Re: [EnergyPlus_Support] Ground Temperatures on weather file

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

The ground temperatures listed in the weather file are "undisturbed" 
ground temperatures, like what you would see in the middle of an open 
field. The ground underneath a building tends to be much closer to 
the indoor temperature of the building than the undisturbed 
temperatures.   

There is a utility included with EnergyPlus called "slab.exe" in the 
EnergyPlus\PreProcess\GrndTempCalc\ folder.  This utility calculates 
monthly core, perimeter, and average ground temperatures using a 
description of the floor slab, the average indoor temperature, the 
soil conditions, and the weather file for a given location.  Docs for 
it are in AuxiliaryPrograms.pdf, p. 38 (v1.0.3).  Otherwise, 18C is a 
reasonable value to use for most commercial applications in the U.S.  
  


On 7 Jan 2003, at 11:38, Linda Lawrie wrote:

> At 11:10 AM 1/7/2003, TangoJim wrote:
> 
> >There seems to be three sets of ground temperatures
> >listed on each of the weather files with five
> >parameters (?) used to generated these ground
> >temperatures.
> If you look at the stats file from a conversion, things are a little
> clearer:
> 
>   - Monthly Calculated "undisturbed" Ground Temperatures °C
>                  Jan     Feb     Mar     Apr     May     Jun     Jul
> Aug     Sep     Oct     Nov     Dec
>            .5 
> m            0.9    -0.1     2.0     6.7    12.9    18.8    22.8   
> 24.0 21.8    17.0    10.8     5.0
>            2.0 
> m           4.9     3.1     3.5     6.2    10.4    15.1    18.9   
> 20.8 20.3    17.6    13.3     8.7
>            4.0 
> m           8.2     6.3     5.9     7.0     9.5    12.7    15.6   
> 17.6 18.0    16.8    14.3    11.1
> 
> Sorry, it probably wraps.  Even clearer is a CSV rendition:
> 
> Number of Ground Temperature Depths,Ground Temperature Depth {m},Soil
> Conductivity {W/m-K},Soil Density {kg/m3},Soil Specific Heat
> {J/kg-K},Jan {C},Feb{C},Mar {C},Apr {C},May {C},Jun {C},Jul {C},Aug
> {C},Sep {C},Oct {C},Nov {C},Dec {C},<repeat to Number of temperature
> depths>
> 3,.5,,,,-22.93,-24.77,-21.07,-12.58,-1.53,9.08,16.38,18.41,14.56,5.92,
> -5.16,-15.69,2,,,,-15.84,-19.12,-18.31,-13.51,-5.90,2.44,9.27,12.78,11
> .91,6.98,-0.68,-9.01,4,,,,-9.93,-13.30,-14.07,-12.00,-7.54,-1.90,3.40,
> 6.97,7.74,5.56,1.05,-4.60
> 
> Lacking a specified soil diffusivity for the particular location, the
> default is used:
> 
>   -- Ground temps produced with a standard soil diffusivity of 
> 2.3225760E-03 {m**2/day}
> 
> (Not the same location in both examples)
> 
> The auxiliary programs document and descriptions of the Weather "IDD"
> format also describe each field that is listed on the EPW and CSV
> files.  CSV file is easier to read as it also includes this
> information in the line preceding.  The algorithm used is adapted from
> that used in the DOE-2 Weather Processor.
> 
> 
> 
> 
> Linda
> 
> EnergyPlus WebSite: http://www.energyplus.gov
> Owner: EnergyPlus_Support list
> Member: EnergyPlus Development Team
> 
> 
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