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P3 = P1 + P2 (first law of thermodynamics)
f3 is recalculated based on the applicable diversity standard, applied on the TOTAL amount of tapflow or TOTAL amount of dwellings on the secondary side.
the supply temperature t3supply is defined by the user
the return temperature t3return is calculated as the mixed return temperature (v3 * t3return = v1 * t1return + v2 * t2return)
the volume flow v3 is calculated