Frequently Asked Questions

Questions & Answers

Welcome to our FAQ section. Our aim is to provide you with the information you are looking for quickly and easily. Frequently asked questions are already answered here.

If you still can’t find the right answer or if you have any further questions, please don’t hesitate to contact us.

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Modeling

How can I model a complex system technology efficiently and comprehensibly?

Always start by modeling the load(s) (building, heating loads, hot water, cooling load, etc.). Cut out thermal circuits and simulate the submodels individually in order to recognize 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.

How can I only model a part of a thermal circuit?

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.

I would like to integrate a transformer into my model to simulate a different electrical grid level. However, when connecting to a connector of the grid model, the model becomes singular. Why?

Transformers are treated differently in the equation system of GreenCity 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).

The volume flow in a thermal circuit in my model is not constant at every point. How can this happen?

GreenCity models utilize 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 modeling, make sure that the input flow rate always corresponds to the target/output flow rate of the pump.

There are two thermal connectors in GreenCity. When are these used?

GreenCity uses a predefined direction of movement of the media flow. Therefore, connectors of the type VolumeFlowIn (colored 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.

When using a heat storage model, I get the error message Index out of bounds. What does this mean?

Heat storage tanks are defined in GreenCity 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.

Parameterization

At an early stage of planning, I do not yet have any indication of the hydraulic conditions in the network and therefore cannot yet design any precise circulation pumps. How can I then define the required conditions of the models (PelFile in the Pump model)?

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.

How can I import annual weather data?

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.

How can I integrate my own weather data sets into the model?

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 GreenCity (and also from the GreenCity data) into an own weather data table and select the new data set in the environment model under UserCity1.

Errors

A singularity is displayed for my model. What could be the reason for this?

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

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