[TRNSYS-users] Convergence problems with type 56 possibly involving cooling load

[David Bradley]

Ethan,
  There are two ways of conditioning a Type56 thermal zone: energy rate 
control and temperature level control and I think that what is happening 
in your simulation is that the two are getting mixed. When you work in 
energy rate control, you define the temperature of the zone and you 
calculate the amount of energy that is required to meet that set point. 
Because you predefined the set point, you are in essence assuming that 
your HVAC system is able to meet that set point. When you work in 
temperature level control, the zone becomes just another component in 
the system; its temperature and humidity are a result of both ambient 
and the systems that try to keep them at set point. In your simulation, 
you have defined a set point and then are modulating the capacity of the 
cooling system at the same time. I think what you want to do is one of 
the following:

Define the set point and allow the capacity to be unlimited and 
calculate the cooling loads, then afterwards, impose those loads on your 
CCU and make sure that it can meet them at all times.

or

Define a thermostat model (Type23 perhaps) that monitors the cabin 
temperature and Type56 ventilation inputs (T, RH, and ach). Have the 
thermostat command your CCU and pass its outlet temperature, flow rate, 
and RH to the Type56 model. The temperature in the cabin will oscillate 
around the set point a bit (as it would in reality) as it turns fans up 
and down.

I hope that helps,
 David


Ethan Lust wrote:
> Hello,
>
> I am trying to simulate the operation of a climate control unit (vapor
> compression air conditioner and electric resistance heater) in a small
> closed space.  The climate control unit (CCU) (Type 202 and the accompanying
> DLL7) is an original component created from manufacturer's data.  Prior to
> the heater and air conditioning code within the Type202.f code, there is a
> switch that keeps the air conditioner and heater from operating
> simultaneously.  The climate control unit is operated via a PID controller
> (Type 23).  In addition, the space also has an internal heat load due to
> some electronics, hence the three type 9a components and the Type 41c.     
>
> If the heat from the CCU is input into Type 56 through the heating function
> in TRNBuild and the cooling output from the CCU is attached likewise, there
> are a number of points over the course of the TMY2 year at which the program
> "bogs down" and stops with the calculations though no error message is
> produced.  Occasionally an error message will pop up stating that there are
> 6 errors (no matter how many I have set to allow within the control cards),
> which all relate to temperature divergence at a wall, according to the list
> file.  I have tried increasing the convergence tolerance with no luck.    
>
> If the cooling portion is removed, the program proceeds fine, with or
> without the internal loads attached.  
>
> I have sought help for a similar problem, to which I was suggested to
> decrease the cooling output and/or decrease the time interval to aid in
> convergence.  I've tried reducing the cooling input to very low values (the
> DLL I'm sending has it cut in half) with no luck.  The current time interval
> is a dreadfully slow 5 seconds.  
>
> I have also tried connecting the cooling output of the CCU to the Type 56
> using the gain function (using a negative value as input) with the same
> result.  
>
> Attached are the project, bui, component (fortran and proforma) files and
> the DLL.    
>
> Please help!
>
> Thanks,
> Ethan Lust
> University of Maryland
>   
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>
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>   

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