TRNSYS Forum - Recent Topics

SketchUp to TRNBuild import issue

Mariem S — Fri, 03 Apr 2026 14:26:04 +0000

Hello everyone,
I’m trying to model a simple zone using SketchUp and then import it into TRNBuild, but I’m running into an issue.
Here’s what I did:
-Created a simple parallelepiped geometry in SketchUp
-Exported the model as an *.idf file
-Imported the file into TRNBuild

After importing, the zone appears to exist, and I can see 9 walls listed (not 6). However, all the surface areas are showing as 0 m².
I’ve attached screenshots for reference.
Has anyone encountered this issue before or knows what might be causing it? Any help would be greatly appreciated!
Thank you in advance.

Mariem

TRNBUILD.jpg

Fortran Compiler

Papillon — Tue, 31 Mar 2026 16:33:12 +0000

Dear TRNSYS users,

I was using Intel Fortran (Ifort 2022) with Visual Studio 2019 for developing and debugging Types, and everything was fine. But I changed my computer and this solution is no longer available.

As far as I know, there is no debugging options with Type Studio, and TRNSYS 18 is not compatible with the new Intel Fortran compiler (Ifx).

What is now the best solution to debug user written types ?

Regards

Philippe

Window frame

SilviaC — Sun, 29 Mar 2026 00:47:52 +0000

Hi everyone,

What is the best way to model the window frame?

I remind these recommendation reported in manuals/slides, which appear to be contradictory:

It is better to model the window frame as a Wall and set FFRAME = 0.
the frame should be defined in TRNBuild (see slide attached)

Does “model the window frame as a Wall” mean that the frame has to be modelled in SketchUp/TRNSYS3D and then assigned the construction type Wall in TRNBuild, while the window frame fraction of the window, again in TRNBuild, should be set to 0?

If drawing the frame in SketchUp/TRNSYS3D is indeed necessary, what is the correct way to do it geometrically? I understand that it should obviously not be modelled as shown in the slide where the framed window is marked as “Doesn’t work in TRNSYS,” but I am unsure what the recommended workflow is.

I sincerely thank you in advance for your support

Warm Regards,

Silvia

slide.png

MCP Server for AI integration

georgekyr — Sat, 28 Mar 2026 06:19:30 +0000

Hi! I have been using TRNSYS ever since my diploma thesis back in 2002 and through my MSc, PhD and post-doc years and have been coming back to it from time to time given the types I have created all these years. My focus is renewable energy systems managed by AI (e.g., check https://doi.org/10.1016/j.apenergy.2012.10.011).

When supporting students from time I see that the difficulty they face and many times they opt to use newer approaches with python libraries etc. even though I still believe TRNSYS is one of the best tools out there.

The first interaction is usually hard as is also the first time you want to do parametric runs or couple it with GenOPT to start using e.g., Particle Swarm Optimization for multi-objective optimizations.

Given also that there is already an officially documented route for calling Python from TRNSYS via CFFI it will not be that hard to develop an MCP server for TRNSYS, which could bring new life to this very useful software and help the user base grow.

How do I derive from ICC-SRCC or Solar Keymark test report the "Incidence angle modifier constant" to use as parameter for a collector?

Ken — Wed, 18 Mar 2026 22:14:15 +0000

How do I derive from ICC-SRCC or Solar Keymark test report the "Incidence angle modifier constant" to use as parameter for a collector (for example Type 45)? Usually, the reports provide various values for different angles.

Type 15 vs Type 45: should surface slope be identical?

Ken — Wed, 18 Mar 2026 22:05:58 +0000

I am working with Type 15 and Type 45 in TRNSYS and have a question regarding the surface slope definition.

In Type 15:

Parameter 8 defines the surface slope
Output 29 provides the incidence angle
Output 30 provides the surface slope

In Type 45:

Parameter 6 defines the surface slope
Input 4 is the incidence angle

My question is:
Is it necessary to ensure consistency between the slope defined in Type 15 and the slope defined in Type 45?

More specifically, since Type 45 already includes the surface slope as a parameter, is there any need (or recommended practice) to link or otherwise enforce the same slope value used in Type 15?

Choice of type when modeling hydronic radiators

jolind — Wed, 18 Mar 2026 15:32:15 +0000

Hi,

I would like to model a hydronic radiator, to be used together with type 56. I have found type 1231 in the TESS library, but I have also read about type 362, but I can´t find the latter in the library. Is it appropriate to use type 1231, or if type 362 is better, where do I find it? I can´t find any radiator types in the standard library...

Best regards, Johan

Effective convective heat transfer coefficient, identical boundary conditions.

Alex Sz — Thu, 12 Mar 2026 14:11:11 +0000

Dear TRNSYS-Team and -users,

I am currently working with Type 56 and have two questions regarding the treatment of heat transfer in TRNBuild / Type 56.

1)
First, regarding the convective heat transfer coefficients:
In the Construction Types, I specify constant convective heat transfer coefficients for the front and back surfaces,
for example 9.72 and 72 kJ/h·m²·K.
However, in the Type 56 outputs, the reported values for the "effective" convective heat transfer coefficient are different from the input values.

This raises a few questions for me:
What exactly is the difference between the input convective heat transfer coefficient and the output “effective” convective heat transfer coefficient?
Is the effective value directly used in the simulation, or is it only a reported/post-processed output quantity?
Is it recalculated during the simulation depending on surface temperature, air temperature, or other boundary conditions?
-Because when i applied different room air temperatures it did not change. It seems to be purely dependent on the surface Area proportions?
Which physical or scientific model is implemented here?

I would have expected the effective convective coefficient to remain equal to the prescribed input value if a constant coefficient is defined.
Since this is apparently not the case, I would like to better understand the underlying formulation in Type 56.

2)
My second question concerns the definition of the category “Boundary” or “Boundary conditions”, especially when it is set to “identical”.
What exactly does “identical” mean in this context?
Does it mean that the heat fluxes on one side of the construction are mirrored to the adjacent side of the neighboring zone,
i.e. that convective and/or radiative heat exchange is transferred consistently between both zones?
Or does it mean that a temperature boundary condition is imposed on the other side?
I could also not find an unambiguous explanation of this point in the Trnsys-Documentation/ Literature.

Any clarification on either of these topics, or references to documentation or publications, would be greatly appreciated.

Best regards,
Alex Sz

Type 88 connection with equation editor issue

Quentin_Courjeau — Tue, 10 Feb 2026 19:03:42 +0000

For a simple thermal modelisation of a machinery room ventilation I used the Type 88.

I connect as input an equation editor with Type 88 to handle the sensible heat loads.

Unfortunately, those are not assumed by the model - ie Type 88.

When I fill directly the heat loads in type 88 they are properly considered in the model.

When I try to interconnect equation editpr with a type 57 for example, in order make a link with the type 88, the heat loads are neither assumed.

Just to complete the message, I use a, equation editor, because I need to add several inputs from a type 9c

Does anyone face to the same issue ?

Thanks to the community.

Regards

Q.Courjeau