11
Discharge (Hot Gas) Line Sizing
The discharge line sizes depend on the velocity
needed to obtain sufficient oil return. It is very
important to minimize line length and restrictions to
reduce pressure drop and maximize capacity.
Upflow hot gas risers need to have a trap at the
bottom and reverse trap at the top. In addition, a
trap and reverse trap arrangement needs to be
spaced every 15 feet in the rise for oil management
(see Figure 5).
The discharge lines should pitch downward, in the
direction of the hot gas flow, at the rate of ½ inch
per each 10 foot of horizontal run. If the chiller unit
is below the condenser, loop the discharge line to at
least 1 inch above the top of the condenser. Install a
pressure tap valve at the condenser to facilitate
measuring pressure for service. Take careful
consideration in the design of the discharge gas
riser.
Check the oil-level sight glass in the compressor to
ensure it is at the appropriate level to verify there is
no trapping of oil in the piping. Use a double riser
system to ensure proper oil return. See
Table for double riser constructions.
Figure 5 – Vertical Riser Traps
Figure 6 - Double Discharge Riser
Note: Discharge line sizing shown in Table 4 and
Table 5 are listed per circuit and applies where
leaving water temperature (LWT) is 40°F or higher.
For applications where LWT is below 40°F, size lines
using the ASHRAE Refrigeration Handbook or other
suitable design guide.
Table 4 - Horizontal or Downflow Discharge Line Sizes for R410A (inches OD)
Circuit
Tons
Total Equivalent Length (Ft)
25
50
75
100
125
150
175
200
225
250
275
300
10
7/8
7/8
7/8
7/8
7/8
7/8
7/8
1 1/8
1 1/8
1 1/8
1 1/8
1 1/8
15
7/8
7/8
1 1/8
1 1/8
1 1/8
1 1/8
1 1/8
1 1/8
1 1/8
1 1/8
1 3/8
1 3/8
20
7/8
1 1/8
1 1/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 5/8
1 5/8
25
1⅛
1 1/8
1 1/8
1 1/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 5/8
1 5/8
30
1⅛
1 1/8
1 1/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 3/8
1 5/8
1 5/8
1 5/8
40
1 5/8
1 5/8
1 5/8
1 5/8
1 5/8
1 5/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
50
1 5/8
1 5/8
1 5/8
1 5/8
1 5/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
60
1 5/8
1 5/8
1 5/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
80
1 5/8
1 5/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 5/8
2 5/8
2 5/8
2 5/8
100
2 1/8
2 1/8
2 1/8
2 1/8
2 1/8
2 5/8
2 5/8
2 5/8
2 5/8
2 5/8
2 5/8
2 5/8
120
2 1/8
2 1/8
2 5/8
2 5/8
2 5/8
2 5/8
2 5/8
2 5/8
3 1/8
3 1/8
3 1/8
3 1/8
