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There isn't a setpoint manager that will adjust a PlantLoop temperature setpoint based on it's load (that I'm aware of). There are air system setpoints that do something similar, but you may need to program a SetpointManager:Scheduled with an EMS actuated schedule to mimic a similar control of your boiler loop.

You can use the Water Heater Tank Temperature, $T_{tank}$, to represent the reading from the aquastat. You can approximate perfect PID control by using the Water Heater Total Demand Heat Transfer Rate, $\dot{Q}_{demand}$, the mass flow rate of your boiler loop, $\dot{m}$, and the Source Side Effectiveness, $\varepsilon$, to calculate the required setpoint temperature:

$$T_{set} = T_{tank} + \frac{\varepsilon \cdot \dot{Q}_{demand}}{\dot{m}\cdot C_p}$$

There isn't a setpoint manager that will adjust a PlantLoop temperature setpoint based on it's load (that I'm aware of). There are air system setpoints that do something similar, but you may need to program a SetpointManager:Scheduled with an EMS actuated schedule to mimic a similar control of your boiler loop.

You can use the Water Heater Tank Temperature, $T_{tank}$, to represent the reading from the aquastat. You can approximate perfect PID control by using the Water Heater Total Demand Heat Transfer Rate, $\dot{Q}_{demand}$, the mass flow rate of your boiler loop, $\dot{m}$, and the Source Side Effectiveness, $\varepsilon$, to calculate the required setpoint temperature:

$$T_{set} = T_{tank} + \frac{\varepsilon \frac{\dot{Q}_{demand}}{\varepsilon \cdot \dot{Q}_{demand}}{\dot{m}\cdot \dot{m}\cdot C_p}$$