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Model using Zero Heating and Cooling

asked 2019-02-04 17:11:12 -0500

mldichter gravatar image

I have a building model with HVAC equipment in it, thermostats, etc. The problem I'm having is zero energy is being used for heating and cooling in the building, as in none of the equipment is ever turning on. The really weird thing though is there are absolutely no warnings generated about it.

image description

Program Version,EnergyPlus, Version 9.0.1-bb7ca4f0da, YMD=2019.02.04 15:04,
   ************* Beginning Zone Sizing Calculations
   ************* Beginning System Sizing Calculations
   ************* Beginning Plant Sizing Calculations
   ************* Testing Individual Branch Integrity
   ************* All Branches passed integrity testing
   ************* Testing Individual Supply Air Path Integrity
   ************* All Supply Air Paths passed integrity testing
   ************* Testing Individual Return Air Path Integrity
   ************* All Return Air Paths passed integrity testing
   ************* No node connection errors were found.
   ************* Beginning Simulation
   ************* Simulation Error Summary *************
   ************* EnergyPlus Warmup Error Summary. During Warmup: 0 Warning; 0 Severe Errors.
   ************* EnergyPlus Sizing Error Summary. During Sizing: 0 Warning; 0 Severe Errors.
   ************* EnergyPlus Completed Successfully-- 0 Warning; 0 Severe Errors; Elapsed Time=00hr 01min 37.26sec

I tried looking at setpoints, availability schedules, run period, thermostats exist, etc. I have no idea what I did wrong. Any ideas? Here is a google drive link to the idf file.

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answered 2019-02-07 17:38:52 -0500

In the table output, the last subtable in the ABUPS reports is "Comfort and Setpoint Not Met Summary" which shows 1000s of hours for cooling/heating setpoint not met. So, why isn't the HVAC operating in this file? Took a little bit to find this:

AirLoopHVAC:UnitarySystem,
< . . . >
,                        !- Cooling Supply Air Flow Rate Method
,                        !- Cooling Supply Air Flow Rate {m3/s}
,                        !- Cooling Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Cooling Fraction of Autosized Cooling Supply Air Flow Rate
,                        !- Cooling Supply Air Flow Rate Per Unit of Capacity {m3/s-W}
,                        !- Heating Supply Air Flow Rate Method
,                        !- Heating Supply Air Flow Rate {m3/s}
,                        !- Heating Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Heating Fraction of Autosized Heating Supply Air Flow Rate
,                        !- Heating Supply Air Flow Rate Per Unit of Capacity {m3/s-W}
,                        !- No Load Supply Air Flow Rate Method

The unitary system flow rates are all zero. This should be more like

SupplyAirFlowRate,                        !- Cooling Supply Air Flow Rate Method
autosize,                        !- Cooling Supply Air Flow Rate {m3/s}
,                        !- Cooling Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Cooling Fraction of Autosized Cooling Supply Air Flow Rate
,                        !- Cooling Supply Air Flow Rate Per Unit of Capacity {m3/s-W}
SupplyAirFlowRate,                        !- Heating Supply Air Flow Rate Method
autosize,                        !- Heating Supply Air Flow Rate {m3/s}
,                        !- Heating Supply Air Flow Rate Per Floor Area {m3/s-m2}
,                        !- Heating Fraction of Autosized Heating Supply Air Flow Rate
,                        !- Heating Supply Air Flow Rate Per Unit of Capacity {m3/s-W}
SupplyAirFlowRate,                        !- No Load Supply Air Flow Rate Method
autosize,                        !- No Load Supply Air Flow Rate {m3/s}

So, why no defaults? Because AirloopHVAC:UnitarySystem is a multipurpose wrapper which may or may not include a fan, might be heating-only, or cooling-only, etc. So, it doesn't really know it's place in life and does whatever the user asks for, in this case, nothing. But, in this case, if it holds a fan, a cooling coil, and a heating coil, and ends up with all zero airflow rates - that should be enough to throw a warning. New issue 7166 posted to request some warnings.

Once this is fixed, I would also recommend the following for this model:

  1. Use Control Type = Load instead of Setpoint, specify the control zone here in the unitary system, and ditch the (awful) SetpointManager:SingleZone:Reheat objects.
  2. Set the availability manager schedules to be always on. The UnitarySystem Fan Operating Mode Schedule will switch between continuous fan and cycling fan and with Load-based controls it won't run unless the thermostat calls for heating or cooling during the cycling fan hours.
  3. Remove the schedules from all of the coil objects - the controls will operate the coils only as needed. Overscheduling can cause problems during unoccupied hours if the system needs to run, the coils won't be available.
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Comments

@MJWitte Thanks! That did the trick.

And thanks for the other recommendations. I'll be sure to change those.

mldichter gravatar imagemldichter ( 2019-02-07 18:11:39 -0500 )edit
0

answered 2019-02-07 16:56:03 -0500

I added some output variables to plot what's going on over Jan 1. It looks like your thermostat schedules are defined, and EnergyPlus is calculating a heating load when zone air temperature dips below heating thermostat temperature.

image description

This tells me that something about availability or setpoint managers is not working. All of your availability managers use a schedule that seems fine. It looks like you are using SetpointManager:SingleZone:Reheat to tell unitary systems when to condition zones on the demand side. However, those zones are connected to AirTerminal:SingleDuct:Uncontrolled, which do not have reheat capacity. I would be surprised if that was the main culprit, but it's worth doing a test by using a different setpoint manager type in one air loop, or replacing the uncontrolled terminals with terminals that can provide reheat in one air loop. If that doesn't work, then keep adding more Output:Variable objects to debug various aspects of the model to see where the controls fall apart, like what I did to generate the image above. Those output variables that I used are below.

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Mean Air Temperature,     !- Variable Name
  timestep; !- Reporting Frequency

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Thermostat Heating Setpoint Temperature, !- Variable Name
  timestep; !- Reporting Frequency

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Thermostat Cooling Setpoint Temperature,  !- Variable Name
  timestep; !- Reporting Frequency

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Heating Setpoint Not Met Time, !- Variable Name
  timestep; !- Reporting Frequency

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Cooling Setpoint Not Met Time,     !- Variable Name
  timestep; !- Reporting Frequency

Output:Variable,
  LGstore1 ZN,                         !- Key Value
  Zone Predicted Sensible Load to Setpoint Heat Transfer Rate,  !- Variable Name
  timestep;    !- Reporting Frequency
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Asked: 2019-02-04 17:11:12 -0500

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Last updated: Feb 07