As an engineer specializing in refrigeration systems, I’d like to highlight that the most common failures in chiller systems statistically occur in the following order: refrigerant leaks, low water flow due to scale and dirt buildup, compressor failures, and electrical system malfunctions.
In this article, we’ll study chiller failures, divided into the following categories:
- Failures in the refrigeration cycle.
- Failures in the control system.
- Failures in the hydraulic circuit.
Chiller Failures in the Refrigeration Cycle
1. Low Suction Pressure in a Chiller
These are the main causes of low suction pressure in chillers:
- Insufficient refrigerant due to leaks or improper recharge process.
- Reduced water flow through the cooler or evaporator, compared to the chiller’s capacity.
- Low thermal load in the application.
- Inadequate chiller control strategy, such as running too many compressors simultaneously.
- Malfunctions in the expansion valve or temperature sensors.
- Lack of maintenance and poor evaporator cleaning.
- Poor adaptation of the chiller to partial loads due to low IPLV values.
2. Flooded Start-Up in Compressors
During downtime, part of the refrigerant in the system migrates to the compressor’s oil sump due to differences in temperature and pressure. This leads to oil dilution or displacement, causing poor lubrication and wear on vital components upon start-up.
To prevent this:
- Ensure proper operation of crankcase heaters.
- Adhere to the manufacturer’s design, including control strategies or oil traps.
3. Liquid Refrigerant in Compressor Suction
Refrigerant should only enter the compressor in vapor form. Liquid refrigerant can damage the compressor, often caused by:
- Incorrect control strategies, like running excess compressors.
- Faulty expansion valves.
- Sensor malfunctions leading to improper control.
4. High Discharge Temperature
Excessive discharge temperatures degrade oil properties like viscosity. Common causes include:
- High superheat levels at the evaporator outlet.
- Insufficient insulation of the suction pipe.
- Refrigerant misapplication, such as switching from R410A to R32.
- Malfunctioning condensers causing elevated high-side pressure.
5. Lubrication Issues
Frequent causes include:
- Alterations to the original oil traps.
- Improper compressor lubrication system maintenance.
- Malfunctioning oil separators.
- Changes to the chiller’s pipe diameter.
- Incorrect refrigerant retrofitting incompatible with the oil type.
- Oil shortages or compressor model changes.
Oil Color Analysis for Diagnosing Compressor Issues
- Clear or Light Yellow: Normal operation.
- Black: Indicates carbonization, often caused by air or wear particles (iron).
- Light Brown: Test for acidity; indicates copper plating due to system moisture.
- Brown: Suggests oxidation from air or excessive heat.
- Metallic Gray: Indicates wear particles, often aluminum.
- Green: Suggests water in the system, often leading to copper plating.
Chiller Evaporator Failures
Common issues include:
- Dirty evaporators with scale buildup.
- Low water flow, potentially leading to freezing.
- Insufficient refrigerant charge.
- Improper control strategies causing inconsistent cooling.
- Faulty water or refrigerant temperature sensors.
Chiller Condenser Failures
Depending on the condenser type:
- Air-Cooled Condensers: Ensure proper fan operation and cleanliness.
- Water-Cooled Condensers: Check for scale deposits and cooling tower performance.
Chiller Control System Failures
Temperature Sensor Issues
Chiller temperature sensors (often thermoresistances like PT1000) provide critical data for system control. Common issues include:
- Faulty sensors causing improper strategies or system shutdowns.
- PT1000 sensors are more precise and less affected by cable length or resistance compared to PT100 sensors.
Pressure Sensor Issues
Pressure sensors monitor and control key processes. Common problems include:
- Malfunctioning discharge or suction pressure sensors affecting control strategies.
- Testing sensor functionality requires a digital multimeter and a pressure gauge.
Hydraulic Circuit Failures
Air in Pipes
Air trapped in pipes can impact heat exchange. This occurs due to:
- Changes in pressure causing dissolved air to be released.
- Accumulation in high points or exchangers, reducing efficiency.
Expansion Tank Issues
Expansion tanks absorb volume changes in the water circuit. Proper sizing and placement are critical to avoid system malfunctions.
Pump Failures in Chiller Installations
Chiller systems use centrifugal pumps for water distribution. Common problems include:
- Air in suction lines.
- Improper motor rotation.
- Worn impellers or seals.
- Overloaded motors due to operational imbalance.
