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Liquid Lines
Line Sizing
Properly sizing the liquid line is critical to a successful split-
system application. The selected tube diameter must provide
at least 5°F [2.7°C] of subcooling at the expansion valve
throughout the operating envelope. Increasing the size of the
liquid line will not increase the available subcooling.
Routing
Install the liquid line with a slight slope in the direction of flow
so that it can be routed with the suction line. Minimize tube
bends and reducers because these items tend to increase
pressure drop and to reduce subcooling at the expansion
valve. Liquid line receivers, other than those that are factory-
installed, are not recommended.
Insulation
The liquid line is generally warmer than the surrounding air, so
it does not require insulation. In fact, heat loss from the liquid
line improves system capacity because it provides additional
subcooling. However, if the liquid line is routed through a high-
temperature area, such as an attic or a mechanical room,
insulation would be required.
Components
Liquid-line refrigerant components necessary for a successful
job include a filter drier, access port, solenoid valve, moisture-
indicating sight glass, expansion valve(s), and ball shutoff
valves.
Figure 48
illustrates the proper sequence for
positioning them in the liquid line. Position the components as
close to the evaporator as possible.
•
Filter drier. There is no substitute for cleanliness during
system installation. The filter drier prevents residual
contaminants, introduced during installation, from entering
the expansion valve and solenoid valve.
•
Access port. The access port allows the unit to be charged
with liquid refrigerant and is used to determine subcooling.
This port is usually a Schraeder
•
Solenoid valve. In split systems, solenoid valves isolate the
refrigerant from the evaporator during off cycles; under
certain conditions, they may also trim the amount of active
evaporator as compressors unload. Generally, the "trim"
solenoid valve is unnecessary for VAV comfort-cooling
applications, and is only required for constant-volume
applications when dehumidification is a concern.
In split systems with mircochannel heat exchanger
condensers (MCHE), solenoid valves isolate the
refrigerant from the evaporator during the off cycles. Trim
solenoids cannot be used with MCHE.
Note: Trane condensing units with MCHE no longer employ
pump-down, but isolation solenoids are required. The
suggested solenoid uses a 120-volt service and
requires code-compliant wiring to the condensing unit.
•
Moisture-indicating sight glass. Be sure to install one
moisture-indicating sight glass in the main liquid line. The
only value of the sight glass is its moisture indication ability.
CLCH-SVX009L-EN
®
valve with a core.
Coil Piping and Connections
Use actual measurements of temperature and pressure
not the sight glass to determine subcooling and whether
the system is properly charged. The moisture indicator/
sight glass must be sized to match the size of the liquid line
at the thermal expansion valve.
NOTICE
Valve Damage!
Failure to protect the valve from high temperatures
could result in damage to internal components.
Disassemble the thermal expansion valve before
completing the brazing connections. If necessary, wrap
the valve in a cool, wet cloth while brazing.
•
Thermal expansion valve. The expansion valve is the
throttling device that meters the refrigerant into the
evaporator coil. Metering too much refrigerant floods the
compressor; metering too little elevates the compressor
temperature. Choosing the correct size and type of
expansion valve is critical to assure it will correctly meter
refrigerant into the evaporator coil throughout the entire
operating envelope of the system. Correct refrigerant
distribution into the coil requires an expansion valve for
each distributor.
The thermal expansion valve must be selected for proper
size and capacity. The size of the expansion valve should
cover the full range of loadings. Check that the valve will
successfully operate at the lightest load condition. For
improved modulation, choose expansion valves with
balanced port construction and external equalization. Cut
the process tube and cap assembly from the liquid
connection as shown in
expansion valve directly to the liquid connections.
Figure 49. Type F refrigerant coil with packed elbow
Panel
Coil
•
Ball shutoff valves. Adding manual, ball-type shutoff valves
upstream and downstream of the filter simplifies
replacement of the filter core.
Figure 49
and install the
Perforated plate
Cut here
(packed elbow)
for piping
Venturi type
distributor
43
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