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
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 EngineeringBudapest University of Technology and Economics
Feladó: TRNSYS-users <trnsys-users-bounces@lists.onebuilding.org>, meghatalmazó: Gergely László Zsolt via TRNSYS-users <trnsys-users@lists.onebuilding.org>
Elküldve: 2022. július 22., péntek 17:48
Címzett: TRNSYS users mailing list at OneBuilding.org <trnsys-users@lists.onebuilding.org>; David BRADLEY <d.bradley@tess-inc.com>
Másolatot kap: Gergely László Zsolt <gergely.laszlo@gpk.bme.hu>
Tárgy: [TRNSYS-users] Type 56 thermal massDear 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 EngineeringBudapest 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@tess-inc.com http://www.tess-inc.com http://www.trnsys.com