Knowledge database

Always start by modelling the load(s) (building, heating loads, hot water, cooling load, etc.). Cut out thermal circuits and simulate the submodels individually in order to recognise and solve subsystem errors at an early stage. Continue successively with distributions, storage tanks, generators and their control and repeatedly carry out test simulations. If the problems continue, feel free to contact us.

Please use the ‘DefineVolumeFlow’ and ‘ExtractVolumeFlow’ elements under GreenCity.Interfaces.Thermal. This allows you to apply a constant assumed temperature and volume flow to a heating circuit, for example, in order to be able to easily check numerical effects in the downstream model area or an initial model reaction.

Transformers are treated differently in the equation system of Green City models due to the definition of the voltage level. Therefore, please select the ‘Transformer’ option for the ‘OutputType’ parameter in the grid model. You will then receive an additional connector for connecting a transformer above the model. The procedure is similar for hierarchical grids (several grid models) and the DC grid (inverter on the DC grid).

Green City models utilise existing knowledge to increase simulation performance. This includes the fact that the direction of the media flow in a heating system is usually unidirectional. In order to avoid numerical problems in the model (i.e. overdetermination of the system of equations), only the output volume flows are set in the ‘Pump’ model and the input volume flow is not included in the model. Therefore, when modelling, make sure that the input flow rate always corresponds to the target/output flow rate of the pump.

Green City uses a predefined direction of movement of the media flow. Therefore, connectors of the type ‘VolumeFlowIn’ (coloured red circle as symbol) indicate that the media flow enters the model at this point and connectors of the type ‘VolumeFlowOut’ (red circle with white inner surface) indicate that the media flow exits the model at this point. An input and an output connector must therefore always be connected to each other to ensure a directed media flow in the model.

Heat storage tanks are defined in Green City as layers of superimposed media (usually water). The number of layers is set via the parameter ‘n’. Each connection (1 to 6) is assigned a layer index as the inlet or outlet height. This is also done via separate indices (iFlow or iReturn). If these indices exceed the number of layers ‘n’, the above-mentioned error message is displayed.

In the ‘Pump’ model, you have the option of removing the calculation of the auxiliary energy quantities via the ‘usePowerCalc’ parameter by setting it to ‘false’. This input is then no longer necessary and the connector to the grid model is no longer visible.

Set the ‘TRY’ parameter in the environment model to true and select a suitable weather data set. If you need additional data for a new location you can create your own record and add it to the library. For further instructions see the corresponding question.

Use the example weather data set ‘UserCity’ and select the annual simulation in the environment model (TRY=true) in the environment model. Duplicate the example weather data set UserCity from the Green City (and also from the Green City data) into an own weather data table and select the new data set in the environment model under UserCity1.

Please check whether all input connectors (especially Modelica inputs) and interfaces are connected to the corresponding connectors (especially controllers).

Modelica-Ouput connectors do not necessarily all have to be connected.