Our calculation engine uses the Bell calculation method. This method says that if the outlet air temperature is below the condensing temperature, it is possible to set the total capacity as the condensing capacity plus the superheating capacity and calculate the resultant capacity using this formula: Q tot = AirFlow * (Condensing Temp – Air inlet temperature) * Coil Efficiency. Bell theory says that the approximation that results, is very acceptable. If the outlet air temperature is higher than the condensing temperature, the approximation may be not acceptable anymore, so for this reason we added another method of calculation that separates the two condensing surface from the superheating surface and calculates them separately, for an higher precision. In conclusion you can set this option when the outlet air temperature is higher than the condensing temperature to improve the calculation results.