Severe errors for Fan Power modelling of VAV system in Energyplus

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Dear all:****


In a baseline building modeling for LEED EApr2 documentation, I have some
troubles with the simulation reports that shows unusually high amounts of
severe errors (over 1000); when I try to model System Fan Power according
G3.1.2.9. and procedure proposed by James V Dirkes II, PE in a previous post
(pro-rating fan power to supply/ret?urn fans per 90.1-2007?).****

I am concerned if we can be observed by LEED reviewer team about this severe

Simulation details:****

-Baseline model consist of six-levels building for typical office usage
(8000m2 area approx.)

-HVAC system type 8, VAV with PFP zones according ASHRAE 90.1-2007 appendix

-Energyplus software has been used.****

-HVAC systems has been modeled with HVAC templates in this configuration:***

-Chilled Water loop with HVACTemplate:Plant:ChilledWaterLoop,
Chiller and Cooling Tower****

-System-side equipment with HVACTemplate:System:VAV****

-Zone-side equipment with HVACTemplate:Zone:VAV:FanPowered****


-System Fan Power modeling details:****

-Supply Fan Total Efficiency = 0.6 ****

-Supply Fan Delta Pressure = 1495 Pa****

-Supply Fan Motor Efficiency = 0.9****



-Severe errors details:****

-When Supply Fan Delta Pressure exceeds 500Pa,
simulation error log exposes unusually high amounts of recurrent severe
errors like that (over 1000 severe errors):


** Severe ** FindRootSimpleController: Controller error for controller =
** ~~~ ** Environment=SANTIAGO, at Simulation time=01/01 04:30 -
** ~~~ ** Controller function is inconsistent with user specified
controller action = Reverse action
** ~~~ ** Actuator will be set to maximum action
** ~~~ ** Controller control type=Temperature
** ~~~ ** Controller temperature set point = 11.41 [C]
** ~~~ ** Controller sensed temperature = 12.17 [C]
** ~~~ ** Controller actuator mass flow rate set to 0.70 [kg/s]
** ~~~ ** Controller actuator temperature = 12.20 [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****

-Also I tried to reduce Supply Fan Total Efficiency and
maintain Supply Fan Delta Pressure less than 500Pa but severe errors also

Suggestions to reduce this errors or modeling system fan power in a
different way? ****

Any comments will be appreciated....****


Alvaro Urrutia Astorga

Alvaro Urrutia's picture
Joined: 2011-10-18
Reputation: 0


I can only speak to the EnergyPlus side of things (not LEED). You will have to look into the created .idf and analyze the individual cases through customized outputs to verify the system is working as you desire.

From the one error you listed in your post, the data center cooling coil is working to heat the air stream on January 1st at 4 in the morning. The air entering the coil is 54F (12.17C) and the setpoint is 52.5F (11.41C). The temperature of the water entering the coil is 54F. The problem here is that 54F water can?t cool the air to 52.5F, but since ?cooling? is required, E+ doesn?t know how to react. With the reported chilled water temperature, the chiller is likely not on. (I?ve seen that error a time or two, and generally the chiller wasn?t on and there was no flow in the chilled water loop, so the model was not particularly compromised.) You?ll want to verify how the system is reacting at that timestep and the one after to make sure there isn?t a deeper issue.

I don?t think the supply fan pressure would be directly causing the issue, possibly just adding enough heat to require cooling at more timesteps. I would check how the Setpoint Managers were set up in the .idf input file, which may likely be the root cause.

I suggest using the Output:Variable objects to verify accurate system performance at the timesteps in question, such as the ones listed below. You may also want to output some air temperatures across the air handling unit and their corresponding setpoints.

*, !- Key Value
Chiller Evap Water Outlet Temp , !- Variable Name
Timestep; !- Reporting Frequency

*, !- Key Value
Chiller Evap Water Mass Flow Rate , !- Variable Name
Timestep; !- Reporting Frequency

*, !- Key Value
Chiller Evap Heat Trans Rate , !- Variable Name
Timestep; !- Reporting Frequency

*, !- Key Value
Total Water Cooling Coil Rate , !- Variable Name
Timestep; !- Reporting Frequency

Cooling Coil Inlet, !- Key Value
System Node MassFlowRate , !- Variable Name
Timestep; !- Reporting Frequency

If you still have questions about the .idf file, you can contact the EnergyPlus Help Desk.

Elyse Malherek

Malherek, Elyse's picture
Joined: 2011-10-02
Reputation: 0