[TRNSYS-users] TRNSYS ground floor

[Loic Tachon]

Hi Hassan,

Thanks for your reply.

What is the difference between THERMAL CONDUCTANCE, U=    37.80000 kJ/h
m2K; U-Wert=     3.77020 W/m2K ? (we find theses wall value in the inf
file) This is not just unit conversion because 37.8 / 3.6 is different that
3.77.

Thanks for the help.

Best regards,



Le mar. 5 juil. 2022 à 10:36, Mahach, Hassan <mahach at izes.de> a écrit :

> Hi Dr. Tachon,
>
>
>
> The U-Wert means how your wall transfer the heat and it’s normal that you
> get this change because you changed the thickness of your materials as well
> as his type (U-wert= Thermal conductivity/thickness). You may also consider
> your ground-on-slab as boundary wall by setting  to the inside (front) and
> outside (back) convective heat transfer coefficients. You can refer to
> volume, page 143 of the documentation
>
>
>
> *“**WALLS WITH KNOWN BOUNDARY CONDITION*
>
>
>
> *A wall having a known boundary condition might be a concrete floor
> resting on ground of a known temperature or a wall adjacent to a zone whose
> temperature is known. The front of the wall is considered to be at the
> inside of the zone. Normally, the boundary condition is the temperature of
> a node connected to the back surface of the wall through a pure resistance.
> It is possible to specify the surface temperature of the outside by setting
> the back side heat transfer coefficient of the WALL Type (HBACK) to a very
> small value (less than 0.001 kJ/h/m²). This WALL Type is then only
> appropriate for use as a wall with a known boundary. The use of a very
> small value may be confusing but was kept for backwards compatibility
> reasons”*
>
>
>
> *I Hope that’s helps *
>
> *Hassan *
>
>
>
>
>
> *Dr. Hassan Mahach*
>
> wissenschaftlicher Mitarbeiter
>
> Arbeitsfeld Technische Innovationen
>
>
>
> +49 681 844 972 23
>
> mahach at izes.de
>
> www.izes.de
>
>
>
>
>
> IZES gGmbH | Altenkesseler Straße 17, Geb. A1 | 66115 Saarbrücken
>
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>
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>
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> [image: cid:image001.jpg at 01D8905B.2921E320]
>
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>
> *Von:* TRNSYS-users [mailto:trnsys-users-bounces at lists.onebuilding.org] *Im
> Auftrag von *Loic Tachon via TRNSYS-users
> *Gesendet:* Dienstag, 5. Juli 2022 09:38
> *An:* TRNSYS users mailing list at OneBuilding.org <
> trnsys-users at lists.onebuilding.org>
> *Cc:* Loic Tachon <dr.loic.tachon at gmail.com>
> *Betreff:* [TRNSYS-users] TRNSYS ground floor
>
>
>
> Dear users,
>
>
>
> I want to simulate a huge building (5500 m2) with a 20 cm concrete ground
> without isolation.
>
> I don't really understand how the direct contact boundary condition works.
>
>
>
> I made a ground wall composed of 20 cm of concret and 80 cm of calcar.
>
>
>
> I realize that the simulation result (Tzone temperature) is very dependent
> of the ground temperature boundary condition.
>
> I use type 77 with the depth of ground temperature of 1m, the amplitude of
> 12 and the mean temperature of 12.
>
> If I change the parameters of type 77, the zone temperature results change
> a lots.
>
>
>
> In the inf file, i get u value result of my floor : THERMAL CONDUCTANCE,
> U=     4.21086 kJ/h m2K; U-Wert=     0.97567 W/m2K
>
>
>
> If I don't put the 80 cm of calcar, I get the following u value :
>
> THERMAL CONDUCTANCE, U=    37.80000 kJ/h m2K; U-Wert=     3.77020 W/m2K
>
>
>
> Is this normal ? What means U-Wert ?
>
>
>
>
>
>
>
>
> --
>
> *Dr. Loïc Tachon *
>
> (+33) 6 7440-0536 (France)
>
>
>
>
>


-- 
*Dr. Loïc Tachon *
(+33) 6 7440-0536 (France)
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