Operating Principles . Trane CVHE-SVX02M-EN, CVHG, CVHF, CVHE
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Operating Principles
General Requirements
Operation and maintenance information for CVHE,
CVHF, and CVHG CenTraVac™ chillers are covered in this section. This includes both 50 and 60 Hz centrifugal chillers equipped with the Tracer® AdaptiView™
UC800 control system. This information pertains to all chiller types unless differences exist, in which case the sections are listed by chiller type as applicable and described separately. By carefully reviewing this information and following the instructions given, the owner or operator can successfully operate and maintain a CenTraVac™ chiller. If mechanical problems do occur, however, contact a Trane service technician to ensure proper diagnosis and repair of the unit.
an ™ chillers can operate through surge, it is NOT recommended to operate them through repeated surges over long durations. If repeated surges of long durations occur, contact your Trane Service
Agency to resolve the issue.
Cooling Cycle
When in the cooling mode, liquid refrigerant is distributed along the length of the evaporator and sprayed through small holes in a distributor (i.e., running the entire length of the shell) to uniformly coat each evaporator tube. Here, the liquid refrigerant absorbs enough heat from the system water circulating through the evaporator tubes to vaporize. The gaseous refrigerant is then drawn through the eliminators
(which remove droplets of liquid refrigerant from the gas) and the first-stage variable inlet guide vanes, and into the first-stage impeller.
CVHE and CVHG 3-Stage Compressor
Compressed gas from the first-stage impeller flows through the fixed, second-stage inlet vanes and into the second-stage impeller. Here, the refrigerant gas is again compressed, and then discharged through the third-stage variable guide vanes and into the thirdstage impeller. After the gas is compressed a third time, it is discharged into the condenser. Baffles within the condenser shell distribute the compressed refrigerant gas evenly across the condenser tube bundle. Cooling tower water circulated through the condenser tubes absorbs heat from the refrigerant, causing it to condense. The liquid refrigerant then passes through an orifice plate and into the economizer.
The economizer reduces the energy requirements of the refrigerant cycle by eliminating the need to pass all gaseous refrigerant through three stages of compression (refer to
). Notice that some of the liquid refrigerant flashes to a gas because of the pressure drop created by the orifice plates, thus
CVHE-SVX02M-EN further cooling the liquid refrigerant. This flash gas is then drawn directly from the first and second stages of the economizer into the third- and second-stage impellers of the compressor, respectively. All remaining liquid refrigerant flows through another orifice plate to the evaporator.
Figure 44.
Pressure enthalpy curve, 3-stage
Figure 45.
Refrigerant flow, 3-stage
CVHF 2-Stage Compressor
Compressed gas from the first-stage impeller is discharged through the second-stage variable guide vanes and into the second-stage impeller. Here, the refrigerant gas is again compressed, and then discharged into the condenser. Baffles within the condenser shell distribute the compressed refrigerant gas evenly across the condenser tube bundle. Cooling tower water circulated through the condenser tubes absorbs heat from the refrigerant, causing it to condense. The liquid refrigerant then flows out of the bottom of the condenser, passing through an orifice plate and into the economizer.
The economizer reduces the energy requirements of the refrigerant cycle by eliminating the need to pass all
67
gaseous refrigerant through both stages of compression (refer to
). Notice that some of the liquid refrigerant flashes to a gas because of the pressure drop created by the orifice plate, thus further cooling the liquid refrigerant. This flash gas is then drawn directly from the economizer into the second-stage impellers of the compressor. All remaining liquid refrigerant flows out of the economizer, passing through another orifice plate and into the evaporator.
Figure 46.
Pressure enthalpy curve
Oil and Refrigerant Pump
Compressor Lubrication System
A schematic diagram of the compressor lubrication system is illustrated in the following figure. Oil is pumped from the oil tank (by a pump and motor located within the tank) through an oil pressure regulating valve designed to maintain a net oil pressure of 18 to 22 psid (124.1 to 151.7 kPaD). It is then filtered and sent to the oil cooler located in the economizer and on to the compressor motor bearings.
From the bearings, the oil drains back to the manifold and separator under the motor and then on to the oil tank.
Figure 47.
Refrigerant flow, 2-stage
68 CVHE-SVX02M-EN
Figure 48.
Oil refrigerant pump
1. Motor coolant return to condenser, 2.125 in. (53.975 mm) OD
2. Oil tank vent to evaporator
3. Oil separator and tank vent manifold
4. Tank vent line
5. Condenser
6. High pressure condenser gas to drive oil reclaim eductors, 0.375 in. (9.525 mm) OD
7. Oil return to tank
8. Oil tank
9. Oil cooler within economizer 0.625 in. (15.875 mm) OD coiled tubing
10. Oil reclaim from evaporator (second eductor), 0.25 in. (6.35 mm) OD
11. Liquid refrigerant to pump, 1.625 in. (41.275 mm) OD
12. Economizer
13. Oil supply to bearings, 0.625 in. (15.875 mm) OD
14. Purge
15. Compressor
16. Liquid refrigerant motor coolant supply, 1.125 in. (28.575 mm) OD
17. Liquid refrigerant to economizer
18. Liquid refrigerant to evaporator
19. Evaporator
CVHE-SVX02M-EN 69
20. Oil reclaim from suction cover (first eductor), 0.25 in. (6.35 mm) OD
21. Motor coolant filter later by a qualified technician as necessary for oil return. A normal operating setting for the valve may range from full closed to two turns open.
viicciin g.. IIff sse g iiss n ecce allll P on
To ensure proper lubrication and prevent refrigerant from condensing in the oil tank, a 750-watt heater is in a well in the oil tank. The heater is used to warm the oil while the unit is off. With the default settings for R-123, the oil heater is de-energized when the unit starts. With the default settings for R-514A, Running Oil
Temperature Control is enabled, and the Running Oil
Temperature Setpoint is factory-programmed at 100°F
(37.8°C). With either refrigerant, the heater energizes as needed to maintain 140°F to 145°F (60.0°C to 62.8°C) when the chiller is not running.
With R-123 and mineral oil, when the chiller is operating, the temperature of the oil tank is typically
100°F to 160°F (37.8°C to 71.1°C). With R-514A, solid state oil heater control is installed and enabled. The oil return lines from the thrust and journal bearings transport oil and some seal leakage refrigerant. The oil return lines are routed into a manifold and separator under the motor. Gas flow exits the top of the manifold and is vented to the evaporator. Oil exits the bottom of the manifold and returns to the tank. Separation of the seal leakage gas in the separator keeps this gas out of the tank.
A dual eductor system is used to reclaim oil from the suction cover and the evaporator, and deposit it back into the oil tank. These eductors use high-pressure condenser gas to draw the oil from the suction cover and evaporator to the eductors and then discharge into the oil tank. The evaporator eductor line has a shut-off valve mounted by the evaporator.The shut-off valve will be set during commissioning, but may be adjusted
sump’s normal operating oil level may vary from just below the bottom sight glass to near the top of the upper sight glass.
Liquid refrigerant is used to cool the oil supply to both the thrust bearing and journal bearings. On refrigerant pump units, the oil cooler is located inside the economizer and uses refrigerant passing from the condenser to evaporator to cool the oil. Oil leaves the oil cooler and flows to both the thrust and journal bearings.
Motor Cooling System
Compressor motors are cooled with liquid refrigerant
(refer to
Figure 48, p. 69 ). The refrigerant pump is
located on the front of the oil tank (motor inside the oil tank). The refrigerant pump inlet is connected to the well at the bottom of the condenser. The connection is on the side where a weir ensures a preferential supply of liquid refrigerant. Refrigerant is delivered to the motor via the pump. An in-line filter is installed (replace the in-line filter only with major service). Motor refrigerant drain lines are routed to the condenser.
Tracer AdaptiView Display
Information is tailored to operators, service technicians, and owners.
When operating a chiller, there is specific information you need on a day-to-day basis—setpoints, limits, diagnostic information, and reports.
Day-to-day operational information is presented at the display. Logically organized groups of information— chiller modes of operation, active diagnostics, settings, graphs, and reports put information conveniently at your fingertips. For more information, refer to
Tracer
AdaptiView Display for Water-Cooled CenTraVac
Chillers Operations Guide
(CTV-SVU01*-EN).
70 CVHE-SVX02M-EN
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