[TRNSYS-users] Convection heat tranfer coefficients in Type 56

[marcello.caciolo at cofelyaxima-gdfsuez.com]

Dear TRNSYS users,

I am currently modeling a building with Thermo-activated building systems (TABS). As a first step, I try to compare TRNSYS results with stationary calculations provided by TABS manufacturer.

A first simulation shows very different results. After few investigation, the main difference between TRNSYS and manufacturer calculation is due to convection heat transfer coefficients. Indeed, I activated in Type 56 automatic calculation for hconv for TABS surfaces. Temperature differences are very low, in the order of 1-2 degrees. In this case, the correlation:

Hconv = alpha * DT ^0.31

Gives convection coefficients in the order of 5-10 (kJ/h)/(m2K) , even lower or much lower than standard coefficient for isothermal surfaces (11 (kJ/h)/(m2K) ). On the other hand, manufacturer data show convection coefficients in the order of 20-40 (kJ/h)/(m2K).

My question is double:

1) Which is the origin of the standard coefficients (constants: 7.2 and 3.888, exponent: 0.31) used in the automatic calculation of hconv?

2) Do you have any experience in TABS? If yes, which value/correlation of hconv seems reasonable to you for these systems?

Thank you for your attention.

Best regards,
Marcello Caciolo
Responsable Outils et Méthodes d'Analyse Energétique
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Cellule Efficacité Energétique et Environnementale - Pôle Projets et Réalisations
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Tél.: +33 02 40 41 06 57
marcello.caciolo at cofelyaxima-gdfsuez.com<mailto:prenom.nom at aximaseitha-gdfsuez.com>
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