×
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

Duct insulation in conditioned air space
5

Duct insulation in conditioned air space

Duct insulation in conditioned air space

(OP)
I know that codes do not require duct insulation when SA or RA ductwork is installed within a conditioned air space. Is there any thermal benefit to installing insulation in/on this duct? I need documentation to prove the point. Thanks.

RE: Duct insulation in conditioned air space

You need general knowledge rather than documentation.

Uninsulated supply duct with temperature bellow space temperature may develop condensation. If air heating is used via supply air, heat distribution will not be achieved according to design hwn having considerable losses over duct surface even if it takes place in heated space.

This is not something code articles should convince you about. You need to learn trade first.

RE: Duct insulation in conditioned air space

(OP)
Thank you for the rapid response. I guess I need to offer more info. This is in south Florida. Heating is not much concern. The temperature difference between the outside and inside of the duct should not reach dewpoint. I am not interested in code articles, I know what code requires. I am searching for research or a response from an engineer that would say if there is any real thermal benefit to insulating duct that is in conditioned air space. I do not think there is any thermal benefit, because it's not like any transference of temperature through the sheet metal is going to an area that isn't supposed to be cooled, anyway. However, this duct does call for R-4.2 acoustical duct liner, but there is an opinion that it should be R-6, which I see as a waste of material. Is there any real thermal benefit to insulating ductwork in conditioned space?

RE: Duct insulation in conditioned air space

Drazen gave you the answer your looking for, research it. Can R4.2 duct condense if the exterior doors are left open? Doubt it. Provide the psych chart calculation to whoever is asking. They may be asking for R6 for sometother reason, acoustics for example?

knowledge is power

RE: Duct insulation in conditioned air space

(OP)
I have researched it and came up empty handed. I think insulating duct in a conditioned air space is like putting a kick stand on a horse. I doubt there is any available test results on that either. I contend that if insulation was a benefit, energy efficiency codes would demand it, but they don't. The codes state no insulation required in indirect or direct conditioned spaces. The situation here is the specs do not match the job. "Cut and paste" method of creating "extra special" specs has had an end result that they think the duct should be insulated AND wrapped. I'm just trying to deliver the product that the project needs based on substantiated facts.

RE: Duct insulation in conditioned air space

Prove your point with calculations, forget about articles on this one

knowledge is power

RE: Duct insulation in conditioned air space

the other response is indeed more specific, and as cdxx says, you need to simply make calculation, assuming worst-case interior humidity scenario. is it not florida humid area?

as per any kind of codes, of course i'm not familiar with florida codes, but in generals it is fire codes that prescribe insulation in some cases, and energy efficiency coded in others, both are prescriptive if applicable.

we also did not learn if supply ducts serve for ventilation only or for cooling as well. i can hardly imaging that condensation is not an issue if duct serve for cooling - how high air flow rate you need to cool with relatively high air temperatures?!

un-elaborated request to apply more insulation resembles mentality of some contractors - they fear of condensation, are not familiar with calculations, but do not want to seek for professional advice.

RE: Duct insulation in conditioned air space

(OP)
Thanks CDXX139, I suppose that is what it will take.
Drazen, I think you missed the point. I was looking for back-up that insulation on duct, that's purpose is to cool, installed in a cooled space, is a waste. (unless for acoustics) Thanks for trying, though.

RE: Duct insulation in conditioned air space


@ Iservem, Please refer to the post Drazen,first paragraph.My experience why a supply duct should be insulated is based solely on geographic location circumstances. In one of my project,US territory in the pacific.the USAF-OICC decided to have the duct insulated after the ductworks and diffusers are having a lot of condensation. they have this condition 9mos in a year.Other buildings have corroded ducts and diffusers due to condensation.
So, it looks like all you need is graphics and calculations to show what is appropriate the situation. HTH

RE: Duct insulation in conditioned air space

(OP)
Dynamo78, Thanks. 1) The ductwork you are talking about was exposed and in it's own air conditioned space? 2) If so, the doors must have stayed open more than closed or the building leaked allowed of untreated air to infiltrate?

RE: Duct insulation in conditioned air space

"there is an opinion that it should be R-6"
did you discuss with the person who gave this opinion?

RE: Duct insulation in conditioned air space

(OP)
Yes, but to no avail. They don't speak Mechanical. One would logically think that if the code does not require duct insulation and R-4.3 liner was being provided the safe conclusion would be it's covered: conditioned air duct in conditioned air space (not some hot attic) with R-4.3 would not have a loss. But they seem to think it should be wrapped as well. This is the result of specs that are cut and pasted together, but don't work together. Logic don't work.

RE: Duct insulation in conditioned air space

(OP)
@ urgross, Thanks that does bring a lot of light to the situation and since the example given on the document results in a thickness of .15" insulation, I feel comfortable that conditioned air duct in conditioned air space is sufficiently insulated with R-4.2 liner (1" thick). With all these thoughts shared here today I should be able to present my case the R-6 would not provide any more benefit than R-4.2 Thanks!

RE: Duct insulation in conditioned air space

@iservem, Yes its ductworks are exposed,unfortunately, maybe the built was not tight enough,I am sure infiltration and human traffic are the major cause aside from the fact that its in the extremely high humid area,an island actually. It maybe be archived, we received an order from DOD or Dept of the USAF to insulate ducts and practice due diligence as far as temperatures are concerned to avoid condensation."How to avoid condensation on ductworks and diffusers in humid climate.their study was in response that is similar to your issue. All the best and please keep us posted of the resolution. Thanks

RE: Duct insulation in conditioned air space

ASHRAE Handbook. Fundamentals, Chapter 23.

It lays out the calculations you should do to determine the necessity of duct insulation.

Armed with ASHRAE and calculations supporting your position you should be good to go.

RE: Duct insulation in conditioned air space

(OP)
Well the engineer left. The GC fired their MEP Supt (second GC on this job, BTW) The Construction Manager's MEP guy quit (Second CM on this job, also) So the junior architect stepped up to the plate (coaxed by the GC's electrical Supt.) and decided the SA & RA duct should get lined and wrapped, to the tune of R-10, using 1" liner and 1.5" ductboard with cloth and mastic. This will be inside mechanical rooms (air conditioned) and in exposed areas (air conditioned). If the ductwork is concealed (like in a return air ceiling) it gets liner & 1.5" duct wrap. LEEDS should have something against wasting material like this.

RE: Duct insulation in conditioned air space

forget about LEED, it is just a propaganda to spend more money and make some business working more and more. what is your position in this project?
if you are the owner tell this architect to support his opinion in written approved from a registered HVAC engineer.
if you are an employee, then make sure you don't bear the responsibility on your shoulder.
as your project has more than one management, you need a lawyer support not an engineer support.

RE: Duct insulation in conditioned air space

(OP)
I agree with your opinion of LEED. If their LEED's REAL motive was to conserve resources, then there would penalty points for installing material that does NOT return a benefit. To me that is a waste of resources. As for the "design team's" decision, been trying to offer the correct solution for months, based on the contract and the building's needs, but they just don't speak "Mechanical" Leaves only one language: Change Order. Sadly no benefit to anybody. Thanks to all of you. I hope your projects are lead by knowledge and experience.

RE: Duct insulation in conditioned air space

Long before LEED came about as an ass-backwards abortion of a cockroach, the term used was "responsible".

RE: Duct insulation in conditioned air space

(OP)
Agreed. Sadly that is becoming more and more rare.

RE: Duct insulation in conditioned air space

urgross: if you could charge a fee for the term "responsible" they still would call it that way. but no owner pays $50k for a plaque that says "responsible". so they use the term "green" and owners happily pay $100K

Regarding insulation: assuming this is cooling and the duct is above the conditioned space, there is no energy waste since all the "cold" would drop down.
As for humidity, it depends on your inside conditions. If you supply 55°F air, the outside of the duct will be a touch above 55°F.

But the approach to insulate in such situations can backfire as well if your insulation ins't vapor-tight. If this isn't an area with high infiltration 9i.e. lobby) this may not be a problem. not sure if in florida lobbies are usually treated differently.

RE: Duct insulation in conditioned air space

(OP)
HerrKaLeun: The "resource" that I claim they are wasting is the insulation material. Since no thermal protection is required (conditioned air duct running through conditioned air space) and the duct is to receive 1" internal liner (R-4.2) for acoustical purposes, any additional insulation will not return a benefit. A responsible designer would not demand additional material be installed that serves no purpose. Neither would LEED (I hope). If LEED was for real, they would penalize inefficient use of material, not just have a positive point system, but negative as well.

RE: Duct insulation in conditioned air space

I think this is a case where you have to pick your battles. They want to add inuslation agaisnt the engineers recommendation?, and its not against code or doesnt negatively affect the system? Let them, move on. Im sure there are bigger issues elsewhere that can use your attention.

knowledge is power

RE: Duct insulation in conditioned air space

If you have the liner, outside condensation likely isn't an issue.

LEED has nothing to do with sustainability. Here some entertainment on LEED
Some interior designers and landscape architects came up with a scheme to make money and give you credits for a building barely meeting code without any verification (no, verification by the design team that profit from additional LEED fees doesn't count).

Take the $30K you pay to USGBC and the $100K you pay the AE for the paperwork, and the $100K the GC needs for the paperwork and use that same money to get a sophisticated HVAC control system and build airtight... that would be truly sustainable. but it doesn't give you a plaque.

RE: Duct insulation in conditioned air space

Herr Ka Leun,
I gave you a star for that link, I watched that lecture to the end, at times I laughed my ass off, But I also learned a few things.
B.E.

You are judged not by what you know, but by what you can do.

RE: Duct insulation in conditioned air space

berkshire: i watch it every once a while. Especially after meetings with architects that "know everything"
a lot to learn from his website. i had spent nights just reading and reading..

RE: Duct insulation in conditioned air space

I thought LEED meant that you got a bicyle rack with your project.

RE: Duct insulation in conditioned air space

WOW what a topic. I know I'm getting in on this late, but let me weigh in with this.

It doesn't matter where you are, south Florida, California, Michigan, Canada; if you put uninsulated ductwork in a conditioned space you are going to have condensation problems. The only possible exception to this would be in a dry arid environment and your space RH is close to or below 40%. The fact is the temperature of the air in the metal duct is going to control the physical temperature of the ductwork as HerrKaLeun mentioned above. It should be noted (and has been observed by me personally) that even insulated ductwork can get condensate if the air temp inside is sufficiently low.

Another benefit of insulation on ductwork is that it keeps the temperature of the air 'in' the duct more constant. This is so the temperature of the air coming out of the most remote diffuser is as close to design as possible. This is beneficial as it helps to maintain constant temperature throughout your space. Without it you will get hot and cold zones.

Based on your statements above, I surmise your argument for not insulating exposed ductwork is from observation of existing installations of exposed spiral metal ductwork. What you may not realize with these installations is that even though the spiral metal duct is not externally insulated, it is in fact internally lined with insulation. The internal lining and metal exterior of these ducts is much more visually appealing than duct with external insulation.

Regarding insulation of the return duct, totally unnecessary as the temperature of the air in the RA duct is about the same as the conditioned space so little to no heat transfer will happen. I would consider lining RA duct near the AHU or a fan for acoustic purposes though.

RE: Duct insulation in conditioned air space

(OP)
I understand and agree with what you are saying. I am not against insulating the SA duct, but to make a point, I was referring to ASHRAE 90.1 and all current mechanical building codes that indicate it is not required in air conditioned spaces. In the risk of getting slightly side-tracked here, I wonder if there was raw air infiltrating the building where you witnessed the condensation? Seems that once the building becomes "climatized" the condensation would stop, unless the building leaked.
I appreciate your input, as it is on topic and I have learned a great deal throughout this thread.
Here's my point (or gripe): The SA & RA ductwork are in conditioned air space and are to receive R-4.2, 1" duct liner. I do not believe any more insulation is of ANY benefit, but because the project specifications seem to be a "cut & paste" compilation of contradictions that were never sorted through until now ... the architect wants to put 1.5" ductboard on the outside of the duct, in addition to the 1" liner. Resulting in R-10+ for no benefit, but a significant waste of material (and labor). which of course will result in a change order request and battle for nothing!

RE: Duct insulation in conditioned air space

Why is it a change order if its in the specification?

knowledge is power

RE: Duct insulation in conditioned air space

(OP)
Because the specifications are a compilation of contradictory information. A better question is why not do what the building and owner needs, instead of trying to make sense of nonsense?

RE: Duct insulation in conditioned air space

The space I got condensation on insulated duct is a fitness center in South Carolina. Trouble shooting revealed a failed control valve resulting in SA temperatures below 50°F. Once the control valve was replaced and SA temperatures where back to design, condensation disappeared and hasn't been an issue since.

As for code, check in your copy of the Florida Mechanical Code. In International mechanical code (to which I happen to have easy access), section 603.12 states "Provisions shall be made to prevent the formation of condensation on the exterior of any duct." Having worked with FMC in the past I know that it closely mimics IMC (early versions were identical and last I checked there were few differences) and would be very surprised if this verbiage is not in it somewhere. Don't expect any code to say "provide insulation on ductwork" because not all ductwork is sheet metal or requires separate insulation.

HerrkaLeun posted earlier about supply air being 55°F, this is a very common temperature for supply air. It also happens to be the dew point for air at 75°F and 50% RH. However, since no-one can guarantee that your space will never stay at this temperature and RH (you will have people in the space right?), the dew point is going to go up and down as well. So any surface that has a temperature close to 55°F is going to be subject to condensation, this includes uninsulated metal duct. Therefore to meet building codes, something needs to be done to raise the temperature of the surface of the duct. The easiest, cheapest, best method is insulation.

I don't know if I missed it earlier or not, but for the architect to want BOTH ductboard and liner is overkill. Go with one or the other.

RE: Duct insulation in conditioned air space

(OP)
Thanks, I agree insulation inside and out is not a responsible use of materials. I also feel confident that the R-4.2 duct liner will prevent any condensation from forming, since the duct is not in an attic, outside or other non-conditioned space. Thanks for you informed opinion. Oh and you are correct, every code I have read includes a "disclaimer" similar to ASHRAE 90.1: "These thicknesses are based on energy efficiency considerations only. Issues such as water vapor permeability or surface condensation sometimes require vapor retarders or additional insulation."

RE: Duct insulation in conditioned air space

iservem: based on supply temp and R4.2 , you could calculate the surface temp of the duct and use psychometric to determine if it condenses or not. Maybe be safe and assume 60% RH or so... it depends a bit on if you get lot of infiltration (lobby etc.)

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