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Tips and Tricks to Work with Designer

Adapting a Template

The easiest way to create a user-defined system scheme is to adapt a similar, existing template. Here, an advantage is that the controllers for the unchanged components are already configured. Below are some tips:

  • Replicability: in order to always be able to revert to a functioning system diagram, always copy the system diagram and save the project after each process step. In addition, the simulation should be started and results should be checked so that any errors can be detected as early as possible.
  • Tank replacement: Should changes be made to connections or internal components of the tank, a new tank is to be entered in the scheme. Following this, controllers should be checked and the relevant sensors be set on the new tank.  If any component is removed from the scheme, the associated references in the controllers will be removed too – therefore, it is advisable to initially only remove pipe connections to the old tank and to remove the old tank from the scheme only after installing the new one and adjusting the controllers. This way, before the old tank is removed, you will still be able to identify in the controllers which in and outputs should be adjusted.

Designing a New System Scheme

If you do not wish to adapt an existing template, you may perform the following steps to design a completely new scheme altogether. Here too, we recommend the system diagrams are regularly copied as a backup. If the scheme to design is a complex one, it may make sense to first design a simplified version of it and gradually add more complex features on a functioning base.

  1. Place all required components on the design area.
  1. Connect components. 
  1. Start simulation. If the simulation is running, Polysun can calculate the designed scheme. Due to the missing controllers, the results are not yet significant (i.e. the calculation can be interrupted, it is enough to check whether or not the simulation is starting). If the simulation does not start, an error message referring to the cause will be displayed. For further information see the trouble shooting section.
  1. Now, controllers can be added step by step. After adding each controller, it is always advisable to check whether the scheme is still functioning.
  1. Check the results, e.g. with the aid of component results.

Controller Settings

  • Where possible, use variable values, e.g. in the heat generator controller set the “Reference for temperature sensors 1“ field on the left-hand side to “Variable value“ and on the right-hand side, in the ”Controller inputs” field, select the hot water demand temperature setting for ”Temperature sensor 1“. This allows hot water tapping temperature to be modified without the need for controllers to be adapted.
  • Should the status of a mixing valve or the flow-rate of a pump be set through a controller, components must be set accordingly. Otherwise, the value pre-set in the components will be used.
    Three-way valve: set “Branching model” option “Set value“
    Pump: set “Flow-rate controlled“ to “Flow-rate setting“
Figure: pump settings
  • If the parameters available for a controller are too few, an OR-operation of both controllers may be performed by means of two pumps arranged in parallel within the circuit, each with a controller.
  • The indication of tank layers in the controllers is important and should be in line with ports and coil heat exchangers. At the same time, care should be taken to ensure that ports and coils are regularly distributed on the displayed tank image; however, for the simulation, the relevant heights are those listed in the tank catalog. In particular, tanks designed for water-pump systems have different port heights. It will be helpful to drag your mouse over the controller to see what height in the tank the sensors are pointing to.

Heat Generator Controller

If a heat generator is connected to the tank, the value for the cut-off condition in the “Heat generator controller“ field must refer to the same or a higher layer than the one the return port is placed on.


Example of an incorrect controller setting:

The return port is at 60%. The boiler cuts in when layer 8 (58.3-66.7%) in the tank drops below 50°C. The cut-off condition is that temperature in layer 6 (41.7 – 50%) is 60°C. This is never reached as the boiler return lies at 60% (above layer 6) and therefore layer 6 cannot be effectively warmed up. Heating occurs on layer 8, where the return port is installed, and above. The heating continues until the maximum tank temperature configured in the controller is reached as the cut-off condition does not become effective.
The correct setting for the cut-off condition is on layer 8 or higher.

Connection Multiplier

With the help of this component, hydraulic components or sets of components can be used several times for the simulation. For example, the multiplier can be incorporated in the inlet of a collector, so that all subsequent components can be multiplied by a chosen factor. In order for the system to work it is then necessary to install the antagonist, the outflow multiplier, in the return of the collector. This method can be used analogously at any point of a hydraulic loop.

Trouble-Shooting

System Scheme Is Not Running

If the simulation cannot start, an error message referring to the cause is displayed. Possible issues are:

  • Open pipe connections (all connections, tank connections included, must be connected with pipes)
  • Undetermined flow direction in a circuit, a pump or a three-way valve are missing. A circuit may also be over-determined, e.g. if two pumps are installed in series within the same circuit.  The following components can determine flow direction:
    • Pump
    • Boiler/heat pump with internal pump
    • Cold + hot water connection
    • Three-way valve
  • If an error message is displayed saying the circuit is too complex (Error n. 5070/21), the three-way valve should possibly be replaced with a T-piece.
Simulation Is Running Slowly

A long simulation time is suggestive of a failure during the simulation. If significant temperature differences are observed between two distinct calculation steps, Polysun reduces the duration of the time step and calculates again, which causes simulation time to increase. Generally, complex and/or large systems have longer simulation times.

In such case, an effective way to find errors is to switch-off controllers consecutively and observe in which case the simulation runs faster. To do so, disable all months in the availability times of the respective controller.

Figure: example of the switched-off auxiliary heater in the controller settings

Possible causes include, for example, a controller that keeps switching on and off or an over-definition of flow direction in a circuit, for example, due to unnecessary three-way valves.

Avoid having two different flow directions in a pipe; particularly, in the case of pipes connected to a tank this may result in incorrect results. A better option is to use an additional port (port heights may be altered through the tank catalog, so, for example, also ports marked on the cap may be used as a connection further down).

Badly placed tank-ports or referencing a layer lying too high or too low in a controller may also be an issue. Temperature distribution in the tank may be suggestive of this problem. The individual tank layers can be seen in the component results, tabular and graphical evaluation.

Energy Demand Not Met

If at the end of the simulation this message is displayed, this may be due to a number of reasons including but not limited to:

  • The tank is too small 
  • The tank cannot reach the required temperature
    • Availability times for auxiliary heating (boiler/heat pump/electric resistance heaters) are set too short in the controller.
    • The boiler is too small/heat pumps and possibly the borehole are too small
  • In the controller, use “Variable value“ instead  of fixed values, e.g. to refer to the hot water temperature setting.
  • The mixing valve (for hot water and/or heating circuit) is set to a temperature that is too low. If required, configure a temperature shift to offset pipe losses.

Additional causes if the hot water demand is not met:

  • For tank-in-tank systems: surface or volume of the inner tank are too small.
  • The piping between the heat source and the tap is too long and this results in significant heat loss (circulation required)
  • For fresh-water stations: pumps or plate heat-exchangers are too small.

Additional causes if the heating energy demand is not met (the desired temperature was not always reached in the building during the heating period):

  • The night temperature set for the building is too low as compared to daytime temperature (the warm-up phase is too long)
  • The number of convectors is too small (in the convector settings, set ”Number of modules automatic“ to ”Yes” )

Possible causes if the cooling demand is not met (= in the cooling period the building was above the desired temperature)

  • The chiller is too small 
  • The number of fan-coils is too small (in the fan coil settings, set ”Number of modules automatic“ to ”Yes” )
  • In the building settings, “Shading” and “Natural ventilation” were not set.
Limitations
  • Non-return check valve: in Polysun, there are no non-return check valves. Indeed, non-return check valves are used for maintenance purposes, however, they are not relevant for the simulation. In addition, non-return check valves are installed to prevent an unwanted flow against the direction of the pump when the latter is switched off. In Polysun, pumps are ideal, i.e. when the pump is off nothing flows in or against the direction of the pump. Flow directions in the pipes are, thus, in any case clearly defined through pumps and three-way valves, which makes non-return check valves irrelevant for the simulation.
  • Multipliers: as a general rule, only a couple of inflow/outflow multipliers should be used in a scheme.
  • Parallel tanks: the connection of parallel tanks is not advisable. The use of a single, large tank provides in most cases good approximation and a more stable simulation. Tanks connected in series are also possible.
  • Flow rate producer / three-way valve: exactly one flow rate producer should be available for each circuit.  Serially connected pumps are not a possibility. If three-way valves are used in places for which a flow direction is already defined, this results in an over-definition for the flow-rate. Below are some examples:
Figure: three-way valve examples – the lower valve is unnecessary as the upper valve and the coil determine where the fluid should be flowing through
Figure: three-way valve examples – without a coil in the tank, the lower three-way valve is required to determine whether the fluid should flow out at the second port from the top.
Figure: three-way valve examples – In the examples above there are too many flow-determining elements

Labels

The properties of a component may be illustrated by adding a label to the drawing area. Furthermore, additional information that the user has regarding the component may be added to the label.

Another feature allows you to modify values directly through the label. In the Designer version the most important labels for a component can be generated automatically in just one click. Select the label symbol from the tool bar and click on the component for which you want to add the labels.