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.

 

[iservem]

Agreed. Sadly that is becoming more and more rare.

 

[EnergyProfessional]

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.

 

[iservem]

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.

 

[cdxx139]

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

 

[EnergyProfessional]

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.

 

[berkshire]

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.

 

[EnergyProfessional]

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..

 

[urgross]

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

 

[dbill74]

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.

 

[iservem]

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!

 

[cdxx139]

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

knowledge is power

 

[iservem]

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?

 

[dbill74]

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.

 

[iservem]

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."

 

[EnergyProfessional]

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.)