Re: [EnergyPlus_Support] Steady State

["Michael J. Witte" <mjwitte@xxxxxxxx>]

Another possible problem is solar values.  If you did not set solar 
to zero, then it will be changing even if the values are identical 
for the entire day.  The direct component will change angles 
throughout the day and it will be "turned off" before sunrise and 
after sunset.

Mike



On 5 Nov 2002, at 10:35, mjwitte@xxxxxxxx wrote:

> It is difficult to tell without seeing your files.  A couple of 
> guesses:
> 
> 1.  Daylight savings time.  Is it active during the time that you are
> simulating?  This would shift the weather relative to the clock time.
> 
> 2.  Interpolation for timesteps less than one hour.  The 
> interpolation scheme assumes that the hourly weather data values are
> point values and will interpolate between them.  So, if the first hour
> of the second day is different, the last hour of the first day will
> start to move toward that value.  Turn on reporting of weather data
> values at the "timestep" frequency so you can see exactly what values
> are being used.  You have three options to correct for this if it is
> important:
> 
> a)  Use timesteps in hour = 1, then there will be no interpolation. 
> However, this may squash some short-term effects you may wish to see
> in your simulation.
> 
> b)  Set the first hour of the second day to be identical to the last
> hour of the first day.
> 
> c)  Change your weather file to have a data frequency equal to your
> simulation.  If you are using 15 minute timesteps (4 per hour), then
> make you weather file have 15-minute data.  Remember that you must do
> this for the entire weather file, you cannot mix the first day at one
> frequency and the remainder be another.
> 
> Mike
> 
> 
> 
> On 4 Nov 2002, at 22:16, jebitsy wrote:
> 
> > I am trying to run a problem to steady state.  I put in a day of
> > constant values in the weather file.  All energy inputs in the model
> > are constant for the day.  I have no heating or cooling controls.  I
> > actually run the model for 4 days, but I expected the end of the
> > first day (at midnight) to be at the steady state conditions I need
> > for the second day.
> > 
> > On the first day, the inside mean air temperature approaches the
> > outside temperature by mid afternoon and things look good until 10pm
> > at which time the inside mean air temperature suddenly starts to
> > decrease.  I expect this to happen at midnight, not at 10 pm. 
> > 
> > Why do the conditions start changing 2 hours early?
> > How do I prevent this and get the changes to start at midnight?
> > 
> > Thanks,
> > Jeb Blakeley  
> > 
> > 
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