Example Problems

Air System

Problem Statement:
A 100 foot square machine shop is supplied by a 100 PSIA service air system. The 2 inch supply header runs around the perimeter of the room. The header has 28 service connections equally spaced around the room. Each connection is required to supply 220 SCFM to the attached device.

The service air system usually supplies up to 5 loads at any given time. The minimum required supply pressure at the load connection is 80 PSIA. Will the system as-built meet these constraints? In addition, during certain operations, an additional 3 loads are added. How much must the inlet pressure be increased to maintain the required supply pressure of 80 PSIA to each of the 8 loads?

Solution:
The network layout is once again built first, but the hardware is left blank. Hardware is then added to one of each type of branch (header and load). These two branches are then saved (as branches), and the hardware loaded into each of the remaining branch icons.

For the first question the fluid is specified as air at 70 degrees Fahrenheit and 100 PSIA. All the connection lines are shut except for the 5 that are the farthest from the inlet. At these 6 open lines an outlet flowrate of 220 SCFM is specified. DesigNet will then solve for the outlet pressure of each line. By displaying pressures it can be determined if the require criteria are met.

For the second question, three additional valves are opened, and in these lines an outlet flow of 220 SCFM is again specified. The inlet pressure of the air is then varied and the solution obtained until a pressure is specified which achieves the desired 80 PSIA at each load.