Specifications

24 JOHNSON CONTROLS
FORM 160.80-EG1 (511)
Application Data - continued
MULTIPLE UNITS
Selection – Many applications require multiple units to
meet the total capacity requirements as well as to provide
exibility and some degree of protection against equip-
ment shutdown. There are several common unit arrange-
ments for this type of application. The 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 water
circuits connected in parallel between the units. Fig. 1 rep-
resents a parallel arrangement with two chillers. Parallel
chiller arrangements may consist of equally or unequally
sized units. When multiple units are in operation, 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 efciency of
the chiller plant. It is recommended to use an evapora-
tor by-pass piping arrangement to bypass uid around
evaporator 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.
Series Arrangement (Refer to Fig. 2) – The chillers may
be applied in pairs with chilled water circuits connected in
series and condenser water circuits connected in parallel.
All of the chilled water ows through both evaporators with
each unit handling approximately one-half of the total load.
When the load decreases to a customer selected load
value, one of the units will be shut down by a sequence
control. Since all water is owing through the operating
unit, that unit will cool the water to the desired temperature.
BRINE APPLICATIONS
The YS Screw Chiller, utilizing the Frick Refrigeration com-
pressor, is a good match for the high head requirements of
low temperature brine applications. This is particularly true
of thermal ice storage systems, typically requiring 22°F
( –5.6°C) to 24°F (–4.4°C) leaving brine temperatures.
This performance is enhanced with the standard thermal
storage control mode described on page 6.
Particular attention must be paid to the application of
two or more chillers with evaporators in parallel or series
when the brine temperature is below 32°F (0°C). The brine
MUST NOT ow through the evaporator of the idle chiller,
because it can cause the condenser water to freeze. A
bypass or other type of arrangement is required that shuts
off ow to the idle evaporator. When units are applied in
series with lead/lag capability, the units should be identical.
REFRIGERANT RELIEF PIPING
Each chiller is equipped with pressure relief devices. The
purpose of the relief devices is to quickly relieve excess
pressure of the refrigerant charge to atmosphere, as a
safety precaution in the event of an emergency such as
a re. They are set to relieve at an internal pressure of
300 psig (2069 KPa) and are located on the condenser,
evaporator and oil separator; and are provided in ac-
cordance with ASHRAE 15 Safety Code and ASME or
applicable pressure vessel code. When required and des-
ignated on the order form, the relief devices will satisfy the
European requirements: (example VBG20). Under these
circumstances the relief devices may be relief valves,
C O ND. 1
C O ND. 2
E VA P. 1
E VA P. 2
T
S 1
S 2
C O ND. 1
C O ND. 2
E VA P. 1
E VA P. 2
T
S 1
S 2
S – Temperature Sensor for Chiller Capacity Control
T – Thermostat for Chiller Capacity Control
S – Temperature Sensor for Chiller Capacity Control
T – Thermostat for Chiller Capacity Control
FIG. 1 – PARALLEL EVAPORATORS PARALLEL CON-
DENSERS
FIG. 2 – SERIES EVAPORATORS PARALLEL CON-
DENSERS