System simulation fact sheet

To estimate the performance of a complex thermal system, such as the HyCool system, a dynamic simulation is an excellent possibility for investigation. The systems’ performance is affected by various aspects, not only by outer parameters, but also by inner parameters. For example, the weather, more precisely the ambient temperature, has an impact on the rate of cooling of a hybrid chiller, which then again affects further circuits and elements in the system, e.g. the compression chillers. Understanding the total system and its single factors and their function within the system is necessary for a reliable simulation.

An important criterion in the simulation is the representing of the solar thermal plant, in fact the Fresnel collector plant. As Fresnel collectors operate very differently compared to flat solar thermal collectors, the most realistic simulation is both important and complex to run. Before a simulation is going to be displayed in an appropriate programme, a first analysis has to be conducted. On the one hand, this analysis is to render the results of the simulation. Simulations can aim on different aspects of a system, such as thermal energy, electric energy, intermediate results or final results. On the other hand, the analysis is required to identify the relevant elements of the system in order to gain information of the simulation targets; these might be solar thermal collectors and thermal storages or pumps and valves. This first analysis is necessary to focus only on system attributes which exert influences directly or indirectly on the simulation target. 

Today, there is a wide variety of different simulation software programmes, offering individual advantages or disadvantages, based on your kind of simulation. Simulations can be held either staticly, using constant parameters, or dynamically, e.g. to run a simulation over a defined timeframe, such as a day or even a year. 

The simulation for the HyCool thermal system was performed in TRNSYS 17 simulation programme. This computer software is able to display single characteristics like valves and pipes, but also technical and mathematical complex elements such as the chillers, thermal storages and an evaporation unit. Target of the simulation is the thermal performance, to say the chilling capacity of the adsorption chiller and the heat capacity and the rate of heating of the solar thermal collectors in combination with steam generation. By connecting the single elements of the system, in TRNSYS called “types”, user-defined information such as inlet-/ outlet temperature or flowrates can be exchanged between the types. Here it is to put focus on a correct connection of types, as the simulation programme does not inform or identify for wrong connection, as long as the connection does not lead to a numerical failure. 

In the end, the understanding of both the observed system and the simulation programme is crucial for a realistic and correct system simulation. A simulation is only a modern and mathematical precise way to estimate a performance, the scientific, in the case of HyCool thermodynamic, background is the base of good simulation.