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[EnergyPlus_Support] Re: Controlling Low Temperature Radiant System manually
Hello Hannes Roth,
I have been trying to do the same thing and could not get a complete functionning system.
I am using cosimulation through MLE+ to externally control a ZoneHVAC:LowTemperatureRadiant:VariableFlow object. This object normally has a constant supply temperature, which is controlled by the schedule of the hot water loop temperature. I have not tried but I assume that playing with this schedule will simply change the supply water temperature.
The flowrate control is more involved. Looking at the EMS actuators (the EMS objects allow to override some default behaviours of the objects in EnergyPlus, cf EMS documentation), I found the following entry:
EnergyManagementSystem:Actuator Available,WEST ZONE RADIANT FLOOR,Hydronic Low Temp Radiant,Water Mass Flow Rate,[kg/s]
So I used an ExternalInterface:Actuator object to control the flowrate with this object. However, I am not actually seeing what I expected to see: when I for example try to force the flowrate to 0 all the time, it works, but if I try to force it to the maximum value, it does not work. I presume that the actuator does not completely override the internal control loop but I don't understand why and how to fix that. I can think of dirty fixes to deal with it, but I would like to understand what is happening. It is as if I was not actually controlling the flowrate but only able to cap it to a max value manually.
One solution I see that given that I know how the flowrate is chosen (basically interpolated between min and max flowrate based on the radiant heating setpoint, throttling range and temperature of the zone served ), I could backcompute the required radiant heating setpoint required to get some particular flowrate. (this means playing with the corresponding schedule). I hve already done it for electric TABS and it worked fine.
However, this solution only works for this particular problem and I would like to understand my issue with the external interface actuators.
Hope this partly answers your question and hope to see further answer to our issues.
I can also share my .idf in case what i said is not clear.
Best
Tomasz
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