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Abbreviations in Polysun Simulation Results

Solar Fractions

When viewing “Results for the system diagram” the different solar fractions SFi (input oriented), SFn (net) and SFg (gross) are displayed. These refer to diverse limits of the system, see the next figure. Only those solar fractions for the system diagrams that can be automatically calculated are displayed.

\(SFi\  = \ \frac{Solar\ energy\ to\ storage\ tank\ }{Solar\ energy\ to\ storage\ tank + Auxiliary\ energy\ to\ storage\ tank} = \ \frac{Ssol\ }{Ssol + Saux}\)

\(SFn\  = \ \frac{Solar\ energy\ to\ the\ system\ }{Solar\ energy\ to\ the\ system + Auxiliary\ energy\ to\ the\ system} = \ \frac{Qsol\ }{Qsol + Qaux}\)

\(SFg\  = \ \frac{Irradiation\ onto\ collector\ area\ }{Irradiation\ onto\ collector\ area + Auxiliary\ energy} = \ \frac{Esol\ }{Esol + Eaux}\)

Figure: limits for the calculation of solar fractions

For the purpose of the analysis of the system’s behaviour it is sometimes required that the solar 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.

\(S_{Fn}^{Heiz} = \frac{\sum_{i}^{}{S_{Fn}^{i} \cdot Q_{Heiz}^{i}}}{\sum_{i}^{}Q_{Heiz}^{i}}\)

\(S_{Fn}^{WW} = \frac{\sum_{i}^{}{S_{Fn}^{i} \cdot Q_{WW}^{i}}}{\sum_{i}^{}Q_{WW}^{i}}\)

In this context Polysun uses for the calculation a variable time-interval ranging from two days to two weeks. The output result will be simply a yearly value as monthly values would not be meaningful.

Interpretation example: During the summer months the heat demand from the heating system is very low and the solar faction is therefore relevant only for the hot water.

Discussion: If compared with the direct calculation (separate buffer tanks) the solar fractions achieved by means of the above formula are much closer. The separated solar fractions of  further consumers (like e.g. swimming pool or solar cooling system) may be defined in analogous manner.

Recommendation: Use reference systems! The specification of separate solar fractions has no significance for design or customer service purposes. A much more crucial role will be played by the use of the reference systems offered as a standard in Polysun. This will enable to elicit the influence of single system components and to optimize the heating system.

Denominations and Representation of the Results

The abbreviations for the energy balances are always based on the same model. Therefore “QparS” means the heat energy transferred from the pump to the solar loop.

“Q” stands for the energy transferred to the system, or rather to the hydraulic system, “par” for parasitic energy and “S” for the circuit, in this case, the solar loop. If the last index is missing, here S, it is meant the transferred heat energy to all loops by all available pumps.

The meaning of the various letters of the alphabet and the positions are explained in the table below.

Heat loss to interior space “Qint” means the losses of all the components present indoors, also including the chemical energy losses in boilers with less than 100% efficiency.

“Qdem” is the energy demand, calculated by Polysun, that should be possibly covered. In the case when the “Quse” (the effective energy consumption) is lower than the “Qdem”, the energy demand can’t be covered and the corresponding warning appears. The causes are sought primarily in the installation height of the connections in the boiler or of controller settings. The availability of hot water and building heating shown in the component results indicate what percentage of energy demand is covered.

In case of the collector, “Esol” is referring to the solar irradiation onto the aperture area of the collector. “Eaux” means the chemical energy (highest value of heat of combustion) of combustible fuel.

Table: Denomination and representation of the results

Letter positionLetterDefinition
1EEnd energy (fuel and electrical power consumption)
 QEnergy to the system or energy withdrawn from the system
 SEnergy to the tank or energy withdrawn from the tank
2. to 4.  
 solSolar energy (example: Qsol = Energy supplied from collector to fluid)
 outEnergy withdrawn
 useEnergy consumption (amount of energy actually consumed for domestic hot water, swimming pool, building and heat sink)
 demEnergy demand (theoretically calculated value referring to the amount of energy required, for example, to heat the cold water of the cold water piping to the desired hot water temperature)
 auxAuxiliary energy (energy of heat generators or electrical air-conditioning devices, for example Qaux = energy supplied from heat generator to fluid)
 parAuxiliary or parasitic energy (pumps and fans)
 intEnergy to indoor room (all components placed indoors, for example Qint = heat loss to indoor room)
 extEnergy to surroundings (all components placed outdoors, for example Qext = heat loss to surroundings)
 defEnergy deficit (difference between energy demand and energy consumption)
 xfrTransferred energy
 ventilEnergy in ventilation of building
 transEnergy transmission in building
 XHeat transmission
 MMidex (solar and auxiliary)
  Total of all loops