Refrigerant Line Sizing - Trane TR-SCS Series Installation, Operation And Maintenance Manual

silver is recommended. General purpose silver brazing
alloy with 45% silver is recommended for brazing
dissimilar metals.
Wrap wet rags around the pipes between the areas to be
soldered and any nearby refrigeration components (such
as the optional head pressure control valve) to keep
excessive heat from traveling through the pipe and
causing damage. Clear all pipe connections of debris and
prep connections for soldering. Use only "L" or "K" grade
refrigerant copper piping. Be careful not to allow solder/
piping debris to get inside refrigerant lines. Dry nitrogen
should be flowing through the tubing while soldering at a
rate of not less than 1–2 CFM (0.03–0.6 M3/minute).

Refrigerant Line Sizing

The following general guidelines may be used to assist in
determining the size of the refrigerant lines between the
evaporator section and the remote air-cooled condenser.
Note: Refrigerant piping between the indoor evaporator
and condenser must not exceed 150 feet (total
equivalent length). The maximum level drop from
the indoor evaporator to the condenser must not
exceed 20 feet.
Refrigerant lines for split systems must be sized according
to the piping distance between the evaporator and the
condenser with consideration to elevation changes. Each
valve, fitting and bend in the refrigerant line must also be
considered in this calculation. Refer to table below for
standard equivalent lengths, in feet, of straight pipe.
Table 3. Pipe equivalent lengths
Equivalent Length (ft) of Straight Pipe
OD (in.) Globe Angle
Line Size Valve Valve Elbow
1/2 9.0 5.0
5/8 12.0 6.0
7/8 15.0 8.0
1-1/8 22.0 12.0
1-3/8 28.0 15.0
1-5/8 35.0 17.0
2-1/8 45.0 22.0
Refer to the installation manual provided with the A/C
system for tables showing the recommended liquid line
and discharge line sizes for the A/C system you are
installing.
Things to consider when sizing refrigerant piping are the
varying BTU capacities of indoor evaporators and the
equivalent length of pipe needed between the remote
condenser and the evaporator.
If the pressure drop is too high, the capacity of the
compressor decreases, and the power required increases.
An excessive refrigerant charge will be applied if the
volume of the piping is too large. Refrigerant line sizing for
discharge and liquid lines should create no more than a 
2–3°F pressure drop.
SS-SVX006C-EN
90º 45º Tee Tee
Elbow Line Branch
0.9 0.4 0.6 2.0
1.0 0.5 0.8 2.5
1.5 0.7 1.0 3.5
1.8 0.9 1.5 4.5
2.4 1.2 1.8 6.0
2.8 1.4 2.0 7.0
3.9 1.8 3.0 10.0
Note: The size of the condenser pipe connections does
not indicate the size of the refrigerant lines to be
used. In cases where the pipe size doesn't match
the size of the connection, reducing fittings must be
used to transition between the connection and the
pipe.
Discharge Line
Since refrigerant may condense during "Off" cycles, all
vertical discharge risers should be designed to prevent
liquid refrigerant from flowing back into the compressor.
If a condenser is installed above the evaporator, the
discharge line should include a shallow P-trap at the
lowest point in the piping (see
The highest point in the discharge line should be above the
condenser coil. Install an inverted trap at the condenser
inlet to prevent liquid refrigerant from flowing backwards
into the hot gas riser during off cycles. Shallow P-traps
must be included in the discharge line for every 20 feet of
vertical rise. All horizontal refrigerant lines should be
pitched in the direction of flow at least 1/4 inch per 10 feet.
Discharge line velocities must be a minimum of 500 fpm
for horizontal runs and 1,000 fpm for vertical risers to
ensure oil is returned to the compressor at both full and
partial load operating conditions.
It is important that the discharge line is sized with a certain
degree of pressure drop. This will ensure the refrigerant
flows at a velocity high enough for the refrigerant vapor to
carry the oil with it to the condenser and to prevent the oil
from returning to the compressor.
Compressor discharge pressure is always higher than
condensing pressure due to the line pressure drop. The
line pressure drop also causes a change in the refrigerant
saturation temperature. The discharge line needs to be
sized so the pressure drop won't cause a corresponding
change in saturation temperature exceeding 2°F.
Discharge piping is typically sized for a total line pressure
drop of 5 psi (+/- 50%), which results in only a 1/2% to 1%
reduction in compressor capacity. Pressure drops greater
than 10 psi will impair system performance.
Figure 9, p. 14 depicts a typical piping diagram when the
condenser is located at a higher level than the indoor
evaporator. In this situation, it is especially important to
size the discharge line properly. If the discharge line is
sized correctly for full load operation, the velocity of the
gas may be too low during minimum load conditions to
carry the refrigerant oil vertically through the discharge
line to the condenser coil.
Decreasing the size of the discharge line will increase the
refrigerant velocity, however, it will also restrict the flow of
refrigerant at full load conditions creating an excessive
refrigerant pressure drop.
To remedy this, dual risers may be used as shown in
Figure 10, p. 14. Discharge riser #1 should be sized to
allow the refrigerant gas to flow at a sufficient velocity
during minimum load conditions to carry the oil.
Installation
Figure 9, p. 14).
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