[TRNSYS-users] active layer

[leen peeters]

Marion,

yes indeed. This is a kind of solar thermal system. This is the way it is
now installed on several roofs. So, the input values are correct.

Leen

On Tue, Mar 17, 2015 at 3:12 PM, hotline <hotline at transsolar.com> wrote:

>  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>
> 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)
>
>
>
> Best,
>
>
>
> Marion
>
>
>
>
>
> *Von:* TRNSYS-users [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
> *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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