Re: [TRNSYS-users] active layer

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@transsolar.com)

Best,

Marion

Von: TRNSYS-users [mailto:trnsys-users-bounces@lists.onebuilding.org] Im Auftrag von leen peeters
Gesendet: Mittwoch, 4. März 2015 11:24
An: trnsys-users@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