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# Find Root Simple Controller: Controller Water Coil Error

I am encountering this error when running my simulation in OpenStudio:

* Severe * FindRootSimpleController: Controller error for controller = "CONTROLLER WATER COIL 5"

* ~~~ * Environment=OMAHA EPPLEY AIRFIELD ANN CLG .4% CONDNS DB=>MWB, at Simulation time=07/21 00:00 - 00:10

* ~~~ * Controller function is inconsistent with user specified controller action = Reverse action

* ~~~ * Actuator will be set to maximum action

* ~~~ * Controller control type=Temperature

* ~~~ * Controller temperature setpoint = 18.00 [C]

* ~~~ * Controller sensed temperature = 35.72 [C]

* ~~~ * Controller actuator mass flow rate set to 10.09 [kg/s]

* ~~~ * Controller actuator temperature = 35.79 [C]

* ~~~ * Note: Chilled water coils should be reverse action and the entering chilled water temperature (controller actuator temperature) should be below the setpoint temperature

* ~~~ * Note: Hot water coils should be normal action and the entering hot water temperature (controller actuator temperature) should be above the setpoint temperature

I am encountering this error for every coil that I have. The entering water temperatures for the heating coil and cooling coil are 170F and 42F respectively. The setpoint temperature is 60F for Cooling and 100F for Heating. Also note that 3/5 of my systems are dual duct systems, while the other two are single duct VAV systems. Also, I am using District Heating and Cooling due to the fact that I am looking at a single university building being served by a central plant; therefore, I have no Condenser Water Loop. Any idea as to what is causing these errors? Also, thoughts on not including the Condenser Water Loop?

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The Controller:WaterCoil object tries to measure air temperature (sensor) in order to know how to alter water flow rate (actuator). From the error message that you posted, it seems like the entering water temperature (actuator) is 35.79 $^{\circ}$C / 96.4 $^{\circ}$F, which is not close to the 42 $^{\circ}$F that you are expecting. I would double-check the setpoint manager controlling the last chilled water supply node after the DistrictCooling object.

It's fine to not have a condenser water loop, since the district heating and cooling components don't have a heat rejection process that needs to be simulated.

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This is a weird problem. I have encountered the same problem, and I solved this by changing the "Central Cooling Design Supply Air Humidity Ratio" of Sizing:System, from 0.008(by default) to 0.01. Actually, I don't understand the underlying reason for this modification, but anyway it works.

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