6
Figure 3 – Condenser Located Above Chiller Unit
Figure 4 - Condenser Located Below Chiller Unit
Caution: Liquid line sizing for each chiller capacity are
in Table 2. These line sizes are listed per circuit and
apply where leaving water temperature (LWT) is 40°F
or higher. For applications where the LWT is below
40°F, size lines using the ASHRAE Refrigeration
Handbook or other suitable design guide.
Determining Equivalent Line Length
To determine the appropriate size for field installed
liquid and discharge lines, it is first necessary to
establish the equivalent length of pipe for each line.
The equivalent length is the approximate friction loss
from the combined linear run of pipe and the
equivalent feet of elbows, valves, and other
components in the refrigeration piping. The sum
total is the equivalent length of pipe that would have
the same pressure loss. See the ASHRAE
Refrigeration Handbook for more information.
Follow these steps when calculating line size:
1.
Start with an initial approximation of
equivalent length by assuming that the
equivalent length of pipe is 1.5 times the
actual pipe length.
2.
Determine approximate line sizes by
referring to Table 2 for liquid lines, Table 3
and Table 4 for the discharge lines.
3.
Check the line size by calculating the actual
equivalent length using the equivalent
lengths as shown in Table 5.
CAUTION: When calculating the equivalent length, do
not include piping of the chiller unit. Only field piping
must be considered.
Table 1 – Equivalent Lengths of Elbows
Line Size
OD (in)
Equivalent Lengths of Refrigerant Pipe (feet)
90°
Standard
90° Long
Radius
90°
Street
45°
Standard
45°
Street
1/2
1.4
0.9
2.3
0.7
1.1
5/8
1.6
1.0
2.5
0.8
1.3
7/8
2.0
1.4
3.2
0.9
1.6
Liquid Line Sizing
The liquid line diameter should be as small as
possible while maintaining acceptable pressure drop.
This is necessary to minimize refrigerant charge. The
total length between the chiller unit and the air-
cooled condenser must not exceed 200 actual feet
or 300 equivalent feet. It is best to pipe the liquid
line so that there is an immediate drop of at least 15
inches at the condenser outlets to make a liquid seal.
Liquid line risers in the system will require an
additional 0.5 psig pressure drop per foot of vertical
rise. When it is necessary to have a liquid line riser,
make the vertical run immediately after the
condenser before any additional restrictions. The
liquid line risers must not exceed 10 feet in height
from the condenser liquid line connection. The liquid
line does not require pitching. Install a pressure tap
valve at the condenser to facilitate measuring
pressure for service.
Liquid lines do not typically require insulation.
However, if exposing the lines to solar heat gain or
temperatures exceeding 110 °F, there is a negative
effect on sub-cooling. In these situations, insulate
the liquid lines.
