How To Size A Suction Line Double Riser - Daikin R-22 Refrigerant Piping Design Manual

How to Size a Suction Line Double Riser

Size a double suction riser for the following air-cooled chiller
with remote evaporator.
The system:
• Uses R-134a
• Has Type L copper pipe
• Evaporator operates at 40°F (4.4°C) Saturated Suction
Temperature (SST)
• Superheat is 10°F (5.6°C)
• Condenser operates at 120°F (48.9°C)
• Capacity is two 50 ton (176 kW) circuits with up to 20%
turn down
• Suction line equivalent length for the horizontal runs is:
— Bottom 10 ft (3.0 m)
— Top 12 ft (3.7 m)
• Equivalent Length is 64 ft (19.5 m)
• Horizontal pipe size is 3-1/8 inch (79 mm) (from previous
example)
Step 1 – Estimate Minimum Capacity
Minimum Capacity = 50 Tons × 20% = 10 Tons
(Minimum Capacity = 176 kW × 20% = 35.2 kW)
Step 2 – Estimate Small Riser Size
To determine the small riser line size to operate the system at
minimum capacity use Table 8
According to the table, a 2-1/8 inch (54 mm) pipe will work for a
20.2 ton (71.0 kW) unit. Note, the table conditions (equivalent
length and condensing temperature) are different than the
design conditions.
www.DaikinApplied.com
Double Pipe
Suction Line
Riser
in Appendix 2.
Step 3 – Correct for Actual Operating Conditions
Sizing the pipe for full load requires a correction for the 120°F
(48.9°C) actual condenser temperature. Referring to the
correction factors at the bottom of
Actual Capacity = Table Capacity × 0.902
Actual Capacity = 20.2 Tons × 0.902 = 18.2 Tons
(Actual Capacity = 71.0 kW × 0.902 = 64.0 kW)
Step 4 – Size Large Riser
At full capacity the cross sectional area of the two risers should
equal the original riser area (in this example a 3-1/8 inch pipe).
Use Table 12 on page 46
Large Diameter Riser = Area Original Pipe – Area Small Pipe
Large Diameter Riser = Area
Large Diameter Riser = 6.812 inch
(Large Diameter Riser = 43.95 cm
Using Table 12 we see that 3.717 square inches is between a
2-1/8 inch (54 mm) riser and a 2-5/8 inch (67 mm) riser. Using
a 2-5/8 inch riser will reduce the pressure drop. So the small
riser should be 2-1/8 inches and the large riser should be
2-5/8 inches.
25 AG 31-011 • REFRIGERANT PIPING DESIGN
Table 8.
to determine the area of the pipes.
– Area
3-1/8 inch pipe 2-1/8 inch pipe
– 3.095 inch = 3.717 inch
2 2
– 19.97 cm = 23.98 cm
2 2
2
)
2