[TRNSYS-users] TMY weather data and humidity ratio

[marcello.caciolo at aximaseitha-gdfsuez.com]

Dear TRNSYS users,

I have an issue not directly related to TRNSYS, but I hope that I can find here someone able to give me some information about it.

For a project, we need to evaluate the condensation risk on the internal surface of the roof of a building with very large openings. Simulation shows that there is a condensation risk in the morning in winter-time.

This is due to the fact that, due to the large airflow in the building, internal temperature profile coincides almost with external temperature profile. During night-time, temperature drops down reaching a minimum value in the morning, at about 8 a.m. (depending on the exact day). After that, the external (and internal) temperature rises quickly. This seems quite logical to me.

However, I did not expect that humidity ratio profile follows the same profile (see picture). This causes condensation in the morning in winter, due to the fact that surface temperature keeps cold and humidity ratio (and consequently dew point temperature) rise quickly.

[cid:image004.jpg at 01CD3A5F.AD4B26A0]

My question is: does this behavior corresponds to reality? I mean, I expected relative humidity to be very variable during the day, due to the variation in external temperature, but I expected that humidity ratio variation was slower. Could this behavior due to the way the TMY files are produced? This behavior is common to all TMY files in France. Any idea on the subject would be greatly appreciated.

Thank you.

Best regards,
Marcello CACIOLO
Responsable Outils et Méthodes d'Analyse Energétique
___________________________________________________

[cid:image001.jpg at 01CD3A5D.48CF3100]

Cellule Efficacité Energétique
Direction Commerciale
46 Boulevard de la Prairie au Duc BP 40119
44000 Nantes Cédex 2
Tel. 02 40 41 06 57

mail: marcello.caciolo at aximaseitha-gdfsuez.com

www.aximaseitha-gdfsuez.com

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