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# E103.3.3 Selection of Pipe Size, Step 6 Column 5

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For SI: 1 foot = 304.8 mm, 1 inch = 25.4 mm.

Total friction loss is determined by multiplying the friction loss per 100 feet (30 480 mm) for each pipe section in the total developed length by the pressure loss in fittings expressed as equivalent length in feet. Note: Section C-F should be considered in the total pipe friction losses only if greater loss occurs in Section C-F than in pipe section D-E. Section C-F is not considered in the total developed length. Total friction loss in equivalent length is determined in Table E.2.

For SI: 1 foot = 304.8 mm, 1 gpm = 3.785 L/m.

The result should always be a positive or plus figure. If it is not, repeat the operation using Columns 5, 6, 8 and 9 until a balance or near balance is obtained. If the difference between Lines J and K is a high positive number, it is an indication that the pipe sizes are too large and should be reduced, thus saving materials. In such a case, the operations using Columns 5, 6, 8 and 9 should again be repeated.

The total friction losses are determined and subtracted from the pressure available to overcome pipe friction for trial pipe size. This number is critical as it provides a guide to whether the pipe size selected is too large and the process should be repeated to obtain an economically designed system.

**Steps 6**

When selecting a trial pipe size, the length from the water service or meter to the most remote fixture outlet must be measured to determine the developed length. However, in systems having a flushometer valve or temperature controlled
shower at the topmost floors the developed length would be from the water meter to the most remote flushometer valve on the system. A rule of thumb is that size will become progressively smaller as the system extends farther from the main source of supply. Trial pipe size may be arrived at by the following formula:

For trial pipe size, see Figure E 103.3(3) (Type L copper) based on 2.77 psi and a 108 gpm = 2

The equivalent length of the friction loss in fittings and valves must be added to the developed length (most remote outlet). Where the size of fittings and valves is not known, the added friction loss should be approximated. A general rule that has been used is to add 50 percent of the developed length to allow for fittings and valves. For example, the equivalent length of run equals the developed length of run (225 ft x 1.5 = 338 ft). The total equivalent length of run for determining a trial pipe size is 338 feet.

**Line J:**(Pressure available to overcome pipe friction) x 100/equivalent length of run total*developed length*to most remote fixture x percentage factor of 1.5 (note: a percentage factor is used only as an estimate for friction losses imposed for fittings for initial trial pipe size) = psi (average pressure drops per 100 feet of pipe).For trial pipe size, see Figure E 103.3(3) (Type L copper) based on 2.77 psi and a 108 gpm = 2

^{1}/_{2}inches. To determine the equivalent length of run to the most remote outlet, the*developed length*is determined and added to the friction losses for fittings and valves. The*developed lengths*of the designated pipe sections are as follows:A-B | 54 ft |

B-C | 8 ft |

C-D | 13 ft |

D-E | 150 ft |

Total developed length = 225 ft |

The equivalent length of the friction loss in fittings and valves must be added to the developed length (most remote outlet). Where the size of fittings and valves is not known, the added friction loss should be approximated. A general rule that has been used is to add 50 percent of the developed length to allow for fittings and valves. For example, the equivalent length of run equals the developed length of run (225 ft x 1.5 = 338 ft). The total equivalent length of run for determining a trial pipe size is 338 feet.

**Step 7**

**Column 6:**Select from Table E103.3(6) the equivalent lengths for the trial pipe size of fittings and valves on each pipe section. Enter the sum for each sect ion in Column 6. (The number of fittings to be used in this example must be an estimate.) The equivalent length of piping is the

*developed length*plus the equivalent lengths of pipe corresponding to friction head losses for fittings and valves. Where the size of fittings and valves is not known, the added friction head losses must be approximated. An estimate for this example is found in Table E.1.

COLD WATER PIPE SECTION |
FITTING/VALVES |
PRESSURE LOSS EXPRESSED AS EQUIVALENT LENGTH OF TUBE (feet) |
HOT WATER PIPE SECTION |
FITTINGS/ VALVES |
PRESSURE LOSS EXPRESSED AS EQUIVALENT OF TUBE (feet) |
---|---|---|---|---|---|

A-B | 3 - 2^{1}/_{2}"Gate valves |
3 | A-B | 3 - 2^{1}/_{2}" Gate Valves |
3 |

1 - 2^{1}/_{2}" Side branch tee |
12 | 1 - 2^{1}/_{2}" Side branch tee |
12 | ||

B-C | 1-2 ^{1}/_{2}" Straight run tee |
0.5 | B-C | 1 - 2" Straight run tee | 7 |

1-2" 90 degree ell | 0.5 | ||||

C-F | 1-2 ^{1}/_{2}" Side branch tee |
12 | C-F | 1 - 1^{1}/_{2}" Side branch tee |
7 |

C-D | 1 - 2^{1}/_{2}" 90 degree ell |
7 | C-D | 1 - ^{1}/_{2}" 90-degree ell |
4 |

D-E | 1-2 ^{1}/_{2}" Side branch tee |
12 | D-E | 1 - 1^{1}/_{2}" Side branch tee |
7 |

**Step 8**

**Column 7:**Add the figures from Column 4 and Column 6, and enter in Column 7. Express the sum in hundreds of feet.

**Step 9**

**Column 8:**Select from Figure E103.3(3) the friction loss per 100 feet (30 480 mm) of pipe for the gallon-per-minute flow in a section (Column 3) and trial pipe size (Column 5). Maximum friction head loss per 100 feet is determined on the basis of total pressure available for friction head loss and the longest equivalent length of run. The selection is based on the gallon-per-minute demand, the uniform friction head loss and the maximum design velocity. Where the size indicated by hydraulic table indicates a velocity in excess of the selected velocity, a size must be selected that produces the required velocity.

**Step 10**

**Column 9:**Multiply the figures in Columns 7 and 8 for each section and enter in Column 9.

Total friction loss is determined by multiplying the friction loss per 100 feet (30 480 mm) for each pipe section in the total developed length by the pressure loss in fittings expressed as equivalent length in feet. Note: Section C-F should be considered in the total pipe friction losses only if greater loss occurs in Section C-F than in pipe section D-E. Section C-F is not considered in the total developed length. Total friction loss in equivalent length is determined in Table E.2.

PIPE SECTIONS | FRICTION LOSS EQUIVALENT LENGTH (feet) | |
---|---|---|

Cold Water | Hot Water | |

A-B | 0.69 X 3.2 = 2.21 | 0.69 X 3.2 = 2.21 |

B-C | 0.085 X 3.1 = 0.26 | 0.16 X 1.4 = 0.22 |

C-D | 0.20 X 1.9 = 0.38 | 0.17 X 3.2 = 0.54 |

D-E | 1.62 X 1.9 = 3.08 | 1.57 X 3.2 = 5.02 |

Total pipe friction losses (Line K) |
5.93 | 7.99 |

**Step 11**

**Line K:**Enter the sum of the values in Column 9. The value is the total friction loss in equivalent length for each designated pipe section.

**Step 12**

**Line L:**Subtract Line J from Line K and enter in Column 10.

The result should always be a positive or plus figure. If it is not, repeat the operation using Columns 5, 6, 8 and 9 until a balance or near balance is obtained. If the difference between Lines J and K is a high positive number, it is an indication that the pipe sizes are too large and should be reduced, thus saving materials. In such a case, the operations using Columns 5, 6, 8 and 9 should again be repeated.

The total friction losses are determined and subtracted from the pressure available to overcome pipe friction for trial pipe size. This number is critical as it provides a guide to whether the pipe size selected is too large and the process should be repeated to obtain an economically designed system.

**Answer:**The final figures entered in Column 5 become the design pipe size for the respective sections. Repeating this operation a second time using the same sketch but considering the demand for hot water, it is possible to size the hot water distribution piping. This has been worked up as a part of the overall problem in the tabular arrangement used for sizing the service and water distribution piping. Note that consideration must be given to the pressure losses from the street main to the water heater (Section AB) in determining the hot water pipe sizes.

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