Liebert XDC user manual Install Double Discharge Risers, Double discharge riser layout

Piping and Filling with Refrigerant: R-134a and R-407c Circuits

2.5.2Piping for Direct Expansion (DX) Circuit—R-407c Air Cooled Units

! WARNING

Risk of refrigerant system explosion or rupture from overpressurization. Can cause death, injury and equipment damage.

Installer must install a 400 psig pressure relief valve in each of the two R-407c refrigerant circuits of the Liebert XDC system. Do not install shutoff valves between the compressors and the pressure relief valves.

For systems requiring EU CE compliance, the pressure relief valves must be CE-certified by a notified body to the EU Pressure Equipment Directive.

2.6Install Double Discharge Risers

For air-cooled systems, double discharge risers must be installed in the hot gas lines that have verti- cal heights of 15 feet (4.6m) or more (see Figure 23). This will allow proper oil return to the compres- sors when the system is running at low loads. A double riser system is constructed of a large diameter riser with a trap at the base and a riser with a smaller diameter in parallel.

At full-load operation, the refrigerant vapor flows up both risers at velocities that are adequate to carry the oil. At low loads, refrigerant vapor velocities are lower and the trap at the bottom of the riser becomes filled with oil. When this happens, refrigerant flows up only the smaller riser.

The trap at the top of the riser must be tied into the top of the line to prevent oil from filling the larger riser. For each double riser used, the maximum height of the riser must not exceed 15 feet (4.6m). Multiple risers must be installed in series as the height of the hot gas line increases. Total maximum height of the hot gas line must not exceed 60 feet (18.3m).

Horizontal discharge lines should be pitched downward in the direction of flow to aid in oil drainage with downward pitch of at least 1/2 inch in 10 feet (13mm in 3m).

Figure 23 Double discharge riser layout

Connection point of upper trap is at the top of the line

Larger riser 1-1/8" O.D. copper

Smaller riser is 5/8" O.D. copper

Trap size is 1-1/8" large riser size with minimum internal

Contact your local Liebert representative for factory approval whenever a refrigerant piping run exceeds 200 feet (60m) equivalent length or when condensers must be installed below the level of the cooling coil.

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