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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.
N N o o t t e e : : 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.
N N o o t t e e : : PVC piping is acceptable for use as a vent-line
material with R-1233zd 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-1233zd:
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
36
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
Line Sizing Reference," p.
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 tables in
"Vent Line Sizing Reference," p. 40
provide 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 figures (in I-P or SI units) in
"Vent Line Sizing Reference," p.
with the total C C value, read across to a pipe curve
and down to find the maximum allowable length
for that size pipe.
N N o o t t e e : : To determine the total C C value for a specific
unit, add the appropriate C 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 C
value(s) for those options to the total as well.
"Vent
40).
40. Enter the figure
CVHH-SVX001G-EN
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