How to add a controller to a hot water loop

edit

I think the SDK documentation is outdated. The PlantLoop.hpp#L209 does mention:

/** Adds a new demand branch for component and returns a bool indicating success.
 * This method will create a new ControllerWaterCoil if hvacComponent is a
 * CoilCoolingWater or a CoilHeatingWater.
 */

but looking at the PlantLoop.cpp# I cannot see anywhere the creation of a Controller:WaterCoil automatically.

A Controller:WaterCoil (doc) is not needed to make a Heating/Cooling Water Coil function. It is only needed if you want to control a coil at one node based on the condition at another node.

As the reader probably noted when reading the descriptions of the coil syntax shown earlier in this section, there were no controls attached directly to a particular component. This is because the input can be simplified somewhat by entering node names to be controlled. This avoids having to search through multiple lists of component types for the sake of simply controlling components. The Controller:WaterCoil shown below is a way of controlling variables at one node based on conditions at another node

Edit: I stand corrected

I tested the behavior using the following:

In [1]:
model = OpenStudio::Model::Model.new
coil = OpenStudio::Model::CoilHeatingWater.new(model)
plant_loop = OpenStudio::Model::PlantLoop.new(model)

In [2]: coil.controllerWaterCoil.empty?
Out[2]: => true


In [2]: plant_loop.addDemandBranchForComponent(coil)
        coil.controllerWaterCoil.empty?
Out[2]: => false

Upon further investigation in the source code, this is done in the CoilHeatingWater::addToNode that's being called when using PlantLoop::addDemandBranchForComponent

See CoilHeatingWater.cpp#L95

A Controller:WaterCoil is only necessary for water coils that are connected to an AirLoopHVAC directly. Coils inside of reheat terminals or unitary equipment objects do not need them, because in these situations the coils are controlled by the object that contains them.

Based on your screenshots, it doesn't look like these coils are connected to an AirLoopHVAC directly. If they were, there would be little circles on the coil icon.

In the screenshot below, the top coil is connected to an AirLoopHVAC directly, while the bottom coil is inside of an AirTerminal:SingleZone:Reheat. The top coil has a Controller:WaterCoil but the bottom coil doesn't.