Maintaining a chiller is essential to ensure its efficiency and extend its lifespan. Chiller maintenance is categorized into three main types:
1. Preventive Maintenance
These tasks aim to prevent major failures in the chiller. Key activities include:
- Cleaning heat exchangers.
- Recording and monitoring operational parameters, such as temperatures, pressures, and flow rates.
- Checking for potential anomalies in the equipment or the chilled water plant.
Daily operational records help create a history that enables trend analysis and problem prevention. Remote monitoring technologies allow continuous machine inspection and generate reports to identify maintenance needs before issues arise.
2. Predictive Maintenance
This type of maintenance seeks to predict potential failures using advanced tools such as:
- Vibration analysis.
- Refrigerant or oil evaluation.
- Thermography.
These techniques help anticipate problems before they develop into major faults.
3. Corrective Maintenance
Focused on resolving existing problems in the chiller, this often involves:
- Replacing components.
- Repairs that may require the machine to be shut down.
Preventive Maintenance for Water-Cooled Chillers
Chillers that use water as a cooling medium require specific care:
- Water treatment:
- Prevent scaling, corrosion, and biological growth.
- Contaminants in the water can reduce heat transfer and system efficiency.
- Check water quality at least once a year or with remote monitoring.
- Chilled water circuits:
- Insufficient flow reduces efficiency and leads to laminar flow.
- Regularly inspect inlets and outlets for leaks.
- Clean and inspect the sump and cooling coils.
- Piping network:
- Detect corrosion or scaling that may affect system efficiency.
Refrigerant and Glycol Maintenance
- Refrigerant charge:
- Chiller efficiency depends on an adequate refrigerant charge.
- Avoid leaks and the entry of air or moisture into the system.
- Use purge units to minimize the presence of non-condensables.
- Oil analysis:
- Perform spectrometric analysis annually.
- Change the oil based on analysis results.
- Check moisture and contaminant levels.
Electrical Maintenance
- Electrical testing:
- Tighten and clean terminals, starters, and control panels.
- Measure motor voltage and amperage.
- Inspect electrical contacts and disconnects.
Air-Cooled Chiller Maintenance
- Condenser coil inspection:
- Check for corrosion, leaks, or bent fins.
- Fan maintenance:
- Clean fans, lubricate bearings, and adjust belts or couplings as necessary.
- Zone control actuators:
- Inspect, clean, and adjust as needed.
This comprehensive approach ensures that chillers operate at maximum efficiency, reducing operating costs and extending their service life.
Maintenance of the Cold Air Distribution System in Chillers for Air Conditioning
Follow these recommendations:
- Air Distribution Maintenance:
- Inspect dampers controlling the return air flow to ensure proper operation, calibrate them, and lubricate the bearings.
- Inspect and calibrate the fresh air damper; lubricate its bearings as well.
- Check the dryer filter and replace any old, dirty, or damaged filters.
Chiller Water Treatment:
- Glycol Concentration in Chiller Water:
Proper water treatment is crucial for optimal heat exchange in the condenser and evaporator sections. This directly affects the chiller’s efficiency and operating costs.- Closed-loop systems in chiller installations usually require chemical treatment to reduce scaling risks.
- Open-loop systems with water-cooled condensers may need continuous chemical treatment.
- Tailor the water treatment to the unique qualities of the local water source.
- The flow rate should generally be between 3 and 12 feet per second. A lower flow can lead to laminar flow, reducing chiller efficiency, while higher flow rates can cause vibrations, shaking, and potential tube damage.
Chilled Water Maintenance:
- Glycol Maintenance:
- Keep tubes clean for efficient heat transfer. Contaminants like minerals, scales, sludge, algae, and impurities increase thermal resistance and reduce overall performance.
- Monitor approach temperatures as they indicate heat transfer efficiency. Higher approach temperatures signify reduced efficiency.
- Clean condenser tubes with a brush at least annually or as per demand maintenance schedules to remove contaminants.
- Regular chemical treatments and frequent filter replacements keep water clean.
- A dirty system will insulate tube interiors, reducing efficiency, inflating operating costs, and causing downtime.
Condenser Cleaning Techniques:
- Chemical Cleaning:
- Water-cooled condensers should be descaled regularly, at least every six months, depending on water quality and local scaling.
- Acidic solutions break down and dissolve scales. Afterward, neutralize with an alkaline solution and rinse thoroughly with water.
- Advantages: Breaks down mineral scales effectively, restoring tubes to bare metal for optimal performance.
- Disadvantages: Risk of copper tube corrosion, residual liquid disposal challenges, and high chemical costs.
- Physical Cleaning:
- Rod and Brush Cleaning: Involves using metal rods with wire or nylon brushes to clean tubes manually.
- Motor Brush Cleaning: Rotary tube cleaners with air or electric motors use rotating brushes to clean efficiently in one pass.
- Advantages: Cost-effective, no chemicals required, reduced waste disposal, and minimal corrosion risks.
- Disadvantages: Not effective for hard deposits; labor-intensive.
- Advanced Methods:
- Tube Cleaning Guns: Use air or water pressure to shoot cleaning projectiles. Best for light deposits but limited for hard scales.
- In-Line Cleaning Systems: These systems clean while the chiller is active, reducing downtime. They use foam balls or plastic brushes installed in each tube.
- Internally Enhanced Tubes:
- Only rotary tube cleaning is effective for these tubes, which include spirals for improved thermal efficiency. Use bi-directional rotary cleaners to match the tube’s spiral pattern.
Borescope Inspection:
Use a borescope to inspect the internal walls of condenser tubes. This is recommended after chemical or brush cleaning to ensure surfaces are free from scaling, allowing for proper heat exchange.
Chiller Leak Testing:
Conduct monthly inspections of all high-pressure chillers to detect potential refrigerant leaks. Maintaining the appropriate refrigerant charge is essential for optimal efficiency.
Cooling Tower Cleaning:
- Water-cooled chillers require a cooling tower circuit. Since cooling towers are exposed to the environment, clean them quarterly or as needed to remove dirt and small particles.
- Neglected cleaning leads to particle accumulation in condenser tubes, reducing condenser cooling efficiency and overall chiller performance.
Water Flow Check:
Ensure the manufacturer-recommended GPM (gallons per minute) is maintained for both the evaporator and condenser to achieve optimal performance.
Predictive Maintenance for Chillers
Vibration Analysis in Chillers:
Chillers and chilled water plants contain rotating components such as water pumps, compressors, and fans, each with its own operating frequency.
- Frequency values are unique to each part, and any changes in these values can be used to identify early-stage issues.
- Problems such as bearing wear, shaft imbalance, and tolerance degradation can be detected early by studying the operating frequencies of the components in a chiller.
Pipe Analysis Using Eddy Currents:
- An eddy current test, sometimes called a magnetic field test, can reveal corrosion, erosion, mechanical damage, and more.
- This test can also indicate whether the walls of the tubes have thinned over the years.
- The test involves inserting a metal probe that creates a full-circle magnetic field inside the tube. As the probe moves through the tube, the magnetic field either remains stable or shows disturbances, indicating a problem at that specific location.
- It is not necessary to perform an eddy current test every time the tubes are cleaned.
- For chillers, perform this test every 2–3 years.
- For evaporators, perform it every 3–5 years.
What Other Eddy Current Analyses Can Be Performed on Chillers?
Heat exchanger tubes often fail due to leaks caused by internal or external corrosion, erosion, mechanical impacts, stress corrosion cracking, or other reasons. Eddy current analysis can detect, locate, and record:
- Internal and external corrosion
- Scaling, wear, or cracks before they begin to damage the installation
Depending on the tube material, characteristics, and defect type, the following methods are used:
- Conventional Eddy Current Inspection: Applicable to non-ferromagnetic materials (e.g., stainless steel, copper, titanium, admiralty brass, CuNi alloys, Hastelloy).
- Remote Field Eddy Current Inspection: Applicable to ferromagnetic materials (e.g., carbon steel, duplex ferritic alloys).
- Rotary Ultrasonic Probe Inspection (IRIS): Suitable for both ferritic and non-ferritic materials.
Thermographic Analysis of Operating Parts:
- Thermography allows for measuring temperature values remotely without direct contact with the equipment.
- It captures infrared radiation from the electromagnetic spectrum using thermal cameras.
- Thermography is a reliable, safe, and non-invasive predictive technique that captures the heat signature of an object and creates a two-dimensional color image of equipment components. This image can then be used to compare a functional component with a defective one, detecting potential risks.
Corrective Maintenance for Chillers
Heat Exchanger Repairs:
- Heat exchangers are one of the most critical parts for overall energy efficiency.
- Chiller tubes and coils can become dirty or scaled over time, reducing their heat transfer capacity.
- As the condenser’s heat transfer capacity decreases, energy consumption increases, sometimes by 30% or more.
Centrifugal Chiller Repair:
- An initial water flush is a good first step toward cleaner tubes but should not be the only method for improving energy efficiency.
- Deposits may remain adhered to tube walls after cleaning, particularly in tubes with grooves.
- Rotary tube cleaners with spinning brushes can reach these grooves effectively.
Newer rotary tube cleaning systems allow the addition of antimicrobials and corrosion inhibitors to tube surfaces, minimizing future scaling.
- Select the brush carefully based on the type of fouling to be cleaned.
- Softer deposits like algae and mud require different brushes than harder mineral deposits or scaling.
- Chemical descalers can handle tougher accumulations like calcium, rust, and lime.
- Ensure compatibility between chemicals and equipment materials before use.
When Opening the Condenser Head:
- You may find scaling, sludge, bacteria, or solid debris in the tubes, obstructing free water flow and reducing heat exchange efficiency.
- For most chillers, rotary tube cleaners with pressurized water are recommended to remove obstructions quickly.
- For grooved tubes, specialized descaling chemicals are needed for complete removal.
Manufacturers typically allow a maximum scaling thickness of 0.025 m.
- Chemical Cleaning:
- A non-aggressive descaling solution suitable for copper is circulated through the chillers for no more than 7 hours.
- Results are then evaluated with a borescope camera.
