[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [EnergyPlus_Support] discrepency with outdoor dry bulb temperature



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]
> 
> 
> 
> To unsubscribe from this group, send an email to:
> EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files are of the Support Web Site.
> 
> 
> 
> 
> 
> 
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx


------------------------ Yahoo! Groups Sponsor ---------------------~-->
Buy Ink Cartridges or Refill Kits for your HP, Epson, Canon or Lexmark
Printer at MyInks.com. Free s/h on orders $50 or more to the US & Canada.
http://www.c1tracking.com/l.asp?cid=5511
http://us.click.yahoo.com/mOAaAA/3exGAA/qnsNAA/dkFolB/TM
---------------------------------------------------------------------~->

To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are not allowed -- please post any files to the appropriate folder in the Files are of the Support Web Site.




 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/