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Energyplus intermediate outputs logging

asked 2020-06-14 09:46:30 -0600

Aly ElHefny gravatar image

updated 2020-06-14 11:01:07 -0600

Hello everyone, Hope you are all well and in good health.

I wonder how could I access the intermediate outputs between time steps in energyplus. The data in the .eso file are are just an output displayed and not actually the values provided to the following timestep.

Please advice, Thanks !

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@Aly ElHefny are you asking about how to get output variables reported at subhourly frequency? Or are you asking about accessing the internal variables that EnergyPlus uses for calculations that are not accessible as output variables? Or something else? A more specific example would help.

Aaron Boranian gravatar image Aaron Boranian  ( 2020-06-14 15:39:36 -0600 )edit

Hello Aaron, what I'm asking about is how to access the output file that is handed from on time step to the other. So for a timestep outputs are generated and then those are used as inputs for the following timestep. Is there a way to access/modify some values of this file ? Thanks!

Aly ElHefny gravatar image Aly ElHefny  ( 2020-06-14 15:47:01 -0600 )edit

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answered 2020-06-14 16:30:44 -0600

updated 2020-06-15 08:15:26 -0600

EnergyPlus doesn't really use the output from the previous timestep as the input to the current timestep. At the beginning of each timestep, all independent variables (weather data, schedule data, etc.) are provided as inputs in order for EnergyPlus to calculate all of the dependent variables (surface heat transfer & storage, electricity use of plug loads, heating/cooling requirements for zones, air & plant system controls to meet zone loads, etc.) for that timestep. This process is repeated for each timestep of the simulation. For example, just because the output for zone terminal supply air temperature was 55$^\circ F$ in the previous timestep doesn't mean that 55$^\circ F$ is used as an input for a calculation in the current timestep because the zone terminal supply air temperature depends upon numerous other dependent variables (changes in zone heating/cooling loads, reset of air system supply air temperature, etc.).

You can read more about this simulation process in the Engineering Reference sections for:

You can certainly use the abundance of potential output variables in EnergyPlus to either find these time-varying parameters you're interested in or at least calculate them. This can be done manually after each simulation, or you could use Energy Management Systems (EMS) to define code and logic in programs to calculate such parameters and generate custom outputs for them. Note that any output variable (or meter) in EnergyPlus can be used in EMS as a sensor.

UPDATE

I should mention that if you do want to use output variables from previous timesteps in order to change controls or other parameters in the current timestep, then that is a specific EMS feature called trend variables. For example, you could monitor the outdoor air temperature from the weather file as a trend variable and apply a custom air system setpoint change when the weekly trend average exceeds a certain value.

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Thanks Aaron for the detailed and helpful answer.

Aly ElHefny gravatar image Aly ElHefny  ( 2020-06-14 16:35:17 -0600 )edit

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Asked: 2020-06-14 09:46:30 -0600

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Last updated: Jun 15 '20