase states: solid, two-phase, and liquid. The heat transfer law \( \begin{equation} \begin{aligned} Q_{max} &= k \cdot A \cdot \Delta T \end{aligned}\end{equation}\) is mainly applied, whereby \(k\) differs for the phase states. The temperature difference \(\Delta T\) is calculated from the Storage temperature and the Estimated charging or discharging temperature.

Technical Input Data

Specify the Mass in storage (mass of phase change material) and the Minimum and Maximum storage temperature as Design parameters.

Under Operating performance, define the Initial filling level and the Minimum and Maximum filling level. The Latent heat storage can be optimized as saisonal storage.

Define the Losses as Relative losses and by the Charging and Discharging efficiency.

Specify the Phase change material by the following material values.

You can specify the Characteristic of heat transfer by one of the following three methods, which you can select from the drop-down list.

After your selction, the form adapts.

Heat Tansition

If you have selected Computation with heat transition, the heat transfer is calculated physically. For this purpose, you need to enter the following additional information about the PCM. The input fields are additionally displayed under the heading Phase change material.

To calculate with heat transition, enter the Amount of tubes (number of pipes), Tube length, Outer and Inner tube diameter, and select from the drop-down list whether the storage tank is arranged vertically or horizontally.

Under the Charging characteristics → Enhancement of Heat Transfer, select from the drop-down list one of the follwing options.

For Fins, enter the Amount of fins, Fin length, Fin thickness, Fin heat conductivity, and Fin spacing.

For Additives, enter the Thermal conductivity in W/m K and the Volumetric Share of the Additives in %.

For Fins and additives, enter the factors of the Enhancement of the power by fins (heat transfer coefficient of solid material) and the Enhancement of the heat conductivity by additives (heat transfer coefficient of liquid material).

Enter the Material data of the transfer medium.

Characteristic Curve

To specify the characteristics of heat transfer, you can enter the characteristic curve with absolute values of the Maximum charging and discharging power (in kW) in relation to the Filling level (in %).

Transition Coefficient

If you want to Enter the transition coefficient, specify the following three heat transfer coefficients in W/m K in addition to the Tube length and Amount of tubes. The coefficients need to consider the influence of fins and additives if used.

Temperatures

Enter the Estimated charging inlet temperature and the Estimated discharging inlet temperature as estimated input values when Computation with heat transition or Entering transition coefficient for the Characteristic of heat transfer is selected.

Specify physically meaningful values of the outlet temperatures (with the Material property Heat/Cooling: Temperature dependent).

Technical Output Data

The Technical output data include the Storage capacity, following information on Operating performance:

and, with the Material property Heat/Cooling: Temperature dependent, following information on Transfer medium each at charging and discharging:

With Computation with heat transition, the Heat tansfer coefficients are output.

In addition, the following information is output.

The charging behavior depending on the phase state, i.e., the state of charge during a charging and discharging process, can be seen in the following figure, which shows the progression of the Storage temperature, the Liquid phase fraction, and the Filling level of the storage unit. At the beginning, between 4 and 8 a.m., the storage temperature (red) remains approximately constant, but the proportion of the liquid phase (blue) increases. Subsequently, between 8 and 12 a.m., the entire phase is liquid, and the storage tank continues to overheat.

Energy Conversion

Under Energy conversion, you find the following information on the energy balance of Heat supply and Heat demand: