SS-APG008H-EN
9
Line Sizing, Routing, and Component Selection
“Refrigerant Piping Examples,” p. 17
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. The Component Selection tables,
found in
, 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 exist for liquid lines that include a liquid riser due
to the normal force of gravity. As the liquid riser grows in
height this normal force create a pressure drop. If the riser
is high enough, this pressure drop results in a loss of
subcooling.
and
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. 17
, illustrate
the proper sequence for positioning the components in the
liquid line. Position the components as close to the indoor
unit as possible. The Component Selection tables, found in
, 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.
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 the Component Selection tables
found in
. The new drier should be installed as
close as possible to the indoor unit and between the TXVs
and compressor. If choosing a filter other than the one
listed in these tables, make sure its volume, filtering, and
moisture-absorbing characteristics are equivalent.
Note:
Due to the reverse flow nature of a heat pump, if the
liquid line exceeds 80 ft, the heat pump will require a
bi-flow filter drier (see
and
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. See Note 1 on
and
for
more details.
Solenoid Valve
For TTA split systems, solenoid valves are not required to
isolate the refrigerant from the evaporator during the off
cycles. The exception is when the suction line is above the
evaporator and is outside piping guidelines. Even then the
use of solenoids is rare and should only be installed when
recommended by the manufacturer. If a solenoid is
required, the installer should use a drop solenoid—open
when the compressor is on, and off when the compressor
is off. If used, the solenoid requires code compliant wiring
to the TTA condensing unit. (The solenoid is not shown on
the unit wiring diagram.)
Notes:
•
Solenoid valves piped in series with a check
valve create the possibility of a dangerous over
pressures. Solenoids should not be used with a
TWA or with a TTA using a check valve.
•
Solenoids are seldom used and not included in
the Component Selection tables found in
