[TRNSYS-users] Type 56 active layer error : inlet fluid mass flow to low (simulating concrete core activation)

[Michaël Kummert]

Pieter,

> I'm currently trying to simulate concrete core activation in a 
> multi-zone building.
> But when I input a certain mass flow rate into the active layer, the 
> mass flow needs to be above a minimum value!?!
> This is strange since there should be no minimum flow rate, in reality 
> flow rates can vary from zero to a limited flow rate maximum!
> What causes this error and/or is there a known workaround?
> I work with prebid 5.0.8 and trnsys 15 with iisibat 3 (version 3.0.0.26) 

That restriction comes from the numerical model, not the physical 
device. My understanding is that the temperature of the active layer is 
somehow averaged in a way that is not valid for very low flowrates. I 
hope the The Type 56 developers will correct me if I am wrong.
You can reduce the minimum acceptable flowrate by splitting the active 
layer in smaller sections. Each section must be connected to the one 
before using Type 56 inputs and outputs so it is a tedious process but 
it works. This is what is meant by the error message:

>   PLEASE REPLACE THIS WALL WITH TWO OR MORE WALLS OF THIS TYPE AND 
> CONNECT THEM
>   IN SERIAL FLUID FLOW WITHIN THE DECK FILE BY CONNECTING ADEQUATE 
> INPUTS AND OUTPUTS TO TYPE 56.

That way, you can reduce the minimum acceptable flowrate to a point 
where the gains from the active layer can be neglected (i.e. you can set 
the flowrate to 0 instead of the small value).

In TRNSYS 16, Type 56 can perform the segmentation for you and it also 
auto-connects the segments, which makes the process painless and fast. 
Furthermore, the new controllers (Type 22 iterative feedback controller 
and Type 23 PID) can both be configured to cope with a minimum 
acceptable flowrate (input 6, "threshold for non-zero output"). Both the 
auto-segmentation and the PID with threshold are used in a standard example:
Examples\Feedback Control\SunSpace - Floor heating PID controller.tpf
(Introduced in 16.00.0037)

I hope this helps,

Michaël Kummert



-- 
_________________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert at engr.wisc.edu

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