UPDATE 2014-10-06 (rev 3): I am finally done with NGAS (I think). Over the weekend, I developed programs to size service connections to meet both the pressure and velocity criteria, not just to meet the pressure criterion as in Revision 2. Here is what is now in the .zip file:
Lusk_NGAS_Distribution Systems.mcdx & .pdf — This worksheet calculates flows and pressures in a natural gas distribution system consisting of a multi-segment Main Line and up to two service connection branches at each Main Line juntion node. Design pipe sizes are found by trial and error, specifically by editing the pipe data until the design criteria are met or met close enough for your purposes.
Lusk_NGAS_Unit Conversions.mcdx & .pdf — This worksheet shows how to convert natural gas demands and flows from one set of units to another and discusses ways to determe the peak demands to use for design. This worksheet functions as an appendix to the other seven worksheets.
Lusk_NGAS_Services_MSC.mcdx & .pdf — This worksheet calculates delivery pressures in multiple, independent natural gas service connections. Design pipe sizes are found by trial and error. This version is appropriate when you want full control over pipe sizing.
Lusk_NGAS_Services_MSC_Direct Design_P.mcdx & .pdf — This worksheet sizes multiple, independent natural gas service connections based on the pressure criterion. If the velocity criterion is not met, trial and error is then required to determine the appropriate pipe sizes. This version is appropriate when the pressure criterion MUST be satisfied, but the velocity criterion is not "hard and fast."
Lusk_NGAS_Services_MSC_Direct Design_PV.mcdx & .pdf — This worksheet sizes multiple, independent natural gas service connections based on both the pressure criterion and the velocity criterion, a feature which required a program. I am still learning Mathcad programming, so if you see a better way to write this program, please let me know. The only programming language for which I claim true expertise is keystroke RPN on my HP-41CX and HP-42S scientific calculators. This worksheet version is appropriate when you want Mathcad to do all the work.
Lusk_NGAS_Services_1SC.mcdx & .pdf — This worksheet is similar to Lusk_NGAS_Services_MSC.mcdx, but it handles only ONE natural gas service connection. Had this worksheet been available back when I first started doing natural gas designs, this would have been my most used worksheet.
Lusk_NGAS_Services_1SC_Direct Design_P.mcdx & .pdf — This worksheet is similar to Lusk_NGAS_Services_MSC_Direct Design_P.mcdx, but it handles only ONE natural gas service connection.
Lusk_NGAS_Services_1SC_Direct Design_PV.mcdx & .pdf — This worksheet is similar to Lusk_NGAS_Services_MSC_Direct Design_PV.mcdx, but it handles only ONE natural gas service connection.
Lusk_NGAS_Family Tree_v2.pdf — This diagram shows how the eight worksheets evolved and their relationships to each other.
Lusk_NGAS_Distribution Systems.dwg and Lusk_NGAS_Services.dwg — These two Autocad files (actually DraftSight) are for the diagrams that I inserted into these worksheets. I have included these drawings so can customize them to fit your own projects. Here is how I make the image files: (1) change all layers to WHITE, (2) change model background color to while, (3) export the drawing elements to an image file (I usually use .png or sometimes .jpg). After I'm done, I reset the model background to black and I DON'T save (that's easier than restoring layer colors).
If you have any questions, comments, or corrections, please let me know.
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UPDATE 2014-10-03: This is a very minor update. Several of the functions in a couple of the worksheets were actually formatted as variables by mistake. This worked fine until I started working on a program to complete the direct design to automatically increase the pipe size if the velocity criteria was not met. The program will incoporate calls to the solve blocks, but the program wasn't happy with them as variables.
UPDATE 2014-10-02: I have made some modifications to these worksheets, including changing from weight flow rate to mass flow rate (the numbers are the same for lbf and lbm, but mass is a better choice because it is a base unit and weight is derived), adding a direct design version of the multiple service connection worksheet, and removing the Appendix from two of the worksheets and making it a stand-alone worksheet. I also cleaned up several minor variable name discrepancies between the worksheets. I added a "family tree" diagram so you can see how the worksheets were developed. The direct design worksheets size pipes based on pressure requirements, but still require manual intervention if the velocity criteria is exceeded. There is probably a way to automate the entire process with a program, but that is for another day.
UPDATE 2014-09-26 (revised): Lusk_NGAS_Service_1SC.mcdx didn't completely recalculate when I saved the final version, from which I made the .pdf file, so here are updated .mcdx and .pdf files for this one. I also added a fourth workseet (Lusk_NGAS_Service_1SC_Direct Design.mcdx) which doesn't require manual trial error and is only one page longer than Lusk_NGAS_Service_1SC.mcdx, on which it is based. Unfortunately, Mathcad wasn't happy with two extra contraint equations inside the solve block (one for the Reynolds Number and one for the Darcy friction factor), so I had to insert these directly into the ICFEq. This required reformatting the worksheet into landscape mode, even after rearranging the ICFEq for space efficiency. I might make a direct design version of Lusk_NGAS_Service.mcdx, but not today. 
Oh, and I added units to the zero condition in the velocity calculation in the first two files listed below.
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This .zip file contains three Mathcad Prime 3.0 worksheets and, for those with other versions of Mathcad, an Adobe Acrobat .pdf file for each one. These worksheets handle pressure calculations for natural gas distribution systems and natural gas service connections. Following are detailed explanations for each worksheet:
NGAS_Distribution.mcdx
The purpose of this worksheet is to calculate flows and pressures in natural gas distribution systems and to estimate the installed cost of the new piping. This worksheet is structured to handle a multi-segment Main Line with up to two service branches at each Main Line node. The user specifies a minimum source pressure (e.g. at a master meter/regulator) and a minimum desired delivery pressure for all service connections. This worksheet can be modified to handle more complex branched networks, other gas types, pipe materials other than HDPE, etc. That effort, I leave to others.
Pressure drop calculations are based on the rational and implicit (for pressure) Isothermal-Compressible Flow Equation (ICFEq), rather than one of the more popular explicit empirical equations. Darcy Friction Factors are estimated using an explicit approximation to the Colebrook-White Equation (CW). See Lusk_Darcy Friction Factors_v2.zip. This worksheet assumes a Compressibility Factor, Z=1.00, which is appropriate for pressures less than about 100 psig. Z be changed as needed, but no equations for estimating Z have been implemented. Gas demands are assumed to be peak simultaneous demands based on weight flow rate. Gas demands in other units (e.g. BTU/hr, SCFM, etc.) will need to be converted first, which is covered in the Appendix.
Lusk_NGAS_Service.mcdx
This worksheet is based on NGAS_Distribution.mcdx. The purpose of this worksheet is to calculate pressures for natural gas service connections for buildings, stationary natural gas engines, or other uses, and to estimate the installed cost of the new piping. This worksheet is structured to handle multiple, independent service connections, each with a peak natural gas demand at its downstream end, such as might occur in a large office complex or a farm with scattered engine-driven pumps. For each service connection, the user specifies a minimum source pressure (e.g. from a meter/regulator or from a distribution main with a minimum design pressure provided by the utility company) and a minimum pressure to be delivered at the point of use.
Lusk_NGAS_Service_1SC.mcdx
This worksheet is a streamlined version of Lusk_NGAS_Service.mcdx and is structured to handle just a single service connection. All of the data and calculations fit onto three pages.
