Boundary condition for condensation check
92 views
Skip to first unread message
Lampham
Jun 29, 2025, 1:26:52 PMJun 29
to THERM
Dear all,
I have a question regarding boundary conditions used in thermal simulations.
According to the NFRC standard, the prescribed boundary conditions are:
i. Interior ambient temperature: 21ºC (69.8ºF)
ii. Exterior ambient temperature: –18ºC (–0.4ºF)
These conditions are standardized and primarily intended for evaluating thermal transmittance (U-value) under severe winter scenarios typically found in colder climates like North America.
However, if this same boundary condition is applied to a country like Vietnam, where the minimum exterior temperature rarely drops below 5ºC, I believe it may not accurately reflect real condensation risks on interior surfaces of glass or aluminum frames.
From my understanding, when the exterior temperature is low, it reduces the surface temperature of the interior face of the frame or glazing. If that surface temperature falls below the dew point of the indoor air, condensation will occur. Therefore, the risk of condensation depends directly on realistic exterior temperatures and interior humidity, not just a standardized condition.
I have a question regarding boundary conditions used in thermal simulations.
According to the NFRC standard, the prescribed boundary conditions are:
i. Interior ambient temperature: 21ºC (69.8ºF)
ii. Exterior ambient temperature: –18ºC (–0.4ºF)
These conditions are standardized and primarily intended for evaluating thermal transmittance (U-value) under severe winter scenarios typically found in colder climates like North America.
However, if this same boundary condition is applied to a country like Vietnam, where the minimum exterior temperature rarely drops below 5ºC, I believe it may not accurately reflect real condensation risks on interior surfaces of glass or aluminum frames.
From my understanding, when the exterior temperature is low, it reduces the surface temperature of the interior face of the frame or glazing. If that surface temperature falls below the dew point of the indoor air, condensation will occur. Therefore, the risk of condensation depends directly on realistic exterior temperatures and interior humidity, not just a standardized condition.
My question is:
What would be a more appropriate set of boundary conditions to use when evaluating condensation risk in climates like Vietnam’s?
Should we define custom boundary conditions based on local climate data rather than applying NFRC's values, which might overestimate or misrepresent the actual condensation behavior?
What would be a more appropriate set of boundary conditions to use when evaluating condensation risk in climates like Vietnam’s?
Should we define custom boundary conditions based on local climate data rather than applying NFRC's values, which might overestimate or misrepresent the actual condensation behavior?
Best regards.
Lam.
Lampham
Jul 18, 2025, 10:45:24 AMJul 18
to THERM
Hello everyone,
Could anyone take a look at my question?.
Thank you very much.
----------------
--
You can view the THERM forum online at:
https://groups.google.com/g/LBNL-THERM
---
You received this message because you are subscribed to the Google Groups "THERM" group.
To unsubscribe from this group and stop receiving emails from it, send an email to LBNL-THERM+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/LBNL-THERM/e7b218df-9f0f-4b79-9c68-a8b17d7714ban%40googlegroups.com.
archi...@gmail.com
Jul 24, 2025, 12:14:03 PMJul 24
to THERM
Hi Lam.
Your considerations are quite right. If the purpose of the finite element calculation is the possible formation of dew on windows inner faces, standard boundary conditions are not suitable.
So the answer to your question is: yes, real data of internal and external temperature and relative humidity should be used.
It could even happen that in summer in case of highly cooled interiors and high levels of external relative humidity, dew formation may occur on windows external side!
Ciao
Fabrizio
Reply all
Reply to author
Forward
0 new messages