How to add a WaterToAir Heat Pump

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To further clarify, you add the OS:ZoneHVAC:WaterToAirHeatPump to a thermal zone by dragging and dropping it from the Library on the right ("under Water to Air HP") into an empty slot in the Zone Equipment column. You have three choices of OS:ZoneHVAC:WaterToAirHeatPump - electric, natural gas or hot water backup. Probably simplest to get you started is electric.

Thank you for the very thorough explanation. This all makes sense to me, and sorry this was my fault for not framing the question clearly, so let me back up and give better context. I am trying to model a DOAS which uses a water-source heat pump. I've been trying to add the coils to the DOAS air loop. I've tried adding the OS:AirLoopHVAC:UnitarySystem object to host these coils, but they come with extra components I don't need (a supplemental heating coil). When I tried to have the object controlled by the load, I notice I have oversizing and an inefficient system. This lead me to my question.

Also, the since the DOAS is only serving the ventilation requirement, I need to control the coils by a setpoint manager, not the load, so using the OS:AirLoopHVAC:UnitarySystem object hasn't been useful since if I remove anything, it breaks the object and I don't see airflows through the airloop, even though the simulation runs completely. For reference, this post gave me an idea of how to approach it, but so far nothing has worked well. I currently have the objects controlled by the load, and am hard sizing the coils.