Chiller System Annual Maintenance – Part Two
Chiller – Annual Maintenance
The chiller is technically a heat pump in that it removes the heat energy from the Chilled Loop. The chiller motor inputs enough additional energy to pump the heat absorbed from the building into the higher temperature condenser water loop. It is central to cooling any large facility. When it is not functional, especially where the building has no redundancy, the urgency and cost to repair can become exponential due to the overtime and expediting shipping for parts. Cooler weather offers a chance to perform maintenance on these expensive machines that could prevent failure and costly repairs during the hotter months.
Chiller Annual Maintenance Tasks
a. Pressure test – Depending on the type and quantity of refrigerant your machine uses, by law it must be leak tested at minimum once per year. Some large HFC systems >300KG should have permanent leak detection. However, in such cases a manual leak test should be performed as well as verifying the function of the permanent leak detection system. Any system found to have an Annual or Rolling leak rate greater than 10% of the total charge must by law be repaired within 30 days.
b. Refrigerant analysis – Used to determine refrigerant quality and the presence of contaminates, especially water which can be extremely detrimental to hermetic systems.
2. Heat Exchanger Cleaning
a. The condenser heat exchanger tubes should be inspected and mechanically (brush) cleaned. Even tubes appearing to be clean due to good water treatment can have debris lodged in the hidden end which could potentially cause damage. Internally enhanced tubes can also harbor debris and hidden scale that only an appropriate brush can remove.
b. Air cooled condenser coils at minimum should be cleaned once per year or more often according to the environment it is in.
c. The cooler heat exchanger, systems flowing water on the interior tube surface should also be mechanically cleaned, if not every year then every second to third year or if high approach is indicative of fouled tubes.
d. Coolers that circulate water on the exterior of the heat exchange tube should be flushed at the bottom of the vessel at regular intervals to remove sediment or other fouling agents (see Chilled Water Loop)
3. Eddy Current Testing: Non-destructive testing of heat exchanger tubes.
a. Condenser – Every third year (or more often due to mitigating issues)
b. Cooler – Every fifth year (or more often due to mitigating issues)
4. Lubrication Service
a. Open drive chiller motors should be correctly lubricated at regular intervals with approved grease
b. Open drive system shaft seals check leakage rates and operating pressure.
c. Lubricating oil should be tested prior to the Annual shutdown by a third party lab to determine the necessity of oil replacement. Some operators require their chiller oil to be changed annually while others, use the test method (change determined by analysis). Testing prior to the Annual Shutdown can also be useful in determining the necessity of other repairs that can be pre-planned during the outage, such as bearing inspection, eddy current, etc.
d. Oil return system- clean devices and replace filters
e. Oil filter – replace at recommended intervals, at minimum annually. Field or lab analysis of the filter is also useful in identifying excess wear metals.
f. Test/Calibrate regulator, differential pressure safeties, oil temperature regulating devices, oil level, etc.
5. Starters & Control
a. Chiller motor starter malfunction is often the cause of motor failure, whether X-line, Wye-Delta, Autotransformer or Variable Speed Drive. Inspection, cleaning and testing of components at a regular interval, no less than annually, is absolutely necessary to the life of the motor. Starter mechanisms wear, VFD’s need cleaning to ensure proper cooling and both types have manufacturer’s recommendations for maintenance which should be followed.
b. The chiller motor starter, whether electromechanical or semiconductor, is started and stopped by the system controls or varied by the system capacity controls and safety controls. Pressure switches, temperature switches, actuators, automatic valves, EXV, thermistors, transducers, flow switches, microprocessor controls, etc. should at a minimum be calibrated where possible and tested for accuracy and function once per year.
6. Purge & Capture System – Chiller machines still using low-pressure refrigerants have a system to remove non-condensable gasses while retaining the majority of the refrigerant within the machine. Some purge systems also have a capture system to lower emissions to near-zero. The purge and capture system should be cleaned, tested, usage reviewed and filters replaced. Depending upon the leakage rate of the chiller, pump-out count and duration, the capture tank fills with the refrigerant that the purge did not capture. Consequently, it periodically should be weighed, submitted for recovery and included in the Annual Leak Rate calculation as required by the EPA.
7. Motor/Wiring Insulation Test – Motors & wiring should be tested in accordance with the IEEE43 standards for electrical machinery (See Here)
8. Estimated Performance Test – Comparing chiller operational parameters against the design conditions of that machine is an important tool in assessing its reliability and efficiency. While field performance tests typically can’t duplicate the precision of the manufacturer’s controlled test, accurate field instrumentation can capture chiller parameters with enough precision to estimate its performance compared to design. This tool is especially effective if performed and recorded annually from the time it was new, establishing a baseline for mid-season comparison.
9. Vibration Test – One of the most important predictive tools is the vibration analyzer, capable of measuring imbalance or detecting failing bearings. A chiller vibration test should be performed at minimum annually, ideally bi-monthly taken under similar conditions. Using the data over time, trends can reveal the deterioration of rotating components which can be repaired prior to failing. Reducing imbalance and vibration also helps to prevent piping and fittings from fatiguing or breaking.
10. Cleanliness – At minimum once per year the chiller exterior ought to be cleaned of dust and oil. A clean machine will quickly reveal minor oil and/or refrigerant leakages.