Ramp Loading; Surge Correction Control - Carrier PIC 5+ User Manual

5.9 - Ramp Loading

The ramp loading control slows down the rate at which the
compressor loads up. This control can prevent the compressor
from loading up during the short period of time when the
chiller is started and the chilled water loop has to be brought
down to CONTROL POINT (Setpoint Table). This helps
reduce electrical demand charges by slowly bringing the
chilled water to CONTROL POINT. The total power draw
during this period remains almost unchanged.
There are two methods of ramp loading:
Temperature ramp loading shall limit the rate at which the
controlled water temperature decreases for cooling and
increase for heating during ramping by reducing on cooling
mode and increasing on heating the Pulldown Set Point
(Maintenance Menu - Capacity) at the configured rate until
the pulldown setpoint is less than for cooling mode Control
point or greater than Control point for heating mode
Pull down ramp type shall be configured to 0 for temperature
ramping.
Motor load ramp loading shall limit the rate at which either
the percent load current or motor percent kilowatts increases
by incrementing the ramp demand limit at the configured
rate.
Pull down ramp type shall be configured to 1 for load
ramping.
PULLDOWN RAMP TYPE (Configuration Menu – General
Configuration) is configured to 1 then motor load shall
determine the ramp rate. If DEMAND LIMIT SOURCE
(Configuration Menu – General Configuration) is set to AMPS
then PERCENT LOAD CURRENT shall be used as motor
load. If DEMAND LIMIT SOURCE is set to kW then MOTOR
PERCENT KILOWATTS shall be used as motor load
The motor load ramp algorithm shall be deactivated when
the Ramp Demand Limit is greater than or equal to the
ACTIVE DEMAND LIMIT (General Parameters). It shall
also be deactivated when Ramp Demand Limit is greater or
equal to 80%. There shall be one minute delay for the
compressor to be uploaded to target load after ramping load
demand limit is set to 80%.
If the power outage more than 3 hours, then Temperature
Ramp Loading will be used regardless user configuration.
And the minimum loading rate (1^F/min) will be used.

5.10 - Surge Correction Control

There are two stages for surge correction, surge prevention
control and surge protection control.
Lift is defined as the difference between the saturated
temperature at the impeller eye and at the impeller discharge.
The maximum lift a particular impeller wheel can perform
varies with the gas flow across the impeller and the size of
the wheel.
A surge condition occurs when the lift becomes so high that
the gas flow across the impeller reverses. This condition can
eventually cause compressor damage. The envelope control
algorithm notifies the operator that chiller operating conditions
are marginal and to take action to help prevent compressor
damage such as lowering entering condenser water temperature.
24
A high sound condition occurs in low guide vane position
case, envelope control valve can be used to decrease the sound
level by opening this valve in low guide vane position case.
To enable this function, we need configure "high efficiency
mode" to "disable" in CFGSURGE table. The default is low
noise mode(this mode is only valid for 19XR6&7)
5.10.1 - Surge Prevention Control
The surge prevention control algorithm is an operator-
configurable feature that can determine if lift conditions are
too high for the compressor and then take corrective action.
If Actual Lift is higher than reference lift, a capacity inhibit
signal will be sent; If Actual Lift is higher than reference lift
plus surge line Upper Deadband, a capacity decrease signal
will be sent; If Actual Lift is lower than reference lift minus
surge line Lower Deadband, these 2 signals will be canceled.
Capacity Control will respond to these 2 signals and make
correction on VFD TARGET SPEED, EC valve actuator IGV1
TARGET POSITION with the priority from high to low.
Before surge protection event occurs, if there is no surge
prevention in the past 5 min, SURGE PROFILE OFFSET
will increment by 1. Reference lift will minus SURGE
PROFILE OFFSET before comparing to actual lift. SURGE
PROFILE OFFSET is configurable in Surge Correction
Configuration Table.
5.10.2 - Surge Protection
The Surge Protection algorithm will run after SURGE
DELAY TIME elapsed when compressor has been
commanded to turn ON. It will compare the present
PERCENT LOAD CURRENT value with the previous value
once every second. If the difference exceeds the maximum
AMPS change value (SURGE DELTA % AMPS +
(PERCENT LOAD CURRENT / 10)), an incidence of surge
has occurred, and surge protection signal will be sent.
When an incidence of surge determined in this manner has
occurred, the SURGE COUNTS will be incremented by one.
On receiving surge protection signal, Capacity Control will
do correction by modulating VFD TARGET SPEED, EC
valve actuator IGV1 TARGET POSITION with the priority
from high to low.
When correction is in effective, Surge Protection Count will
be increased by 1 when either one of IGV, VFD or EC
actuator is operated to do correction.
Guide vane should be inhibited for 1 minute after surge
protection ends.
Chiller will do alarm shutdown under following conditions:
- If SURGE PROTECTION COUNTS exceed 20 within
a SURGE TIME PERIOD and VFD speed has reached
the maximum speed
- If IGV, VFD and EC are not able to be operated to do
surge protection, when surge count is greater than 4.