Thermal Storage (1D Model)

DistrictHeatingSim models thermal storage with a one-dimensional, vertically stratified tank model provided by the external package thermal-energy-storage-1d (import name thermal_energy_storage_model). This single model replaces the previous STES, StratifiedThermalStorage and SimpleThermalStorage implementations, which have been removed.

Two wrappers in districtheatingsim.heat_generators.thermal_storage adapt the model to the two storage roles used in the tool:

ThermalStorageAdapter — network-level / seasonal storage that participates in the energy-system dispatch and economic analysis.
BufferStorage — a short-term buffer tank attached to an individual generator (CHP, biomass boiler).

Underlying model

ThermalStorage1D discretises the tank into n_nodes vertical layers and advances the temperature profile per timestep:

Solver — "implicit" (default) is unconditionally stable and avoids CFL restrictions at hourly resolution; "explicit" is also available.
Advection — "tvd" (default, 2nd order) or "upwind" (1st order).
Buoyancy — optional convective-mixing correction (default on).
Geometry — cylinder, truncated cone, or truncated pyramid.
Loss model — constant U-value, split lid/wall U-values, or a ground-temperature model.
Fluid — temperature-dependent water properties (default) or constant rho / cp / lambda_fluid.

Per timestep the adapter stores heat loss, port temperatures (top / middle / bottom node), state of charge, and net storage flow, so they can be plotted in the results tab.

Network / seasonal storage

ThermalStorageAdapter is added to an EnergySystem via add_storage() and implements the storage interface the dispatch loop expects (simulate_stratified_temperature_mass_flows, current_storage_temperatures, current_storage_state, Q_loss, calculate_efficiency, calculate_costs).

Generators charge the tank at a fixed supply temperature T_charge and discharge against a fixed return temperature T_discharge_return; these are deliberately decoupled from the variable network supply curve (VLT_L), which is the consumer side.

Configuration options

These are exposed in the Thermischer Netzspeicher dialog and accepted by the ThermalStorageAdapter constructor.

Parameter	Default	Description
`volume` / `height`	1000 m³ / 10 m	Tank volume and height.
`n_nodes`	50	Number of vertical layers.
`T_min` / `T_max`	40 / 95 °C	Temperature limits used for the state-of-charge calculation.
`initial_temp`	60 °C	Uniform initial temperature.
`geometry_type`	`"cylinder"`	`"cylinder"`, `"truncated_cone"` or `"truncated_pyramid"`.
`loss_model_type`	`"constant"`	`"constant"` (`U_loss`), `"split"` (`U_top` lid / wall avg of `U_side`, `U_bottom`) or `"ground"` (`U_top`, `z_ground`).
`T_ambient`	10 °C	Ambient (or ground-surface) temperature for the loss model.
`fluid_type`	`"water"`	`"water"` (temperature-dependent) or constant `rho` / `cp` / `lambda_fluid`.
`solver`	`"implicit"`	`"implicit"` or `"explicit"`.
`advection_scheme`	`"tvd"`	`"tvd"` or `"upwind"`.
`buoyancy`	`True`	Enable convective-mixing correction.
`lambda_eff_factor`	5.0	Effective vertical conductivity multiplier (stratification mixing).
`T_charge` / `T_discharge_return`	90 / 50 °C	Fixed generator-side charge / discharge temperatures.
`spez_Investitionskosten`	50 €/m³	Specific investment cost for the VDI 2067 annuity.

Generator buffer storage

BufferStorage is a thin wrapper used by CHP and biomass-boiler dispatch to replace the previous inline scalar energy bucket (speicher_fill / speicher_kapazitaet). It tracks heat losses and a real stratified temperature profile.

It is configured from a few simple inputs — tank volume plus the generator flow / return temperatures (T_flow / T_return, which set the SOC limits) — and derives a tank height from the volume (aspect ratio \(h \approx (2V/\pi)^{1/3}\)). The dispatch loop calls step(Q_net_kw, dt_h) once per timestep with the net power into the tank (positive = charge, negative = discharge) and reads back get_soc(), get_capacity_kwh() and get_heat_loss_kw().

Loading old projects

There is no automatic migration of legacy storage configurations. When ThermalStorageAdapter.from_dict() encounters keys from an old format (e.g. storage_type, dimensions, lambda_top) it logs a warning and returns None; the energy system still loads, and the storage must be re-configured in the GUI.