30 CVHH-SVX001A-EN
Vent Piping
Refrigerant Vent Line
General Requirements
State and local codes, and ASHRAE Standard 15 contain
requirements for venting the relief device on the chiller to
the atmosphere outside of the building. These
requirements include, but are not limited to, permitted
materials, sizing, and proper termination.
Note: The following information is a general outline of
vent-line installation requirements based on
ASHRAE Standard 15. Most codes contain similar
requirements but may vary in some significant
areas. The installer must check state and local
codes and follow the specific requirements
applicable to the location.
Purge Discharge
To comply with ASHRAE Standard 15, the discharge
piping from purge units that remove noncondensible gas
from refrigerating systems must conform to the ASHRAE
Standard 15 requirements for relief piping. To help meet
this requirement, the purge discharge is factory-piped to
the relief device assembly.
Vent Line Materials
All materials in the relief device vent system must be
compatible with the refrigerant in use. Commonly used
and accepted piping materials include steel and DWV
(drain/waste/vent) copper. Consult local codes for
restrictions on materials. Consult with the manufacturers
of any field-provided components or materials for
acceptable material compatibility.
Note: PVC piping is acceptable for use as a vent line
material with R-1233
zd
(E), but the glue that joins
the sections of plastic pipe may not be. When
considering a vent system constructed of plastic
piping, such as PVC, ensure that both the pipe
material and the adhesive have been tested for
refrigerant compatibility. In addition, verify that the
local codes permit PVC for refrigerant vent lines;
even though ASHRAE Standard 15 doesn’t prohibit
its use, some local codes do.
The following materials for PVC pipe construction are
recommended for use with R-1233
zd
(E):
Primer/Cleaner:
• Hercules—PVC Primer #60-465
• RECTORSEAL
®
PVC Cleaner—Sam™ CL-3L
Adhesives:
• Hercules—Clear PVC, Medium Body/Medium Set,
#60-020
• RECTORSEAL—PVC Cement, Gene™ 404L
Vent Line Sizing
Vent line size must conform to local codes and
requirements. In most cases, local codes are based on
ASHRAE Standard 15. ASHRAE Standard 15 provides
specific requirements for the discharge piping that allows
pressure-relief devices to safely vent refrigerant to the
atmosphere if over pressurization occurs. In part, the
standard mandates that:
• The minimum pipe size of the vent line must equal the
size of the discharge connection on the pressure-relief
device. A larger vent line size may be necessary,
depending on the length of the run.
• Two or more relief devices can be piped together only
if the vent line is sized to handle all devices that could
relieve at the same time.
• When two or more relief devices share a common vent
line, the shared line must equal or exceed the sum of
the outlet areas of all upstream relief devices,
depending on the resulting back pressure.
ASHRAE Standard 15 provides guidance for determining
the maximum vent line length. It also provides the
equation (shown in
Figure 23, p. 36) and data necessary to
properly size the vent line at the outlet of a pressure-relief
device or fusible plug.
The equation accounts for the relationship between pipe
diameter, equivalent pipe length, and the pressure
difference between the vent line inlet and outlet to help
ensure that the vent line system provides sufficient flow
capacity.
Table 8, p. 35 provides additional information based on
ASHRAE Standard 15, including:
• Capacities of various vent line sizes and lengths.
However, this data applies only to conventional
pressure-relief valves and NOT to balanced relief
valves, rupture members (as used on Trane
®
centrifugal chillers), fusible plugs, or pilot-operated
valves.
• A simplified method to determine the appropriate
vent-line size, with
Figure 23, p. 36. Enter the figure
with the total C value, read across to a pipe curve and
down to find the maximum allowable length for that
size pipe.
To determine the total C value for a specific unit, add
the appropriate C values for the evaporator, standard
condenser, and economizer. If the unit is equipped with
any options (e.g., heat recovery, free cooling, or an
auxiliary condenser), add the applicable C value(s) for
those options to the total as well.
Note:
Table 8, p. 35 and Figure 23, p. 36 are applicable
only for non-manifolded vent-line runs connected
to a 344.7 kPa (50 psi) rupture disk relief device. The
pipe length provided by the table is in “equivalent
feet.” The vent-line length in equivalent feet is the
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