Expansion Valves - Trane TTA Series Application Manual

Expansion Valves

Expansion valves meter refrigerant into the evaporator under controlled conditions. If there is too
much refrigerant, the refrigerant will not completely vaporize and the remaining liquid will slug the
compressor. If there is too little refrigerant, the system won't make capacity and there may not be
enough cooling for the compressor.
Note: Expansion valves are pre-installed on the TWE product and the superheat has been set
Table 4, p.
valve in order to maintain proper coil distribution. The expansion valve should be selected to match
the capacity of the coil that the distributor feeds.
Example 1: 10-ton coil (one refrigerant circuit) with two equal distributors
10 / 2 = 5
Each TXV should be selected for 5 tons.
Example 2: 10-ton coil (one refrigerant circuit) with two distributors and a 60/40 coil
split
10 x.6=6 and 10 x.4=4
One TXV should be sized for 6 tons, and one TXV should be sized for 4 tons.
If the coil or distributors have a difference of only one circuit tube, the difference should be ignored.
The proper balance for feeding refrigerant for a TTA/TWA system is to provide 18°F of superheat—
the difference between the saturated and actual refrigerant temperature leaving the evaporator.
Expansion valve superheat is preset from the factory, but it isn't set to 18°F . Use the turns listed in
Table 1
Table 1.
Sporlan
Standard off-the-shelf nominal valve settings (90 PSIG air test setting)
Valve
ERZE or
RCZE
OZE
SS-APG008-EN
properly.
21, lists expansion valves. Each evaporator distributor requires a dedicated expansion
to adjust them to the correct 18°F superheat.
Expansion valves
Superheat, °F CW turns available CCW turns available
12 4.5 4.5
Field adjust for 18°F
Superheat change
per turn
2.4°F 2 1/2 CW
3.4°F 1 3/4 CW
9