[TRNSYS-users] TRNBLD - active layer - Thickness of adjacent layers

[Schrade, Johannes]

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 <mailto:johannes.schrade at ibp.fraunhofer.de> 
Telefon 0711 / 970-3416
Telefax 0711 / 970-3399
www.ibp.fraunhofer.de/wt/ <http://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 <mailto:johannes.schrade at ibp.fraunhofer.de> 
Phone +49 711 / 970-3416
Fax +49 711 / 970-3399
www.ibp.fraunhofer.de/wt/ <http://www.ibp.fraunhofer.de/wt/> 

 

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