Coil Piping and Connections
CLCH-SVX009A-EN
35
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 32
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
®
valve with a core.
•
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. 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.
•
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
Figure 33
and install the expansion valve directly to the
liquid connections.
•
Ball shutoff valves. Adding manual, ball-type shutoff
valves upstream and downstream of the filter
simplifies replacement of the filter core.
NOTICE:
Valve Damage!
Disassemble the thermal expansion valve before
completing the brazing connections. If necessary, wrap
the valve in a cool, wet cloth while brazing. Failure to
protect the valve from high temperatures could result
in damage to internal components.
Figure 33.
Type F refrigerant coil with packed elbow
Cut here
for piping
Perforated plate
(packed elbow)
Panel
Venturi type
distributor
Coil
