CVHE-SVX02M-EN
37
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.
NNoottee:: 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 non-condensable
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 drain/
waste/vent (DWV) copper. Consult local codes for
restrictions on materials. Consult with the
manufacturers of any field-provided components or
materials for acceptable material compatibility.
NNoottee:: PVC piping is compatible with the refrigerant 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.
Testing conducted in Trane laboratories has qualified
the following materials for PVC pipe construction as
being compatible with the refrigerant:
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
Flexible connection devices for vibration isolation must
also be compatible with the vented refrigerant. A
flexible stainless-steel pump connector (such as the
stainless-steel type MFP, style HNE, flexible pump
connector from Vibration Mounting and Control, Inc.)
or equivalent is recommended.
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 27, p. 42) 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 12, p. 41 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 27, p. 42. Enter the figure
with the total CC value, read across to a pipe curve
and down to find the maximum allowable length
for that size pipe.
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