When setting both run_period and start_dow in the HB Simulation Parameter, the latter isn’t written correctly into the IDF. It seems Honeybee assumes the Start Day refers to January, picks a reference year that matches that condition, and then shifts the Start Day based on that year. But EnergyPlus wants the Start Day of the selected Run Period, not of the year.
For example here I chose May as Run Period and Thursday as Start Day (as in 2025). In the IDF I get year 2009 and Start Day = Friday, because 1 May 2009 was a Friday (and 1 January 2009 was a Thursday). The simulation confirms the issue: it starts on Friday (occupied) then weekend (unoccupied), rather than starting on the Thursday.
RunPeriod,
Run Period 1, !- Name
5, !- Begin Month
1, !- Begin Day of Month
2009, !- Begin Year
5, !- End Month
31, !- End Day of Month
2009, !- End Year
Friday, !- Day of Week for Start Day
No, !- Use Weather File Holidays and Special Days
No, !- Use Weather File Daylight Saving Period
No, !- Apply Weekend Holiday Rule
Yes, !- Use Weather File Rain Indicators
Yes; !- Use Weather File Snow Indicators
It looks like a bug to me, but I’m not sure if it’s already fixed in a newer LBT version (I’m on 1.8).