Expand does create sizing:zone object. make sure you specified in simulationcontrol sizing.

simulationControl,
imulationControl,
  Yes,                                    !- Do Zone Sizing Calculation
  Yes,                                    !- Do System Sizing Calculation
  Yes,                                    !- Do Plant Sizing Calculation
  Yes,                                    !- Run Simulation for Sizing Periods
  Yes;                                    !- Run Simulation for Weather File Run Periods