[TRNSYS-users] TESS library (Hydronics) variable speed Fan - outlet temperature problem

[Mariam Elnour <mariam.elnour@outlook.com>]

Dear,

    I am using TRNSYS to simulate a full HVAC system for a simple 2 zone building. I am using variable speed fans - controlled by PID controllers- to modulate the amount of cool air (of constant temperature) from AHU to each zone to maintain its temperature at desired set points. 

Although the temperature of the zones are controlled properly according to the set points, the issue I am facing is that the dynamics of outlet  temperature of the variable speed fan is very unstable and unpredictable. It shows very rapid spikes (reaches up to 60 degrees) provided that the fan inlet temperature is constant at around 10 degrees. I tried to look up how outlet temperature of the fan is calculated by checking the source code but there is no line of code that define that. The only thing I found in the fan source code regarding outlet temperature is when fan is Off To = Ti. I connected all the inputs of the fan (flow rate, temperature, pressure, RH% + setting the corresponding mode, control signal). I tried decreasing simulation step size up to 0.125 Hr and i tried increasing it up to 2 Hr, but still couldn't figure or solve the problem. 

I keep getting the following :

**notices

1. "The controller was stuck during           0 time steps, i.e.      .000000000000000     % of the time (Note that you have set NStick < 1. In that case the controller is stuck when further oscillations would trigger the 'maximum number of iterations' warning. Use a large number if you do not want this behavior)."
   
2. "The TRNSYS processor has reported a potential problem with the connections in your input file. In version 16, there is a very specific calling order after convergence has been reached at each timestep. One of your connections flows against this calling order - for example you may have the output of an integrator connected as an input to a standard component (one that is being called iteratively at each timestep). While this is not technically an ERROR - it may cause incorrect values to be passed to the component. For example, the input to an iterating component from an integrator will be from the previously converged timestep and not the current timestep. Refer to the TRNSYS Manual - Volume 1 - for more information on the calling order for TRNSYS components"
   

**Warning at multiple timesteps

Fan mass balance failed during 1443 timesteps. Please check the connections.

In addition, I have an inquiry about the power calculation.  How can I choose the number of coefficients and their values?

Thank you.

Regards,

Mariam