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Dear Trnsys users,
I have set the boundary conditions of two side walls in my zone to IDENTICAL (because i am actually considering one span out of eight for a greenhouse) however i am surprised when viewing the result of QCOMO : (energy to outside surf. incl. conv. to air and longwave radiation to other surfaces or Tsky) for these two walls the amount was huge xxE8.
Shouldn't it be 0 or close to 0 since adiabatic ?
if not how to set these two walls to adiabatic ?
Thank you.
My apologies for the delay in responding; I wanted to do some testing to make sure that my understanding of the situation is correct. What it comes down to is that there is an adiabatic surface within the BOUNDARY wall that you have defined. However, the BOUNDARY wall may have mass (unless you defined it not to). Because it has mass, its temperature may be different than the air temperature on either side of the wall at a given point in time and thus QCOMI and QCOMO are non zero.
In the test I did, I set up a zone that has three external walls (all with solar radiation set to be calculated by an external component) and one BOUNDARY wall that is set to IDENTICAL. I then set the inputs to Type56 so that the ambient temperature, sky temperature, and ground surface temperature are all 10C, the ambient RH is 50%, and the solar is always zero on all surfaces. I ran the project and the building temperature starts at 20C then falls off to 10C. QCOMI and QCOMO start with a non zero value but as the zone cools to equal the ambient temperature (and therefore the system goes to steady state) the values drop off to zero.
I went back in then and set the ambient (and sky and ground surface) temperature to be 10C for the first 70h of the simulation and then to jump to 40C. At the 70h mark, the values of QCOMO and QCOMI become non zero again since the air temperature in the zone begins to change and the wall (having thermal mass) lags behind in temperature.
If you want a massless adiabatic boundary between your zone and another the easiest thing to do is to remove the wall altogether; no wall, no heat transfer! If that is not appealing then you can define the wall as having a single massless layer; QCOMO and QCOMI will both be zero throughout the simulation at that point.
kind regards,
David
