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

[David BRADLEY]

Johanes,
   I have not had a chance to look entirely at the issue yet. However, 
as to your comment:

"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. "

I run into similar problems with a lot of common radiant floor 
configurations in the US. Radiant floors are often around 30cm pipe 
spacing embedded in about 10cm of concrete. My sense was that because 
the Type56 model is semi-empirical, what they were looking to avoid in 
developing the correlation was any significant variation in floor 
surface temperature (hotter right above a pipe, measurably cooler 
between pipes). I also had the impression that European installations 
also tended to favor less temperature variability. My solution has 
usually been to keep the floor thickness as designed and to reduce the 
pipe-to-pipe spacing as needed to get within the model's allowable 
range. I wanted to avoid having more thermal capacitance in my building 
that was really there and since we usually ignore pressure drop, having 
more, thinner, closer spaced pipes doesn't have a huge impact. I would 
be interested in hearing other people's thoughts as well.

Kind regards,
  David






On 12/12/2011 06:48, Schrade, Johannes 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 
> <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/>
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20111212/d37fcdbc/attachment-0005.htm>