Attaching a Generator:InternalCombustionEngine unit to a plant loop

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I am attempting to create a plant loop which provides heat recovery from a Generator:InternalCombustionEngine object to a building hot water loop to reduce demand via a heat exchanger. I am getting turned around in how to set this up.

Currently i have the Generator:InternalCombustionEngine on the supply side of a heat recovery plant loop I have defined, as it is supplying the heat. I then have a HeatExchanger:FluidtoFluid on the demand side of this loop, which in turn is attached to the supply side of the building Hot Water loop, in parallel with a number of boilers. The setpoint of this loop is the cogen outlet node, set to a constant 90C. This node is the outlet node for the Plant Side of the loop.

The result of this is that my building hot water loop has for an unknown reason is now supplying only about 30-35C, whereas before these connections it was supplying as intended (between 82-65C or so). I have not made any changes to the Hot Water Loop aside form connecting the heat exchanger. Node temperatures of the heat exchanager do not indicate that heating is flowing the other way. Heat is flowing from the Generator Loop to the HW loop, just nowhere near as much as it should be.

My questions: - Why do I not have the option to choose my Generator:InternalCombustionEngine in a PlantEquipmentList? I am not clear on how to 'control' this plant lop otherwise, or what my PlantEquipmentList should include. - The example file HeatRecoveryPlantLoop.idf seems to put all of its generators on the demand side of the loop. I cant make sense of this. I also am not sure its possible for me as this means my heat exchanger would be on the supply side of the loop, and I had issues getting this to work as it was basically on the 'wrong' side.

Essentially I am trying to control the heat exchanger to provide heat to the supply side of the hot water loop and offset the boiler load when it can. Any insights in how to set this up would be great.

Relevant objects:

HeatExchanger:FluidToFluid,
    HR HX,                   !- Name
    Cogen_Maint_Sch,         !- Availability Schedule Name
    HX HR Side Inlet,        !- Loop Demand Side Inlet Node Name
    HX HR Side Outlet,       !- Loop Demand Side Outlet Node Name
    autosize,                !- Loop Demand Side Design Flow Rate {m3/s}
    HX HW Side Inlet,        !- Loop Supply Side Inlet Node Name
    HX HW Side Outlet,       !- Loop Supply Side Outlet Node Name
    autosize,                !- Loop Supply Side Design Flow Rate {m3/s}
    Ideal,                   !- Heat Exchange Model Type
    autosize,                !- Heat Exchanger U-Factor Times Area Value {W/K}
    HeatingSetpointModulated,!- Control Type
    HX HW Side Outlet,       !- Heat Exchanger Setpoint Node Name
    0,                       !- Minimum Temperature Difference to Activate Heat Exchanger {deltaC}
    LoopToLoop,              !- Heat Transfer Metering End Use Type
    ,                        !- Component Override Loop Supply Side Inlet Node Name
    ,                        !- Component Override Loop Demand Side Inlet Node Name
    Loop,                    !- Component Override Cooling Control Temperature Mode
    1;                       !- Sizing Factor

Generator:InternalCombustionEngine,
    Cogen,                   !- Name
    1000000,                 !- Rated ...