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Schedules that never produce a load or water consumption

asked 2015-02-24 04:52:12 -0500

updated 2020-01-20 13:42:59 -0500

Assume you have defined the flow rates for showers, which are only used for intervals of 15 minutes. However in simulation results you may find that these showers never seem to have produced any flows and energy consumption.

As I have observed, the reason can be that the number of simulation time steps is too low. However, If you use a weather file where the number of intervals per hour is not 1 (one), but e.g. 2 (timestep=30 minutes), EnergyPlus does not allow to increase the simulation time step number, which in this case paradoxically has to be 2 also. If you increase the number of simulation time steps, EP will respond with the error message:

Number of intervals per hour on Weather file does not match specified number of Time Steps Per Hour

and the simulation will fail.

To me this seems as a logical inconsistency in EnergyPlus, in my view it would be plausible to set the time step numbers to multiples of the number of intervals/hour in the weather file.

Why does EnergyPlus not allow this and can this be rectified in future releases ?

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Don't really have an answer for you, but in OpenStudio (a GUI for E+) you can control the number of timesteps per hour... OS defaults to 6 per hour. This would seem to suggest that you can changes the number of timesteps per hour without an error.

Benjamin's avatar Benjamin  ( 2015-02-24 12:28:01 -0500 )edit

Yes, but this does not work, if you use a weather file with two intervals per hour.

OS-user-AT's avatar OS-user-AT  ( 2015-02-24 16:37:52 -0500 )edit

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answered 2015-02-25 08:39:59 -0500

Archmage's avatar

The number of timesteps is independent of the weather data interval if using hourly weather data. EnergyPlus knows how to interpolate hourly weather data and schedules down to one minute intervals. If properly formulated, a 15-minute scheduled load can easily be modeled.

Interpolating weather data properly is not trivial. If you create a custom weather file with data that have time intervals that are shorter than one hour, then you need to use the same interval in the weather data as you want the simulation to use when stepping through time. The simulation needs to run with timesteps that align with custom-frequency weather data because EnergyPlus is only setup to interpolate hourly weather data.

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Asked: 2015-02-24 04:52:12 -0500

Seen: 138 times

Last updated: Feb 25 '15