Water Chillers and Maintenance
 parti 4
Extended (long-term) maintenance checks


Extended (long-term) maintenance checks




Extended (long-term) maintenance checks:

1. Every 5 years (or more frequently as the chiller ages), perform eddy current
(electromagnetic) testing of heat exchanger tubes. [This testing will
typically detect tube pits, cracks, and tube wear (thinning).] If only 1–5
tubes are found defective, plug tubes. If more than 5 are found defective,
replace tubes. (Any tube that is replaced as a result of this testing should
be examined and cross-sections cut so the cause of the defects can be
evaluated.)
2. Other components must be serviced, inspected, and/or replaced at the
intervals recommended by the chiller manufacturer.
Recommended maintenance procedures for water-cooled electric-drive rotary
compressor water chillers are as follows:
Daily monitoring/visual inspection: The majority of chiller operating problems
and maintenance needs are discovered by visual inspection and
frequent monitoring of equipment operating parameters.

Monthly, quarterly, and annual preventative maintenance:
1. Clean the evaporator tubes every 2–4 years (annually for chillers serving
air washers or other “open” cooling loads).
2. Clean the condenser tubes every year.
3. Quarterly, calibrate pressure, temperature, and flow controls.
4. Annually, inspect starter wiring connections, contacts, and action. Tighten
and adjust as required. Perform thermographic survey every 5 years.
5. Annually, test the operation of safety interlocks devices, such as flow
switches, pump starter auxiliary contracts, phase-loss protection, and so
on. Repair or replace as required.
6. Annually, perform dielectric motor testing to identify failures in motor
winding insulation. For large chillers (100 tons or larger), additional
annual motor tests are required to test for the imbalance of electrical
resistance among windings, imbalance of total inductance with phase
inductances, power factor, capacitance imbalance, and running amperage
versus nameplate amperage.
7. Annually, check the tightness of the hot-gas valve (as applicable). If the
valve does not provide tight shutoff, replace it.
8. Annually, replace lubricant (oil) filter and drier.
9. Laboratory analysis of the lubricant should be performed annually during
the first 10 years of chiller life and every 6 months thereafter. Analysis
must address oil moisture content, acidity, and chiller wear as follows:
a. Maximum moisture content of 50 ppm. Higher levels may indicate
air leaks in low-pressure chillers or heat exchanger tube leaks.
b. Maximum acidity of 1 ppm is normal for a new or reclaimed refrigerant.
Higher levels may be caused by oxidation of oil during aging
and/or degradation of refrigerant. If higher levels are found, contact
the chiller manufacturer.
c.Trace amounts of metals could be metal oxides formed from moisture
in the oil or may indicate excess wear conditions. Due to variations
in metals used by different chiller manufacturers, there are no
standard limits. However, if metal content increases from year to
year, one or more of the following excess wear conditions may be
responsible:
Aluminum: impellor or bearing wear
Chromium: wear on rechromed shafts
Copper: corrosion
Iron: corrosion and/or gear wear
Tin: bearing wear
Silicon: leakage of silica gel from dehydrator cartridge or dirt
in system
Zinc: zinc left over from the manufacturing process or loss
of galvanizing from some parts
10. Valve and bearing inspection in accordance with manufacturer’s
recommendation.
11. Relief valves (both refrigerant and water) should be checked annually.
Disconnect the vent piping at the valve outlet and visually inspect the
valve body and mechanism for corrosion, dirt, or leakage. If there are
problems, replace the valve; do not attempt to clean or repair it.
12. Annually, inspect gearbox for wear and repair or replace it as needed.
13. Perform chemical testing of system water at least quarterly. Treat as
needed to ensure proper water chemistry.

Extended (long-term) maintenance checks:
1. Every 5 years (or more frequently as the chiller ages), perform eddy current
(electromagnetic) testing of heat exchanger tubes. [This testing will
typically detect tube pits, cracks, and tube wear (thinning).] If only a
limited number of tubes are found defective, plug tubes. If more than few
are found defective, replace tubes. (Any tube that is replaced as a result
of this testing should be examined and cross-sections should be cut so
that the cause of the defects can be evaluated.)
2. Every 3–5 years, perform vibration test and analysis to evaluate motor
and rotor balance, bearing and gear alignment, and bearing and gear
wear. Use accelerometer-type sensors for gears and bearings (high frequency)
and piezoelectric velocity sensors for compressor motors, rotors,
and bearings (low velocity).
3. Every 5 years, perform an acoustic emission test to identify potential
stress cracks in pressure vessels, tubes, and tube sheets.
4. Other components must be serviced, inspected, and/or replaced at the
intervals recommended by the chiller manufacturer.

  
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