Size section (1) in the drawing above using the branch length method.
Understand the Problem
The question is asking to determine the appropriate pipe size for a gas delivery system using the branch length method based on the given details, including outlet BTUs and specifications.
Answer
The appropriate pipe size is $1 \frac{1}{4}$ in.
Answer for screen readers
The correct pipe size is $1 \frac{1}{4}$ in.
Steps to Solve
- Calculate Total BTU Demand
Add the BTU requirements of all outlets:
- Outlet D: 120,000 Btuh
- Outlet C: 50,000 Btuh
- Outlet E: 40,000 Btuh
- Outlet B: 75,000 Btuh
- Outlet A: 35,000 Btuh
Total BTU = $120,000 + 50,000 + 40,000 + 75,000 + 35,000 = 320,000$ Btuh.
- Determine Equivalent Length of Pipe for Each Outlet
Use the branch length method to find the equivalent length of the pipe run to each outlet. The equivalent lengths are calculated based on the lengths provided and any fittings used (for simplicity, this can be approximated or found in tables, but typically a rule is to add extra feet for bends).
- Identify Branch Lengths for Each Outlet
- For Outlet D: 20 ft (straight)
- For Outlet C: 20 ft + 10 ft (adding fitting length)
- For Outlet E: 17 ft
- For Outlet B: 10 ft + 15 ft (adding fitting length)
- For Outlet A: 5 ft
- Calculate Total Equivalent Length of Pipe
Add all the lengths:
- From Point of Delivery to Outlet D: $20 + 20 + 17 + 25 + 5 = 87$ ft.
- Determine Required Pipe Size Using BTU Charts
Consult the gas pipe sizing chart for the specific natural gas BTU demand. Locate the total BTU demand (320,000 Btuh) and the total equivalent pipe length (87 ft) to select the appropriate pipe size.
- Select the Pipe Size
Based on common charts (for example, those specifying pressure drops and pipe sizes), find which pipe size handles 320,000 Btuh at an 87 ft equivalent length. Usually, this would direct you to a specific size based on installation codes.
- Finalize Size Selection
Review options:
- a. 1 1/4 in
- b. 1 in
- c. 1 1/2 in
- d. 3/4 in
Refer to the chart for pressure loss calculations and identify the optimal choice.
The correct pipe size is $1 \frac{1}{4}$ in.
More Information
When sizing gas piping, a critical aspect is to ensure the selected pipe can handle BTU loads while maintaining the pressure drop below acceptable limits. The branch length method ensures the flow remains optimal throughout the system.
Tips
- Failing to account for fittings and bends when measuring equivalent lengths can lead to incorrect sizing.
- Not checking the gas volume capacity of the chosen pipe compared to the system’s total demand can also result in issues.
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