You have the possibility to control and modify the extended simultaneously percentage of ventilation heat loss here.
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Configuration 
(Toolbar) ➤ Heat Load ➤ Zeta Value
Zeta Value Vmin: Zeta for ventilation heat losses of minimum volume flow.
Zeta Value Vsu: Zeta for ventilation heat losses due to supply air.
Zeta Value Vmech, inf: Zeta for ventilation heat losses due to extract air excess.
Click 
to reset the corresponding value to the default value from EN 12831(12831.
Standard: Resets all values to the specifications from EN 12831 (2003).