[TRNSYS-users] "floor in direct contact with ground"

[David Bradley]

Christophe,
   Your translation is perfectly fine. Sometimes the effect is called 
"ground coupling" as well.

   To answer your question, the "standard" method is to define a massless 
layer with a high thermal resistance underneath your floor and connect it 
to either ambient temperature or some time varying deep earth ground 
temperature. You might get such a temperature from the Type77 Kasuda 
correlation. In some parts of the world, there are maps of equivalent 
ground temperatures available just for this purpose. Alternatively, there 
are a number of ground coupling models in the TESS Ground Coupling library 
that you might use. These are a bit complicated to implement but the idea 
of them is more physically correct than the equivalent resistance method. 
In the Ground Coupling Library models, you define a volume of soil 
underneath and around the floor. That volume of soil is called the "near 
field" and is broken up into finite elements that normally increase in size 
as they get farther from the floor edge and bottom. Beyond the near field 
is a region called the far field, which acts as an infinite thermal source 
/ sink. When using a ground coupling model with Type56, you define a 
boundary wall for your floor and pass the inside surface temperature of the 
floor out of Type56 and to the ground coupling model. The ground coupling 
model solves the 3D finite element conduction problem and calculates the 
temperature at the outside boundary of the floor. This outside boundary 
temperature is passed back to Type56 as an input.

   We have had some good success with the model and have been working with 
the developers of one of the International Energy Agency Tasks to compare 
this model against an analytical solution and against other models that 
have been created over the years. The 3D finite element methodology seems 
to be uniquely flexible and shows quite good comparison with the analytical 
solution.
Kind regards,
  David



At 05:55 2/17/2006, Enertech wrote:
>Dear TRNSYS Users,
>
>I would like to model a "floor in direct contact with ground" (I don't 
>know the exact traduction for the french term "plancher sur terre plein"). 
>My goal is to estimate the interest of using the ground thermal 
>capacitance, as a heat storage, in the global thermal capacitance of my 
>building.
>
>My first idea was to define a boundary wall with the ground temperature 
>for boundary. But in this case, I don't use ground capacitance. My new 
>idea is to introduce a layer in my wall (defined as an external wall) 
>composed by 5 m of ground ? Do you think it's a good way to take ground 
>capacitance into account ?
>
>Thanks for your answers,
>Christophe.
>
>===========================
>ENERTECH
>F-26160 FELINES SUR RIMANDOULE
>tel-fax : 04 75 90 18 54
>Email : sidler at club-internet.fr
>Web  : http://sidler.club.fr
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