Logic relation to other controls
In case multiple controllers access a common output (and only in this case) it will be necessary to define which is the logical link between the different signals. In this case in particular the identification of clear controller priorities will be crucial.
The list shown in the controller mask restores the priority of all controllers. The relevant controller will be identified as «this controller». Selecting a controller within the list the relevant controller will be listed directly ahead of the remaining controllers. Should two controllers be linked special care should be paid to ensure these appear consecutively in the list and that the link option is selected for the latter of the two. Options are as follows:
- And-Operation: if the current status is «on» and the relevant controller is likewise «on» the resulting status will be «on». When either status is «off» the output signal will be switched off.
- Or-Operation: if the current status is «on» or the relevant controller is likewise «on» the resulting status will be «on». If both statuses are «off» the output signal will remain «off».
- Exclusive-or-Operation: If the current status and the relevant controller are different the resulting status will be «on». If both statuses are alike the output signal will be switched off.
Priority of control
The list shown restores the priority of all controllers. The relevant controller will be identified as «this controller». Selecting a controller within the list the relevant controller will be listed directly ahead of the remaining controllers.
All values shown in the graphical evaluation are hourly averages. The actual hot water demand with the respective design flow rate will be often obtained only for 10 minutes. That's why hourly averages often lie below the design flow rate.
The graphical evaluation will be available starting from the Professional level version.
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:
- 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).
So as to obtain defined conditions in all pipings across the hydraulic system flow rate producers should be carefully selected. In a first step Polysun analyses before each simulation the piping and the use of flow rate producers. If these have not been consistently selected the system will need to be reviewed paying particular attention not to use too many or too few pumps within a single loop.
It may happen that also on very fast computers some systems have very long simulation times. The numeric algorithm of Polysun is optimized for typical solar systems. A very slow simulation occurs in particular when some parameters have extreme values. For example, if a pump is under- or over-dimensioned, the consequence would be a slow simulation. Solution: begin with an existing template and don´t change too many values at the same time.
It's a matter here of a deliberately allowed rounding error. The reference amount will be tapped with the design flow rate and a variable duration. For this purposes time units will be measure in seconds and always rounded up to whole seconds.
When the hot water system is not running the water left in the pipes cools off. That's why typically when first tapping water you will get a certain amount of too cold water. The resulting energy deficit will be added up and amounts as a rule to a monthly 2-5% of the energy demand.
Under energy demand the monthly energy demand will be listed in kWh. Since not all months have the same number of days monthly variations may be observed (for example February/March = 28/31).
It may happen that the energy produced by the solar collectors and the auxiliary heating is insufficient to meet the energy demand of the planned system. In such cases, the temperatures of the domestic hot water and the building are different from the nominal values that were set in the project. Polysun marks these systems in the graphs and reports with the message «Energy demand not met».
To meet the demand, the energy consumer must be supplied with more solar thermal energy or auxiliary energy. In some cases, it is possible to obtain it by increasing the collector area or the power of non-solar auxiliary heating. However, the message "Energy demand not met" often means that the energy use is inefficient and the project must be revised.
The hot water withdrawal of a simulation will be defined through the following parameter:
- Nominal flow rate (for example 360 l/h)
- Daily profile (for example maximum daily peaks, that is for the 24 hours of the day in %: 0, 0, 0, 2.3, 2.3, 2.3, 2.3, 8, 8, 8, 2.3, 2.3, 8, 8, 8, 2.3, 2.3, 8, 8, 8, 2.4, 2.4, 2.4, 2.4)
- Daily hot water demand for single months (for example always 200 l/day from January to December)
In Polysun the amount of hot water that will be obtained during a given hour will always be determined at the beginning of such hour (for example 8% of the daily demand of 200 l, that is 16 litres, will be obtained in the morning between 8:00 and 9:00). In the Polysun simulation reference will always be made at the beginning of an hour to the total amount of hot water for such hour together with the nominal flow rate (in the above example 16 litres will be obtained with 360 litres/h that is water will be drawn for 2.66 minutes.
In the variant results display the user will be able to view the different solar fractions: Sfi (input-oriented), Sfn (net) and Sfg (gross). These refer to different limits of the system.