T.S. Patriot State Engineering Manual

Patriot State was the training ship of the Massachusetts Maritime Academy from 1986 to 1998.

Refrigeration Plant Operation

Safety Considerations for R-12

  1. R-12, Dichloro-diflouro-methane is a non-toxic, odorless, colorless gas at room temperature, but if itis exposed to extreme heat (900°F) or open flame, an acrid (rotten egg) smell will develop - this is a toxic gas (phosgene gas)! When making a round, if the cadet notices this smell, vacate immediately and notify the Engineer on watch.
  2. When a leak is expected or noticed, never feel with a bare hand. Freeze burns can develop upon contact with R-12.
  3. Never open to atmosphere any part of the R-12 plant! It is Illegal to vent R-12 to the atmosphere. Proper procedures must be met for vapor recovery of HCFC refrigerants.
  4. If on watch oil is noticed leaking, Freon is also leaking. Notify the Watch Engineer.

Refrigeration Facts

  1. Each of the four R-12 units is 8.55 tons
  2. One refrigeration ton is equal to the energy required to melt 2000 lbs. (1 ton) of ice at 32° F., in 24 hours
  3. The latent heat of fusion of water (or ice) is 144 BTUs
  4. Therefore, 144 BTU x 2000 lbs. = 288,000 BTU/TON/DAY of refrigerating capacity
  5. Adjusted one ton of refrigeration capacity is equal to 12,000 BTUs of heat removed per hour and each unit is capable of 8.55 tons

Starting Procedures For R-12 Cargo Units Or Ship's Stores Units

Before the system is put into operation, the following valves should be in the following position:

Normally Open

  1. Condenser Inlet and Outlet Valves
  2. Condenser - Receiver Equalizing Line Valve.
  3. Condenser Water Regulator Control Line Valves.
  4. Suction Pressure Regulator Cutouts (If provided)
  5. Cooling Coil Outlet Valves (If provided)
  6. Heat Exchanger Suction and Liquid Line Valves.

Normally Closed

  1. Purge Valve
  2. Charging Valve
  3. Dryer Cutout Valves
  4. Hand Expansion valves.
  5. Liquid By-pass Valve for Heat Exchanger (If provided)
  6. Drain Valves.

Proceed as follows:

  1. Insure a lube oil level exists in the compressor crankcase about 3/4 of a glass is sufficient.
  2. Insure an R-12 level exists in the receiver about 1/2 to 3/4 on the gauge.
  3. Provide a cooling water flow through the condenser in the engine room (sanitary water is the cooling medium); on the foc'sle deck (1 hold - glycol cools the condenser); open the cooling water by-pass valves to insure flow, vent air from water side at top of condenser head.
  4. Start air circulating fans for all of the spaces being cooled
  5. Provide power to solenoid valves
  6. Line up the R-12 piping:
    1. open discharge of compressor
    2. open outlet of condenser
    3. open outlet of receiver
    4. open suction valve about 1/2 turn
    5. open TEV and solenoid stop valves at each box
  7. Start compressor (push reset, then push start button):
    1. slowly open suction valve, but maintain a positive suction pressure
    2. also, as Freon flows through the system, compressor oil will travel with it, insure an oil level is maintained in the crankcase. Check oil pressure (it should be between 35-50 psi)
  8. Adjust cooling water by-pass valve to maintain 125 psi, discharge pressure:
    1. opening by-pass brings head pressure down -closing by-pass brings head pressure up
  9. Continuously monitor compressor operation for 15 minutes:
    1. discharge pressure 125-130 psi.
    2. suction pressure 2-5 psi
    3. oil pressure (normally 35-50 psi)
  10. Make rounds of boxes to insure temperatures are coming down.

Starting Procedure for Carrier Compressor (Turbine)

  1. Check oil levels, etc., for compressor, turbine, couplings, etc.
  2. Start sea water circulation through condenser. Avoid water hammer.
  3. Start water or brine circulation through cooler. Avoid water hammer.
  4. Be sure air pressure is available for the air operated controls (the temperature recorder-controller and the hot gas bypass thermostat).
  5. If a great deal of air is in the machine, run purge unit to remove it. This will practically never be necessary unless a vacuum of more than ten inches has broken by admitting air. In any case, start the purge recovery unit before the machine. The purge unit should be left in operation while the main machine is running.
  6. The Fulscope recorder-controller is equipped with an "Automatic to Manual" switch. With control air supplied to the controller, the machine may be started either under Manual or Automatic control. With the switch in the "Manual" position, control air bleed to the turbine air motor is accomplished by use of a hand regulator. Air pressure is read on the branch air gauge for manual control.
  7. Warm up the turbine as required. Refer to the manufacturer's instructions.
  8. Depress the compressor "start" pushbutton on the control panel and set the solenoid trip mechanism at the turbine. Bring the turbine up to speed as soon as possible. The turbine should not be idled at low speeds since this may cause possible damage to the seal of the compressor. (Due to the delayed action of the timed relay after the "start" pushbutton is depressed, the operator has approximately three minutes in which to start and bring the turbine up to speed).
  9. Observe the seal oil gauge to see if oil pressure is developed. If oil pressure does not develop within the time allowed by the time delay relay after start up, the turbine will stop. This occurs due to the opening of the time delay relay contact and the failure of the oil pressure switches to close.
  10. If the machine was started under manual control, it may now be brought under the supervision of the automatic speed control system. The transfer of control is accomplished at the recorder-controller.
  11. Open cooling water valve supplying compressor oil cooler, turbine oil cooler and compressor seal jacket. The water to compressor oil cooler should be kept low until the highest bearing temperature reaches 130° F. Then adjust to give 140° F. to 180° F. bearing temperature. Observe the temperatures of all compressor and turbine bearings until they have leveled off at a satisfactory point.

Immediately after starting, there may be a period of surging until evacuation of air from the condenser has been completed. During this period, the machine should be run at high speed. The high speed will produce a high condenser pressure and accelerate the process of purging. However, the condenser pressure should not exceed 15 psi gauge during this period. Do not overcool the evaporator or the non-freeze control will stop the machine. As soon as the machine has steadied and all of the air has been purged, the speed may be manually adjusted to give the desired "brine" temperature or the control may be transferred to automatic.

Surging that persists after all of the air has been purged and speed has been adjusted to give the desired brine temperature is an indication of a light load. Surging operation is perfectly normal for centrifugal compressors and is no cause for alarm. At very low loads, (10% to 20% of full load) surging will cause the compressor to overheat and bearing temperatures will go above normal. Continuous operation under such conditions is inadvisable. For operation under these extremely light load conditions an automatic hot gas by-pass system is provided.

Starting Procedure for Carrier Compressor (Electric)

  1. Omit turbine start up steps.
  2. When starting electric motor, notify watch as it will draw up to 600 amps.
  3. Use caution when switching over both the cooling water circulators and brine circulators. The discharge from the pump on line will cause the pump being started to spin. Keep the pump discharge (for the pump being started) closed until after the pump is started. Open immediately once started.

Starting Procedure for York Compressor

  1. Start the chilled liquid pump(s). The chilled liquid flow switch interlock will not allow the Turbopak to start unless liquid flow is established through the unit.
  2. To start the Turbopak, depress the "START-ON-STOP RESET" switch to the "START" position. (If the unit was previously started, depress the switch to "RESET" and then depress the switch in the "START" position.) (This will turn off lights, placing them in an operating mode for the purpose of indicating any unit malfunction.) The Prerotation Vanes are closed automatically to prevent over- loading the compressor on start-up.
  3. The oil pump will start to pump oil and begin a 30 second pre-run to establish adequate lubrication to all bearings, gears and rotating surfaces within the compressor. The oil pressure (OP) and high oil temperature (HOT) are in operating position to sense any malfunction in the oil lubrication system.
  4. If the oil pressure has been established and all safety controls are satisfied at the end of the 30 second pre-run, the condenser water pump will start automatically to establish water flow through the condenser and the York solid state starter or the electro-mechanical starter will start the compressor. The anti-recycle light will light to indicate a 30 minute delay before another start is permitted.

After the compressor reaches its operating speed, the Prerotation Vanes will begin to open under the control of the solid state Temperature Module (TM) which senses the leaving chilled liquid temperature. The unit capacity will vary to maintain leaving chilled liquid temperature. The Prerotation Vanes are modulated by an actuator under the control of the solid state temperature module (TM) A drop in chilled liquid temperature will cause the actuator to close the Prerotation Vanes to decrease the Turbopak capacity. When the chilled liquid temperature rises the actuator will open the Prerotation Vanes to increase the Turbopak capacity.

However, the current draw (amperes) by the compressor motor cannot exceed the setting of Maximum Load Adjustment in percent at any time during the unit operation since the solid state overload current limiter (CM) will override the temperature control module (TM) and prevent the Prerotation Vanes from opening beyond the Maximum Load Adjustment in percent setting.

If the load continues to decrease after the Prerotation Vanes are entirely closed, the Turbopak will be shutdown by the Low Water Temperature Cutout (LWT), lighting the Low Water Temperature Cutout amber light. The LWT is part of the solid state temperature module (TM). During normal operating periods, the Prerotation Vanes will modulate in accordance with load requirements and the unit will cycle on and off, automatically under the control of the TM.

Hot Gas Defrost Procedure: No. 1 Hold R-12 Units

Hot gas defrosting is a procedure which utilizes the hot gases (Freon) from the compressor which gets pumped directly into the cooling (evaporator) coils. The hot gases condense inside the cooling coils, gets expanded by a hand expansion flow control valve and is sent either through another evaporator coil or a reevaporator before returning to the suction side of the compressor.

The procedure is as follows:

Notify Reefer Engineer and Watch Personnel before starting!

  1. Secure power to freeze box solenoid valve (lower switch)
  2. Close inlet and outlet valves to Thermostatic Expansion Valve (TEV)
  3. Close Back Pressure Regulator (BPR) bypass valve
  4. Shut compressor off
  5. Secure freeze box recirculating fan -open drain valves (2) for evaporator cond. -energize drain line heater
  6. Close compressor discharge valve to condenser
  7. Open hot gas valve from compressor discharge line
  8. Open hot gas valve at inlet to freeze box evaporator
  9. Open hand expansion valve (located in overhead between R-12 machines)
  10. Secure power to chill box solenoid valve -close inlet and outlet to TEV
  11. Open BPR bypass two (2) turns on chill box
  12. Start compressor
  13. Load up all cylinders (back out control valve stem)
  14. If compressor suction is in a vacuum, open hand expansion valve on liquid line to chill box about three (3) turns -this feeds refrigerant into defrost loop
  15. Close valve when suction pressure is approximately 5 psi

    Be sure not to open the hand expansion valve too much! Feeding the evaporator with too much liquid could cause slugging at compressor! Watch for frost on suction valve. This is an indication of liquid returning to suction of compressor.

  16. Adding refrigerant to defrost loop may have to be repeated to keep suction pressure from running in a vacuum.
  17. Check the freeze evaporator for defrosting. There should be a definite indication of defrosting by water draining away from evaporator and down drain.
  18. As the evaporator becomes defrosted, the compressor discharge pressure will rise. It will become necessary to open the discharge valve to the condenser to maintain the discharge pressure below 150 psi. (the high pressure. cutout point).

    Make sure that when bleeding off excess pressure to the condenser, that the suction pressure does not drop below 5 psi. If suction pressure decreases as excess pressure is being bled, close discharge valve to condenser and continue defrost.

  19. When evaporator is completely defrosted and no more water is draining from coil, defrost is complete.
  20. Secure compressor.
  21. Close both hot gas defrost valves.
  22. Open compressor discharge to condenser valve.
  23. Open freeze box BPR bypass valve.
  24. Close hand expansion valve between R-12 units.
  25. Close chill box BPR bypass valve.
  26. Make sure all water has drained from freeze box condensate pan.. Close drain valves and secure drain heaters.
  27. Make sure evaporator inspection door is closed and dogged.
  28. Start recirculating fan on slow. When up to speed, place fan on fast.
  29. Start compressor.
  30. Energize freeze box solenoid and open TEV inlet and outlet valves. Check to see if TEV is feeding evaporator by:
    1. placing hand over TEV power assembly (refrigerant can be felt passing through valve )
    2. watching superheat thermometer drop in temperature
  31. Watch compressor discharge pressure and regulate to maintain 125-135 psi.
  32. Make sure compressor is fully loaded
  33. Frost may appear on suction valve due to overfeeding of freeze box TEV. This is normal. However, at no time should there be a "knocking" sound coming from the compressor or the frost line reach the shaft seal. If this happens, secure the compressor.
  34. When suction pressure reaches 10 psi or when chill box reaches 40° F., energize chill box solenoid valve and open inlet and outlet TEV valves.
  35. Watch all temperatures and pressures until machine settles out. Make sure freeze box temperature is going down.

Trouble Shooting for R-12 Units

The refrigeration units aboard, both forward and on the reefer flat do not cycle off automatically, so if the running unit has stopped, there must be a reason and it should be corrected.

Causes of low suction pressure (running in a vacuum)

  1. lack of refrigerant in the system (low or empty receiver, bubbles in the bullseye)
  2. moisture freezing at TEV's
  3. clogged suction filter/strainer
  4. insufficient load for the compressor

Causes of high suction pressure (above 10 psi)

  1. too much refrigerant charged in the system
  2. air in the system, (vent air at condenser leads)
  3. hand expansion valve possibly open at box (accompanied by frost at suction side)
  4. too much load on the compressor
  5. TEV overfeeding

Causes of high discharge (head) pressure

  1. air in the system
  2. lack of cooling water flow through condenser
  3. overcharge of R-12

Low discharge (head) pressure

  1. too much cooling water flow through condenser
  2. insufficient charge of R-12
  3. faulty discharge valves

Trouble Shooting for Carrier Units

  1. Purge unit should run with a suction of 30" vacuum, discharge of 80 psi.
    1. If not, check that the unit is correctly lined up.
    2. Check for excessive water/Freon in site glasses.
    3. Check for proper lube oil level.
  2. Compressor unit should run at suction of 0 psi, discharge of 7 psi (varies with load)
    1. If discharge is running in or near a vacuum, raise pressure by closing condenser discharge valve.
    2. Keep lube oil pressure to bearings at or above 3 psi. If it drops below, check with the Watch Engineer and shut down A.S.A.P.
    3. Brine out should be between 42° - 45° F. Adjust by opening damper, adjusting hot gas bypass or speeding up the turbine (to be made by Watch Engineer).

Direct comments to William Haynes whaynes@maritime.edu
Mon, Jul 1, 1996
TSPS Engineering Manual ©1995 Massachusetts Maritime Academy