In many industrial processes, large quantities of heat are generated, which must be dissipated as quickly as possible in order to prevent damage to sensitive equipment and to maintain the quality of finished products. Most of the companies need to use screw chillers. So it is vital to understand how to maintain the screw chiller to keep it operational for as long as possible.

Correctly Commissioning, Startup, and Shutdown Procedures the screw chiller is crucial for the proper operation of the cooling system unit, saving energy, and extending its service life.

During the installation of large and medium-sized cooling systems, commissioning should first be required by the design drawings, familiar with the layout and connection of the entire system, to understand the shape and structure of each device and component, as well as the electrical control system and water supply system.

Therefore, refrigeration and plumbing engineers should participate in the commissioning. Before commissioning, users should carefully read the product operation manual provided by the factory, and proceed according to the instructions. Operators must receive special training from the factory and obtain the certification of the unit before they are allowed to operate it, in order to prevent fatal damage to the equipment from incorrect operation.



The following is an overview of how to commission, startup and shut down a screw chiller:

A. Pre-commissioning preparation of the screw chiller

(1)Because the screw chiller is part of the large water chiller system, it requires tight coordination of the design, installation, and use of the three aspects during commissioning. For the commissioning process to proceed in an orderly fashion, the relevant parties should form a temporary trial run team to become fully familiar with the commissioning process.

(2) The personnel responsible for commissioning should be fully familiar with the construction and performance of the unit equipment, familiar with water chiller system safety technology, clear methods, steps, and technical requirements to be achieved for commissioning, develop a detailed and specific commissioning plan, and make the commissioning personnel of each post clear about their tasks and requirements.

(3) Check whether the installation of the water chiller unit meets the technical requirements, whether the foundation of the unit meets the requirements, and whether the size, specification, and material of the connecting pipeline meet the design requirements.

(4) The power supply system of the unit should be fully installed and passed the commissioning.

(5) The cold water and cooling water system should be tested separately, the dirt in the waterway system should be flushed, the pump should work normally, and the circulating water volume should meet the requirements of working conditions.

(6) Clean up the environmental site for commissioning to be clean, bright, and clear.

(7) Prepare all kinds of general tools and special tools needed for commissioning.

(8) Prepare all kinds of pressure, temperature, flow, quality, time, and other measuring instruments and meters required for debugging.

(9) Prepare the necessary safety protection equipment for commissioning operation


B. Screw Chiller Commissioning

After the end of refrigerant charging (such as the need to charge refrigerant), load commissioning can be carried out. As the screw chiller unit has made great progress in performance and electrical control in recent years, many chiller units can do simulated action check side of the main electric control system before the official start-up, that is, the screw chiller unit host is not energized, the control system is energized, and then the electric control system of the unit is tested through the internal setting of the unit, and whether the components are running normally. If there is any problem with the electronic control system, it can be solved in time. Finally, the main unit is powered on again for commissioning. In the commissioning process, special attention should be paid to the following points:

a. Check whether the valves in the water chiller system are in the normally open state, especially the exhaust shut-off valve, do not close.

b. Open the cooling water valve of the condenser and the cold water valve of the evaporator, and the flow of cold water and cooling water should meet the requirements proposed by the factory.

c. Pay attention to observing whether the power supply voltage of the unit is normal before starting.

d. Start the unit according to the start-up manual provided by the factory.

e. After the unit is started, check whether the parameters of the unit are normal according to the start-up manual provided by the factory.

f. The data of the unit can be recorded according to the unit operation data record sheet provided by the factory, especially some main parameters that must be recorded clearly.

g. During the operation of the unit, attention should be paid to whether the pressure of the compressor is working normally.

h. The safety protection devices installed in the cooling system, such as high and low-pressure protection devices, cold water and cooling water cut-off flow switches, safety valves, and other equipment should be used correctly and replaced in time if damaged.

i. If the chiller unit appears abnormal, it should be stopped immediately for an inspection.

Be sure to clean and dry the interior of the air conditioning system before you commission the Screw Chiller system. Before commissioning the Screw Chiller, clean and dry the interior of the air conditioning system thoroughly. By not carefully completing the preliminary work, during the commissioning, many people will be overworked, and there will be many hidden dangers to the cooling unit’s future operation.


C. The Screw Chiller Start-up Procedures

Screw chiller compressor after a trial run operation, and the problems found between the processing, you can enter the normal operating procedures.

The operation method is:

  1. Confirm whether the status of each valve in the cooling unit is in line with the start-up requirements.
  2.  Supply power to the electrical control device of the cooling unit and turn on the power switch to make the power control indicator light on.
  3. Start the cooling water pump, cooling tower fan, and water pump, and you should see the operation indicator light of the three.
  4. Check whether the lubricant oil temperature reaches 30 ℃. If less than 30 ℃, should open the electric heater for heating, at the same time can start the oil pump, make the lubricating oil circulation temperature evenly rise.
  5. After the oil pump starts running, the energy regulating control valve will be in the load-reducing position and make sure the slide valve is in the zero position.
  6. Adjust the oil pressure regulating valve. Make the oil pressure reach 0.5~0.6MPa.
  7. Close the compressor power supply, start the control switch, open the compressor suction valve, after the delay compressor starts running, after the compressor runs for the adjustment of the lubricant pressure, so that it is higher than the exhaust pressure 0.15 ~ 0.3 MPa.
  8. Close the solenoid valve control circuit in the liquid supply line and start the solenoid valve. Supply liquid refrigerant to the evaporator, but the energy regulating device is in the loading position and increase the load step by step as time goes by. At the same time, observe the suction pressure and make the suction pressure stable at 0.36~0.56MPa by adjusting the expansion valve.
  9. After the compressor runs, when the lubricating oil temperature reaches 45 ℃, disconnect the power supply of the electric heater, and at the same time open the inlet and outlet valves of the cooling water of the oil cooler, so that during the operation of the compressor, the oil temperature is controlled within the range of 40~55 ℃.
  10. If the cooling water temperature is low, the fan of the cooling tower can be temporarily closed.
  11. Open the oil injection valve 1/2 ~1 turn, and at the same time, the suction continent and the liquid outlet valve of the unit should be in the fully open position.
  12. Adjust the energy regulating device to 100% position and adjust the expansion valve at the same time to keep the suction superheat above 6℃.
  13. Check the unit during start-up operation. After the unit is started and put into operation, attention should be paid to the inspection of the following contents to ensure the safe operation of the chiller unit.
  • Water pump, cooling tower fan running sound, vibration, pump outlet pressure, water temperature, and other indicators are within the normal operating parameters.
  • Whether the oil temperature of the lubricating oil is below 60 ℃, whether the oil pressure is higher than the exhaust pressure 0.15~0.3MPa, whether the oil level is normal.
  • When the compressor is running at full load, is the suction pressure value within 0.36~0. 56MPa.
  • Whether the compressor exhaust pressure is below 1.55MPa, and whether the exhaust temperature is below 100 ℃.
  • During the operation of the compressor, is the motor running current within the specified range. If the current is too high, it should be adjusted to reduce load operation to prevent the motor from burning due to excessive running current.
  • Whether the sound and vibration of the compressor are normal during operation.


If any of the above is found to be abnormal, the compressor should be stopped immediately to find out the cause and remove the fault before restarting the unit. Do not let the cooling unit run with the problem, so as not to cause major accidents


D. The Normal Operation of the screw chiller compressor

The normal operation of the screw-type compressor are:

  1. the compressor exhaust pressure of 1.8 to 1.47MPa (gauge pressure);
  2. the compressor discharge temperature of 45 ~ 90 ℃, the highest shall not exceed 1.05 ℃;
  3. The oil temperature of the compressor is about 40~55 ℃;
  4. The oil pressure of the compressor is 0.2~0.3MPa (gauge pressure);
  5. The sound during the operation of the compressor should be uniform and smooth, without abnormal sound;
  6. The condensing temperature of the unit should be 3~5 ℃ higher than the cooling water temperature; the temperature of the cold pole should generally be controlled at about 40 ℃, and the temperature of the condenser inlet water should be below 32 ℃;
  7. The evaporation temperature of the unit should be 3~4 ℃ lower than the water outlet temperature of the refrigerant water, and the water outlet temperature of the refrigerant water is generally about 5~7 ℃.


Screw Chiller Project



E: the screw chiller compressor shutdown operation

Screw chiller compressor shutdown is divided into normal shutdown, emergency shutdown, automatic shutdown and long-term shutdown and other shutdown methods.


  • The normal shutdown operation method

(1) The manual unloading control device in the position of load reduction.

(2) Close the solenoid valve and liquid outlet valve on the liquid supply line between the condenser and the swallow.

(3) Stop the compressor operation and close its suction valve at the same time.

(4)Stop the oil pump operation after the energy derating to zero.

(5) Put the energy regulating device in the “stop” position.

(6) Close the cooling water inlet valve of the oil cooler.

(7) Stop the operation of the cooling water pump and cooling tower fan.

(8) Stop the operation of the refrigerant water pump.

(9) Turn off the main power supply.


  •  The emergency shutdown of the screw chiller

Screw chiller compressor in the normal operation process, such as the development of abnormalities; in order to protect the safety of the unit, the implementation of emergency shutdown. The operation method is:

(1) stop the compressor operation.

(2) close the suction valve of the compressor.

(3) Close the solenoid valve on the liquid supply pipe of the unit and the liquid discharge valve of the condenser.

(4) Stop the oil pump.

(5) Close the cooling water inlet valve of the oil cooler.

(6) Stop the water pump, cooling water pump, and cooling tower fan.

(7) Cut off the main power supply.

Unit in the process of operation of power failure, water failure, and other fault stopping methods can refer to the centrifugal compressor emergency stop in the content of the relevant treatment.

After the emergency stop of the screw unit, the cause of the fault should be identified in time, and the unit can be restarted according to the normal starting method after the fault is removed.


  • Automatic shutdown of the screw unit

Screw chiller compressor in the process of operation, if the pressure and temperature value of the unit exceed the specified range, the protection device in the unit control system will come into play and automatically stop the compressor work, this phenomenon is called the automatic shutdown of the unit. When the unit is automatically stopped, the corresponding fault indicator on the electrical control board of the unit will light up to indicate the part where the fault occurs. When this happens, after the main unit stops, the stop operation of other parts can be handled according to the emergency stop method. After completing the shutdown operation, the chiller unit should be inspected and restarted according to the normal starting procedure only after the fault is eliminated.


  • The screw chiller unit’s long-term downtime

As the screw chiller compressor used for the central air conditioning cooling source is a seasonal operation, the unit has a long downtime. In order to ensure the safety of the unit, when shutting down in the season, the shutdown operation can be carried out according to the following methods.

(1 ) When the unit is in normal operation, close the liquid outlet valve of the unit to make the unit run at reduced load and pump all the refrigerant in the unit to the condenser. In order that the unit will not be shut down due to low suction pressure, the setting value of the low-pressure relay can be set to 0.15MPa. When the suction pressure drops to about 0.15MPa, the compressor stops, and when the compressor stops, the low-pressure pressure value can be set back again.

(2) Unload the water in the oil cooler, condenser, and evaporator after stopping operation, and release the residual water to prevent the heat transfer tube inside from freezing in winter.

(3) Close the relevant valves in the chiller unit and check whether there is any leakage.

(4) Start the lubricating oil pump for 10~20min every week, so that the lubricating oil can be evenly distributed to each working surface in the compressor for a long time, to prevent the unit from being shut down for a long time and causing a lack of oil on the surface of the machine parts, which will cause difficulties when restarting the screw water chiller.


The Screw Chiller


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For over 20 decades, Lando Chiller has been manufacturing and maintaining industrial screw chillers. We have experienced and dedicated staff on hand to assist you with all industrial chiller needs.

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