Liquid Lines - Daikin R-22 Refrigerant Piping Design Manual

Liquid Lines

Liquid lines connect the condenser to the evaporator and
carry liquid refrigerant to the TX valve. If the refrigerant in
the liquid line flashes to a gas because the pressure drops
too low or because of an increase in elevation, then the
refrigeration system will operate poorly. Liquid sub-cooling is
the only method that prevents refrigerant flashing to gas due to
pressure drops in the line.
The actual line size should provide no more than a 2 to 3°F
(1.1 to 1.7°C) pressure drop. The actual pressure drop in PSI
(kPa) will depend on the refrigerant.
Oversizing liquid lines is discouraged because it will
significantly increase the system refrigerant charge. This, in
turn, affects the oil charge.
Figure 2 on page 6 shows the condenser below the
evaporator. As the liquid refrigerant is lifted from the condenser
to the evaporator, the refrigerant pressure is lowered. Different
refrigerants will have different pressure changes based on
elevation. Refer Table 2 to for specific refrigerants. The total
pressure drop in the liquid line is the sum of the friction loss,
plus the weight of the liquid refrigerant column in the riser.
Table 2: Pressure Drop in Liquid Lines by Refrigerant
Refrigerant
R-22
R-407C
R-410A
R-134a
Based on saturated liquid refrigerant at 100°F (37.7°C)
Only sub-cooled liquid refrigerant will avoid flashing at the TX
valve in this situation.If the condenser had been installed above
the evaporator, the pressure increase from the weight of the
liquid refrigerant in the line would have prevented the refrigerant
from flashing in a properly sized line without sub-cooling.
It is important to have some sub-cooling at the TX valve so
that the valve will operate properly and not fail prematurely.
Follow the manufacturer's recommendations. If none are
available, then provide 4 to 6°F (2.2 to 3.3°C) of sub-cooling
at the TX valve.
Liquid lines require several refrigerant line components and/
or accessories to be field selected and installed (Figure 6).
Isolation valves and charging ports are required. Generally,
it is desirable to have isolation valves for servicing the basic
system components, such as a condensing unit or condenser.
In many cases, manufacturers supply isolating valves with their
product, so be sure to check what is included. Isolating valves
come in several types and shapes.
AG 31-011 • REFRIGERANT PIPING DESIGN
Pressure Drop PSI/ft (kPa/m) Riser
0.5 (11.31)
0.47 (10.63)
0.43 (9.73)
0.5 (11.31)
Figure 6: Refrigerant Accessories
Aux SideConnector
Distributor
TX Valve
Photos courtesy of Sporlan Division – Parker Hannifin Corporation
Referring to Figure 2 on page
1. Working from the condenser, there is a liquid line
filter-drier.The filter drier removes debris from the liquid
refrigerant and contains a desiccant to absorb moisture
in the system. Filter driers are either disposable or a
permanent with replaceable cores.
2. Next there is a sight glass that allows technicians to view
the condition of the refrigerant in the liquid line. Many
sight glasses include a moisture indicator that changes
color if moisture is present in the refrigerant.
3. Following the sight glass is the TX valve. (More
information about TX valves is available under
Expansion Valves" on page
10
Filter-Drier
Solenoid Valve
Sight Glass
6:
"Thermal
28.)
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