Comments on: Duct Design 5 — Sizing the Ducts

By: abailes

abailes — Tue, 29 Sep 2020 13:52:41 +0000

In reply to Alexander Verrigni. Alexander, with two returns

Alexander, with two returns in a duct system, the total effective length counts only the one with the most restrictive path. It may not be the one with the actual longest length as measured with a tape measure. It's the one with the greatest sum of actual straight duct length plus equivalent fitting length. The bottom line is that only one of the return pathways will count in the TEL.

By: Alexander Verrigni

Alexander Verrigni — Tue, 29 Sep 2020 13:28:10 +0000

If you have two return ducts
If you have two return ducts/registers for any given zone, is the longest TEL comprised of the entire length of both returns or just the longest return? I am intuitively thinking only the return nearest the longest supply branch would be counted for the TEL, and not both?

By: Dick Cokhuld

Dick Cokhuld — Mon, 04 May 2020 12:52:01 +0000

In reply to Drew Clausing. Drew,
Drew, I think 5 is the last article. this article was made in 2017, it probably ends at 5.

By: Aydar

Aydar — Tue, 17 Dec 2019 07:21:52 +0000

Thank you, Allison!
Thank you, Allison!
Great articles which helped me to understand the duct design process.
I’ve read here a lot of comments suggesting various (possibly better different) duct design methodologies. But what I experienced as a new residential hvac service technician.
A) unfortunately, majority of residential hvac contractors have no idea of the heat gain/loss calculations and duct design. They don’t do it and don’t care. And I’ve seen a lot of times how hvac contractors changed duct designs made by engineers. That is really shocking.
B) as a result of point A, I see a lot of customers who complain about cold/hot rooms or floors and who has oversized/undersized equipment.
I think this is a must read for all hvac technicians.

By: Gabe Colon

Gabe Colon — Mon, 17 Jun 2019 20:02:09 +0000

This was an incredible series
This was an incredible series. Thanks for taking the time to prepare this. It would be helpful if "Duct Design 5 — Sizing the Ducts" contained the duct size formulas for round steel, rectangular, and Flex ducts, similar to how you included the Friction Rate formula in Duct Design 4.

By: Drew Clausing

Drew Clausing — Thu, 07 Mar 2019 15:00:33 +0000

In reply to abailes. Hey Allison, thanks for the
Hey Allison, thanks for the great articles! Did you ever finish the series or did it end with 5? Thanks!

By: Andrew

Andrew — Wed, 27 Feb 2019 20:47:42 +0000

My apologies again. The real
My apologies again. The real spin is I actually found the first parts to be very informative and well written. The last part was well written, I didn’t fully get to see it all figured out in the end so I guess I felt let down, but didn’t mean it in a personal way. I shouldn’t have put it the way I did and I regret the wording.

By: abailes

abailes — Wed, 27 Feb 2019 19:52:47 +0000

In reply to Andrew. Andrew,

Andrew,

Thank you for coming back to explain your comment. So what you're asking is for me to apply the stuff I explained to an example duct system to show how it all works. I agree that would help make it real. I think I actually had a thought about doing that back when I wrote this series. But other work got in the way and I moved on to other topics and never managed to do that. I'll add it to my list and come back around to it sometime this year (I hope).

I apologize for my snarky response to your terse first comment. And I have no problem with a reader telling me I failed, miserably or otherwise, as long as they tell me why. I don't always get it right. And I'm far from complete in these articles because I try to keep things short and tight enough for someone to read without too much difficulty. But thanks again for coming back and explaining yourself. Your second comment has been much more helpful.

~ ab3

By: Andrew

Andrew — Wed, 27 Feb 2019 19:09:00 +0000

I guess my comments were in
I guess my comments were in haste and abrupt. I’m sorry for that. But I’ll explain in a minute. But Im glad you let the real you out here in the open. Your attitude speaks volumes. Your comments do not. The point is you wrote an article. I get from reading the series that you are trying to sell a service.
I am just a casual reader trying to learn about ac design who saw your site. You – the writer of the article – placed a diagram from your software at the top of the article. The article failed for me because you did not incorporate the discussion around the diagram you provided, instead you discussed some simple calculations and how to use an approximation device.
Had you used the article in a fashion that 1. Discussed and showed the calculations based upon a design such as the one you provided, and 2. Added in the use of the dampers you spoke about, and then discussed how the final results changed your basic assumptions, and explained if the design parameters were still applicable afterward, then I would have found the article useful.
To put it another way from reading your series didn’t you write about having an available amount of static pressure kind of used a budget analogy- but then you put in dampers because the flow is wrong, but the friction was right, so then you just stick in dampers. What happened to the budget?
So I understand you may not like a review from a reader who states that the article failed miserably for them. It’s like that sometimes. Maybe I just expected more after reading the first parts of the series.

By: David Butler

David Butler — Mon, 18 Feb 2019 06:00:59 +0000

In reply to David Butler. @Cal, as I've never specified
@Cal, as I've never specified or evaluated wood grilles, I'm unable to recommend a particular brand. I just checked Hart & Cooley website and current catalog and they apparently discontinued its Classics line, which included some wood floor grilles (although without any engineering data). Can't say I'm surprised. If I were forced to design a distribution system with wood grilles, I would obtain samples of the grilles so I could measure the net free area (simple to do) and then increase the grille area and/or number of supplies per room accordingly to ensure those thick vanes don't create more resistance than a baseline grille. And I would make sure the installer tests the blower to ensure it produces the design airflow without exceeding my static pressure budget. Note that the throws produced by a wood grille are typically straight (non adjustable), but throw distance and direction have become relatively less important in homes built to today's energy codes. The main objective in duct design is to get the right amount of air to the room without expending more energy than necessary to deliver it.