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# Calculation Of The Seasonal Performance Factor

## Question

How are the seasonal performance factors (SFP) calculated?

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In the program three different seasonal performance factors are shown on the "Simulation Results" page. In addition the SPF according to the VDI 4650 is presented.

Generally the SPF is calculated as follows:

SPF = benefit / expenditure

Depending on the system boundaries which are considered, the energies taken into account differ. It should thus be compared only SPF of the same type.

SPF Heat pump

This SPF limits the energy balance to the heat pump. It is the largest of all SPF and can usually help in assessing the operation of the heat pump. In the monoenergetic operation mode it is usually somewhat higher, since at very low source temperatures (= bad seasonal performance factor of the heat pump), the heating element takes over the supply.

Benefit: The heat supplied by the heat pump heat.

Expenditure: The electricity consumption of the heat pump without external pumps and without heating element.

SPF of heat pump system

This SPF is a good benchmark for the entire system. The efficiency of the heating element is set at 100 %. Furthermore, existing heating circuit pumps on the sink side are not considered.

Benefit: The heat supplied by the heat pump + the energy from the heating element.

Expenditure: The electricity consumption of the heat pump + heating element energy consumption + electricity consumption of external pumps on the heat source side of the heat pump.

SPF Generator system (Heat pump + Solar)

This SPF is usually much higher than the previous SPF, because for the low expenditure of the solar circuit pump a large amount of energy is delivered as a benefit.

Benefit: The total heat supplied by the HP + the energy from the heating element + the energy from the solar collector.

Expenditure: The electricity consumption of the heat pump + heating element energy consumption + electricity consumption of external pumps on the heat source side of the HP + electricity consumption of the solar loop pump.

SPF according to VDI 4650

It is especially relevant for the approval of funding in Germany. This SPF is calculatedby using simple equations decribed in the VDI 4650 (2009). So they may differ from the simulated SPF.