Maintenance and Repair of Screw Type Cold Water Heaters

Screw chiller is a kind of vapor compression refrigeration unit.

It is named because of the selection of screw compressor. It is mainly composed of screw refrigeration compressor, condenser, evaporator, electric control components, instruments, etc. Due to its advantages of compact structure, small size, few wearing parts, simple and convenient use and maintenance, and high operation stability and reliability, it is currently widely used in large-scale industrial refrigeration and central air conditioning systems.

The screw chiller unit is generally used for about 3000 hours per year.

In order to ensure the long-term safe and reliable normal operation of the unit and prolong the service life of long-term use and reduce operating costs, regular scientific maintenance and care of the unit are very important.

I. Maintenance of main components
(1) During operation, pay close attention to the exhaust and suction pressures of the system. If any abnormality is found, find the cause in time and troubleshoot.
(2) Do not adjust the set points of control and protection elements arbitrarily.
(3) Regularly check whether the electrical wiring is loose. If it is loose, tighten it in time.
(4) Regularly check the reliability of electrical components and replace failed or unreliable components in time.

II. Descaling
After long-term operation, the heat transfer surface on the water side of the shell-and-tube heat exchanger of the unit will deposit calcium oxide or other minerals. When there are many scales on the heat transfer surface, it will affect the heat transfer performance and lead to an increase in power consumption and an increase in exhaust pressure. Organic acids such as formic acid, citric acid, and acetic acid can be used for cleaning.

III. Start-up and shutdown
When shutting down in winter, clean the inner and outer surfaces of the unit and dry it; the drain valve must be opened to drain the water stored in the shell-and-tube heat exchanger to prevent freezing accidents.

Start-up in spring
When starting the unit after a long shutdown, the following preparations should be made:
(1) Thoroughly inspect and clean the unit.
(2) Clean the water pipeline system.
(3) Check the water pump.
(4) Tighten all line connectors.
(5) Preheat the unit compressor as required.

IV. Complete refrigerant leakage
If this happens, use high-pressure nitrogen (15-20 kilograms of air pressure) or refrigerant to detect leaks in the system. If welding is required, the gas in the system must be exhausted before welding. Before filling refrigerant, the entire refrigeration system must be dry and evacuated.

Refilling refrigerant
(1) Connect the refrigerant filling bottle to the fluorine injection nozzle on the suction pipe of the compressor.
(2) Start the unit while circulating chilled/cooling water.
(3) Slowly fill the refrigerant into the system and check the suction and exhaust pressures.
(4) Note: When conducting leak detection and airtightness tests, never fill oxygen, acetylene, etc. into the refrigeration system.

V. System antifreeze
If serious icing occurs in the flow channel of the shell-and-tube heat exchanger, it may cause the shell-and-tube heat exchanger to rupture and leak. Frozen cracking damage is not covered by the warranty. Therefore, special attention should be paid to the antifreeze of the unit. When the unit is shut down for standby at a lower ambient temperature, if the unit is placed outdoors and the ambient temperature is lower than 0°C, the water in the evaporator and condenser must be drained completely. See the drain mark on the whole machine for the specific operation steps of draining water.

During operation, if the chilled water flow switch fails, it may cause the water pipe to freeze.

Therefore, the flow switch must be interlocked with the unit. During maintenance, when filling refrigerant into the unit or draining refrigerant for maintenance, it may cause the water in the evaporator to freeze. Be sure to keep the water in the evaporator flowing or drain the water completely.