[TRNSYS-users] Solar radiation in high glazed spaces

[hotline]

Dear Wirich,

in general, matching simulation with measured data is a really challenge task.

One reason is that doing good measurements especially on larger spaces is difficult (what needs to be measured, where are sensors located, are sensors working correclty, ...) .
Often measurements aren't taken for delivering inputs for building simulation model. Important data especially for longwave radiation exchange with the environment and convection is missing.
Local effects which aren't typically modelled may be crucial for a good match.

Lately, I did a comparison between simulation results of special glazing system using the CFS model and measurements taken at an outdoor test facility.
It turned out that for this glazing system modelling the capacity of the glazing and the heat transfer in detailed played an important role.
(http://www.ibpsa.org/proceedings/BS2019/BS2019_211101.pdf)

Without knowing anything of your test set up. I don't think that radiation modelling is the problem. The critical path is often modelling the convective heat transfer and flow patterns good enough.
How is the spacial temperature distribution in the glazed space? Can this be represented by a nodal model like type 56 which assumes that the air volume associated to then ode has a uniform temperature?

We as other TRNSYS users did successful comparison between measured data of highly glazed spaces with simulation results using Type 56.
So yes, Type 56 can be used for this. However, it is a lot of work because you need to consider all relevant heat flows adequately.

Best regards,

Marion


Dipl.-Ing. Marion Hiller
+49 711 679 76 32 | hiller at transsolar.com

Transsolar
Stuttgart | Munich | Paris | New York

Transsolar Energietechnik GmbH | Curiestrasse 2 | 70563 Stuttgart | Germany
CEO: Matthias Schuler, Thomas Auer, Stefan Holst, Dieter Schnelle
Registered at Amtsgericht Stuttgart HRB 23347 | USt-IdNr.: DE 152272639

Von: TRNSYS-users <trnsys-users-bounces at lists.onebuilding.org> Im Auftrag von Freppel, Wirich via TRNSYS-users
Gesendet: Sonntag, 8. November 2020 19:41
An: TRNSYS USERS (trnsys-users at lists.onebuilding.org) <trnsys-users at lists.onebuilding.org>
Cc: Freppel, Wirich <Wirich.Freppel at saint-gobain.com>
Betreff: [TRNSYS-users] Solar radiation in high glazed spaces

Dear Trnsys users,

I'm trying to assess thermal comfort in a high glazed space (like a porch/veranda) with TRNSYS 18. I built a model, which geometrically corresponds to an experimental veranda we have at the lab.
I did temperature measurements in the experimental facility under solar radiation and then I compared it to the simulation.

All calculation are set in "detailed mode" to take view factors into account. As a result, air temperature is much lower in the simulation, a lot much lower. And the most surprising fact is that when I set the solar to air factor to 1, both air temperatures match pretty well.
I concluded from this result that, if I transform all the supposed radiative flux into convection, the thermal balance in the simulation is equal to the experimentation. But when I consider radiative flux from glazings, the radiative part is missed by the simulation, resulting in a much lower air temperature in the simulation. It is like a part of radiative flux disappeared right after passing through the glazings.

I only used Type 56 to model the high glazed building. Is there a better solution, like a specific type which can do solar radiation calculation in a 100% glazed building ? Or should it work fine with Type 56 only ?
(of course I can send the project if needed)

Many thanks in advance
Best regards

Wirich FREPPEL
Development engineer
COSMOS - Buildings Energy Performance & Daylighting Group
Cell: +33 637 053 174
Saint-Gobain Research Compiègne

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