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CVHE-SVX005C-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 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.
Note: 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
and data necessary to properly size the vent line at the
outlet of a pressure-relief device or fusible plug (for more
information, refer to “Vent Line Sizing Reference,” p. 44).
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.
The table in “Vent Line Sizing Reference,” p. 44 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, using the figure in “Vent Line Sizing
Reference,” p. 44. 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.
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