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Re: [TRNSYS-users] Inside surface energy flux interpolation over the wall timebase

Dear Pedro,
I have to admit that I am not an expert on z-transfer functions. But from what I understand, the calculation of the coefficients for the transfer functions depends on the characteristics of the wall. Therefore, a very thin wall will result in coefficients that do not go too far back on time. This could be the reason of the mathematical instability that you are seeing. I put together a very simple example according to your description, and I got a very smooth response. I will attach it in a separate email.
If you want, please feel free to send me your project. I will be happy to help you. I will appreciate it if anybody else has a better explanation. 
Best regards,

Diego


Pedro Rodrigo wrote:


Hi all:

We have developped a TYPE56 building model for control
desing purposes.

We are trying to identify transfer functions (G(s))
for the zone energy gain, provided that only one
external signal is exciting the zone (i.e. outside
temp, solar radiation, etc..). 
We excited the zone with a step function, varying the
temperature difference between outside and inside air
from 0 to 10ºCelsius in a single simulation timestep.
Simulation timestep is set to 0.02 hours.

The output for QCSURF (from TYPE56) showed a strange
function. For each wall timebase (that is set to 1
hour) the function starts with a high value (i.e. 2500
kJ/h) and quickly decreases to get the zero value at
the end of the hour; suddenly it jumps again to a high
value and the process repeats.

We don´t find an explanation to a such extrange energy
response.

Thanks for your suggestions.

Regards,





Pedro Manuel Rodrigo Cruz
University of Jaen, Spain
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Diego A. Arias
TRNSYS Coordinator
Solar Energy Laboratory
University of Wisconsin - Madison
1500 Engineering Drive
Madison, WI 53706