In the group kind of calculation you can choose if to recalculate a unit known to you with different conditions or to calculate a new unit. If you choose recalculion, please enter the exact identification of unit and then the corresponding thermal data.
The "calculation" / "recalculation" to be started with button "start calculation!". In the lower part of the window of group result, the result will be displayed in case of a successful calculation. You always get the optimum heat exchanger for this case of application.