Round versus Square ducts

[slhill]

Ballast/PPI advocates that a round duct is the "best" shape because it has the lowest area for friction loss. (MEEB says the same thing without the "best" clarifier.)

While I can understand this, the only place I have ever seen round ducts used is in expose ceiling cavity spaces. Otherwise, we always have square (ok, rectangular)ducts in buildings. Am I naive to think "best" should consider more than one characteristic of a product or system, but rather the best compromise between all the various options? After all, if "best" was viewed as "cheapest" option, then we'd have square ducts in places it would look ugly.

Also, does "most economical" always mean "least expensive"?

Mostly venting - I get what the publisher is trying to say. I just think they're over-simplifying the issue.

[banda]

Best, is best. I think the reason we see rectangular ducts, so much is due to maximized ceiling heights.

[stl-guy]

slhill wrote:
Ballast/PPI advocates that a round duct is the "best" shape because it has the lowest area for friction loss. (MEEB says the same thing without the "best" clarifier.)For high velocity duct systems Round ducts will be most efficient. This has little to do with aesthetics, only physics. MEEB is a general text howeverthe focus and case study tends to be basedon large buildings while the ARE is based on buildings of around 10,000 Sq. Ft.or less.

While I can understand this, the only place I have ever seen round ducts used is in expose ceiling cavity spaces. Otherwise, we always have square (ok, rectangular)ducts in buildings. Am I naive to think "best" should consider more than one characteristic of a product or system, but rather the best compromise between all the various options? After all, if "best" was viewed as "cheapest" option, then we'd have square ducts in places it would look ugly.

Also, does "most economical" always mean "least expensive"? Not always, least expensive normally equates to most efficient, regardless of round. square or oval duct.

Mostly venting - I get what the publisher is trying to say. I just think they're over-simplifying the issue. The exams are after all, simplistic by design. Your direction is for schematic design, at least on the graphic portions of the exams.

[Leifikins]

Also, Kaplan mentions that installing interior duct insulation is for acoustical reason, but at the same time is not good practice because of IAQ issues-mold growth.

On a recent project I told this to the engineer and he said they always spec out interior duct insulation and that it does not cause mold.

So who's right??:X

[the prisoner]

Leifikins wrote:
Also, Kaplan mentions that installing interior duct insulation is for acoustical reason, but at the same time is not good practice because of IAQ issues-mold growth.

On a recent project I told this to the engineer and he said they always spec out interior duct insulation and that it does not cause mold.

So who's right??:X

according to this, the engineer is wrong.

http://www.ehs.ucsb.edu/units/ih/ihrsc/ihpdf/ihductliner.pdf

[Leifikins]

I agree, but I have noticed that when seniour personal have been doing the same thing for over 30 years, they get defensive when you provide alternate solutions.

I really dont know how to deal with this. Any thoughts?

[the prisoner]

Leifikins wrote:
I agree, but I have noticed that when seniour personal have been doing the same thing for over 30 years, they get defensive when you provide alternate solutions.

I really dont know how to deal with this. Any thoughts?

could it be a climate and use issue? if he/she has done a lot of new office buildings in jersey, but has never done an adaptive reuse high school auditorium in louisiana, maybe mold has never been an issue (don't quote me, as i'm completely making this up). if so, they would be correct in a vernacular kind of way. or, maybe he just means that no one has died yet from bronchitis due to one of his systems.

i'm not the most passive guy, but i generally let engineers do their thing since my role is to coordinate/interpret/communicate instead of second guess. granted, i'm in a firm that works w/ only a couple of egr firms (can't afford a bad relationship in a smallish town).

your post has stirred my curiosity, though, so i'm definitely going to ask our main, trusted mep guy about this.

[Leifikins]

well, the project was for an office interior space...and mep guy was adding just one duct...so it wasnt a big deal. If it was up to me, I would not put interior insulation.

[MNA]

I've had a MEP engineer say their firm calls forinstalling interior duct liner by default. I was told it's a cya sort of thing to eliminate complaints of noisy ducts from the owner. I'm for anything that cuts out the moaning and groaning. :D