[TRNSYS-users] Problem with active layer in type 56b

[Amirreza Heidari]

Hello,

I am trying to model a ceiling heating system in type 56b. The actual
heating system is actually some hot water heating panels that are located
in the ceiling. The actual sizes or thickness of layers are not important,
and I only expect the model to reflect a realistic behavior. To model the
ceiling heating system, I putted an active layer between two layers of
common concrete. The specifications of active layer, common concrete, and
the ceiling structure are shown below. However, the model does not show a
reasonable behavior because:

1- The temperature increment of the zone is very small (with 11000 L/H
flowrate and 26 C inlet water for a 50 m2 zone)
2- The temperature increment of zone does not change with the change of
inlet flowrate
3- When I change the specifications of active layer (for example by
reducing the pipe spacing), the minimum required flowrate of water reaches
to unreasonable high values

I tried to get a reasonable behavior by trying following actions:
1- *Reducing the thermal capacity of common cement:* It did not work
because when I have a big surface with very low thermal capacity, the solar
radiation from windows increases the zone temperature to very high values
(e.g. 30 C). The same happens with the use of low-capacitance layers like
hollow brick.
2- *Trying the chilled ceiling: *Although it is not exactly what I need, I
tried it to see if it can have a reasonable behavior. But it does not do
any change of indoor air temperature (maybe it is only coded for cooling!)
3- *Huge increase in inlet flowrate: *Does not change anything !!!

I have attached the .b18 file as well. The inlet temperature and flow to
the active layers are as inputs (from other components). The simulation
timestep is 30 minuts. Would you please let me know why the zone
temperature variation versus the inlet water temperature is extremely low
and how I can fix it?

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