Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
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.
| | 2 | No.2 Revision |
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.
