York YR Owner's Manual page 20

Application Data (continued)
evaporator and condenser when the pumps are shut off.
Piping should be adequately supported and braced inde-
pendently of the chiller to avoid the imposition 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 perfor-
mance of routine maintenance work, some or all of the
following steps may be taken by the purchaser. Evapora-
tor 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 con-
nections (water nozzles) to these circuits are furnished
with grooves for Victaulic 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 lo-
cated 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 electrically connected to the chilled water inter-
lock 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 pos-
sible 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 wa-
ter flow during unit operation. The loss or severe reduc-
tion of water flow could seriously impair the chiller per-
formance 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
following equation:
20
°F Min ECWT = LCHWT + 16 + [(% load/100) x
(10 - full-load condenser water T)]
°C Min ECWT = LCHWT + 8.9 + [(% load/100) x
(5.6 - full-load condenser water T)]
Where: ECWT = entering condenser water temperature
LCHWT = leaving chilled water temperature
MULTIPLE UNITS
Selection – Many applications require multiple units to
meet the total capacity requirements as well as to pro-
vide flexibility and some degree of protection against
equipment shutdown. There are several common unit
arrangements for this type of application. The M
chiller has been designed to be readily adapted to the
requirements of these various arrangements.
Parallel Arrangement (Refer to Fig. 1) – Chillers may
be applied in multiples with chilled and condenser wa-
ter circuits connected in parallel between the units. Fig.
1 represents a parallel arrangement with two chillers.
Parallel chiller arrangements may consist of equally or
unequally sized units. When multiple units are in op-
eration, they will load and unload at equal percentages
of design full-load for the chiller.
Depending on the number of units and operating char-
acteristics of the units, loading and unloading schemes
should be designed to optimize the overall efficiency of
the chiller plant. It is recommended to use an evaporator
bypass piping arrangement to bypass fluid around evapo-
rator of any unit which has cycled off at reduced load
conditions. It is also recommended to alternate the chiller
cycling order to equalize chiller starts and run hours.
FIG. 1 – PARALLEL EVAPORATORS
PARALLEL CONDENSERS
Series Arrangement (Refer to Fig. 2) – The chillers
may be applied in pairs with chilled water circuits con-
FORM 160.81-EG1
E
AX
LD00507
YORK INTERNATIONAL