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Duct Pressure Loss Calc

I am attempting to set up a worksheet to calculate the pressure loss through duct work for HVAC. I could not find any examples in the collab and I was hoping someone can point me in the right direction. I have a feeling (still looking into it) that I may have to solve using user-defined functions. I'm still confussed by user-defined functions, so a good place for a primer would also be appreciated.

Thank you for for any assistance
47 REPLIES 47

Duct Pressure Loss Calc

On 7/17/2009 12:18:12 PM, ElSid wrote:
>I am attempting to set up a worksheet to calculate the pressure loss through duct work for HVAC. I could not find any examples in the collab and I was hoping someone can point me in the right direction. I have a feeling (still looking into it) that I may have to solve using user-defined functions. I'm still confused by user-defined functions, so a good place for a primer would also be appreciated.

Thank you for for any assistance <<br> __________________________________

Though I spent over 30 years in that stuff: pressure, flow ++++, I won't spare a minute on that HVAC for 3 reasons:

1. Physical formulation of pressure drop, flow are just theoretical. When it comes to applied Engineering, all that is governed by more exact formulation and varies with the range of applications, fluid properties ...etc. The theoretical school stuff is then useless, totally.

2. When it comes to duct networks, things complicate beyond recognition because of the negative pressure effect at the branching points and the form of the branches ... etc. Solution is via a matrix representation and is very complex and there are software for that... example water distribution.

3. HVAC goes by codes (regional ?, national ?). ASHREA was a good reference years ago. It might still be or other codes. What that means here is that no matter how smart your result will be, it must be traceable by part and in all.

In conclusion, you are asking to re-invent the wheel. That's the way I see your request. Bits and pieces go nowhere if they can't be collected and certified. Consulting HVAC experienced specialist is probably the first approach. Further the formulas that you might pass in this collab would have to sourced and certified acceptable. There are HVAC Engineering Firms.

I wish you good luck within this collab and outside.

jmG

Duct Pressure Loss Calc

jmG,
As I re-learn Mathcad and hopefully get better with it's programming features (never had to go in depth before) I am looking for guidance. All calculations need to be transparent and double checked, this includes packaged software solutions. A Mathcad sheet is considered an alternative method for verification and much more transparent than excel sheets and faster than hand hand calculations.

Duct Pressure Loss Calc

One Mathcad 14 WebSheet (Evaluation of the resistance coefficient of friction � as function of Re and relative roughness �):
http://twt.mpei.ac.ru/MCS/Worksheets/Hydro/La-De-Re.xmcd
And I have WebTasks from the text book "Fundamentals of hydraulics, heattransfer and aerodynamics" - sorry - in Russian. But I am going to translate intu English:
http://twt.mpei.ac.ru/GDHB/OGTA.html
Val

Duct Pressure Loss Calc

I am attaching a version of my current main branch sheet. It is a work in progress and all constructive input is welcome. I have a few questions in red text that I would like some assistance with. I would like to eventually "condense" it by making a program. Still learning and taking baby steps.
Thanks to the collab for all your assistance

Duct Pressure Loss Calc

I know I am working too hard on this. I need to figure out how to program. Can someone take a look and answer some questions in the work sheet. For some reason, I can not add up or display an array I created using functions.

I am NOT posting in version 11 due to some formatting that I know breaks when save as version 11.

Duct Pressure Loss Calc

On 8/4/2009 3:42:26 PM, ElSid wrote:
== I know I am working too hard on this. I need to figure out how to program. Can someone take a look and answer some questions in the work sheet. For some reason, I can not add up or display an array I created using functions.

The first question (why ... inWg); I this may be a bug in the in-line display - I think there was a recent report of a bug in this feature but I can't remember what or when.

The second question (why won't array display) is because there is no array to display. ΔP is a function name, hence the display you do see telling you what kind of parameter it takes and the type of result. You have used ΔP.i (giving a literal subscript) as the variable rather than ΔP[i (indexed subscript). Even if you had used the latter, your function definition would have over-riden any previous results. I suggest a change to δP for the function and convert literal subscripts to indexed ones.

Unfortunately, I don't have time to look at the programming bit right now ...

Stuart

Duct Pressure Loss Calc

inWg is a unit definition I added to my sheet (inches water gage/column). I imagined it had something to do with the function ... still learning how to use them properly. I'll look into the δP change as recommended.

I would also like to carry over the diameters. See revised sheet. Will look into a program loop next. Any ideas are welcome.

Duct Pressure Loss Calc

>I am NOT posting in version 11 due to some formatting that I know breaks when save as version 11<<br> _____________________

Your project goes by a minimal combinations of solving functions root(,,)... Given/Find ...and that has nothing to do with what you figure Mathacd 11 wouldn't do. Your choice. Maybe start by engineering the project.

jmG