[TRNSYS-users] "floor in direct contact with ground"
David Bradley
bradley at tess-inc.com
Fri Feb 17 05:42:06 PST 2006
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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E-mail: bradley at tess-inc.com
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