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# Section A7 Examples of Piping System

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Solution

If the volume of the piping system is unchanged, then the formula based on Boyle's and Charles' law for determining the new pressure at a reduced temperature is as follows:

where:

Therefore, the gauge could be expected to register 18 psig (124 kPa) when the ambient temperature is 40°F (4°C).

For 1-inch pipe: Δ

For 1

Minimum pressure drop to farthest appliance:

Δ

Larger pressure drop to the farthest appliance:

ΔH = 0.06 inch w.c. + 0.06 inch w.c. + 0.3 inch w.c. = 0.42 inch w.c.

For SI units: 1 Btu/hr = 0.293 W, 1 cubic foot = 0.028 m

**. Determine the required pipe size of each section and outlet of the piping system shown in Figure A.7.1, with a designated pressure drop of 0.5-inch w.c. (125 Pa) using the Longest Length Method. The gas to be used has 0.60 specific gravity and a heating value of 1,000 Btu/ft**

A7.1 Example 1: Longest length method

A7.1 Example 1: Longest length method

^{3}(37.5 MJ/m

^{3}).

Solution:

Solution:

(1) Maximum gas demand for Outlet A:

Maximum gas demand for Outlet B:

Maximum gas demand for Outlet C:

Maximum gas demand for Outlet D:

Maximum gas demand for Outlet B:

Maximum gas demand for Outlet C:

Maximum gas demand for Outlet D:

(2) The length of pipe from the point of delivery to the most remote outlet (A) is 60 feet (18 288 mm). This is the only distance used.

(3) Using the row marked 60 feet (18 288 mm) in Table G2413.4(1):

(a) Outlet A, supplying 35 cfh (0.99 m

^{3}/hr), requires^{3}/_{8}-inch pipe.(b) Outlet B, supplying 75 cfh (2.12 m

^{3}/hr), requires^{3}/_{4}-inch pipe.(c) Section 1, supplying Outlets A and B, or 110 cfh (3.11 m

^{3}/hr), requires^{3}/_{4}-inch pipe.(d) Section 2, supplying Outlets C and D, or 135 cfh (3.82 m

^{3}/hr), requires^{3}/_{4}-inch pipe.(e) Section 3, supplying Outlets A, B, C and D, or 245 cfh (6.94 m

^{3}/hr), requires 1-inch pipe.(4) If a different gravity factor is applied to this example, the values in the row marked 60 feet (18 288 mm) of Table G2413.4(1) would be multiplied by the appropriate multiplier from Table A.2.4 and the resulting cubic feet per hour values would be used to size the piping

Section A.7.2 through A7.4 note: These examples are based on tables found in the Fuel Gas Code of New York State.Section A.7.2 through A7.4 note: These examples are based on tables found in the Fuel Gas Code of New York State.

FIGURE A.7.1FIGURE A.7.1

**PIPING PLAN SHOWING A STEEL PIPING SYSTEM****A7.2 Example 2: Hybrid or dual pressure systems.**Determine the required CSST size of each section of the piping system shown in Figure A.7.2, with a designated pressure drop of 1 psi (6.9 kPa) for the 2 psi (13.8 kPa) section and 3-inch w.c. (0.75 kPa) pressure drop for the 13-inch w.c. (2.49 kPa) section. The gas to be used has 0.60 specific gravity and a heating value of 1,000 Btu/ft

^{3}(37.5 MJ/m

^{3}).

Solution

Solution

(1) Size 2 psi (13.8 kPa) line using Table 402.4(16).

(2) Size 10-inch w.c. (2.5 kPa) lines using Table 402.4(14).

(3) Using the following, determine if sizing tables can be used.

(a) Total gas load shown in Figure A.7.2 equals 110 cfh (3.11 m

^{3}/hr).(b) Determine pressure drop across regulator [see notes in Table 402.4 (16)].

(c) If pressure drop across regulator exceeds

^{3}/_{4}psig (5.2 kPa), Table 402.4 (16) cannot be used. Note: If pressure drop exceeds^{3}/_{4}psi (5.2 kPa), then a larger regulator must be selected or an alternative sizing method must be used.(d) Pressure drop across the line regulator [for 110 cfh (3.11 m

^{3}/hr)] is 4-inch w.c. (0.99 kPa) based on manufacturer's performance data.(e) Assume the CSST manufacturer has tubing sizes or EHDs of 13, 18, 23 and 30.

(4) Section A [2 psi (13.8 kPa) zone]

(a) Distance from meter to regulator = 100 feet (30 480 mm).

(c) Table 402.4 (16) shows that EHD size 18 should be used.

Note: It is not unusual to oversize the supply line by 25 to 50 percent of the as-installed load. EHD size 18 has a capacity of 189 cfh (5.35 m

Note: It is not unusual to oversize the supply line by 25 to 50 percent of the as-installed load. EHD size 18 has a capacity of 189 cfh (5.35 m

^{3}/hr).(5) Section B (low pressure zone)

(a) Distance from regulator to furnace is 15 feet (4572 mm).

(b) Load is 60 cfh (1.70 m

^{3}/hr).(c) Table 402.4 (14) shows that EHD size 13 should be used.

(6) Section C (low pressure zone)

(a) Distance from regulator to water heater is 10 feet (3048 mm).

(b) Load is 30 cfh (0.85 m

^{3}/hr).(c) Table 402.4 (14) shows that EHD size 13 should be used.

(7) Section D (low pressure zone)

(a) Distance from regulator to dryer is 25 feet (7620 mm).

(b) Load is 20 cfh (0.57 m

^{3}/hr).(c) Table 402.4(14) shows that EHD size 13 should be used.

FIGURE A.7.2FIGURE A.7.2

**PIPING PLAN SHOWING A CSST SYSTEM****A7.3 Example 3: Branch length method.**Determine the required semi-rigid copper tubing size of each section of the piping system shown in Figure A.7.3, with a designated pressure drop of 1-inch w.c. (250 Pa) (using the Branch Length Method). The gas to be used has 0.60 specific gravity and a heating value of 1,000 Btu/ft

^{3}(37.5 MJ/m

^{3}).

Solution

Solution

(1) Section A

(a) The length of tubing from the point of delivery to the most remote appliance is 50 feet (15 240 mm), A + C.

(b) Use this longest length to size Sections A and C.

(c) Using the row marked 50 feet (15 240 mm) in Table 402.4(8), Section A, supplying 220 cfh (6.2 m

^{3}/hr) for four appliances requires 1-inch tubing.(2) Section B

(a) The length of tubing from the point of delivery to the range/oven at the end of Section B is 30 feet (9144 mm), A + B.

(b) Use this branch length to size Section B only.

(c) Using the row marked 30 feet (9144 mm) in Table 402.4(8), Section B, supplying 75 cfh (2.12 m

^{3}/hr) for the range/oven requires^{1}/_{2}-inch tubing.(3) Section C

(a) The length of tubing from the point of delivery to the dryer at the end of Section C is 50 feet (15 240 mm), A + C.

(b) Use this branch length (which is also the longest length) to size Section C.

(c) Using the row marked 50 feet (15 240 mm) in Table 402.4(8), Section C, supplying 30 cfh (0.85 m

^{3}/hr) for the dryer requires^{3}/_{8}-inch tubing.(4) Section D

(a) The length of tubing from the point of delivery to the water heater at the end of Section D is 30 feet (9144 mm), A + D.

(b) Use this branch length to size Section D only.

(c) Using the row marked 30 feet (9144 mm) in Table 402.4(8), Section D, supplying 35 cfh (0.99 m

^{3}/hr) for the water heater requires^{3}/_{8}-inch tubing.(5) Section E

(a) The length of tubing from the point of delivery to the furnace at the end of Section E is 30 feet (9144 mm), A + E.

(b) Use this branch length to size Section E only.

(c) Using the row marked 30 feet (9144 mm) in Table 402.4(8), Section E, supplying 80 cfh (2.26 m

^{3}/hr) for the furnace requires^{1}/_{2}-inch tubing.

FIGURE A.7.3FIGURE A.7.3

**PIPING PLAN SHOWING A MODIFICATION TO****EXISTING PIPING SYSTEM****A7.4 Example 4: Modification to existing piping system.**Determine the required CSST size for Section G (retrofit application) of the piping system shown in Figure A.7.4, with a designated pressure drop of 0.5-inch w.c. (125 Pa) using the branch length method. The gas to be used has 0.60 specific gravity and a heating value of 1,000 Btu/ft

^{3}(37.5 MJ/m

^{3}).

Solution

(1) The length of pipe and CSST from the point of delivery to the retrofit appliance (barbecue) at the end of Section G is 40 feet (12 192 mm), A + B + G.

(2) Use this branch length to size Section G.

(3) Assume the CSST manufacturer has tubing sizes or EHDs of 13, 18, 23 and 30.

(4) Using the row marked 40 feet (12 192 mm) in Table 402.4(13), Section G, supplying 40 cfh (1.13 m

^{3}/hr) for the barbecue requires EHD 18 CSST.(5) The sizing of Sections A, B, F and E must be checked to ensure adequate gas carrying capacity since an appliance has been added to the piping system (see A.7.1 for details).

FIGURE A.7.4FIGURE A.7.4

**PIPING PLAN SHOWING A MODIFICATION TO****EXISTING PIPING SYSTEM****A7.5 Example 5: Calculating pressure drops due to temperature changes.**A test piping system is installed on a warm autumn afternoon when the temperature is 70°F (21°C). In accordance with local custom, the new piping system is subjected to an air pressure test at 20 psig (138 kPa). Overnight, the temperature drops and when the inspector shows up first thing in the morning the temperature is 40°F (4°C).

If the volume of the piping system is unchanged, then the formula based on Boyle's and Charles' law for determining the new pressure at a reduced temperature is as follows:

where:

T

T

_{1}= Initial temperature, absolute (T

_{1}+ 459)

T

T

_{2}= Final temperature, absolute (T

_{2}+ 459)

P

P

_{1}= Initial pressure, psia (P

_{1}+ 14.7)

P

P

_{2}= Final pressure, psia (P

_{2}+ 14.7)

Therefore, the gauge could be expected to register 18 psig (124 kPa) when the ambient temperature is 40°F (4°C).

**Using the layout shown in Figure A.7.1 and Δ**

A7.6 Example 6: Pressure drop per 100 feet of pipe method.

A7.6 Example 6: Pressure drop per 100 feet of pipe method.

*H*= pressure drop, in w.c. (27.7 in. H

_{2}O = 1 psi), proceed as follows:

(1) Length to A = 20 feet, with 35,000 Btu/hr.

For

For

^{1}/_{2}-inch pipe, Δ*H*=^{20 feet}/_{100 feet}× 0.3 inch w.c. = 0.06 in. w.c.(2) Length to B = 15 feet, with 75,000 Btu/hr.

For

For

^{3}/_{4}-inch pipe, Δ*H*=^{15 feet}/_{100 feet }× 0.3 inch w.c. = 0.045 in. w.c.(3) Section 1 = 10 feet, with 110,000 Btu/hr. Here there is a choice:

For 1 inch pipe: Δ

For

For 1 inch pipe: Δ

*H*=^{10 feet}/_{100 feet }× 0.2 inch w.c. = 0.02 in w.c.For

^{3}/_{4}-inch pipe: Δ*H*=^{10 feet}/_{100 feet}× [0.5 inch w.c. +^{(110,000 Btu/hr-104,000 Btu/hr)}/_{(147,000 Btu/hr-104,000 Btu/hr)}× (1.0 inches w.c. - 0.5 inch w.c.)] = 0.1 × 0.57 inch w.c.≈ 0.06 inch w.c.

Note that the pressure drop between 104,000 Btu/hr and 147,000 Btu/hr has been interpolated as 110,000 Btu/hr.Note that the pressure drop between 104,000 Btu/hr and 147,000 Btu/hr has been interpolated as 110,000 Btu/hr.

(4) Section 2 = 20 feet, with 135,000 Btu/hr. Here there is a choice:

For 1-inch pipe: Δ

For

For 1-inch pipe: Δ

*H*=^{20 feet}/_{100 feet}× [0.2 inch w.c. +^{(}Δ^{14,000 Btu/hr)}/_{(}Δ_{27,000 Btu/hr)}× Δ0.1 inch w.c.)] = 0.05 inch w.c.)]For

^{3}/_{4}-inch pipe: Δ*H*=^{20 feet}/_{100 feet}× 1.0 inch w.c. = 0.2 inch w.c.)

Note that the pressure drop between 121,000 Btu/hr and 148,000 Btu/hr has been interpolated as 135,000 Btu/hr, but interpolation for the 3/4-inch pipe (trivial for 104,000 Btu/hr to 147,000 Btu/hr) was not used.Note that the pressure drop between 121,000 Btu/hr and 148,000 Btu/hr has been interpolated as 135,000 Btu/hr, but interpolation for the 3/4-inch pipe (trivial for 104,000 Btu/hr to 147,000 Btu/hr) was not used.

*(5)*Section 3 = 30 feet, with 245,000 Btu/hr. Here there is a choice:

For 1-inch pipe: Δ

*H*=

^{30 feet}/

_{100 feet}× 1.0 inches w.c. = 0.3 inch w.c.

For 1

^{1}/

_{4}-inch pipe: Δ

*H*=

^{30 feet}/

_{100 feet }× 0.2 inch w.c. = 0.06 inch w.c.

Note that interpolation for these options is ignored since the table values are close to the 245,000 Btu/hr carried by that section.

Note that interpolation for these options is ignored since the table values are close to the 245,000 Btu/hr carried by that section.

*(6)*The total pressure drop is the sum of the section approaching A, Sections 1 and 3, or either of the following, depending on whether an absolute minimum is needed or the larger drop can be accommodated.

Minimum pressure drop to farthest appliance:

Δ

*H*= 0.06 inch w.c. + 0.02 inch w.c. + 0.06 inch w.c. = 0.14 inch w.c.

Larger pressure drop to the farthest appliance:

ΔH = 0.06 inch w.c. + 0.06 inch w.c. + 0.3 inch w.c. = 0.42 inch w.c.

*Section*

Notice that

Notice that

*2 and the run to B do not enter into this calculation, provided that the appliances have similar input pressure requirements.*

For SI units: 1 Btu/hr = 0.293 W, 1 cubic foot = 0.028 m

^{3}, 1 foot = 0.305 m, 1 inch w.c. = 249 Pa.

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