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Duct Pressure Loss Calc

ELSID
4-Participant

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

On 10/16/2009 12:11:03 PM, ElSid wrote:
>jmG,
>I understand the issue with
>the math in the text box. I
>will get away from doing that
>(yes, there is a glitch with
>it and I need to shut down the
>sheet and re-open to fix).

==> don't shut anything, use mine "Blank"

>I don't see what is wrong with
>CFM:=xxxcfm. Lower case cfm
>is a built in unit and CFM
>(uppercase) is a user defined
>variable.

==> CFM is not buit-in in version 11,
==> thus you have to define all the red ones
==> for 11 users to start understanding something.
==> The other point is that if the main formula is based on the imperial system, then don't use units at all.

>I did a hand calculation and
>the file posted above (DUCT
>PRESSURE SHRINK (5).MCD)
>checks out.

==> I don't understand: before you had the
==> Colebrook friction factor, not in your last posting !

>I am trying hard to understand
>how to "fix" my worksheets and
>what is the best way to
>use/construct them. This may
>be why I am struggling to
>learn to program in Mathcad.

==> In this project, there is no programming involved
==> or so little depending the scope.
==> Do a readable drawing, c/w all the variables ...

Applied physics is the mathematical representation of the "represented/exposed" . Also, think in terms of having some measuring/controlling equipment in the system. They must appear on a drawing, with most of the times lot more details and specifications attached. What will you remit to a prospective client if you don't have engineering drawings, documents, easily traceable calculations. You just can't tell "trust me, I'm right"... not like Bush when he banished brocooli (the most consumed vegetable in the US) from the entire Air force ... who cares Jo Blo farthing in the blue ! Just trust my 30 years in Process Control & Instrumentation as designer/consultant, a polished project leaves no grip for the attacking vampires. Directly or indirectly, any project involves public safety.

Nothing wrong with math regions in text box when the project has become frozen religion. Very useful in the case you want to plug the graph on the right side of the text box for a perfect split page presentation, newspaper/book style. Don't you have a piece of drawing to can scan and paste in the work sheet ?

jmG
ELSID
4-Participant
(To:ptc-1368288)

==> CFM is not buit-in in version 11,
==> thus you have to define all the red ones
==> for 11 users to start understanding something.
** How would you like me to know this? I have M14 on my machine and it works.

==> The other point is that if the main
formula is based on the imperial system,
then don't use units at all.
** Units are a must for me. I know that you and others in the collab differ differ with this philosophy. I subscribe to keeping units

==> I don't understand: before you had the
==> Colebrook friction factor, not in your last ==> posting !
** Colebrook is still in sheet, just not called out as Colebrook equation. Will fix

==> In this project, there is no programming
>==> involved or so little depending the scope.
>==> Do a readable drawing, c/w all the variables
** Calculation will derive the drawing. Yes I have a sketch ... more like chicken scratch. I am focused on learning the ins and outs of Mathcad. From original calculation, I cut pages in half by doing calculation in parallel (something I have been working on learning since I joined the collab). I would like to now focus on how to convert this reduced sheet into a "programmed" sheet and possibly reduce the calculation to a couple of sheets instead of 10.

Good learning tutorials/documentation is hard to come by. I have been trying to build up a set of tools based on what I have found in the collab. As I mentioned at the begining, I am working towards programing, one step at a time
RichardJ
19-Tanzanite
(To:ELSID)

On 10/16/2009 2:29:15 PM, ElSid wrote:

>** Units are a must for me. I
>know that you and others in
>the collab differ differ with
>this philosophy.

Which others?

Richard
ELSID
4-Participant
(To:RichardJ)

As an EXAMPLE, Tom is USUALLY a proponent for units while jmG is not.
RichardJ
19-Tanzanite
(To:ELSID)

My point was that everyone (at least everyone I can think of, and I did think about it) is a proponent of using units at least some of the time, with the notable exception of Jean.

Richard

You just can't help yourself, can you?

😉

TTFN,
Eden
RichardJ
19-Tanzanite
(To:IRstuff)

On 10/17/2009 12:27:52 AM, eden_mei wrote:
>You just can't help yourself,
>can you?

I try, but sometimes I am weak 😞

Richard

On 10/16/2009 4:12:18 PM, ElSid wrote:
>As an EXAMPLE, Tom is USUALLY
>a proponent for units while
>jmG is not.
......................................

My point was that everyone (at least everyone I can think of, and I did think about it) is a proponent of using units at least some of the time, with the notable exception of Jean. [Richard].

====================

In my times (years +++), we had 3 types of calculators:

1. mechanical ones
2. the neon tube (beginning)
3. the cracks in maths

This last class could only use type 1/2 without units, but more wisely than the green fellow. The things to feed in were then only the quantities and the working formula designed in the unit system. This practice is the basis of Engineering works and checker's work, i.e: the traceability. The units users (engineering) are thus dismantling the basis of the work at their risk, and many project can't be done with units because they have to be carried "scalar". My recommendation to never use units comes out of applied engineering, take or leave.

Consider the list of errors messages that can either help or not.

"Can�t determine what units the result of this operation should have.

You have raised an expression involving units to a power involving a range variable or a vector. As a result, there is no way to determine the dimensions of the result. If an expression is defined with units, you can raise it only to a fixed real power.

Can�t have anything with units or dimensions here.

This expression uses units somewhere units are not permitted.

Units are not permitted in the arguments of most functions, in exponents, in subscripts and superscripts.

If you want to use an expression with units, you can first divide the expression by the UnitsOf(expression) so the units are cancelled out.

Can�t raise an expression having units to a complex power.

This expression contains units, and you are raising it to a complex power. You can only raise an expression with units to a real power.

If you want to raise an expression with units to a complex power, you can first divide the expression by the UnitsOf(expression) so the units are cancelled out.

The units in this expression do not match.
This error message has two likely causes:
You are adding or subtracting two terms with different units.
You have created a matrix in which the elements do not have the same units.
You are trying to solve a system of equations for unknown variables of different units. Here is an example of how to properly do so:

Must be dimensionless."

Go by your preference: Tom, jmG, yours ?
I can't help because you have no working formula or the conversion 14 ==> 11 zaped it. You said you checked some result, fine with f = 1 fine, then why did you have another formulation with Colebrook ? My work sheets "Valve Sizing", "Orifice plate sizing" carry no units. None of my work sheets carry units. How come I can wok today w/o units like before the CAS and that now some user can't work w/o units ? Examine the attached (not new) and ask yourself where to plug units if the formula is designed and dimensioned in the appropriate unit system.

For instance, "Valve sizing" is essentially SI, if you need Imperial, plug your quantities and plug the corresponding coefficients in the working formula.

jmG



Sorry, why in your WebSheet:

we have Ro:=1.293 etc
but not Ro:=1.293*kg/m^3 etc
Val
http://twt.mpei.ac.ru/ochkov/v_ochkov.htm
RichardJ
19-Tanzanite
(To:ptc-1368288)

On 10/16/2009 9:53:48 PM, jmG wrote:
> My recommendation to never use
>units comes out of applied engineering,
>take or leave.

Leave, I think.

Richard
ELSID
4-Participant
(To:ptc-1368288)

Enough with the flaming everyone.

I am in no way a power user and each and every ones comments/suggestions is invaluable. Everyone has their style, I can deal with that.

jmG, units are required per our procedures. Sorry it it is "ZAPP'd" when I convert to version 11.
It is easy enough to use engineering scalar formula and "manipulate" units instead of working with scalars values. An extra step on my end, but required to be compliant.

I have been using this sheet to further my Mathcad education. Something simple, yet can use some of the programs' features.

I now have to track down how to import data from an excel sheet. Test data input into rows and I need to filter them out to be run in parallel. Any assistance on how to import is appreciated.

I hope to be back on this topic shortly ... trying to program my steps

>... to be run in parallel<<br> ==> Run what in parallel, Pentium is a serial machine/
==> Read the qs for importing data from Excel.
==> or store them in file in Excel and read the file in Mathcad.

Plug units as you wish and not knowing in advance the solving procedure and if it will take units or not, to be done again w/o units. This is why no project should start with units as you never know in advance if the maths will take units. You qualify and quantify all the intrants c/w the corresponding factors as per the base unit system the formula(s) was/were designed for. As long as you will not show the project in diagram, can't help. Linear loses are not problem but branching "Tees" are singular depending upon the flow. In all your sheets you had Colebrook, but in the last one, Colebrook is gone with the wind ? and you don't refer to an Engineering formula stipulated as "local/national code". So far, no project on the design board.

jmG

tcrouse
3-Visitor
(To:ELSID)

Did you ever get your duct pressure mcd working?  Could I see a copy?

Thanks

Tim C.

ELSID
4-Participant
(To:tcrouse)

I have not touched this in a while.  I think the attached files above are the latest iteration.  I lost my hard drive on a move and some files are corrupt.  This one, I flat out cannot find.  Sorry

>I have been trying to build up a set of tools based on what I have found in the collab.<<br> _____________________

How much have you found since your first visit ?
100's of pages of good tools ready made to use.

jmG

>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
ELSID
4-Participant
(To:ptc-1368288)

>Your choice. Maybe start
>by engineering the project.
>
>jmG

What does that mean? I solved some of the quirks and re-posted with Version 11 file format.

On 8/4/2009 6:42:25 PM, ElSid wrote:
>>Your choice. Maybe start
>>by engineering the project.
>>
>>jmG
>
>What does that mean? ...
__________________________

1. either your 14 construct is incorrect or the saved 11 version is screwed.



2. Don't use text box up until a project is completely debugged.

3. Wise to have a project work w/o units first.
Plug units afterward.

4. Google this collab for C O L E B R O O K
4.a/ Open the work sheet ... DO NOTHING
just wait it has finished what is in view.
4.b/ scroll down the page in one shot
wait the last item is calculated.
4.c/ scroll at will back up and navigate.

5. serious project need an abstract & diagram.

Can't help: too much red

jmG




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