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Fluid Overview

The various loops of the system with all of their respective components and fluids are listed. In this window the fluid can also be modified at any time. All you need to do is select a fluid and click on “Change heat transfer medium”.

Fluid Transport

Polysun was designed so as to allow users to create the desired system layout by means of the available components. The first step of the simulation foresees hence a careful analysis of the system layout. The process includes in the sequence the identification of fluid domains and subsequently the identification of fluid loops.

Definition: The term fluid refers to the fluid that circulates the different components and transports energy. As fluids often contain different substances Polysun includes a catalog of main fluid components showing the pure substances (like, for example, water, ethylenglycol, propylenglycol) as well as a fluid mixture catalog showing the fluids that are actually employed (like, for example, potable water, ethylene mixture, propylene mixture).

Definition: A fluid domain is a continuous hydraulic area permeated by a common fluid. A system typically consists of several different fluid domains. System components belonging to a defined fluid domain are circulated by the same fluid.
Definition: A fluid domain consists of one or more fluid loops. A fluid loop always includes a flow-rate producer. Results are given for fluid loops (not fluid domains).

Definition: A component is defined as a flow rate producer when fluid transport between component connections is determined through physical processes in the same components.
The following components are flow rate producers:

  • Pump
  • Boiler with inbuilt pump
  • Hot water outlet (in which case a direct connection to the cold water outlet may be thought of to close the fluid loop).

Example: The system diagram 1f: hot water (2 collector fields, heating oil) should serve as an example for the analysis of the system topology. In this system there are three fluid domains (hot water, auxiliary heating, solar). The solar domain comprises two loops, each one activated by a pump. It is clear that there can be components that belong to two different loops (like the solar coil heat exchanger). On the contrary from the point of view of drinking water, there is only one loop, from the moment that there is only one flow rate producer (the hot water tap) and the three-way valve clearly sets at all times the mix ratio.

Figure: example for fluid domain and fluid loop

The algorithm ensures that the fluid transport is determined for each section of the system in an unequivocal manner. In this way, for example, it prevents two pumps from working counter-productively in the same circuit.