SS-APG008-EN 5
Line Sizing, Routing, and Component Selection
“Refrigerant Piping Examples,” p. 13, provides illustrations of TTA/TWA split system component
arrangement. Use them to determine the proper, relative sequence of the components in the
refrigerant lines that connect the TTA/TWA outdoor unit to an evaporator coil. The TTA/TWA units
are R-410A machines and all the selected components installed in the field must also be rated for
use with R-410A.
Liquid Lines
Line Sizing
Properly sizing the liquid line is critical to a reliable split system application. Tabl e 2, p . 2 0, and
Ta b l e 3 , p . 2 1, show the recommended liquid-line sizing for each TTA/TWA model based on its
nominal capacity. Using the preselected tube diameter to uniformly size the liquid line will maintain
operating requirements and is the line size around which the TTA/TWA installation literature
charging charts were generated (see IOM). Increasing the line size will not increase the allowable
line length.
Routing
Install the liquid line with a slight slope in the direction of flow so that it can be routed with the
suction line.
A height limitation exists for liquid lines that include a liquid riser because of the loss of subcooling
that accompanies the pressure loss in the height of the liquid column. Figure 3 and Figure 4, p. 4,
depict the permissible rise in the liquid line (without excessive loss of subcooling). Again, system
designs outside the application envelope of the TTA/TWA unit require Trane review.
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. If the liquid line is routed through a high temperature area, such as an attic or
mechanical room, insulation would be required.
Components
Liquid-line refrigerant components necessary for a successful job include a filter drier, access port,
moisture-indicating sight glass, and expansion valve(s). The examples in “Refrigerant Piping
Examples,” p. 13, illustrate the proper sequence for positioning the components in the liquid line.
Position the components as close to the indoor unit as possible. Tabl e 2, p . 20 , and Table 3, p. 21,
identify suitable components, by part number, of each TTA/TWA model. Note there are two access
ports: one located at the TTA/TWA and one located at the evaporator. Table 4, p. 21, lists suitable
expansion valves.
Liquid Filter Drier
There is no substitute for cleanliness during system installation. The liquid filter drier prevents
residual contaminants, introduced during installation, from entering the expansion valve. The
TTA/TWA outdoor units have a filter drier pre-installed. However, if the refrigerant line length
exceeds 80 ft, this filter should be removed and a new one selected from Ta bl e 2 or Ta ble 3 should
be installed close to the indoor unit. If choosing a filter other than the one listed in Tab le 2 or Ta b le 3 ,
make sure its volume, filtering, and moisture-absorbing characteristics are equivalent.
Note that TWA units will require two liquid filters and two check valves due to the reverse flow
nature of a heat pump (see Figure 8 and Figure 9, p. 15).
Access Port
The access port located at the TTA/TWA allows the unit to be charged with liquid refrigerant and
is used to determine charge level. This port is usually a Schraeder valve with a core.
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