York YST - Capacity Controls Screen-Variable Speed Mode; Figure 22 - Capacity Controls Screen-Variable Speed Mode

JOHNSON CONTROLS
60
FORM 160.67-O1
ISSUE DATE: 4/1/2015
SECTION 2 - OPTIVIEW CONTROL CENTER INTRODUCTION
CAPACITY CONTROLS SCREEN-VARIABLE SPEED MODE
LD09262
FIGURE 22 - CAPACITY CONTROLS SCREEN-VARIABLE SPEED MODE
OVERVIEW
This screen appears when MSSP7-Speed Control
Mode on Capacity Control Setpoints Screen 1 is set to
Variable. The Variable speed mode is the default mode
and is used to provide the greatest efficiency of opera-
tion in plants where the condensing water is cooled to
as low as 55 °F. This allows the turbine speed to be
reduced to the minimum rated speed and the compres-
sor pre-rotation vanes to be closed completely prior
to opening the hot gas valve. This screen is a detailed
view of the capacity control system logic including
various override and anti-surge control setpoints and
parameters. It is also the gateway to screens for enter-
ing the tuning parameters of the various PID control-
lers and other setpoints pertinent to the operation of
the capacity controls. The Auto/Manual Screen is also
accessible from this screen.
DISPLAY ONLY
Graphics and Animation
The arrows on the interconnecting lines indicate the
logical direction of signal flow between the controlling
devices. An HSR (High Select Relay) will select the
higher of the two signals entering it and pass it on to
the next device. An LSR (Low Select Relay) will select
the lower of the two signals entering it and pass it on to
the next device. The line within the relay will toggle to
show which input is currently being selected.
Override Limit Box
This box displays parameters pertinent to the over-
ride limiting controls that take control of the capacity
control devices during off-design operation in order to
prevent unsafe operation and prevent the chiller from
shutting down.
Override Limit - Evaporator Pressure Setpoint
Displays the present setpoint of the Evaporator Pres-
sure PID controller that is entered on PID Setup Screen
1. If the evaporator pressure falls below this value, the
output of this block will decrease below 100%. The
text color changes to Yellow if this controller is active.
Override Limit - Evaporator Pressure
Displays the present refrigerant pressure in the evapo-
rator.
Override Limit - Condenser Pressure Setpoint
Displays the present setpoint of the Condenser Pres-
sure PID controller that is entered on PID Setup Screen
1. If the condenser pressure rises above this value, the
output of this block will decrease below 100%. The
text color changes to Yellow if this controller is active.
NOTE: OptiView
™
Control Center Screens shown may NOT represent the exact screens according to the software version utilized.