×
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

Efficient chilled water piping insulation

Efficient chilled water piping insulation

Efficient chilled water piping insulation

(OP)
Hopefully someone from a tropical area can help here; have a real goofy problem.

Currently doing some work in a hospital in the tropics.  Chilled water supply temps are 42F, return is 57F.  Needed the large delta t in order to use existing piping and still meet load requirements of 480 tons now, 720 tons when all areas are conditioned.

The problem is condensation.  Using 3 layers of 1" thick  Armaflex/Rubatex cellular foam product, with the smooth-skin vapor barrier, the system works most of the time in the un-air conditioned corridors.  However, the piping passes through several "fales", or large open seating areas with openable windows.  This added load makes the supply line insulation condense - not a lot, but enough to keep buckets in the corridor under the drips.  

They now want to provide air conditioning to another building, which will require a 6" supply/return lines to run under a breezeway type cover about 70 feet.  This will subject the piping to the full outside air design conditions of 90F at 90%RH; this yields a dewpoint of about 87F.

Unfortunately I cannot just add more insulation.  The concrete structure that supports the piping will not accommodate piping any larger.  I've talked to some of the engineering staff at hospital facilities in Honolulu, and they get by with 2" of insulation; it's just a lot more humid here. The only solutions I can come up with is:

1. Using a pair of 4" chws pipes and increase the insulation to 4", or

2. Install some anti-freeze type heaters on the last layer of insulation, and then cover with aluminum weather cover.  The heaters could be controlled by dewpoint sensors, similar to chilled beam condensate controllers.

Both of these solutions seem...nuts to me.  Unless someone has any recommendations for other insulation?  We actually tried 3" fiberglass with vapor barrier.  But it did not work as well as the Rubatex, and worked WORSE when abused and crushed; condensation would form and saturate 40' lengths of insulation, making a mess to clean up.


    

RE: Efficient chilled water piping insulation

Specify pre-insulated chilled water pipe with polyurethane foam insulation.  You should be able to get to 2"thk on 6" pipe in these conditions.  The polyurethane foam is probably around 2/3 the heat loss of armacell.  Phenolic foam also would be an option.

The 3" of armacell should be enough - it is possible you have barrier gaps and this is an installation problem.  Specifying pre-insulated pipe almost eliminates this.
 

RE: Efficient chilled water piping insulation

I'd recommend trying a couple materials using the 3EPlus software. Phenolic, PIR and polyurethane, at the least.

RE: Efficient chilled water piping insulation

relation between insulation thickness and pipe diameter is not linear, which is visible from thermal equations, so the question is what is diameter of you piping

I made quick calculation for Armacell product with ordinary lambda, and 2 inches insulation should suffice for pipes up to 3".

Apparently, using new pipes with larger dimeter make things worse, while I did not get whether you want to install 4" pipes instead of existing ones or you actually have 4" pipes.

4" pipes should need just several milimeters more than 2" of insulation, so I am surprised with your results.

Is it possible that your chiller is overloaded, so as it controls return temperature, supply temperature went very low? Some controls have low-temp limit adjustable and people sometime set it lower than 4 degrees Celsius.

Do you have glycol inside?

 

RE: Efficient chilled water piping insulation

There are other factors that may be more important than insulation thickness to preventing sweating. If the insulation is not perfectly sealed you will get sweating under the insulation. If the pipe runs through a confined space with no ventilation you can still get sweating even with thick insulation. Insulation is simply a resistor of heat flow. By itself it does not control temperature between the two sides. Ventilation or air movement around the pipe is also needed.

I've seen lots of insulated pipes drip at the joints in the insulation.   

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