[TRNSYS-users] type 660 simple building model

[David BRADLEY]

Thibaut,
   You are correct; the assumption that underlies the lumped capacitance 
approach is that the entire building (envelope and air) is at a single 
temperature. Moving the setpoint requires the HVAC system to move the 
temperature of the air and the structure. I have seen three workarounds 
to this issue.

   One is to simply limit the heating and cooling capacity of the system 
so that the air and structure warm up at a realisitc rate. You need to 
use the "temperature level control" version of Type660 and you need to 
find the peak iteratively instead of letting the model calculate it for 
you.

   The second is to model the building as two lumped capacitances, one 
for the air and the other for the shell (Type953 is available in the 
TESS Loads and Structures library). Unfortunately, this gets farther 
away from allowing you to set any "physical" values; for instance it is 
hard to know how to appropriately couple the two capacitances.

   The third is to artificially reduce the capacitance of the building 
so that most of what you are accounting for is the air (with a little 
bit for the structure and furnishings).
Best,
  David


On 3/29/2012 09:29, Thibaut VITTE wrote:
> Dear Trnsys users,
>
> I'm using type 660 to modelize "quickly" a simple building. Having 
> troubles to analyse the results, I've tested it and compared it with 
> regular type 56.
>
> the building is an office building with high internal loads, large 
> glazed surfaces.
> the heated area is 9200m², with an overall loss coefficient of 0.7 
> W/m²°C, 69 kJ/K.m3.
>
> The annual results seem quite good, since I'm finding diffrences in 
> annual heating/cooling loads less than 10%.
>
> As far as temperatures and free floating building functionning (see 
> picture attached), it's not that good, but I understand that a simple 
> capacitance model is limited for that purpose.
>
> But the problem is for maximum heating/cooling power. I have inputed 
> night set back for cooling and heating. And I think that the whole 
> building capacitance is taken into account when a moving setpoint is 
> applied! Which implies great instantaneous power. ( 6 times greater 
> than the one calculated by type 56.) (see picture). The wole building 
> (air + walls) is heated or cooled when a setpoint changes (as I 
> understand the model), which is not quite the reality..
>
> Am I right? Is there a simple model that can calculate approximately 
> the instantaneous power with moving setpoint (in Trnsys type 12, 
> setpoints are only parameters)?
>
> Thanks in advance.
>
> Thibaut
>
>
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-- 
***************************
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

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