[TRNSYS-users] Problems with results in heating system

[Ale Vargas]

Hi everyone! I have read previous mails about problems with convergence in
closed loops but I can't solve my problem...I have tried with diferents
options: rearranging components in control cards (in logic order),
decreasing time step, putting types with higher thermal mass at the end of
the order of calculation. Just one option I haven't tried: putting type 31
instead of just links between types.

But one option worked and helped with convergence: putting type 661
(delayed output device). The problem about this is that results are not
correct.

About my simulation: I'm working on a hybrid heating system for a house. It
consists in a heat pump that gives heat to the house through radiant floor,
and extracts heat through horizontal ground heat exchanger and flat plate
solar collectors. This system has two tempering valves:

1. First valve controls that mass flow does not pass through horizontal
ground heat exchanger if soil is very cold (mass flow goes through a
bypass)

2. Second valve controls that mass flow does not pass through tank if tank
outlet towards the load is colder than mass flow.

The diagram is attached to this mail.

I ran the simulation and I obtained results so weird: sometimes the
thermostat gives the signal of 1 (on, when the house need heating) and the
flow out (to source) of heat pump is 0. And sometimes thermostast gives the
signal 0 (off, house doesn't need heating) and the flow out (to source) of
heat pump is 1532 kg/hr or 3065,83 kg/hr. Mass flow of heat pump to load is
ok, but to source is strange. Then I realized that all mass flows of the
side of the source were weird in the system: diverters, pumps, ICG,
tank...The side of load is ok.

I think that some type is giving outputs in a different time compared to
other types, but I don't know what type is giving the problem: when I see
the list file, it says:


*** Warning at time       :      2935.000000
    Generated by Unit     : Not applicable or not available
    Generated by Type     : Not applicable or not available
    TRNSYS Message    441 : The inputs to the listed units have not
converged at this timestep. The values at the last iteration will be used
and the simulation will proceed.
    Reported information  : UNITS: 21  23  42  46  45  38  40  22


*** Warning at time       :      3000.000000
    Generated by Unit     :    27
    Generated by Type     :     2
    Message               : The controller was stuck during 12 percent of
the simulation timesteps.



*** Warning at time       :      3000.000000
    Generated by Unit     : Not applicable or not available
    Generated by Type     : Not applicable or not available
    Message               : The simulation failed to converge during 2
timesteps (2% of the time).


*** Warning at time       :      3000.000000
    Generated by Unit     :    23
    Generated by Type     :   114
    Message               : Pump mass balance failed during 7 timesteps.
Please check the connections.

So I don't know which type is giving the problem (messages indicate problem
with heat pump, pump, tees, tempering valves and tank) , and I don't know
if type 661 can help in this situation. Somebody can help me please or give
me some idea of what is happening? I can't detect the problem since two
weeks!

Thank you in advance! And sorry about this too large text!


-- 

*Alejandra Vargas Cáceres*

*Estudiante Ingeniería Civil Mecánica*

*Facultad de Ciencias Físicas y Matemáticas*

*Universidad de Chile *
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