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About the implication of the timestep in simulation

asked 2019-07-18 05:58:14 -0500

Ivanita's avatar

updated 2019-07-18 11:21:27 -0500

Hi all,

I am using Honeybee to perform the e+ simulation. I originally performed the simulations on annual basis but now I need to extract the hourly electricity demand and hence I need to rerun the simulations on hourly basis. I found that the simulation time increases a lot and the result file size becomes enormous, especially the .eso and .sql file. May I ask

1) I thought that simulations, no matter which timestep is chosen, are ran on a hourly basis, so the simulation time shouldn't be that different. Am I totally wrong? 2) What is the contributor to such a mega size of .eso and .sql file? 3) Is there any solution if I just want to extract the hourly electricity demand and PV generation?

Thanks a lot.

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answered 2019-07-18 09:46:33 -0500

updated 2019-07-18 13:15:12 -0500

EnergyPlus simulations are run at timesteps no larger than an hour. HVAC equipment can have smaller timesteps, but generally, most of the components will use the timestep that you define in the SimulationControl object. The .eso and .sql file contain the output variables that you requested, and its size is a function of both the frequency and the number of variables requested.

If you first requested the variables to be yearly (RunPeriod) you would get a single reported value. Changing them to hourly would give you instead 8760 values. However, this should not be a problem if you are requesting a single variable, such as the Facility Total Building Electric Demand Power. However, if you requested X variables, now you have X times 8760 results.

Check how many variables you are requesting, and delete any of them that you do not need for the time being. It will reduce your file size.

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Thanks a lot. It really helps! Then I guess it means I have no chance to get the hourly result if I chose a different timestep.

Ivanita's avatar Ivanita  ( 2019-07-18 10:46:41 -0500 )edit

If you run EnergyPlus with a sub-hourly timestep, you can still request outputs with an hourly frequency.

shorowit's avatar shorowit  ( 2019-07-18 11:22:53 -0500 )edit

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Asked: 2019-07-18 05:58:14 -0500

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Last updated: Jul 18 '19