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

[Linda Lawrie <linda@xxxxxxxxxxxxxx>]

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
>
> <*> 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/

__._,_.___

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.

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___