Vent Piping . Trane CVHE-SVX02M-EN, CVHG, CVHF, CVHE
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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.
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.
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
CVHE-SVX02M-EN
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
) 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.
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
and down to find the maximum allowable length for that size pipe.
37
evaporator, standard condenser, and economizer. If the unit is equipped with any options (e.g., heat recovery, free cooling, or value(s) for those options to the total as well.
otte
and
are applicable only for non-manifolded vent-line runs connected to a 15 psig (103.4 kPaG) rupture disk relief device. The pipe length provided by the table is in “equivalent feet.” The vent-line length in equivalent feet is the sum of the linear pipe length plus the equivalent length of the fittings (e.g., elbows).
Vent Line Installation
line, consult local codes for applicable guidelines and constraints.
All CenTraVac™ centrifugal chillers are equipped with rupture disks. If refrigerant pressure within the evaporator exceeds 15 psig (103.4 kPaG), the rupture disk breaks and shell pressure is relieved as refrigerant escapes from the chiller.
A cross-section of the rupture disk assembly appears in
along with an illustration indicating the location of the rupture disk on the suction elbow.
an ™ is to be installed, remove and discard the factory-installed rupture disk; for more information, refer to
Installation, Operation, and Maintenance:
RuptureGuard Pressure Relief System
Option
(CTV-SVX06*-EN).
Several general recommendations for rupture disk vent line installation are outlined as follows.
vent-line piping installation, the rupture disk must be reinstalled (as shown in
Refer to the following procedure and contact
CenTraVac ™ Chiller Technical Service when reinstalling the rupture disk.
• Verify that the vacuum support side of the rupture disk is positioned as shown in the cross-section view that appears in
.
–
Install the two bottom bolts though the pipe flanges.
– Install the rupture disk with a gasket on each side between the pipe flanges. Orient the disk with the reference arrow or vacuum support bar facing the chiller side as shown in
– Install the two top bolts.
–
Center the disk and gaskets to the flange bore.
– Hand-tighten all bolts assuring equal pressure.
38
– Use a torque wrench set to 240 in·lb (27.1 N·m) with a 9/16-in. socket.
– Tighten bolts in a star pattern, one half turn each, to maintain even pressure on the disk.
– Final torque on all bolts should be 240 in·lb
(27.1 N·m).
• When attaching the vent line to the chiller, do NOT apply threading torque to the outside pipe of the rupture disk assembly.
da ma
• Provide support as needed for the vent line. Do
NOT use the rupture disk assembly to support the vent-line piping.
• Use a flexible connection between the vent line and the rupture disk assembly to avoid placing stress on the rupture disk. (Stress can alter rupture pressure and cause the disk to break prematurely.) The flexible connector used to isolate the rupture disk from excessive vent line vibration must be compatible with the refrigerant in use. Use a flexible, steel connector (such as the stainless-steel type MFP, style HNE, flexible pump connector from
Vibration Mounting and Control, Inc.), or equivalent. Refer to
for a recommended relief piping arrangement.
• An individual vent line is normally installed for each relief device. It is permissible to manifold the rupture disks of several machines into a common vent line provided that the appropriate ASHRAE
Standards and local code requirements for manifolded relief devices are followed.
otte
does NOT apply for manifolded vent lines.
de atth
Wh en eq pp uiip me
CVHE-SVX02M-EN
Figure 24.
Rupture disk location and cross section of rupture disk
• Route the vent-line piping so that it discharges outdoors in an area that will not spray refrigerant on anyone. Position the vent-line discharge at least
15 ft (4.6 m) above grade level and at least 20 ft
(6.1 m) from any building opening. Provide a ventline termination that cannot be blocked by debris or accumulate rainwater.
• Provide a drip leg on the vent line (refer to
25, p. 40 ). Provide a standard 1/4-in. FL x 1/4-in.
NPT, capped refrigerant service valve to facilitate liquid removal.
eq uiip o h d tth
250E evaporator/250L condenser units with heat recovery which have a 4 in. (101.6 mm) NPT pipe connection.
• Consult local regulations and codes for any additional relief line requirements and refer to appropriate refrigerant handling guidelines. For R-
123 chillers, refer to
Installation, Operation, and
Maintenance: R-123 Low-Pressure Refrigerant
Handling Guidelines Conservation and Safe
Handling of R-123 Refrigerant in Trane Chillers for
Service Technicians
(CTV-SVX05*-EN). For R-514A chillers, refer to
Installation, Operation, and
Maintenance: R-514A Low-Pressure Refrigerant
Handling Guidelines Conservation and Safe
Handling of R-514A Refrigerant in Trane Chillers for
Service Technicians
(CTV-SVX008*-EN).
CVHE-SVX02M-EN 39
Figure 25.
Arrangement for rupture disk relief piping Figure 26.
RuptureGuard™ drip leg (not provided)
40
exhaust connection point MUST be lower than the purge height. Do NOT create a Utrap; extend to drip leg if necessary to avoid a trap.
• If a RuptureGuard ™ is to be installed, remove and discard the factory-installed rupture disk; for more information, refer to
Installation, Operation, and Maintenance:
RuptureGuard Pressure Relief System
Option
(CTV-SVX06*-EN).
• The rated flow capacity of the
RuptureGuard ™ disk/valve assembly is based on having straight pipe extending past the spring mechanism downstream of the valve. Be sure there are no crosses (a derate on the rated flow capacity for this configuration is published in
Engineering
Bulletin: RuptureGuard Selection Guide
[E/
CTV-EB-10]), elbows, tees or any other obstructions within the first 9 in. (228.6 mm) of valve discharge. Refer to ASHRAE
Standard 15 for additional requirements on piping rupture disk and relief valve vent lines.
• Use Loctite ® 242 or Loctite® 277 on all threaded joints on chillers charged with refrigerant; use of other pipe thread sealants is NOT recommended. Ensure all threaded pipe joints are properly cleaned and prepared before assembly. An alternative to the use of Loctite
® is to thread and weld the inlet adapter to the pipe. Care must be taken to ensure that the flange mating surface remains flat. Do NOT weld on the Inlet
Adapter flange while connected to the
RuptureGuard ™.
• The drip leg is required and must be drained periodically for proper chiller purge operation.
an ™ is to be installed, it
MUST be installed properly. Failure to properly install RuptureGuard ™ will likely result in a start-up delays and required rework and expenses that result from a failure to properly install RuptureGuard ™ will NOT be paid by Trane.
CVHE-SVX02M-EN
Vent Line Sizing Reference
Table 12.
“C” values used to determine rupture disk vent line sizes; for use with the following figure
Evap.
Size
(EVSZ)
Cond.
Size
(CDSZ)
032S 032S
Total
“C”
Value
50.00
“C” Values for Unit Components
Short
H.R.
Cond.
Long H.
R.
Cond.
Aux.
Cond.
Free
Cooling
Econ.
18.87
25.19
15.30
3.66
032S
032L
050S
050S
050L
050S
050L
080S
080S
080L
080L
142M
142L
142E
210L
032L
032L
050S
050L
050L
080S
080L
080S
080L
080L
142L
142L
142L
142L
210L
61.32
65.09
64.20
72.10
83.17
69.71
90.52
86.48
96.22
111.50
117.53
127.49
134.89
143.11
149.91
23.55
N/A
29.06
N/A
51.01
31.45
N/A
38.80
N/A
56.80
15.30
N/A
15.30
N/A
15.30
5.50
N/A
5.38
N/A
7.13
Table 12.
“C” values used to determine rupture disk vent line sizes; for use with the following figure
(continued)
Evap.
Size
(EVSZ)
Cond.
Size
(CDSZ)
250E 250L
“C” Values for Unit Components
Total
“C”
Value
175.74
Short
H.R.
Cond.
N/A
Long H.
R.
Cond.
62.12
Aux.
Cond.
15.30
Free
Cooling
Econ.
N/A
210D 210D 112.93
15.30
7.13
250D 250D 122.62
N/A N/A
250M 250M 146.36
15.30
N/A
250X 250X 164.74
Notes:
1
.
Rupture disk diameter is 3 in. (76.2 mm), with the exception of
250E evaporator/250L condenser units with heat recovery which have a rupture disk diameter of 4 in. (101.6 mm).
2
.
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” values to this total. With this new sum, refer to the following figure to determine the vent-line pipe diameter.
3
.
If piping multiple rupture disks to a common vent line, first determine the total “C” value for each rupture disk, then add all “C” values together and apply the result to the following figure.
4
.
RuptureGuard™ size based on “C” value:
3-in. (76.2 mm) valve: “C” value 0 to 104.20
4-in. (101.6 mm) valve: C value 104.21 to 223.9
RuptureGuard™ is not available for 250E evaporator/250L condenser units with heat recovery.
CVHE-SVX02M-EN 41
Figure 27.
Rupture disk vent pipe sizing; for use with the preceding table
42
dictated by state or local code which may be different from ASHRAE Standard 15 requirements.
CVHE-SVX02M-EN
For CenTraVac™ chillers using a rupture disk relief:
•
L
= equivalent length of discharge piping, ft (m)
•
C r
= rated capacity as stamped on the relief device in lb/min (kg/s), or SCFM multiplied by 0.0764 lb/ min (convert multiplier in lb/min to kg/s for SI)
C r
in lb/min to kg/s for SI)
•
f
= Moody friction factor in fully turbulent flow
•
d
= inside diameter of pipe or tube, in. (mm)
• ln = natural logarithm
•
P
2
= absolute pressure at outlet of discharge piping, psi (kPa)
•
P
0
= allowed back pressure (absolute) at the outlet of pressure relief device, psi (kPa)
P
0
= (0.50
P
) + atmospheric pressure
otte ™ chillers, P is 15 lb (6.8 kg). Atmospheric pressure is at the elevation of the installation above sea level; a default value is the atmospheric pressure at sea level, 14.7 psi (101.34 kPa).
CVHE-SVX02M-EN 43
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