Vent Piping; Refrigerant Vent Line; General Requirements; Purge Discharge - Trane CVHE Installation, Operation And Maintenance Manual

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 compatible with R-123, 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 R-123:
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
30
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 22, p.
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 9, p. 33 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 22, p.
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 9, p. 33 and
only for non-manifolded vent-line runs connected
34) and data necessary to
®
34. Enter the figure
Figure 22, p. 34 are applicable
CVHE-SVX02H-EN