JOHNSON CONTROLS
FORM 160.80-EG1 (808)
and initial chiller selections should be made accordingly to
permit proper range of flow while maintaining the minimum
velocity noted above. Variable flow in the condenser is not
recommended, as it generally raises the energy consump-
tion of the system by keeping the condenser pressure
high in the chiller. Additionally, the rate of fouling in the
condenser will increase at lower water velocities associ-
ated with variable flow, raising system maintenance costs.
Cooling towers typically have narrow ranges of operation
with respect to flow rates, and will be more effective with
full design flow. Ref. Table 1 for flow limits.
Temperature Ranges –
For normal water chilling duty,
leaving chilled water temperatures may be selected
between 38°F (3.3°C) [36°F (2.2°C) with Smart Freeze
enabled) and 70°F (21.1°C) for water temperature ranges
between 3°F and 30°F (1.7°C and 16.7°C).
water quality –
The practical and economical applica-
tion of liquid chillers requires that the quality of the water
supply for the condenser and evaporator be analyzed by
a water treatment specialist. water quality may affect the
performance of any chiller through corrosion, deposition of
heat-resistant scale, or sedimentation or organic growth.
These will degrade chiller performance and increase op-
erating and maintenance costs. Normally, performance
may be maintained by corrective water treatment and
periodic cleaning of tubes. If water conditions exist which
cannot be corrected by proper water treatment, it may be
necessary to provide a larger allowance for fouling, and/or
to specify special materials of construction.
General Piping –
All chilled water and condenser water
piping should be designed and installed in accordance
with accepted piping practice. Chilled water and con-
denser water pumps should be located to discharge
through the chiller to assure positive pressure and flow
through the unit. piping should include offsets to provide
flexibility and should be arranged to prevent drainage of
water from the evaporator and condenser when the pumps
are shut off. piping should be adequately supported and
braced independently of the chiller to avoid the imposi-
tion of strain on chiller components. Hangers must allow
for alignment of the pipe. Isolators in the piping and in
the hangers are highly desirable in achieving sound and
vibration control.
Convenience Considerations –
To facilitate the per-
formance of routine maintenance work, some or all of the
following steps may be taken by the purchaser. Cooler and
condenser water boxes are equipped with plugged vent and
drain connections. If desired, vent and drain valves may be
installed with or without piping to an open drain. pressure
gauges with stop cocks, and stop valves, may be installed
in the inlets and outlets of the condenser and chilled water
line as close as possible to the chiller. An overhead monorail
or beam may be used to facilitate servicing.
Connections –
The standard chiller is designed for 150
psig (1034 kpa) design working pressure in both the
chilled water and condenser water circuits. The connec-
tions (water nozzles) to these circuits are furnished with
grooves for ANSI/AwwA C-606 couplings. piping should
be arranged for ease of disassembly at the unit for tube
cleaning. All water piping should be thoroughly cleaned
of all dirt and debris before final connections are made
to the chiller.
Chilled water –
A flow switch must be installed in the
chilled water line of every unit. The switch must be located
in the horizontal piping close to the unit, where the straight
horizontal runs on each side of the flow switch are at least
five pipe diameters in length. The switch must be electri
-
cally connected to the chilled water interlock position in
the unit control center. A water strainer of maximum 1/8”
(3.2 mm) perforated holes must be field-installed in the
chilled water inlet line as close as possible to the chiller.
If located close enough to the chiller, the chilled water
pump may be protected by the same strainer. The flow
switch and strainer assure chilled water flow during unit
operation. The loss or severe reduction of water flow could
seriously impair the chiller performance or even result in
tube freeze up.
Condenser water –
The chiller is engineered for maxi-
mum efficiency at both design and part-load operation
by taking advantage of the colder cooling tower water
temperatures which naturally occur during the winter
months. Appreciable power savings are realized from
these reduced heads.
The minimum entering condenser water temperature for
other full and part load conditions is provided by the fol-
lowing equation:
For R-22; Min ECWT = LCHWT + 11+ [(% load/100)
x
(15 - full load condenser water
∆
T)]
For R-134a; Min ECWT = LCHWT + 16 + [(% load/100)
x
(10 - full load condenser water
∆
T)]
where: eCwT = entering condenser water tempera-
ture
LCHwT = leaving chilled water temperature
MULTIPLE UNITS
Selection –
Many applications require multiple units
to meet the total capacity requirements as well as to
provide flexibility and some degree of protection against
equipment shutdown. There are several common unit
arrangements for this type of application. The
Millennium
Chiller has been designed to be readily adapted to the
requirements of these various arrangements.
