[EnergyPlus_Support] Re: Differences in weather data between csv and epw files

["Liam O'Brien" <liambrn@xxxxxxxxx>]

Thanks, Linda.  I performed the simulation at 1 timestep/hour and the weather data values match.  So that is reassuring.

Liam


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Linda Lawrie <linda@...> wrote:
>
> This is also answerd in the Tips and Tricks document.
> 
> 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 = 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 = 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.
> 
> At 10:48 AM 5/26/2010, Liam O'Brien wrote:
> >Hi All,
> >
> >I've been comparing the weather data in the simulation output to the 
> >EPW and was surprised to see differences.  For instance, the outdoor 
> >dry bulb temperature is -13.9C vs. -11.9C, respectively, in day 1, 
> >hour 1.  Is this normal?  What could be happening?
> >
> >Thanks in advance.
> >Liam O'Brien
> >
> >
> >
> >------------------------------------
> >
> >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 currently allowed but be mindful that not everyone 
> >has a high speed connection.  Limit attachments to small files.
> >
> >EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf 
> >under the Documentation link and press the "search" button.
> >Yahoo! Groups Links
> >
> >
> >
>




------------------------------------

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 currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/join
    (Yahoo! ID required)

<*> To change settings via email:
    EnergyPlus_Support-digest@xxxxxxxxxxxxxxx 
    EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx

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

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