It looks like this is just a matter of how -by default- OpenStudio translates the CoilSystem:Cooling:DX object to IDF. By default, the exported object doesn’t include the Dehumidification Control Type (and related fields).
What OpenStudio exports:
CoilSystem:Cooling:DX,
Two Stage DX Coil With Humidity Control CoilSystem, !- Name
Always On, !- Availability Schedule Name
Node 6, !- DX Cooling Coil System Inlet Node Name
Node 10, !- DX Cooling Coil System Outlet Node Name
Node 10, !- DX Cooling Coil System Sensor Node Name
Coil:Cooling:DX:TwoStageWithHumidityControlMode, !- Cooling Coil Object Type
Two Stage DX Coil With Humidity Control; !- Cooling Coil Name
What it needs to be in IDF to enable dehumidification control:
CoilSystem:Cooling:DX,
Two Stage DX Coil With Humidity Control CoilSystem, !- Name
Always On, !- Availability Schedule Name
Node 6, !- DX Cooling Coil System Inlet Node Name
Node 10, !- DX Cooling Coil System Outlet Node Name
Node 10, !- DX Cooling Coil System Sensor Node Name
Coil:Cooling:DX:TwoStageWithHumidityControlMode, !- Cooling Coil Object Type
Two Stage DX Coil With Humidity Control, !- Cooling Coil Name
CoolReheat, !- Dehumidification Control Type
Yes, !- Run on Sensible Load
Yes, !- Run on Latent Load
No, !- Use DOAS DX Cooling Coil
2.0; !- DOAS DX Cooling Coil Leaving Minimum Air Temperature
After adding these fields, it’s “just” a matter of right-sizing capacities, configuring the outdoor air economizer, and setting supply/return airflows. With those tweaks, I’m getting good results (constant 45% RH) using the Barcelona EPW (TMY) file.