The chiller compressor continuously draws large quanti- ties of refrigerant vapor from the cooler at a rate determined by the amount of guide vane opening. This compressor suc- tion reduces the pressure within the cooler, allowing the liq- uid refrigerant to boil vigorously at a fairly low temperature (typically 38 to 42 F [3 to 6 C]).
The liquid refrigerant obtains the energy needed to va- porize by removing heat from the water or brine in the cooler tubes. The cold water or brine can then be used in air con- ditioning and/or other processes.
After removing heat from the water or brine, the refrig- erant vapor enters the ®rst stage of the compressor, is compressed, and ¯ows into the compressor second stage. Here it is mixed with ¯ash-economizer gas and is further compressed.
Compression raises the refrigerant temperature above that of the water ¯owing through the condenser tubes. When the warm (typically 98 to 102 F [37 to 40 C]) refrig- erant vapor comes into contact with the condenser tubes, the relatively cool condensing water (typically 85 to 95 F [29 to 35 C]) removes some of the heat, and the vapor con- denses into a liquid.
The liquid refrigerant passes through an ori®ce into the FLASC chamber. The coolest condenser water ¯ows through the FLASC and allows a lower saturated temperature and pressure. Part of the entering liquid refrigerant will ¯ash to vapor once it has passed through the FLASC ori®ce, thereby cooling the remaining liquid. The vapor is then recondensed by the condenser water ¯owing through the FLASC chamber.
The subcooled liquid refrigerant drains into a high-side valve chamber that meters the refrigerant liquid into a ¯ash economizer chamber. Pressure in this chamber is interme- diate between condenser and cooler pressures. At this lower pressure, some of the liquid refrigerant ¯ashes to gas, fur- ther cooling the remaining liquid. The ¯ash gas, having ab- sorbed heat, is returned directly to the compressor second stage. Here it is mixed with discharge gas that is already com- pressed by the ®rst-stage impeller. Since the ¯ash gas has to pass through only half the compression cycle to reach con- denser pressure, there is a savings in power.
The cooled liquid refrigerant in the economizer is me- tered through the low-side valve chamber, reducing the re- frigerant pressure. Pressure in the cooler is lower than in the economizer. Some of the liquid ¯ashes as it passes through the low side ¯oat valve. The cycle is now complete.
OIL COOLING CYCLE
Compressor Oil Cooling Ð The compressor oil is water cooled. Water ¯ow through the oil cooler is manually adjusted by a plug valve to maintain an operating tempera- ture at the reservoir of approximately 145 F (63 C). An oil heater in the reservoir helps to prevent oil from being di- luted by the refrigerant. The heater is controlled by the PIC (Product Integrated Control) and is energized when the oil temperature is outside the operating temperature range of 150 to 160 F (66 to 71 C).
External Gear Oil Cooling Ð The external gear oil is also water cooled. Water ¯ow through the gear oil cooler is manually adjusted by a plug valve to maintain an oper- ating temperature of approximately 130 F (54 C). If so equipped, an oil heater in the reservoir helps to maintain the oil tem- perature under cold ambient operating conditions. The heater is controlled by an internal thermostat.
LUBRICATION CYCLE
Compressor Lubrication Cycle (Refer to item numbers shown in Fig. 4) Ð The compressor oil pump and oil reservoir are contained in the compressor base. Oil is pumped through an oil cooler and ®lter to remove heat and any foreign particles. A portion of the oil is then di- rected to the shaft-end bearing and the shaft seal. The bal- ance of the oil lubricates the thrust and journal bearings and the thrust end seal. The bearing and transmission oil returns directly to the reservoir to complete the cycle. Contact-seal oil leakage, however, is collected in an atmospheric ¯oat cham- ber to be pumped back to the main reservoir as the oil accumulates.
Oil may be charged into the compressor oil reservoir (Item 8) through a charging valve (Item 6) which also func- tions as an oil drain. If there is refrigerant in the chiller, how- ever, a hand pump will be required for charging at this connection.
An oil-charging elbow (Item 3) on the seal-oil return cham- ber allows oil to be added without pumping. The seal-oil re- turn pump (Item 4) automatically transfers the oil to the main reservoir. Sight glasses (11) on the reservoir wall permit ob- servation of the oil level.
A motor-driven oil pump (Item 10) discharges oil to an oil cooler/®lter (Item 16) at a rate and pressure controlled by an oil regulator (Item 10). The differential oil pressure (bearing supply versus oil reservoir) is registered on the control panel.
Water ¯ow through the oil cooler is manually adjusted by a plug valve (Item 17) to maintain the oil at an operating temperature of approximately 145 F (63 C). During shut- down, the oil temperature is also maintained at 150 to 160 F (65 to 71 C) by an immersion heater (Item 7) in order to minimize absorption of refrigerant by the oil.
Upon leaving the cooler section of the oil cooler/®lter, the oil is ®ltered (Item 15) and a portion is directed to the seal- end bearing (Item 1) and the shaft seal (Item 2). The remain- der lubricates thrust (Item 14) and journal bearings (Item 12). Thrust bearing temperature is indicated on the PIC controls. Oil from both circuits returns by gravity to the reservoir.
The shaft seal of the open compressor drive must be kept full of lubrication oil, even when the chiller is not operating, to prevent loss of refrigerant.
If the chiller is not operating and the oil pump has not operated during the last 12 hours, the control system auto- matically runs the oil pump for one minute in order to keep the contact seal ®lled with oil.
IMPORTANT: If the control power is to be deener- gized for more than one day, the chiller refrigerant should be pumped over to the economizer/storage vessel.
