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SS-APG008H-EN
pressure drop had the unintended consequence of
requiring line sizes with large internal refrigerant volumes.
With R-410A refrigerant and POE oil, this pressure drop
can be as high as 50 psid. Within these guidelines,
refrigeration operation is maintained while minimizing the
refrigerant charge. It is still required to limit the liquid line
velocity to 600 ft/min to help avoid issues with water
hammer.
Suction Lines
R-410A is a high-pressure refrigerant and allows higher-
pressure drops in the suction lines. With R-410A
refrigerant, that a 2°F loss is equivalent to a 5 psi drop.
Additional pressure drop may be tolerated in certain
applications.
R-410A refrigerant suction lines must be sized to maintain
oil-entrainment velocities in both the horizontal lines and
vertical risers. Oil entrainment for R-410A is based on
suction temperature as well as tube diameter. At the time of
this writing, no known direct oil-entrainment tests have
been published. Trane has used ASHRAE data to create
equation-based formulas to predict the entrainment
velocities of R-410A refrigerant and POE oil. These
minimum velocities are reflected in the line sizes listed in
the component selection summary tables, see Parts
chapter.
Equipment Placement
Minimize Distance Between Components
For a split air-conditioning system to perform as reliably
and inexpensively as possible, the refrigerant charge must
be kept to a minimum. To help accomplish this design goal:
•
Site the outdoor unit (cooling-only condensing unit or
heat pump) as close to the indoor unit as possible.
•
Route each interconnecting refrigerant line by the
shortest and most direct path so that line lengths and
riser heights are no longer than absolutely necessary.
•
Use only horizontal and vertical piping configurations.
•
Determine whether the total length of each refrigerant
line requires Trane review. Be sure to account for the
difference in elevations of the indoor and outdoor units
when calculating the total line length.
Interconnecting lines of 150 lineal ft (45.7 m) or less do not
require Trane review, but only a limited amount may be in a
riser, see allowable elevation difference figures in the
following Refrigerant Piping Guidelines.
