Reset Type 2: Remote Temperature Reset; Surge Prevention; Hgbp Option =1; Hgbp Option =2 - Carrier AquaEdge 19XRV series Operation, Maintenance And Installation Manual

RESET TYPE 2: REMOTE TEMPERATURE RESET —
Reset Type 2 is an automatic chilled water temperature reset
based on a remote temperature sensor input signal. Reset type 2
permits ± 30 F (± 16 C) of automatic reset to the set point based
on a temperature sensor wired to the CCM module (see wiring
diagrams or certified drawings). The temperature sensor must
be wired to terminal J4-13 and J4-14. To configure Reset Type
2, enter the temperature of the remote sensor at the point where
no temperature reset will occur (REMOTE TEMP –> NO RE-
SET). Next, enter the temperature at which the full amount of
reset will occur (REMOTE TEMP –> FULL RESET). Then,
enter the maximum amount of reset required to operate chiller
(DEGREES RESET). Reset Type 2 can now be activated.
RESET TYPE 3 — Reset Type 3 is an automatic chilled water
temperature reset based on cooler temperature difference.
Reset Type 3 adds ± 30 F (± 16 C) based on the temperature
difference between the ENTERING CHILLED WATER and
LEAVING CHILLED WATER temperature.
To configure Reset Type 3, enter the chilled water tempera-
ture difference (the difference between entering and leaving
chilled water) at which no temperature reset occurs (CHW
DELTA T –> NO RESET). This chilled water temperature dif-
ference is usually the full design load temperature difference.
Next, enter the difference in chilled water temperature at which
the full amount of reset occurs (CHW DELTA T –> FULL RE-
SET). Finally, enter the amount of reset (DEGREES RESET).
Reset Type 3 can now be activated.
A surge condition occurs when the
Surge Prevention —
lift becomes so high that the gas flow across the impeller re-
verses. This condition can eventually cause chiller damage.
The surge prevention algorithm notifies the operator that chiller
operating conditions are marginal and to take action to help
prevent chiller damage such as lowering entering condenser
water temperature.
The surge prevention algorithm is an operator-configurable
feature that can determine if lift conditions are too high for the
compressor and then take corrective action. Lift is defined as
the difference between the saturated temperature at the impeller
eye and at the impeller discharge. The maximum lift a particu-
lar impeller wheel can perform varies with the gas flow across
the impeller and the size of the wheel.
Variable Primary Flow Surge prevention is the current stan-
dard for both constant and variable primary flow chilled water
systems. Variable Primary Flow Surge Prevention does not re-
quire a measurement of COOLER DELTA T and is thus unaf-
fected by changes in flow. With Variable Primary Flow Surge
Prevention there is no difference in field configuration between
constant and variable flow water systems.
The controls calculate the conditions at which the compres-
sor will surge based on operating conditions and configured
values entered into the OPTIONS screen.
The configurations as used by the controls would plot out
on a graph as a curved line. If the present operating conditions
plot at or above this line, surge prevention is turned on.
The way in which surge prevention functions will differ
with the presence or absence of hot gas bypass.
HGBP OPTION = 1 — The HGBP is only energized if a
SURGE PROTECTION COUNT is registered, the ACTIVE
DELTA T STAT falls below the SURGE LINE DELTA T STATor
the VFD LOAD FACTOR approaches 1.0 and it is not possible
to increase VFD speed. The VFD speed cannot increase when
the VFD TARGET SPEED is equal to VFD MAXIMUM
SPEED or if the VFD TARGET SPEED is FORCED to a fixed
value.
HGBP OPTION = 2 — This option energizes the HOT GAS
BYPASS RELAY solely based on the ACTIVE DELTA T (actual
temperature difference between the LEAVING CHILLED WA-
TER and ENTERING CHILLED WATER). Evaluation of the
ACTIVE DELTA T begins at the completion of ramp loading.
The hot gas bypass valve is energized if the ACTIVE DELTA T
is less than the HGBP ON DELTA T. The hot gas bypass relay
will be turned off when the ACTIVE DELTA T is greater than or
equal to the sum of HGBP ON DELTA T plus HGBP OFF
DELTA T See Fig. 28. The HGBP ON DELTA T must be set to
a value larger than the minimum delta T to which the chiller
can unload.
∆P
HGBP
On
HGBP ON
DELTA T
LEGEND
ECW — Entering Chilled Water
HGBP — Hot Gas Bypass
LCW — Leaving Chilled Water
P = (Condenser Pressure) – (Cooler Pressure)
T = (ECW) – (LCW)
Fig. 28 — Hot Gas Bypass/Surge
Surge Prevention Algorithm —
configurable feature that can determine if lift conditions are too
high for the compressor and then take corrective action. 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 through the impeller and the diameter of the impeller.
With a VFD the lift capability and the position of the surge line
also vary with ACTUAL VFD SPEED.
The surge line constructed from the guide vane position and
the differential saturated refrigerant temperature between cool-
er and condenser is based on full load conditions and 100%
compressor speed. As ACTUAL VFD SPEED is reduced, the
SURGE/HGBP DELTA Ts MAX and Ts MIN values are auto-
matically reduced so that the surge line duplicates the compres-
sor lift capability at the reduced speed. If the actual operating
point (lift vs. load) goes above the surge prevention line then
the controls enter SURGE PREVENTION mode.
Changing the SURGE LINE SHAPE FACTOR and the
SURGE LINE SPEED FACTOR adjusts the surge line for dif-
ferent speeds and mid lift conditions. See the section on Surge
Prevention Configurations.
When the controls enter SURGE PREVENTION mode the
first response is to increase ACTUAL VFD SPEED and in-
crease the lift capability of the compressor while preventing the
guide vanes from opening further. Should the compressor reach
100% ACTUAL VFD SPEED and still be in the surge preven-
tion region, the controls will energize the HOT GAS BYPASS
RELAY (if the SURGE LIMIT/HGBP OPTION is configured
for Hot Gas Bypass).
If load decreases while the chiller is in SURGE PREVEN-
TION mode the ACTUAL GUIDE VANE POSITION will close
but the ACTUAL VFD SPEED will not decrease.
54
HGBP OFF
DELTA T
HGBP Off As ACTIVE
DELTA T Decreases
HGBP
HGBP On As ACTIVE
DELTA T Increases
∆T
a19-1864
This is an operator
Off