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

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Effective convective heat transfer coefficient, identical boundary conditions.

Type 88 connection with equation editor issue