Hello, i read the Engineer references and get the " Ideal Loads Sizing Simulations" and "ideal zonal system". It seems complicated for me. As far as my understanding, the setting " Do zone/system/plant sizing calc" work with design day period by " Ideal Loads Sizing Simulations" and "ideal zonal system". But: 1/ what is difference between an ideal zonal system/ideal load sizing simulations and a real hvac in this process ? 2/ What is the purpose for Run simulation for sizing period ? i read that E+ sizing process also does time-step calc for Do zone/system/plant sizing calc (please explain in detail if i am wrong). Thank