Re: [EnergyPlus_Support] Dry bulb differs from EPW to Output Report

[Linda Lawrie <linda@xxxxxxxxxxxxxx>]

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.

At 08:04 AM 4/6/2010, frorv wrote:
> Fellow E+ users,
>
> I used an EPW file along with an example file provided with E+ and chose
> as an output report variable the 'Outdoor Dry Bulb' hourly. It happens
> that the temperatures are different in the weather file and in the output
> results... for example:
> EPW -> E+
> 8.1 -> 7.1
> 7.4 -> 7.7
> 6.6 -> 6.9
>
> I am using E+ v4.0.0, but I also tried with v1.2.2 and the results are
> similar!
>
> Is this normal?
> If so, why does it happen? If not, how do i avoid it?
>
> Thank You and Best Regards,
> FrOrv

__._,_.___

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

__,_._,___