8 Useful Chiller Maintenance Tips

Chillers represent one of the largest capital investment and they are the main contributors to the operating cost in both commercial and institutional facilities. In most organization chillers are the single largest energy users hence the need to maintain them so that they remain efficient and reliable during their operation.

Though some organizations use predictive maintenance including infrared thermography, rotor bar testing and vibration analysis to diagnose any problem chillers could have in advance, preventive maintenance still remains the key in ensuring the efficiency of good performance of chillers.

Efficiency of chillers has steadily improved in the recent past due to improvements in control, equipment design and changes in refrigerant. Due to this, chillers today have tighter operational tolerance which makes regular maintenance critical. The following are 8 useful chiller maintenance tips which are critical for the overall performance of chillers

1. Keep a Daily Operating Log
Chiller operators should document the performance of chillers every day with a detailed and accurate log and regularly compare this performance with the start up and design data so as to detect any inefficiency or problems in advance.

The documented logs can be analyzed and reviewed to provide advance warning of any potential problems.

For example, if chiller operators notice an increase in the condensing pressure in a month, they can refer to the documented operating log and correct the possible cause of the problem which could either be non condensables or fouled condenser tubes.

Chiller manufacturers can provide the recommended data points specific to the equipment if requested. Today’s chillers are controlled using microprocessor controls, therefore, managers can automate the process using microprocessor controlled automation system.

2. Keep the Tubes Clean
A large hindrance to the performance of chillers is heat transfer efficiency. Chillers efficiency rate relate directly to its heat transfer ability that begins with clean condenser and evaporator tubes. Large chillers have long tubing in the heat exchangers and keeping the tubes clean is essential in maintaining high performance.

Chillers performance deteriorates as the tubes become stained and when mud, scale, algae, sludge or other contaminants accumulate on the sides of the tubes. The rate of fouling highly depends on the system type; whether closed or open as well as the quality of water, its temperature and cleanliness. 

Chiller tubes should be cleaned annually, those with closed system should be cleaned at least once in every three years while those with an open system should be inspected and cleaned at least once in every six months.

3. Maintain proper water treatment
Most chillers use water to transfer heat, therefore the water should be treated properly to prevent biological growth, corrosion and scale. A chemical water treatment is required for the closed water system which is typical in chilled water system connected to chiller evaporator.

Open system are usually used for condenser water system connected to chiller condenser. Condenser systems that use cooling towers require chemical water treatment continuously and managers should involve a chemical water treatment vendor who is familiar with local water supply and one who can provide full service maintenance for the entire water system.

In addition, all system strainers should also be cleaned at least once in every three months. If properly maintained, side stream filters and sand filters for condenser systems effectively maintain clean water. To determine if cleaning is required, a technician should monitor any drop in pressure and check manufacturer’s recommendation when cleaning the filters. However, regardless of a drop in pressure, filters should be cleaned quarterly. 

4. Analyze Refrigerant and compressor oil
Regular chemical analysis of refrigerant and oil help to detect any contamination problems before they become severe. Testing usually consist of spectrometric chemical analysis that detects contaminants like metals, acids and moisture that hinder chiller’s efficiency and performance.

This analysis should only be performed by a qualified chemical laboratory technician who specializes in HVAC equipment and should follow the outlined instructions in the manufacturer’s manual.

The analysis process involves taking a sample of the oils when the chiller is operating and changing the oil according to the results of the analysis. The technician should also monitor the oil filters for pressure drop and change them if need be.

Oil analysis helps to detect other problems with chillers including high content of moisture in the oil which signals a problem with the purge unit and changes in oil characteristics which signals the potential development of an unacceptable compressor wear.

Refrigerant testing is used to determine contaminants that can lead to efficiency and reliability problems. Oil is a common contaminant that migrates to the refrigerant.

5. Lower the entering water temperature
Lowering the entering water temperature helps to improve a chiller’s efficiency. Some operators lower the chilled water set point so as to overcome air handler deficiency like dirty coils but this only cures the symptoms but not the problem and it makes the chiller to work harder to achieve the same net cooling effect.

6. Install variable speed drives
Since chillers are one of the largest electrical load in any building, installing variable speed drives offers significant energy saving. Variable speed drives also act as soft starter which helps to lower the inrush current. This is an important factor for chillers operating on power from emergency generators.

7. Check wiring
For efficient motor and starter operation, you should check the safety as well as sensor calibration on the microprocessor controls. Check the electrical connections, switchgear and wiring for the hot spots. To prevent any insulation faults, test the motor windings for resistance to winding to windings and ground. 

Also, check the shaft seal on open drive motors for any leaks and clean the cooling air vents to enhance cooling.

8. Purge non-condensables
Non condensables such as moisture and air can leak in to low pressure chillers since their evaporators work in a vacuum. These non condensables lower chiller’s efficiency by as much as 4 per cent at 60 per cent load and 7 per cent at 100 per cent load. Installing purge units minimizes the effect of non condensables, the modern purge units can limit both refrigerant and ingress loss.