Dynamic simulation - model-based design

Dieser Artikel ist bislang nur auf Englisch verfügbar, aber eine deutsche Version ist auf dem Weg

In Added Values, we use model-based design and dynamic simulation. Not many other technical advisors do so, which is unfortunate as the benefits are significant: This approach allows us to simulate various operating situations and identify any flaws before commissioning. This both saves time and money. Moreover, not only does the dynamic simulation ensure an efficient and smooth commissioning, but the process also delivers a quality assurance of the subsequent daily plant operation.

"Model-based" means that we use mathematical calculation models to predict or simulate how a physical system behaves. "Dynamic" refers to a particular type of equations describing how the physical system changes over time ؘ– e.g., how a warm system gradually loses heat to its surroundings.

We set up these mathematical models with the simulation language Modelica, which is particularly suitable for modeling large, complex dynamic systems. Modelica allows us to both simulate the physical processes (pumps, valves, fluid flows, heat exchange, etc.) and their associated control systems (controllers, logic, operator intervention, etc.). For example, we can simulate how a pump group controller behaves during high load, low load, outage, start-up of secondary pump, etc.

Modelica is also used by other professional actors in the energy industry and is widely used in the aviation and automotive industries.

Modeling and simulation of "Ny Krone"

We have applied model-based design in the project Fremtidens Fjernvarme  – Green District Heating –  for our customer DIN Forsyning in Esbjerg.  In short, the purpose of this comprehensive and complex project is to replace Esbjergværket’s coal-based heat production with a sustainable source of energy.

Together with DIN Forsyning, we have identified a solution comprising two seawater-based heat pumps, a woodchip boiler, and an electric boiler. The heat from these plants must be transferred to the district heating network, and this is where we and Modelica come into the picture.

In Esbjerg, district heating from these new plants must be distributed to consumers through the new pumping station — Ny Krone. This and more, Added Values ​​has modelled and simulated prior to the commissioning.


Illustration:  Diagram and simulation model ”Ny Krone”

The work processes

Added Values ​​designed the control system for Ny Krone. Such a design process usually consists of four steps. This also applied in this case:

First, we design the control concept "on paper". This includes continuous PID controllers, logic interlocks and sequences for starting and stopping the plant. It is also important to describe these in a functional description with an overview of the parts we are dealing with, how they interact, etc. It is essential to gain an overview from the beginning.


Illustration: Part of functional description

Next (and parallel to step one) we transfer the design to Modelica. Here we also model the physical components and parameterize them (pump/valve characteristics, nominal temperatures, pressure, etc.). During the implementation, we can basically see if our design is sound or if the "paper design" needs to be corrected.

In the third phase, we simulate or test the various operating scenarios. Here we can test the system at high/low load, load changes, different temperatures, fault situations, interaction with associated systems and much more. This approach enables us to go into detail and examine the individual signals in our controllers. The purpose is to test as many realistic scenarios as possible so that errors are detected and corrected before commissioning.


Illustration: Simulation model for Fremtidens Fjernvarme

Finally — when the system is sufficiently simulated — we put it into commissioning on site. Our experience shows that most design errors are remedied when we apply the model-based design and simulate the operation of a system. It saves time and money for the customer, and it provides high operational reliability and availability.

In the project for DIN Forsyning, we thus designed and simulated how district heating from Ny Krone is distributed to the customers in the best possible way. To this end, the model-based method meant a well-organised and successful commissioning on time and without any major surprises.


Interested in more on dynamic simulation?

In this article, we explain how we used dynamic simulation for Sønderborg Fjernvarme with the purpose of improving the operation of their complex district heating plant.