[TRNSYS-users] Type 56 thermal mass

[David BRADLEY]

László,

   The capacitance of the walls is definitely taken into account 
although not in the same way that the capacitance of the stuff in the 
zones is taken into account. The walls are made up of layers; for each 
layer you provide the material's density, specific heat, and thermal 
conductivity. Those values as well as the thickness of each layer and 
the order of the layers are used to generate a set of values called 
conduction transfer function coefficients. Those coefficients are made 
for discreet steps backwards in time (like a time step but in this case 
it is called a time base). If there is a mismatch between the time 
constant of your wall and the timebase that you have selected (in the 
"outputs" window of TRNBuild) then I suppose that changes in the 
capacitance of the walls might not show up in the results. Say for 
example you have selected a 1hr timebase but the wall has a low thermal 
capacitance such that its time constant is more like 15 minutes. Changes 
to the capacitance that don't significantly extend the time constant of 
the wall might not show in the results.

   You can also get into some problems if you have a high thermal 
capacitance wall, which sometimes you have to treat as "resistive only" 
in TRNBuild due to the way that the conduction transfer function 
coefficients are generated. If you have had to treat the wall as a 
thermal resistance then the capacitance doesn't enter into the treatment 
of the walls.

kind regards,

  David




On 07/25/2022 05:42, Gergely László Zsolt wrote:
> Dear All,
>
> Still need your help with this.
> Running some simulations changing capacitance values (despite the 
> manual mentions that this value stands for the air and the furnitures 
> and walls shall not be considered here) of the airnode and capacitance 
> of the layers I am not convinced that calculations consider the 
> capacitance of the walls!
>
> Could you help me out?
>
> Regards,
>
> *László GERGELY*
> PhD student, Building Energy Engineering
> Budapest University of Technology and Economics
>
> ------------------------------------------------------------------------
> *Feladó:* TRNSYS-users <trnsys-users-bounces at lists.onebuilding.org>, 
> meghatalmazó: Gergely László Zsolt via TRNSYS-users 
> <trnsys-users at lists.onebuilding.org>
> *Elküldve:* 2022. július 22., péntek 17:48
> *Címzett:* TRNSYS users mailing list at OneBuilding.org 
> <trnsys-users at lists.onebuilding.org>; David BRADLEY 
> <d.bradley at tess-inc.com>
> *Másolatot kap:* Gergely László Zsolt <gergely.laszlo at gpk.bme.hu>
> *Tárgy:* [TRNSYS-users] Type 56 thermal mass
> Dear All,
>
> For some reasons I believe that my simulations do not consider thermal 
> capacitance of my building.
> I have no idea what goes wrong... I thought about overwriting the 
> capacitance value of the zones however based on the documentation that 
> value shall not include wall capacitance.
>
> In the enclosed project there is a nightime setback and the problem is 
> visible as the temperature drops as soon as the heating is off and 
> rises as soon as it is on.
>
> To make things in context the aim of the project is testing different 
> options reducing heating demand.
>
> Do you have any suggestions for overcoming the problem?
> I would be grateful!
>
> Thanks in advance,
>
> *László GERGELY*
> PhD student, Building Energy Engineering
> Budapest University of Technology and Economics
>
-- 
***************************
David BRADLEY
Principal
Thermal Energy System Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI  53703 USA

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

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