[TRNSYS-users] Lumped capacitance model

[Sophie Masson <smasson@andrew.cmu.edu>]

Hi Folks,

I am modeling a zone both in TRNSYS and in Matlab with ventilation but 
no infiltration and no occupancy or lighting gains.
(conditions:
- initial room temperature = 10C
- outside air temperature = 10C
- ventilation air temperature = 26C
- ventilation air change = 3 ACH/hr (432 kg/hr) )

In TRNSYS, I have 2 different zone models (Type 56 and Type 88, lumped 
capacitance). The model in Matlab is a lumped capacitance model (with a 
1 second - simulation time step).

I am using the same inputs (building dimensions, capacitance, loss 
coefficient...) for the 3 models. The room air temperature reaches the 
setpoint (20C) in 20 min with the Matlab model and ... 8hr with the 
TRNSYS model (whatever time step or wall base I choose).
Why such a difference? Is it linked to the way TRNSYS calculates the 
results (hourly based and not calculate the energy accumulation each 
second)?
8hr seems to be not reasonable, but I can not figure out where the 
problem comes from.

Thanks for your help,

Sophie

--
Sophie V. Masson
Research Engineer
Center for Building Performance and Diagnostics
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213
Phone: 412 268 3939
Fax: 412 268 6129
Email: smasson@andrew.cmu.edu