Re: [EnergyPlus_Support] Steady State

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

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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