Will air turbulence in flexible airduct causes water condensation?

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LMC
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In a normal aircond system using flexible airduct, assume airflow with temperature & humidity conditions (Tdry=23°C; Tdew=13.4°C; RH=55% ) go through a bended flexible airduct where air turbulence is formed:
1. Can condensation happens at the bended flexible airduct due to air turbulence?
2. Will the temperature increased at the air turbulence area due to decreased air flow?
3. If yes, how high can it be? Will temperature raises so high that the Tdewpoint at this turbulence point = 23deg.C (the air that flow next to the turbulence) and caused condensation? 4. Under what condition change will water condensation at the bended flexible duct happens and accumulate water? For how long?
 

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  • #2
Lnewqban
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In a normal aircond system using flexible airduct, assume airflow with temperature & humidity conditions (Tdry=23°C; Tdew=13.4°C; RH=55% ) go through a bended flexible airduct where air turbulence is formed:
1. Can condensation happens at the bended flexible airduct due to air turbulence?
2. Will the temperature increased at the air turbulence area due to decreased air flow?
3. If yes, how high can it be? Will temperature raises so high that the Tdewpoint at this turbulence point = 23deg.C (the air that flow next to the turbulence) and caused condensation? 4. Under what condition change will water condensation at the bended flexible duct happens and accumulate water? For how long?
1. No.
2. Very little.
3. No.
4. Location of bend is low and water is being carried away from thecolling coil or condensate pan. Perhaps too much humid fresh air is entering the system and relative humidity is much higher than assumed for that temperature (the coil is unable to condensate some of it due to high velocity or few rows or refrigerant temperature).

There is turbulence in the blower and the whole duct system.
 
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  • #3
LMC
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Lnewqban, thanks for your reply.

In another word, is my understanding correct that only when there's an increase in moisture content (at/almost near dew point temperature) inside the airduct that condensation will happen, regardless of straight/bended airduct?
 
  • #4
russ_watters
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2. Will the temperature increased at the air turbulence area due to decreased air flow?
3. If yes, how high can it be? Will temperature raises so high that the Tdewpoint at this turbulence point = 23deg.C (the air that flow next to the turbulence) and caused condensation?
#2 is yes, a little, but #3 is backwards. The [dry bulb] temperature goes up, but the dew point stays the same. So it decreases the chance of condensation, not increases.
 
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LMC
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#2 is yes, a little, but #3 is backwards. The [dry bulb] temperature goes up, but the dew point stays the same. So it decreases the chance of condensation, not increases.
Thanks russ_watters for your reply.
 
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Lnewqban
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Lnewqban, thanks for your reply.

In another word, is my understanding correct that only when there's an increase in moisture content (at/almost near dew point temperature) inside the airduct that condensation will happen, regardless of straight/bended airduct?
You are welcome.
A surface, which remains cooler than the air, is needed for abundant condensation to happen.
The insulation of that flex duct should avoid the heat transfer or energy loss, that a massive flow of cool air needs to reach the condensation point.

Because of that, I believe that water is finding its way into the duct layout somehow.
In Florida, it is common to find internal mold growth a few feet away from the coil in commercial installations, mainly due to splashing.
One case, had a pipe leak dropping on top of a metal duct, and water was finding its way inside the insulation and duct, via leaky seams: mold was growing inside that section only.
 
  • #7
LMC
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#3 is backwards. The [dry bulb] temperature goes up, but the dew point stays the same. So it decreases the chance of condensation, not increases.
Hi russ_watters, is my understanding correct that dew point stays the same because moisture content remains the same?
 
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  • #8
russ_watters
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Hi russ_watters, is my understanding correct that dew point stays the same because moisture content remains the same?
Yep! Dew point is a direct function of just moisture content. Unlike relative humidity which is a function of moisture content and temperature.
 
  • #9
Lnewqban
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Please, see:
https://web.ornl.gov/sci/buildings/conf-archive/2007 B10 papers/010_Morse.pdf

https://www.engineeringtoolbox.com/humidity-measurement-d_561.html

https://www.practicalhvac.com/uncategorized/the-psychrometric-chart/

sensible-heat-factor.jpg
 
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