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Re: [EnergyPlus_Support] Ground Temperatures on weather file



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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