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Beyond the Flange:
Maintaining Chiller Systems
L
arger buildings, process facilities,
and other applications use chilled
water cooling systems for its many
advantages, including refrigerant
and maintenance containment, energy effi-
ciency, and lower first cost.
While the chiller is typically the most
expensive, most energy consuming, and most
visible part of the system, other key compo-
nents include chilled and condenser water
pumps, cooling towers, heat exchangers, and
hydronic specialties such as water pressure
regulators, air separators, and chemical feed
pots. Controls are also critical to the system
because they operate water valves, control
setpoints, and schedule equipment. All these
components and capabilities support the
delivery of cooling water to the airside or pro-
cess loads and carry unwanted heat to sources
of heat rejection. This article will focus on
maintaining these components “beyond
the flange,” which are found in most typical
building comfort cooling applications.
Mechanical water chillers are available in
many types and configurations typically cat-
egorized by compressor type — reciprocating,
scroll, screw, and centrifugal. These types are
further segmented by air-cooled or water-
cooled designations. Most air-cooled chillers
are packaged units, which come as complete
assemblies. Some air-cooled chillers are even
available with integral pumping packages.
Water-cooled chillers have condensers that
are cooled by cooling towers or other sources
to reject the heat. This article will focus on the
water-cooled chiller system.
Chillers
As we review maintenance issues for the
larger chiller system, we need to recognize that
other system component issues may in fact
manifest themselves at the chiller. Yet we need to
keep in mind that the true causes of these symp-
toms can be based elsewhere in the system. Real
detective work may be necessary to identify the
real cause somewhere in the ancillary compo-
nents of the chilled water system.
Water Pumps
Chilled water pumps carry the heated
(54˚F) water from the airside coils back to the
By Richard Grenz
For The NEWS
Pumps.
Chiller plant room.

2. chiller for re-cooling to 44˚. Condenser water
pumps deliver the 95˚ water rejected by the
chiller to the cooling tower for cooling back
down to 85˚. The principal maintenance issues
are a result of chilled water loops being typi-
cally a closed system, while condenser water
loops are open. These differences are impor-
tant maintenance factors we will discuss later.
Common centrifugal impeller pump types
include end-suction and split case construc-
tion. Service considerations include pump
and motor bearing lubrication and water seal
cooling on larger pumps. Motor-pump shaft
alignment is important and should be checked
periodically as heavy piping and supports may
shift over time. Providing positive suction pres-
sure is important to prevent cavitation and air
erosion. Pressure regulator stations maintain
water loop pressure and air separators remove
unwanted air from the chilled water.
Cooling Towers
Condenser water carries the unwanted heat
load removed by the chiller and the chiller’s
compressor work (heat of compression) to the
cooling towers. These towers come in several
common types: forced or induced draft and
single and cross draft. Typically, towers are
constructed of steel, fiberglass-reinforced
plastic, wood, or concrete. Service require-
ments across all types of cooling towers are
consistent. Fan motors, gear drives, fan belts,
and water make-up float assemblies all require
routine maintenance and inspection. Tower
basins, and fill and distribution pans all need
periodic cleaning.
Airside
This is where the heat load is transferred to
the chilled water loop via a chilled water coil.
Coils are part of an air handler unit, which
also contains air filters, fans, mixing boxes/
dampers, and other air handling devices.
Coils are commonly constructed of copper
tubes and aluminum fins, requiring routine
service such as air filter replacement and fin
cleaning. Drain pans and lines also need to
be cleaned of accumulated biological growth
and dirt to maintain proper indoor air quality.
Dirty coils can account for significant reduc-
tions in heat transfer and increased energy use
since operators typically must lower chilled
water temperatures to overcome the reduction
in heat transfer caused by dirty coils.
Hydronic Specialties
Pressure water feed and relief stations
should be checked periodically to ensure
proper water loop pressure. Pressure that’s
too low may prevent circulation to high
level air handler coils or cause pump cavita-
tion. Expansion tanks and air separators that
require minimal attention should also be
checked. Chemical feed pots are used to intro-
duce chemicals or glycol to closed loops. Heat
exchangers are used to isolate different loops
and used in economizer systems. Larger heat
exchangers are field cleanable, yet that can be
a time-consuming task due to the complexity
of the procedure.
Water Treatment
Both loops require treatment for the pre-
vention and control of corrosion, scale, and
biological growth. Closed chilled water system
loops are not exposed to the atmosphere, but
still need inhibiters to control corrosion. Open
cooling tower systems are more demand-
Coils in an air handler. Water treatment system.

3. ing. Cooling towers act like a large air washer
that requires regular maintenance to combat
corrosion problems. Many water treatment
approaches are successfully used in systems
today, including chemical, magnetic, and
ozone types. Fouled water or scaled pipe inhib-
its heat transfer at the chiller and cooling coils.
A miscue in water treatment can quickly cause
major damage to the chiller’s tubes. Therefore,
regular eddy current testing of tubes is critical
combined with consistent, effective water treat-
ment. Because cooling towers evaporate large
amounts of water with some drift to the atmo-
sphere, control of biological matter is an impor-
tant health issue. Several antimicrobial growth
products are available that will minimize bio-
logical growth in the cooling tower basin.
Controls
New digital-based controls are fairly low
maintenance other than occasional software
updates and control device calibration. Older
pneumatic systems employ air compressor/
driers that require specific routine service.
Moisture in a pneumatic system can be det-
rimental to proper operation, causing expen-
sive cleanup costs. Dampers and water control
valves also should be checked for operation and
lubed where necessary. Controlling the chiller
plant pump sequence, air handler scheduling,
and exhaust fan operation can all impact chiller
operation and performance. Chilled water tem-
perature pull down rates need to be slow and
steady. Fast temperature and/or flow changes
can cause erratic and inefficient chiller opera-
tion. On variable flow systems, minimum flows
should be confirmed.
Summary
We have covered only a few of the most
important maintenance tasks. As with all
equipment and components, the manufac-
turers’ operation and maintenance manu-
als should be consulted for specific service
tasks and frequency. As illustrated, many
components contribute directly to a properly
operating and efficient chilled water system.
Developing a service schedule plan and exe-
cuting it will help minimize unscheduled and
costly shutdowns, while protecting the invest-
ment in equipment.
Many factors impact the chiller and are not
always immediately apparent without further
investigation. Pumps not sequencing properly
or low flow conditions may fault a chiller and
not be understood until operation is restored.
All system factors must then be thoroughly
examined and confirmed.
There are many variations and types of
chilled water systems. Understanding the
one you have and how it operates will make
identifying and implementing the right ser-
vice procedures more effective, ensuring the
full life of the equipment. Proper commis-
sioning and establishing an energy baseline
can also help in noting any service trends
that require attention.
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Chiller economic energy analysis.
Richard Grenz is national service sales manager
for McQuay International. For more information,
visit www.mcquay.com.