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5 Thermal systems
This section provides an overview of the basic simulation-algorithms used in Polysun for thermal
components as well as useful background information on the physical models to be implemented.
5.1 Solar fractions
When viewing “Results for the variant” the different solar fractions SFi (input oriented), SFn (net)
and SFg (gross) are displayed. These refer to diverse limits of the system, see fig. 5. Only those
solar fractions for the variants that can be automatically calculated are displayed.
SFi =
S sol
Solar _ energy _ to _ storage _ tank
=
Solar _ energy _ to _ storage _ tank _+ Auxiliary _ energy _ to _ storage _ tank S sol + S aux
SFn =
Qsol
Solar _ energy _ to _ the _ system
=
Solar _ energy _ to _ the _ system _+ Auxiliary _ energy _ to _ the _ system Qsol + Qaux
SFg =
E sol
Irradiance _ onto _ collector _ area
=
Irradiance _ onto _ collector _ area _+ Auxiliary _ energy E sol + E aux
For the purpose of the analysis of the system’s behaviour it is sometimes required that the solar
Figure 8: limits for the calculation of solar fractions
fraction for hot water and heating are specified separately. This is only possible for special system
configurations where the heat for heating and hot water are run and stored separately. In systems
equipped with return flow bypass or with a tank used as a hydraulic compensator choosing whether
in the consumer the heat was generated at some point at an earlier time-interval through the solar
collectors or the auxiliary heating is not possible.
Polysun employs just like Polysun 3 an approximate calculation method that may be applied in all
situations. The separate specification of solar fraction for hot water and heating is based on the
weighting of the overall solar fraction with the heat demand over a defined time interval.
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