Hi Jim, even when your zone temps are stable, they look pretty unstable to me. Did you try this with smaller timesteps? This "looking ahead" kind of PID control is possibly set up to work well with zones at normal temps, but is having trouble with zones at -18C. It's very hard to write algorithms that are one-size-fits-all for this kind of control. I've had to do this kind of thing in TrnSys and one ends up building kind of dynamically adjusting PID control. I won't be supprised if the code is having problems. Are there any other factors causing step changes that may need to be "ramped" to help with this issue?
Jean
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Jean Marais
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On 01.05.2015, at 21:09, "Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Dear forum,I have used a couple of the "Zone Predicted..." output variables in the past with the assumption that they provide a reasonable indication of the cooling or heating load that is present for a particular timestep. I'm now working on a refrigerated warehouse that is maintained at -18C and am doubting my previous understanding of what the variable means.The "Zone Predicted..." definition seems straightforward, but my energy model results don't seem to agree...The table below shows results for the summer design day afternoon.
- It's 30C (86F) outdoors
- The zone temperature is reasonably close to the setpoint (consistently about 1C colder than setpoint)
- The "Zone Predicted Load..." (in red) shows that most of the time there is a heating load, indicated by a positive value. That makes some sense because the zone is colder than setpoint and needs some "heating".
- It makes no sense to me that an adjacent timestep has a cooling load (negative value) while the zone temperature is also colder than setpoint.
- Will you please help me understand what is going on?
â??<image.png>â??--The I/O Reference definition:Zone Predicted Sensible Load to Cooling Setpoint Heat Transfer Rate [W]
This is the predicted sensible load in W required to meet the current zone thermostat cooling setpoint. A positive value indicates a heating load, a negative value indicates a cooling load. This is calculated and reported from the Predict step in the Zone Predictor-Corrector module. This value is not multiplied by zone or group multipliers
â??James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504
Direct: 616.450.8653
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx
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