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EnergyPlus Results biased towards Thermal Load not SetPoint Temperature

asked 2020-04-22 17:35:32 -0600

santle's avatar

updated 2020-04-30 21:40:55 -0600

Did a basic EnergyPlus simulation to understand its behavior towards thermal load and setpoint temperature. The thermal loads are achieved through occupancy whereas different setpoints are set for working hours and non-working hours. The sample result from Energyplus simulation is attached:

image description

it is summer and outside temperature is hot. From the graph

  1. Energyplus over-cools the zone temperature to handle the thermal load (due to occupancy)
  2. Energyplus performance is based on thermal load and not on zone setpoint temperature
  3. Energyplus sees future thermal loads to set the current zone temperature

Are these expected behaviors of EnergyPlus. if yes, how to set EnergyPlus to prioritize setpoint temperature rather than thermal load to estimate the current zone temperature.

Cooling loads are attached below: image description

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answered 2020-04-24 09:49:07 -0600

aubr's avatar

Hello, it is difficult to give any definitive answer without knowing more about your model, but I would venture to write this much:

  • EnergyPlus does not "see future loads". Temperatures and cooling/heating loads are calculated on the basis of current conditions at each time step.
  • From the fact that your actual temperatures seem equal to the setpoint during occupancy but under the setpoint the rest of the time, I would guess that there is no cooling demand and no cooling load outside of occupancy, and that cooling demand only arises due to internal gains during occupancy.
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I am wondering if there is no cooling load other than the occupancy, why EnergyPlus cools down the zone further (from the graph) after occupancy when the SetPoint temperature should be maintained. This coolness does not come from outside either as it is hotter out. Also, Energyplus tries to maintain SetPoint temperature during occupancy but not during unoccupied hours. why this happens?

santle's avatar santle  ( 2020-04-25 01:43:50 -0600 )edit

The setpoint seems to be a cooling setpoint, so EnergyPlus controls zone temperature to be equal to it or below it, not necessarily equal to it. I am not able to explain where the "coolness" comes from. Maybe the building mass is cold? It would be helpful to plot the cooling loads (I guess you have an ideal air system so it would be Zone Ideal Loads Supply Air Total Cooling Rate).

aubr's avatar aubr  ( 2020-04-29 05:03:39 -0600 )edit

I have attached the cooling loads

santle's avatar santle  ( 2020-04-30 21:40:07 -0600 )edit

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Asked: 2020-04-22 17:35:32 -0600

Seen: 347 times

Last updated: Apr 30 '20