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A.6.2 Example 2: Hybrid or Dual Pressure Systems
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Determine the required CSST size of each section of the piping system shown in Figure A.6.2, 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/ft3 (37.5 MJ/ m3).
- Size 2 psi (13.8 kPa) line using Table 402.4(18).
- Size 10-inch w.c. (2.5 kPa) lines using Table 402.4(16).
- Using the following, determine if sizing tables can be
- Total gas load shown in Figure A.6.2 equals 110 cfh (3.11 m3/hr).
- Determine pressure drop across regulator [see notes in Table 402.4(18)].
- If pressure drop across regulator exceeds 3/4
psig (5.2 kPa), Table 402.4(18) 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.
- Pressure drop across the line regulator [for 110 cfh (3.11 m3/hr)] is 4-inch w.c. (0.99 kPa) based on manufacturer's performance data.
- Assume the CSST manufacturer has tubing sizes or EHDs of 13, 18, 23 and 30.
- Section A [2 psi (13.8 kPa) zone]
- Distance from meter to regulator = 100 feet (30480 mm).
- Total load supplied by A= 110 cfh (3.11 m3/hr) (furnace+ water heater+ dryer).
- Table 402.4(18) shows that EHD size 18 should
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 m3/hr).
- Section B (low pressure zone)
- Section C (low pressure zone)
- Section D (low pressure zone)
- Distance from regulator to dryer is 25 feet (7620 mm).
- Load is 20 cfh (0.57 m3/hr).
- Table 402.4(16) shows that EHD size 13 should be used.
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