For the water-to-air heat pump, you need to use coils of the type WaterToAirHeatPump.

Depending on your project, you need to use:

• A cooling coil
  • Coil:Cooling:WaterToAirHeatPump:ParameterEstimation
  • Coil:Cooling:WaterToAirHeatPump:EquationFit
  • Coil:Cooling:WaterToAirHeatPump:VariableSpeedEquationFit
• A heating coil
  • Coil:Heating:WaterToAirHeatPump:ParameterEstimation
  • Coil:Heating:WaterToAirHeatPump:EquationFit
  • Coil:Heating:WaterToAirHeatPump:VariableSpeedEquationFit

These coils can live in a ZoneHVAC:WaterToAirHeatPump or in a AirLoopHVAC:UnitarySystem. The documentation is pretty obscure about this fact, but this question - Using Coil:Cooling:WaterToAirHeatPump:EquationFit - confirms that fact.

So in your you case, you need to use the AirLoopHVAC:UnitarySystem, and place that on your DOAS AirLoopHVAC loop. The UnitarySystem is a bit weird in the sense that you can choose or not to package the fan in there or not...

not... In OpenStudio, you might get into a problem if you put everything (cooling coil, heating coil, fan) in the same unitary system because you won't be able, without an E+ measure, to add the required setpoint manager on the outlet of each coil. See these two questions for more information:

• Unitary System: where to add the supply fan?.
• Add Setpoint Manager to Cooling Coil Air Node of Unitary System