×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Ventilation Ducting - Psychometric Chart

Ventilation Ducting - Psychometric Chart

Ventilation Ducting - Psychometric Chart

(OP)
I am ventilating a second floor area in a recip engine power plant with just outside air.  I will distribute the air through a duct with registers.  The duct will be insulated inside with 1" insulation and outside with 2" insulation. The area gets very warm (120+ with engines running during the summer and 90+ during the winter with not engines running). I don't think I will have a problem with condensation during the summer however I am concerned with condensation during the winter.  I have done some heat tranfer - temperature calulcations.  I calculated the ducting sandwiched between the outside and inside insulation will have a temperature of 60 deg. F. I started out with 110 deg outside and 32 deg inside temperatures (outside and inside of ducting).  If I were to use the psychometric chart and with 30% RH, the dew point temperature is above the 60 deg duct temperature. 1. Can I assume that there will be condensation on the duct even if sandwiched between insulation? 2. Or if the duct is properly insulated and sealed condensation will not be an issue?  3. Does this application warrant the use of the psychometric chart?  Thanks in advance for any comments.

AJ

RE: Ventilation Ducting - Psychometric Chart

The reason we insulate cold ducts (well one of the reasons) is to prevent condensation.

If you calculate the surface temperature of you duct through the insulation, and that temp is below the dewpoint of the space you will have condensation.

If the duct is insulated with a continuous vapour barrier you shouldn't have probelms.

RE: Ventilation Ducting - Psychometric Chart

Chris is right. It would depend heavily on vater vapor generation in the space and air exchange rates. If you have relatively low humidity generation in the space (which it sounds like you might if it's an engine plant and not a steam plant) and a decent air exchange rate, the dew point inside and outside might be nearly the same. This would mean that you might not even need to insulate the duct.

3 inches of duct insulation sounds almost overkill for this application, unless there's a substantial moisture source in the room.

CB

RE: Ventilation Ducting - Psychometric Chart

If you are just ventilating with outside air to remove engine heat, why are you insulating the ducts?

As for moisture, where is it coming from, people?  Moisture will migrate towards the cold side and condense only if the surface is at or below the dew point.  If you are supplying cold outside air during the winter, the inside temperature of the building will be warmer so how can it condense?

RE: Ventilation Ducting - Psychometric Chart

As I read the original question, the generator is NOT running during the winter

snip
The area gets very warm (120+ with engines running during the summer and 90+ during the winter with not engines running).
snip

Why would you be ventilating in winter if the engines are not running? It is possible to condense on the duct in the summer, but OA would have to be pretty low and inside have very high wet-bulb.

Is the inside temp heat gain mostly sensible as it would be with an engine? If not, what is the moisture source?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources