General

Positively Gassed calculates the size related requirements of the piping, the fittings, and the valves of a positively pressurized gas piping system with a sole source of gas, to provide sufficient flow and pressure at the appliances (outlets) served by the source.

The intended applications for Positively Gassed are relatively low pressure constant temperature gas piping systems, where treating the gas as an ideal gas will result in an accuracy acceptable for the application.

Segments

All of the pipe segments from the gas supply to the appliances served are input. The input for each segment includes the length, the valves, and other components, as applicable.

Elbow quantities are automatically assigned to each segment, however the quantities can be overridden. See Elbows for additional information.

Sizes also are automatically assigned to each segment, however the sizes of the individual segments can be overridden. See Sizes for additional information.

Pressure

The pressure loss of the piping due to friction is calculated using the Darcy Weisbach Equation.

K factors are used to determine the equivalent lengths of fittings (elbows and tees) and valves.

Each appliance is assigned an independent required pressure.

The pressure required at the gas supply is the sum of the pressure losses of the segments serving the critical path appliance plus the pressure required at that appliance.

Sizes

Multiple profiles can be created for the automatic sizing of segments. Each profile includes all of the sizes (1/2" to 18"), with a flow range for each size.

The sizes assigned by the profiles can be overridden for each segment, however doing so reduces the automatic sizing effectiveness.

Additionally, a 'solver' (Excel goal seek) generates profiles by calculating the flow rates corresponding to an input pressure loss rate, with a single click.

Groups

Appliances can be assigned in groups, thereby allowing for individual segments to serve multiple appliances, to expedite data entry.

Elbows

Multiple profiles can be created for automatically adding elbows to segments. Each profile has a length to elbow quantity ratio for each size.

The number of elbows assigned by the profiles can be overridden for each segment.

Diversities

Diversities can be applied to both individual appliances and to convenience outlets, to accommodate the numerous piping systems that have either or both modulating and cycling appliances and outlets.

Features

• Supports both Inch-Pound (I-P) and International System (SI) units.
• 240 segments.
• 1/8" to 12" pipe.
• 40 pipe types (pipe roughnesses and inside diameters).
• 8 sets of automatic elbow profiles.
• 8 groups of appliances.
• 7 appliances per group, appliance quantity unlimited.
• 48 appliances.
• Diversities assignable to every appliance.
• 4 convenience outlets.
• 7 convenience outlet diversity profiles.

All of the data is editable!

Limitations

'Tree' type systems only are supported; systems where there is more than one path from the gas supply to any appliance are not supported.

The methodologies for calculating friction factors in the transition regime differ for various gases, and incorporating such methodologies in Positively Gassed would be onerous for the intended applications - applications where the flow is generally in the turbulent regime. Therefore Positively Gassed incorporates a simplified approximation methodology for flows in the transition regime that is the same for all gases, and therefore that will result in inaccuracy proportional to the amount of the critical path piping that is in the transition regime.

Elevation differences are not incorporated in the calculations. Therefore the accuracy of the calculations will result in inaccuracy proportional to the extent that elevation differences affect the results.

Other Considerations

Positively Gassed is not inherently a critical path calculator. However, where (by experience) the critical path is apparent, Positively Gassed can be used as a critical path calculator. Doing so, however, reduces the utility of Positively Gassed with respect to automatic pipe sizing.