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



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



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_________________________________________________________

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@engr.wisc.edu

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