Duct insulation in conditioned air space 5

[iservem]

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.

 

[Drazen]

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.

 

[iservem]

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?

 

[cdxx139]

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

 

[iservem]

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.

 

[cdxx139]

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

knowledge is power

 

[Drazen]

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.

 

[iservem]

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.

 

[dynamo78]

@ 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

 

[iservem]

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?

 

[317069]

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

 

[iservem]

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.

 

[urgross]

This site might be helpful.

http://www.jm.com/content/dam/jm/gl...nsation Control on Air Conditioning Ducts.pdf

 

[iservem]

@ 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!

 

[dynamo78]

@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

 

[MintJulep]

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.

 

[iservem]

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.

 

[317069]

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.

 

[iservem]

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.

 

[urgross]

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