JOHNSON CONTROLS
Application Data
- continued
FIG. 1 –
pARALLeL COOLeRS
pARALLeL CONDeNSeRS
FIG. –
SeRIeS COOLeRS
pARALLeL CONDeNSeRS
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 efficiency of
the chiller plant. It is recommended to use an evapora-
tor by-pass piping arrangement to bypass fluid 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 flows through both evaporators
with each unit handling approximately one-half of the
total load. when the load decreases to a customer se-
lected load value, one of the units will be shut down by a
sequence control. Since all water is flowing 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
flow 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 flow 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 fire. 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,
overflow valves or type tested Safety Pressure switches
or a combination of these devices.
In addition to the spring-loaded, re-seating-type relief
valves that are sized for pressure vessel volume, each unit
is equipped with a rupture disk. This rupture disk is able
to relieve the entire pumping capacity of the compressor
if electronic safeties fail, providing protection for property
and personnel. This device is set for 345 psig (2379 Kpa)
[45 psig above the re-seating relief valves set at 300 psig
(2069 Kpa)].
Sized to the requirements of applicable codes, a vent line
must run from the relief device to the outside of the build-
ing. This refrigerant relief piping must include a cleanable,
