Severe Error: FindRootSimpleController: Controller error for controller

asked 2024-08-15 12:08:34 -0600

Nathalia

281 ●1 ●5

updated 2024-08-15 13:03:05 -0600

Aaron Boranian

14145 ●83 ●24 http://bigladdersoftware.com/

Hello, I am conducting a simulation for a building that has a water-cooled chiller air conditioning system with a central chilled water plant, and heating by electric resistance. The system has one VAV per floor. When I finish the simulation, the following error appears for all of my VAV systems. I would like to understand why this error is being generated and what I need to review in the simulation. I am using EnergyPlus version 24.1.0.

** Severe  ** FindRootSimpleController: Controller error for controller = "2 PAV COOLING COIL CONTROLLER"
**   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=04/20 06:02 - 06:03
**   ~~~   **   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 = 17.65 [C]
**   ~~~   ** Controller sensed temperature = 19.46 [C]
**   ~~~   ** Controller actuator mass flow rate set to 12.43 [kg/s]
**   ~~~   ** Controller actuator temperature = 19.46 [C]
**   ~~~   ** The entering chilled water temperature (controller actuator temperature) should be below the setpoint temperature.

Thank you

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You may have stumbled upon an open issue. You may want to look up past UMH posts, e.g.:

Denis Bourgeois ( 2024-08-16 05:47:35 -0600 )edit

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answered 2024-08-16 07:31:36 -0600

rraustad

13804 ●79 ●12 http://www.fsec.ucf.edu/

The cooling coil outlet air set point temperature is 17.65 C and the coil entering water temperature is 19.46 C so it is not possible to reduce the air temperature below 19.46 C. The problem here is that the chilled water is not cold enough. Either the plant leaving water temperature set point is too high or the plant is not able to reduce the water temperature to the set point.

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Thank you for your response. This is my first project involving a chilled water plant, so I'm not entirely sure what to check to address this issue. How could I carry out this investigation? In the HVACTemplate:Plant, I set the Chilled Water Design Setpoint = 7°C and the Delta Temperature = 6°C. I'm using the default temperatures for the Chilled Water Setpoint Outdoor dry-bulb low, Reset outdoor Dry-bulb low, Setpoint Outdoor dry-bulb high, and Reset outdoor Dry-bulb high. What else could I modify in the HVACTemplate? Or should I review the values in the expanded file?

Nathalia ( 2024-08-16 08:19:58 -0600 )edit

You could look at the plant outlet water temperature and the chiller evaporator heat transfer to see if the chiller is running at max capacity. If the chiller is max'd out then increase the size. If there is more chiller capacity available then investigate the expanded idf for why the plant is not targeting a lower temperature.

rraustad ( 2024-08-16 08:29:44 -0600 )edit

Hi. I investigated using the "Chiller Evaporator Outlet Temperature" output and noticed that, generally, between 08:15 and 19:30, the chiller has a water outlet temperature of 7°C, but outside of these hours, there is an increase in temperature, sometimes reaching 18°C. Typically, around 08:00, the first chiller has a temperature of 7°C, while the second chiller still has a higher temperature. Then, in the next timestep, both chillers equalize. Since my project is a hospital, the air conditioning schedule operates 24 hours a day.

Nathalia ( 2024-08-22 12:02:01 -0600 )edit

(continuation) I would like to know if this could be causing the error and if it is something I should be concerned about. If so, where can I adjust in EnergyPlus to ensure that the outlet temperature always stays at 7°C? Thank you!

Nathalia ( 2024-08-23 07:07:30 -0600 )edit

Look for something that schedules a plant on and off, in the Plant Equipment Operation Scheme:

PlantLoop,
  Chilled Water Loop,      !- Name
  Water,                   !- Fluid Type
  ,                        !- User Defined Fluid Type
  CW Loop Operation,       !- Plant Equipment Operation Scheme Name

rraustad ( 2024-08-23 07:39:42 -0600 )edit

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Severe Error: FindRootSimpleController: Controller error for controller

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Severe Error: FindRootSimpleController: Controller error for controller