[TRNSYS-users] TRNBLD - active layer - Thickness of adjacent layers
Marion Hiller
hiller at transsolar.com
Fri Dec 16 03:58:16 PST 2011
Johannes and Leen,
thanks for pointing out the confusion about the active layer boundary
conditions due to mistakes in the manual documentation.
I checked the equations with the original literature and the code.
The base equation is for all three systems is Eq. 5.4.4.-15:
For the following boundary conditions
the summation can be neglected and yield to Eq. 5.4.4. -16 (which is
wrong in the manual!)
For the capillary tube system the “ln” can be replaced by 1/3 if
is less than 1.85718.
Thus, for both capillary tube system and ordinary TAB the above
mentioned conditions have to be valid!
For the floor heating the conditions are the same for layer 1 with d1,
For layer 2 with d2 different condition apply.
(On page 5-187 of the manual there is a mistake: the “lower then” has to
be “greater then” for the condition of d1!)
The conditions are checked by entering the layers in TRNbuild.
Further details about the model can be found in the following book (it
is written in German):
„Thermoaktive Systeme tabs“ von Markus Koschenz und Beat Lehmann, 2000
If you are interessted I can double check if you can buy the book at
Transsolar.
Best regards,
Marion
P.S.: We will upate the documentation for the next release.
Dipl.-Ing. Marion Hiller
TRANSSOLAR: KlimaEngineering - Technologien für energieeffizientes Bauen
und Nutzerkomfort in Gebäude
Munich - New York - Stuttgart + 49.711.67976.0
Transsolar Energietechnik GmbH, Curiestrasse 2, 70563 Stuttgart
Amtsgericht Stuttgart - HRB 23347, Steuernummer 99073/00911, USt-IdNr.:
DE152272639
Geschäftsführer: Dipl.Ing. Matthias Schuler, Dipl.Ing. Thomas Auer,
Dipl.Phys. Stefan Holst, Prof. Dipl.-Ing. Bleicher
_____
Von: leen peeters [mailto:l.f.r.peeters at gmail.com]
Gesendet: Dienstag, 13. Dezember 2011 20:08
An: Schrade, Johannes
Cc: trnsys-users at cae.wisc.edu
Betreff: Re: [TRNSYS-users] TRNBLD - active layer - Thickness of
adjacent layers
Johannes,
I know they violate one another. As I cannot access the code of type 56,
I cannot check the implementation. We are currently working on finding
out where the limits of the model are ...
The model is based on an EMPA model, but there are no international
publications I found that really discuss the implementation of the
active layer model.
It is a numerical derivation, so emperics are not the cause. I will get
back to you once I figured out more.
Leen
On Tue, Dec 13, 2011 at 1:29 PM, Schrade, Johannes
<Johannes.Schrade at ibp.fraunhofer.de> wrote:
Dear Leen, dear TRNSYS users,
Thanks for your quick reply.
However, I’m not really satisfied with your suggestion, as I want to
understand the reason behind it.
If you are right, I violated the requirement “outside diameter over pipe
distance < 0.2”. But, this requirement is completely independent from
the layer thickness of the adjacent layer, isn’t it?
On the other side, if both adjacent layers must be conform to the
minimum thickness of 0.3 times pipe spacing, I would have caused a
violation of this requirement by setting the pipe spacing to 24 cm and
the layer thickness to 8mm. But for this, I didn’t receive any warning.
Last but not least, there are oppositional specifications for the
required ratio between thickness of adjacent layer(s) and pipe spacing
in the TRNBLD user manual. On page 5-186 the ratio should be greater
than 0.3, on page 5-187 the ratio should be equal or smaller than 0.3
and on page 5-59 the ratio should be equal or greater than 0.3. So,
nearly all possibilities are mentioned. I’m a bit confused.
Looking forward to some light into the dark,
Kind regards,
Johannes Schrade
Johannes Schrade
Abteilung Wärmetechnik
Fraunhofer-Institut für Bauphysik
Nobelstr. 12
70569 Stuttgart
johannes.schrade at ibp.fraunhofer.de
Telefon 0711 / 970-3416
Telefax 0711 / 970-3399
www.ibp.fraunhofer.de/wt/
Johannes Schrade
Department Heat Technology
Fraunhofer Institute for Building Physics
Nobelstr. 12
70569 Stuttgart, Germany
johannes.schrade at ibp.fraunhofer.de
Phone +49 711 / 970-3416
Fax +49 711 / 970-3399
www.ibp.fraunhofer.de/wt/
Von: leen peeters [mailto:l.f.r.peeters at gmail.com]
Gesendet: Montag, 12. Dezember 2011 22:09
An: Schrade, Johannes
Cc: trnsys-users at cae.wisc.edu
Betreff: Re: [TRNSYS-users] TRNBLD - active layer - Thickness of
adjacent layers
Johannes,
as soon as you decrease the distance between the pipes, you come closer
to the limits set regarding the modeling of the heat transfer in the
direction of the water flow (direction z in the mathematical model). The
stability of that model requires that you achieve a certain boundary
condition, which is a.o. function of the thermal resistance of the
water-pipe-inter pipe distance. In order to ensure these boundary
conditions are satisfied the ratio of pipe outside diameter over pipe
distance < 0.2 AND the ratios of layer thickness over pipe distance >
0.3. The 0.024-value you received for the minimum layer thickness comes
from this limitation. I assume the extra measure is invoked once you
come close to the 0.2-limit.
As soon as you take 0.1 for the pipe distance, you can again select
0.008 m for layer thickness ...
Playing around with conductivity or capacity does not help, as the
measure seems to be implemented through the above limits only ....
Leen
On Mon, Dec 12, 2011 at 1:48 PM, Schrade, Johannes
<Johannes.Schrade at ibp.fraunhofer.de> wrote:
Dear TRNSYS users,
I have some problems with the active layer module of TRNBLD, which I
used for modeling a floor heating system.
The active layers, which should be displayed in the model, are defined
as following:
Layer 1:
* Pipe spacing: 24 cm
* Pipe outside diameter: 16 mm
* Pipe wall thickness: 2 mm
Layer 2:
* Pipe spacing: 8 cm
* Pipe outside diameter: 16 mm
* Pipe wall thickness: 2 mm
By specifying the thicknesses of the layers adjacent to the active
layers, the following curiosity appeared.
For case 1, I set the thickness of the layer above the active layer to
73 mm, which is greater than 0.3 times the pipe spacing, and I set the
layer below to 0.5 times the pipe outside diameter (requirements taken
from manual TRNSYS 17, 5-187, table). This step had worked pretty good
and the simulation was running without any problems.
In a second step, I revised the model and included the second active
layer into the TRNBLD model. As the floor screed should be identical for
both cases, I tried to define the thicknesses of the adjacent layers the
same way as I did it in case 1. But when I tried to reduce the thickness
of the adjacent layer below, the following warning appeared: “thickness
must be in the range of 0.024 to 1.0”.
In order to understand this warning I had a closer look to the manual of
TRNBLD. On page 5-58 (TRNSYS 17) I found a remark that both layers
adjacent to the active layer must be greater than 0.3 times pipe
spacing. This would explain, why the warning appears, but I do not
understand, why the first case should be unproblematic, as the required
minimum thickness in this case should be 72mm and why this is not
mentioned in the mathematical description.
Does anyone has an idea, what could be the reason behind that, or might
this be a known or unknown bug? If this requirement dependent on the
pipe spacing should be really used for both layers, this would mean that
extremely thick floor screeds of +15cm are necessary to model a floor
heating system with a pipe spacing of 24 cm. This sounds absolutely
unrealistic.
Hoping for some help,
Kind regards,
Johannes Schrade
Johannes Schrade
Abteilung Wärmetechnik
Fraunhofer-Institut für Bauphysik
Nobelstr. 12
70569 Stuttgart
johannes.schrade at ibp.fraunhofer.de
Telefon 0711 / 970-3416
Telefax 0711 / 970-3399
www.ibp.fraunhofer.de/wt/
Johannes Schrade
Department Heat Technology
Fraunhofer Institute for Building Physics
Nobelstr. 12
70569 Stuttgart, Germany
johannes.schrade at ibp.fraunhofer.de
Phone +49 711 / 970-3416
Fax +49 711 / 970-3399
www.ibp.fraunhofer.de/wt/
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