Capacity Control; Chiller Operation Overview; Figure 2 - Refrigeration Flow Through Rotary Screw Chiller - York YR Manual

SECTION 1 - DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
The major components of a chiller are selected to han-
dle the refrigerant, which would be evaporated at full
load design conditions. However, most systems will be
called upon to deliver full load capacity for only a rela-
tively small part of the time the unit is in operation.

CAPACITY CONTROL

The major components of a chiller are selected for full
load capacities; therefore capacity must be controlled
to maintain a constant chilled liquid temperature leav-
ing the cooler. A slide valve arrangement located on the
rotary screw compressor compensates for various load
conditions. The slide valve arrangement is controlled
by the OptiView™ Control Center and unit controls
that sense the building load conditions. The control
center sends signals to the solenoid valve that loads and
unloads the slide valve with the use of compressor oil
under hydraulic pressure. A cylinder located in the inlet
end of the compressor houses a spring loaded shaft and

FIGURE 2 - REFRIGERATION FLOW THROUGH ROTARY SCREW CHILLER

12
pistons (slide valve) which is fed through its ports by
pressurized compressor oil. The flow of the oil is con-
trolled by the equalizing solenoid valve which modu-
lates to load and unload the slide valve that increases
or decreases the amount of refrigerant flowing to the
compressor, thus controlling the chiller capacity.

CHILLER OPERATION OVERVIEW

In the following description, reference is made to pro-
cedures that should be performed only by a Service
Technician. Instructions for these procedures are in
OptiView Control Center Service Instructions (Form
160.81-M1 and require SERVICE access level.
The chiller will be permitted to start only if there are no
Safety or Cycling shutdown conditions in effect.
When a Local or Remote start signal is applied, the
"Start Sequence Initiated" period begins. The duration
of this period depends on whether or not the Refriger-
FORM 160.81-O1 (1020)
ISSUE DATE 10/05/2020
LD04976
JOHNSON CONTROLS