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Weather data lag for 1-hour

asked 2015-10-21 12:45:43 -0600

updated 2020-01-20 13:37:57 -0600

I did a simulation with 1-minute interval weather data and ask how to Use 1-minute interval weather data in EnergyPlus earlier.

I created the 1-minute interval EPW file. However, there are 1 hour lag between the EPW file and the results.

In EPW weather file: image description

In simulation results: image description

Did anyone have similar problem?

Seems to be a bug. I just shift all the data by 1 hour to "work around" the problem.

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Chandan Sharma gravatar image Chandan Sharma  ( 2015-10-21 13:49:15 -0600 )edit

No, there are not daylighting saving time object. I change the "Use Weather File Dayligh Saving Period" in RunPeriod from Yes to No. However, the results are the same.

Yixing Chen gravatar image Yixing Chen  ( 2015-10-21 13:53:34 -0600 )edit

Does the EPW file begin with hour 00:00 or hour 01:00 ?

Aaron Boranian gravatar image Aaron Boranian  ( 2015-10-21 13:57:27 -0600 )edit

It starts with 01:01

Yixing Chen gravatar image Yixing Chen  ( 2015-10-21 15:22:16 -0600 )edit

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answered 2015-10-21 15:58:00 -0600

In an hourly EPW file, the first entry is for hour 01:00, because it assigns weather data for the first HOUR of the simulation (STARTING at 00:00 and ENDING at 01:00). For your case of using minute intervals, the first entry assigns weather data for the first MINUTE of the simulation (STARTS at 00:00 and ENDS at 00:01) instead. To follow the same convention as the hourly EPW files, your first minute-interval entry should have a time stamp of 00:01, not 01:01.

Really, EnergyPlus is reading the data at the correct intervals (shown in the simulation results). My hunch is that it's offset by one hour too late in your minute-interval EPW file.

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After changing the EPW file to start with 00:01, I got the error: Unexpected error condition in middle of reading EPW file, 1993/10/10:1. I checked the WeatherManager.cc line 2820 and line 2852-2855 (as shown below). It seems the hours should between 1 and 24. 2820: for ( Hour = 1; Hour <= 24; ++Hour ) { 2852: if ( Hour != WHour ) { 2853: BadRecord =... 2854: ShowFatalError( "Unexpected error condition in middle of reading EPW file, " + BadRecord

Yixing Chen gravatar image Yixing Chen  ( 2015-10-21 16:57:59 -0600 )edit

I also changed the minute to start with 01:00. It ran without errors, however, the results are messed up. The WeatherManager.cc line 2821 shows the time step started with 1, rather than 0. 2821: for ( CurTimeStep = 1; CurTimeStep <= NumIntervalsPerHour; ++CurTimeStep )

Yixing Chen gravatar image Yixing Chen  ( 2015-10-21 17:13:00 -0600 )edit

Hmm, maybe the conventions are different between initial time starts for .epw file and schedules in .idf files. If you look at the very first outputs from EnergyPlus, do they start with 00:01 or 01:01?

Aaron Boranian gravatar image Aaron Boranian  ( 2015-10-22 12:50:18 -0600 )edit
1

@Aaron Boranian, the output results start with 00:01. The 1-hour lag by using EPW file seems to be an E+ bug.

Yixing Chen gravatar image Yixing Chen  ( 2015-10-22 13:04:55 -0600 )edit

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Asked: 2015-10-21 12:45:43 -0600

Seen: 271 times

Last updated: Oct 24 '15