I've been trying to figure out how to the IndirectHeatAlternateSetpoint option works for "Source Side Flow Control Mode" on the waterheater:mixed model in EnergyPlus. The scenario I would like to simulate is a water heater that is indirectly heated by a boiler that also has a backup electric heater. The tank setpoint is 60°C with a 2°C dead band. I only want the electric resistance heater to run if the tank temperature drops below some threshold (let's say 55°C).
Based on the documentation for the waterheater:mixed model, it seems like using the IndirectHeatAlternateSetpoint should allow me to do this, however I haven't been able to figure it out. Using the 5ZoneWaterSystems.idf example file to test this with the following setup:
Set the the "Setpoint Temperature Schedule Name" for the water heater to the lower threshold temperature schedule (55°C) with a 2°C dead band and 10000 W heater capacity
Set the "Source Side Flow Control Mode" to IndirectHeatAlternateSetpoint
Set the "Indirect Alternate Setpoint Temperature Schedule Name" to the the 60°C schedule name
My expectation was that the the electric heater would turn on only once during the example simulation, however what I get with the above configuration is that the tank temperature is controlled to 55°C and both the electric heater and the source side heater run at the same time.
Reversing the schedule names results in the water heater being controlled to 60°C and both the electric heater and the source side heater run at the same time.
What am I missing here? Any help would be greatly appreciated.
