Surge Correction Control; Envelop/Hot Gas Bypass (Hgbp) Control; Economizer Damper Valve Control - Carrier AquaEdge 19XR Controls Operation And Troubleshooting

SURGE CORRECTION CONTROL — There are two stag-
es for surge correction: envelop control (surge prevention) and
surge protection.
Envelop Control — A surge condition occurs when the lift be-
comes so high that the gas flow across the impeller reverses.
This condition can eventually cause compressor damage. The
surge prevention algorithm notifies the operator that chiller op-
erating conditions are marginal and to take action, such as low-
ering entering condenser water temperature, to help prevent
compressor damage.
If a high sound condition occurs at low guide vane posi-
tion, the EC/HGBP valve is used to decrease the sound lev-
el. The envelop control algorithm is an operator-configu-
rable feature that can determine if lift conditions are too
high for the compressor and then take corrective action.
High efficiency mode or low noise mode can be selected.
Lift is defined as the difference between the saturated tem-
perature 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.
If Actual Lift is higher than reference lift, a capacity in-
hibit signal will be sent. If Actual Lift is higher than refer-
ence lift plus Envelop High Deadband, a capacity decrease
signal will be sent. If Actual Lift is lower than reference lift
minus Envelop Low Deadband, these 2 signals will be can-
celed. Capacity Control will respond to these 2 signals and
make correction on IGV1 TARGET POSITION, VFD TAR-
GET SPEED, and EC/HGBP actuator. To improve system
performance SURGE PROFILE OFFSET will be incre-
mented by 1 if no surge prevention has been active in the
past 5 minutes. The Reference Lift will subtract the SURGE
PROFILE OFFSET prior to comparing to Actual Lift.
Surge Protection — The Surge Protection algorithm will run
after SURGE DELAY TIME has elapsed when compressor
has been commanded to turn on. It compares the present PER-
CENT LOAD CURRENT value with the previous value once
every second. If the difference exceeds the maximum AMPS
change value (SURGE DELTA % AMPS + [PERCENT LINE
CURRENT / 10]), an incidence of surge has occurred, and the
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 the surge protection signal, Capacity
Control will make corrections on IGV1 TARGET POSI-
TION, VFD TARGET SPEED, and EC/HGBP actuator.
When correction is in effect, Surge Protection Count will in-
crease by 1 when a command for either IGV decrease, VFD
speed increase, or EC/HGBP actuator activation is required
for correction. Guide vane movement will be inhibited for
1 minute after surge protection ends.
Chiller will do 259 Alarm shutdown under the following
conditions.
• If Surge Protection Counts exceed 20 within a Surge Time
Period. Note that if VFD, then VFD target speed must equal
max before this alarm is activated.
• If IGV, VFD, and HGBP cannot be further adjusted for
surge protection when Surge Protection Counts exceed 4
within a Surge Time Period.
If IGV, VFD, and HGBP control cannot correct the prob-
lem, the chiller will initiate a shutdown alarm when the surge
count is greater than 4.
ENVELOP/HOT GAS BYPASS (HGBP) CONTROL — This
function is used to artificially load the chiller and keep it run-
ning under low load conditions or to prevent surge conditions.
Since this also reduces the performance of the machine, EC/
HGBP Control is a user-selectable option.
PIC 5 supports 3 different types of EC/HGBP control
valve types:
1. Continuous; modulating valve controlled by two contac-
tors, one to open and another to close. If both contactors
are open the valve will hold its position. Valve has a feed-
back signal for fully open/closed position.
2. On/off; valve controlled by one contact. It has no position
feedback and is unable to hold its current position.
3. mA; valve controlled by 4 to 20 mA signal. The type can
be configured in the Option Configuration menu.
Envelop/hot gas bypass operation has three different modes
when installed (hgbp_opt > 0) and enabled (hgbp_sel > 0):
• Envelop control and surge protection — Each compressor
has unique lift characteristics that can be plotted to deter-
mine performance. The controller will determine operating
conditions that could result in compressor surge and activate
the bypass valve to prevent surge until the chiller operating
parameters are in a safe area on the curve where the valve
may be closed again.
• Envelop (HGBP) low load operation — In this condition,
the valve will be opened to prevent a recycle shutdown
from occurring. The valve will remain open until this
minimal loading condition has passed and there is no
surge condition present.
• Combination for envelop control and surge correction, as
well as low load operation — When this option is selected,
both EC for envelop control/surge protection and EC for
low load operation will be performed. Surge protection
will take higher priority if both conditions are satisfied.
ECONOMIZER DAMPER VALVE CONTROL (FOR
APPLICABLE UNITS) — The economizer maintains the
difference between evaporator pressure and economizer pres-
sure. Economizer pressure should always be higher than evap-
orator pressure.
When the chiller is initially powered on, or when the com-
pressor shuts down, the damper valve will be commanded to
close. These and other conditions are shown in Table 14.
Table 14 — Economizer Damper Valve Status
SYSTEM CONDITION
Chiller initially powered on
Compressor shut down
During damper valve action delay
Economizer pressure > evaporator
pressure + Damper valve open DB
Economizer pressure < evaporator
pressure + Damper valve close DB
All other conditions
If the damper valve has been commanded to open for a con-
tinuous 5 minutes, and the Damper Valve Full Opened condi-
tion is still not TRUE, the control system generates an alert
154. Similarly, if the damper valve has been commanded to
close for a continuous 5 minutes, and the Damper Valve Full
Closed condition is still not TRUE, the control system gener-
ates an alert 154.
If the compressor is running and if economizer pressure be-
comes less than or equal to evaporator pressure, an alarm 268
will be tripped and compressor will be shut down.
DEMAND LIMIT — The PIC 5 controls provide a feature for
limiting AVERAGE LOAD CURRENT or MOTOR KILO-
WATTS by limiting capacity via guide vane control/VFD con-
trol. The limit may be applied in two ways. The first is called
ACTIVE DEMAND LIMIT, which is equal to a BASE DE-
MAND LIMIT value (set in the SETPOINT screen, default
value 100%). ACTIVE DEMAND LIMIT may also be forced
to be different from BASE DEMAND LIMIT by manually
overriding (forcing) the value via a CCN network device. If the
21
ECONOMIZER DAMPER
VALVE STATUS
Fully closed
Fully closed
Fully closed
Open
Closed
Current position maintained