[TRNSYS-users] active layer

[hotline]

Leen,

before I start looking deeper into this one question concerning the “active layer design”.

The pipes of your active layer have an outside diameter of 2 cm and the pipe spacing (center to center)
is only 5 cm. This is very dense. If you subtract half the outside diameter this means that you have 3 cm material in between only!
Also, the coverage above/below is very small. The adjacent layer thickness is 0. 15. If you subtract half the
outside diameter there is only 5 mm coverage. This really low!

Are you sure that this is the system you like to simulate?

Marion

Von: TRNSYS-users [mailto:trnsys-users-bounces at lists.onebuilding.org] Im Auftrag von leen peeters
Gesendet: Dienstag, 17. März 2015 08:52
An: TRNSYS users mailing list at OneBuilding.org
Betreff: Re: [TRNSYS-users] active layer

Marion,

sorry it took me some time, but I was mostly offline last week.
The model is in attach. I simulated with the weather file of Casablanca.

Thanks already for your input!

Leen

On Thu, Mar 5, 2015 at 1:59 PM, Marion Hiller <Hiller at transsolar.com<mailto:Hiller at transsolar.com>> wrote:
Dear Leen,

The minimum mass flow rate is checked in order to assure the validity of the linear approximation
of the e-function between inlet and outlet temperature. In the attached figure
you see that the deviation between linear approach and the e-function is to large
(Read line). If you split the tab into two segments in series the linear approach is used
for each segment and it matches well the e-funtion (see the two green lines).

A smaller time step doesn’t help for this problem, that’s correct.

In general, the min. mass flow rate is checked in TRNbuild prior the simulation.
The calculated min. mass flow rate during the simulation might differ from the one in TRNbuild,
because Type56 differentiates between a laminar and turbulent flow, respectively.
(TRNBuild doesn’t.)

Without knowing the simulation files it is hard to tell what might go wrong with your simulation.
It sounds strange to me that the last segment is causing the error as well as the large difference between
12 kg/h m² and 30 kg/h m².

If you can’t find anything, we may have a quick look at the inputs file.(Hotline at transsolar.com<mailto:Hotline at transsolar.com>)

Best,

Marion


Von: TRNSYS-users [mailto:trnsys-users-bounces at lists.onebuilding.org<mailto:trnsys-users-bounces at lists.onebuilding.org>] Im Auftrag von leen peeters
Gesendet: Mittwoch, 4. März 2015 11:24
An: trnsys-users at cae.wisc.edu<mailto:trnsys-users at cae.wisc.edu>
Betreff: [TRNSYS-users] active layer

Dear all,

we are using the active layer model of EMPA, built in in type 56, to simulate a solar boiler of the type equal to floor heating. In our case we used the auto segmentation leading to 3 different segments of the active layer.
With 66 kg/h at 1,055 specific weight, inlet temperatures below 25 DC gave a fluent simulation at 15 minutes timestep. However, once simulating with higher inlet temperatures warmer climatic zones (e.g. Casablanca) fail at around 3400 hours in the simulation. In this case, we get a specific message that the inlet mass flow rate for the third part of the segmented roof requires a minimum mass flow rate that is higher than the input one. Opening the TRNBUILD file, the minimum is around 12 kg/h. The message in the list file mentions a minimum of over 30. A smaller timestep did not change the error.

Are we too close to the safety limits built in the EMPA model, or is there another thing we forgot to take into account?

Thanks already!

Leen

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