Chiller Fault Finding

Chiller Fault Finding is divided into:

1. Chiller failures in the refrigeration cycle.
2. Chiller failures in the control system.
3. Chiller failures originating in the hydraulic circuit.

Chiller failures in the refrigeration cycle include:

• Low suction pressure in a chiller:
  • Caused by a lower amount of refrigerant in the circuit due to leaks or improper recharge.
  • Insufficient water flow through the cooler or evaporator compared to the chiller’s capacity.
  • Reduced thermal load in the application.
  • Inadequate chiller control strategy with an excessive number of compressors operating.
  • Issues with the expansion valve or temperature sensors.
  • Lack of maintenance and poor cleaning of the evaporator.
  • Chiller not adequately adapted to partial loads due to low IPLV values.
• Compressor with a flooded start:
  • Occurs when refrigerant migrates into the compressor crankcase while it is off.
  • Migration is caused by temperature, concentration, and pressure differences.
  • The presence of liquid refrigerant in the crankcase displaces and dilutes the compressor oil, leading to wear in vital parts.
  • Proper operation of the heating elements in the compressor crankcase and adherence to manufacturer’s design and control strategies are crucial to prevent this failure.
• Refrigerant liquid in the suction of the compressor in operation:
  • Refrigerant should only enter the suction of the chiller compressor in a vapor state.
  • Liquid refrigerant cannot be compressed by the compressor and can cause severe damage.
  • Improper control strategies or issues with the expansion valve can result in liquid refrigerant in the compressor suction.
  • Modern chillers may experience inadequate control strategies due to sensor problems.
  • Proper functioning of the expansion valve is essential to eliminate this problem.
• High discharge temperature:
  • High discharge temperatures degrade the compressor oil and affect vital properties such as viscosity.
  • Potential causes should be investigated and addressed.
• Lubrication-related failures:
  • Check oil traps, the compressor station’s lubrication system, oil separator, and details in new installations such as pipe diameter.

What failure presents the compressor according to the color of the oil?

• Colorless or light yellow:
  • Indicates good performance.
• Black oil:
  • Indicates carbonization caused by air in the system or the presence of wear particles containing iron.
  • Change compressor oil and oil filter.
• Light brown oil:
  • Use an acid test kit to test for acidity in a sample of the compressor oil.
  • Change the compressor oil if the test indicates acidity.
  • Indicates that dissimilar metal surfaces have become coated with copper due to moisture in the system.
• Brown oil:
  • Indicates air in the system or high compressor temperature.
  • Chemicals can cause oxidation, resulting in the oil turning brown.
  • Change compressor oil if the test indicates acidity.
  • Copper plating may occur due to moisture combining with the refrigerant, forming an acidic solution that dissolves copper-containing materials.
  • Inspect and replace worn or damaged components.
• Metallic gray oil:
  • Indicates the presence of wear and particles containing aluminum.
  • Usually caused by bearing wear or piston scoring.
  • Disassemble the compressor and inspect for worn or damaged components.
  • Change the oil and oil filter.
• Green oil:
  • Green compressor oil indicates water in the system, and copper coating may have occurred.
  • Disassemble the compressor and shaft seal.
  • Inspect wheels, gears, and rotors.
  • Replace the oil separator, oil, and oil filter.

What are the breakdowns of a chiller evaporator?

The problems in the evaporator of a chiller are presented by:

• A dirty evaporator with scale buildup that hinders heat exchange between the refrigerant in the refrigeration circuit and the chilled water.
• A low flow of water to be cooled can cause the evaporator to freeze.
• A low refrigerant charge in the chiller’s refrigeration cycle can result in poor cooling quality.
• Inadequate chiller control strategies can lead to excess or insufficient cooling in the chiller evaporator.
• Failure of water or chiller refrigerant temperature sensors can result in inadequate control strategies.

Chiller condenser high-pressure faults:

Depending on the cooling method of the condenser, the following issues may arise:

• For air-cooled condensers, verify the adequate fan speed.
• Check the condition and cleanliness of the condenser for efficient thermal exchange.
• If the condenser is water-cooled, check for the concentration of embedded particles on the condenser walls that may impede heat exchange.
• Insufficient cooling tower performance can hinder proper freshwater conditioning.

Chiller failures in the control system:

Chiller sensor failures:

• Temperature sensor failures:
  • Temperature sensors in chillers are often of the thermoresistance type.
  • Resistance thermometers, such as the PT1000, provide linear temperature signals.
  • Use an acid test kit to check the acidity of the compressor oil sample.
  • Change the compressor oil if the test indicates acidity.
  • Failure of temperature sensors can cause the unit to stop to prevent damage due to insufficient water flow.
  • The compressor discharge temperature sensor informs the controller of the superheated steam temperature at the compressor outlet.
  • Monitor values provided by the temperature sensor to prevent damage to the oil or compressor components.
• Pressure sensor failures:
  • The discharge pressure sensor allows control measures to be taken to prevent chiller problems.
  • The suction pressure sensor recognizes refrigerant overheating at the chiller evaporator outlet.
  • Use a digital multimeter to measure the supply voltage and signal and a pressure gauge to measure exact pressures.
  • Compare the pressure values from the gauge with those transformed by the sensor.
  • If the pressure sensors send out-of-range signals to the controller, the equipment will be stopped.

Ensure proper functioning of sensors and address any faults in the thermistor, engine cooling system solenoid, or wiring.

Hydraulic circuit failures:

Air inside pipes: Air can be introduced into the pipes, affecting heat exchange. The percentage of air dissolved in the water depends on the temperature and pressure. Higher pressure leads to a higher content of dissolved air in the water. With higher temperatures, the dissolved air content decreases. Under conditions of high temperature and low pressure, oxygen is released in greater proportion. Changes in pipe slope cause pressure variations that can release dissolved air, forming air pockets. The air pockets move through the pipeline and accumulate in higher areas. Air pockets also accumulate in exchangers, affecting their performance.

Issues with the expansion vessel: The expansion vessel has a gas-filled membrane that can absorb changes in water volume without affecting the system. To avoid failures, it is necessary to know the manometric height and the minimum and maximum working pressures when calculating an expansion vessel. Having very large or small vessels does not achieve the desired function. The operation of the vessel at different locations (highest point, basement, before or after pumping equipment) differs. A pressure measuring device should be installed in the supply line to the vessel as a standard requirement. The expansion vessel marks the reference pressure value of the closed circuit. Pressure measuring equipment must be installed in the supply line to the vessel.

Failures with pumps in installations with chillers: Installations with chillers require centrifugal pumps to move water through the pipes.

PRIMARY PUMPS: Responsible for sending water to the chiller.

SECONDARY PUMPS: Responsible for sending chilled water to the desired point.

CONDENSER PUMPS: In the case of chillers with a water-cooled condenser, an additional pump system is required to deliver water to the condenser and cooling tower.

Possible pump failures and solutions:

• Pump on but no water supply:
  • Verify that the suction pipe is full and free of air or obstructions.
  • Check the condition of the foot valve and filter for any blockages.
  • If there is no water in the suction pipe, prime the pump by removing the priming plug and adding water until no air comes out and the water overflows. If the pipe doesn’t fill, replace the foot valve.
  • Check the motor’s rotation direction.
• Low water flow:
  • Air ingress in the suction pipe or through the seal.
  • If the pump has gaskets, replace them if excessive fluid leakage is observed.
• Motor overload:
  • Check if the equipment is operating within the correct range.
  • Throttle the discharge valve to decrease pump flow.
  • Inspect impeller blades for damage that may cause imbalance and vibrations affecting motor operation.
  • Check motor bearings, pump shaft, and insulation in motor coils.
  • Ensure proper alignment.
  • Loss of prime in the pump.
  • Defective foot valve and water leakage.
  • Water leaks due to damaged seals or gaskets.
  • Leaks in piping or fittings.
  • Air ingress in the suction pipe or excessive leakage in the discharge area.
  • Premature failure of seals or gaskets.
  • Unbalance or misalignment.
  • Lack of lubrication.
  • Verify that the pump is not running idle.