SS-APG010C-EN
7
Line Sizing, Routing, and Component Selection
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 ensure that 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.
For improved modulation, choose expansion valves with balanced port construction and external
equalization. Table 4, p. 17, identifies the part number of the valve recommended for (4) TTA/TWA
systems.
The tonnage of the valve should represent the tonnage of the portion of coil that the TXV/distributor
will feed.
The expansion valve is inclusive on the outdoor (4) TWA units for reverse flow heat pump
operation.
Compressor Crankcase Heater
Smaller split systems may not ship with a compressor crankcase heater. For line lengths over 60
feet, compressor crankcase heaters are a requirement. Be sure to consult the product data
catalogue to determine if the crankcase heater ships with the unit. If it does not, a Trane field-
installed crankcase heater may be obtained from your local sales office.
Gas Line
Line Sizing
Proper line sizing is required to guarantee that the oil returns to the compressor throughout the
system’s operating envelope. At the same time, the line must be sized so that the pressure drop
does not excessively affect capacity or efficiency.
Note: Preselected suction-lin
e di
ameters shown in Ta ble 3, p. 16, are independent of total line
length for properly charged (4) TTA/TWA units in normal air-conditioning applications.
Routing
Route the line as straight (horizontally and vertically) as possible. Avoid unnecessary changes of
direction. To prevent residual or condensed refrigerant from “free-flowing” toward the
compressor, install the suction line so that it slopes by ¼ to 1 inch per 10 feet of run (1 cm per
3 m) toward the indoor coil.
Do not install riser traps. With two circuit blower coils and one circuit outdoor units, what appears
to be a riser trap is located at the coil outlet; see Figure 8, p. 14 for an example. This piping
arrangement, which isn’t a riser trap, is the result of two requirements:
• Drain the coil to the low point
• Rise at least 1 ft (30 cm) from the common low
point to prevent any
off-cycle condensed
refrigerant in the coil from attempting to flow to the compressor.
Double risers must not be instal
le
d. All (4) TTA and TWA units gas line size, preselected in Ta bl e 3,
p. 16, provides sufficient velocity to push entrained oil up the permissible riser height.
Note: If a gas riser is properly sized, oil will return to the compressor rega
rdless of whether a trap
is present. If a gas riser is oversized, adding a trap will not restore proper oil entrainment.
Avoid Underground Refrigerant Lines
Refrigerant condensation during the off cycle, installation debris inside the line (including
condensed ambient moisture), service access, and abrasion/corrosion can quickly impair
To Next Page
Loading...
