I'm not sure what you mean by "design capacity", so the following information may not answer your question, but I'll do my best with an assumed definition..
EnergyPlus does allow you to enter the design capacity for DX coils ("Gross Rated Total Cooling Capacity" and "Gross Rated Sensible Heat Ratio" fields in the DX coil object)
If you autosize the capacity, it will display that capacity in the Equipment Summary report.
E+ - distinguishes between "Nominal" capacity and "Rated" capacity in the Equipment Summary report. "Rated" is the capacity at the AHRI test conditions. "Nominal" is the capacity needed by the coil to produce the "rated" capacity PLUS the additional load imposed by the fan energy.
E+ also distinguishes between the "Calculated" and "User" loads. "Calculated" is the load E+ determines in its sizing calculations. "User" is "Calculated" x the Sizing Factors that you have defined in Sizing:Parameter, Sizing:Zone or Sizing:System
