Re: [EnergyPlus_Support] discrepency with outdoor dry bulb temperature

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

This is expected.  The difference comes from interpolating hourly weather data 
for subhourly timesteps in EnergyPlus.  In an hourly weather file, the 
temperatures and other state-point readings are the value at the time the 
reading was taken.  For example, in the USA_IL_Chicago-OHare_TMY2.epw file, the 
outdoor dry bulb value for July 2, hour 1, is 19.4C.  This is the temperature 
at 1:00 am.  

If you set TIMESTEP IN HOUR = 1, then EnergyPlus will report 19.4C for 07/02 
01:00 and will use that value for the entire one hour timestep.  

If TIMESTEP IN HOUR = 4, then 19.4C is used only for the time step which ends 
at 01:00.  The other timesteps use linearly interpolated values between the 
hourly weather file values.  When you report at the "hourly" frequency in 
EnergyPlus, you see the average temperature over the hour.  If you report at 
the "timestep" frequency, you will see the values from the weather data file 
appear at the last timestep of each hour.

Mike



On 12 Dec 2003, at 13:21, Ian Doebber wrote:

> I just compared my outdoor dry bulb temperature from the Energy Plus output to
> the outdoor dry bulb temperature listed in the weather file and they are not the
> same.  Is there any reason for this?
> 
> Thanks
> Ian
> 
> [Non-text portions of this message have been removed]
> 
> 
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx


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