I'm a student Engineer and I am new with EnergyPlus. I am doing a simulation to obtain the heating and cooling loads in peak winter and summer conditions. I am doing the simulation setting through the class: "SizingPeriod:DesignDay" the worst winter day (by considering no internal heat gains and no solar radiation) and the worst summer day(by considering internal and solar heat gains). The building has two thermal zones and the HVAC system is ideal.

I do not know how to proceed. The first question is: since, as prescribed by the UNI EN 12831 for a winter design day, I should set a constant temperature throughout the day (-8°C for my location), where I can set this value (and also considering solar radiation equal to zero)? Should I not use the Weather File? Moreover, Should I consider the design day in the SizingPeriod class or set it also in the section RunPeriod (by selecting also system sizing)?

The last question is: Can I run a simulation for these two different days and obtaining the required values of cooling and heating loads or should I run them separately?