Johnson Controls York YKEP Series User Manual

FORM 160.77-O2
ISSUE DATE: 11/15/2011
SECTION 1 - YKEP CHILLER OVERVIEW
JOHNSON CONTROLS
13
1
On start-up, the PRV's are closed to reduce the
starting load torque of the compressor.
The compressor pre-rotation vanes are closed on shut-
down to reduce backflow of high-pressure gas from
the condenser, which might otherwise cause the com-
pressor to spin backwards at a high rate of speed.
A shaded pole motor operates the mechanical
pre-rotation vane linkage, at the compressor. The
shaded pole motor is operated by a contact closure
to either open or close the vanes. A pre-rotation
vane position potentiometer senses the position of
the vanes and reports it to the controller as a per-
centage open value.
2. Hot Gas Bypass Valve
The hot gas bypass valve is used primarily at low
loads to maintain a minimum suction gas flow re-
quired by the compressor for stability. When the
compressor has reduced capacity to its minimum
flow (via pre-rotation vane throttling), further ca-
pacity reductions are accomplished by opening
the hot gas bypass valve. This maintains the flow
to the compressor by bypassing the discharge gas
back to the compressor suction.
However, the hot gas flow replaces the useful
evaporation in the cooler since the compressor
flow is at minimum. Thus, the net chilling capac-
ity is reduced (albeit not efficiently).
The minimum suction flow or minimum com-
pressor PRV position will vary. As the differential
“head” pressure is lowered (due to colder con-
denser water) the compressor is capable of stable
operation at lower loads. The programming in the
chiller panel thus uses the differential “HEAD”
pressure to establish when the hot gas may be
needed.
• On a water chilling application, this valve
goes open on shutdown.
FIGURE 5 - CAPACITY CONTROL MODEL
CHILLED WATER
TEMPERATURE
CONTROLLER
>
GREATER
THAN
SELECTOR
RATIO CONTROLLER
= 100-(100*LESS THAN
SELECTOR)/ANTISURGE)
HOT GAS
RECYCLE
VALVE
COMPRESSOR
PRE-ROTATION
VANES
ANTISURGE VANE
POSITION FOR A
GIVEN LIFT
CONDTION
<
LESS THAN
SELECTOR
MOTOR CURRENT LIMIT
CONTROLLER
(DOES NOT UNLOAD
LESS THAN ANTI-SURGE)
EVAPORATOR
PRESSURE
OVERRIDE
CONTROLLER
CONDENSER
PRESSURE
OVERRIDE
CONTROLLER

Johnson Controls York YKEP Series Specifications

General

Brand	Johnson Controls
Model	York YKEP Series
Category	Chiller
Language	English