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Hi,
I model an apartment as a single zone in TRNSYS 18 using type 56. The apartment is part of a multi-family house. Around the modeled apartment, I have added walls in type 56 with boundary walls with boundary condition = identical. My question concerns the heat capacity of these boundary walls. If I model all these boundary walls with their real mass (and corresponding heat capacity), I am afraid that the heat capacity of the modeled apartment gets bigger than it should be. For instance, I have concrete intermediate floor structures both below and above the modeled apartment. If I let the mass of these structures belong to the modeled apartment, then I suspect that the heat capacity is overestimated (since one of these floors belong to another apartment in the building).
So... how should I model the surrounding boundary walls in such a way that the heat capacity of the apartment gets equivalent to the building as a whole?
/Johan
@jolind You could treat the intermediate floor structure above as a thermal resistance rather than as a thermally massive structure. Another thing I would encourage you to do is to first try changing the zone's capacitance (there is a field right under the zone volume field in TRNBuild) by an amount that is something close to the thermal capacitance of the intermediate floor structure and to run your simulation both with and without that mass. It may be that the mass of those intermediate floor structures does not have a very significant impact on the building performance metrics you are looking at. If the results are insensitive to the mass assumption then you can feel more confident in not worrying too much about the value. If the results are highly sensitive to the thermal mass assumption then you can spend a bit more time deciding how best to account for the mass.
kind regards,
David
