Справочник Пользователя для Carrier 30XW325-400
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Microprocessor
The chiller microprocessor controls overall unit operation
and controls a number of processes simultaneously. These
processes include internal timers, reading inputs, analog to
digital conversions, display control, diagnostic control, out-
put relay control, demand limit, capacity control, head
pressure control, and temperature reset. Some processes
are updated almost continuously, others every 2 to 3 sec-
onds, and some every 30 seconds. The microprocessor
routine is started by switching the emergency ON-OFF
switch to the ON position.
and controls a number of processes simultaneously. These
processes include internal timers, reading inputs, analog to
digital conversions, display control, diagnostic control, out-
put relay control, demand limit, capacity control, head
pressure control, and temperature reset. Some processes
are updated almost continuously, others every 2 to 3 sec-
onds, and some every 30 seconds. The microprocessor
routine is started by switching the emergency ON-OFF
switch to the ON position.
Control sequence
Pre-start — After control switches on, the prestart takes
place. The microprocessor checks itself, and if configured,
energizes the evaporator and condenser pumps to the
internal (or CCN) time schedule (or input occupied signal
from an external system) and waits for temperature to
stabilize.
Start-up — The chiller will receive a call for cooling when
chilled fluid temperature increases above the set point plus
a dead band, or if an override start command is received.
If flow has been proven, the first compressor starts 1 to 3
minutes after the call for cooling. The controlled pulldown
feature limits compressor loading on start up to reduce
demand on start up and unnecessary compressor usage.
Capacity control — On the first call for cooling, the
microprocessor starts the compressor on the lead circuit.
The microprocessor maintains leaving fluid temperature
set point through intelligent positioning of the slide valve.
As the load increases above the compressor's capacity, the
compressor on the lag circuit is started and both compres-
sors are staged together.
Maintaining set point — The control monitors entering
and leaving chilled water temperature to anticipate
changes in cooling load. The speed at which capacity is
added or reduced is controlled by temperature deviation
from set point and rate of temperature change of the
chilled fluid. The basic logic for determining when to add
or remove capacity is a time band integration of deviation
from set point plus rate of change of leaving fluid tempera-
ture. When leaving-fluid temperature is close to the set
point and slowly moving closer, logic prevents additional
capacity. Accuracy depends on loop volume, loop flow
rate, load and condenser water temperatures.
Return fluid temperature compensation — No adjust-
ment for cooling range or evaporator flow rate is required
because the control automatically compensates for cooling
range by measuring both return fluid temperature and leav-
ing fluid temperature.
Low temperature override — This feature prevents
LWT (leaving water temperature) from overshooting the
set point to prevent nuisance low suction temperature
trips.
High temperature override — This feature allows the
chiller to add capacity quickly during rapid load variations.
Temperature reset (chilled water reset) — When
latent loads in the conditioned space are reduced, it may be
possible to reset the leaving chilled water temperature set
place. The microprocessor checks itself, and if configured,
energizes the evaporator and condenser pumps to the
internal (or CCN) time schedule (or input occupied signal
from an external system) and waits for temperature to
stabilize.
Start-up — The chiller will receive a call for cooling when
chilled fluid temperature increases above the set point plus
a dead band, or if an override start command is received.
If flow has been proven, the first compressor starts 1 to 3
minutes after the call for cooling. The controlled pulldown
feature limits compressor loading on start up to reduce
demand on start up and unnecessary compressor usage.
Capacity control — On the first call for cooling, the
microprocessor starts the compressor on the lead circuit.
The microprocessor maintains leaving fluid temperature
set point through intelligent positioning of the slide valve.
As the load increases above the compressor's capacity, the
compressor on the lag circuit is started and both compres-
sors are staged together.
Maintaining set point — The control monitors entering
and leaving chilled water temperature to anticipate
changes in cooling load. The speed at which capacity is
added or reduced is controlled by temperature deviation
from set point and rate of temperature change of the
chilled fluid. The basic logic for determining when to add
or remove capacity is a time band integration of deviation
from set point plus rate of change of leaving fluid tempera-
ture. When leaving-fluid temperature is close to the set
point and slowly moving closer, logic prevents additional
capacity. Accuracy depends on loop volume, loop flow
rate, load and condenser water temperatures.
Return fluid temperature compensation — No adjust-
ment for cooling range or evaporator flow rate is required
because the control automatically compensates for cooling
range by measuring both return fluid temperature and leav-
ing fluid temperature.
Low temperature override — This feature prevents
LWT (leaving water temperature) from overshooting the
set point to prevent nuisance low suction temperature
trips.
High temperature override — This feature allows the
chiller to add capacity quickly during rapid load variations.
Temperature reset (chilled water reset) — When
latent loads in the conditioned space are reduced, it may be
possible to reset the leaving chilled water temperature set
point to a warmer temperature thereby reducing compres-
sor power usage and saving energy. Three reset options
are offered. With any chilled water reset application, hu-
midity control should be considered since higher coil tem-
peratures will reduce latent capacity. For details on apply-
ing a reset option, refer to the Controls, Start-Up, Opera-
tion, Service and Troubleshooting guide.
Return fluid temperature reset — This feature
increases LWT set point as return (entering) fluid tempera-
ture decreases (indicating load decrease). This option may
be used where return fluid temperature provides accurate
load indication. No additional hardware is required.
Outdoor-air temperature reset — This feature
increases LWT set point as outdoor ambient temperatures
decreases (indicating load decrease). This reset should only
be applied where outdoor ambient temperature is an indi-
cation of load. A field-installed thermistor is required.
Space temperature reset — This feature increases the
LWT as space temperature decreases (indicating load
decrease). This reset should only be applied where space
temperature is an indication of load. A field-supplied ther-
mistor is required.
Minimum load control — The main base board (MBB)
responds to the supply chilled water temperature to match
cooling load requirements and controls the minimum load
control valve. The minimum load control valve allows hot
gas to pass directly into the evaporator circuit permitting
the unit to operate at lower loads with less compressor
cycling. Minimum load control should be given consider-
ation when operation is anticipated below the minimum
unloading step.
Pull down control — If pulldown control has been
selected (adjustable setting), no additional capacity is added
as long as the difference between fluid temperature and the
set point is greater than 4 F (2.2 C) and rate of change in
leaving water temperature is greater than the 90 seconds
since the last capacity change, compressors will continue
to run unless a safety device trips. This prevents rapid
cycling and also helps return oil during short operating
periods.
Maximum operating pressure control — If the enter-
ing fluid temperature is 95 F (35 C) and the saturated suc-
tion temperature is 50 F (10 C) or higher, the maximum
operating pressure (MOP) feature limits the suction to keep
the chiller online. The control automatically starts the
chiller in the unloaded state to eliminate the potential of
compressor overload due to high head pressure or low suc-
tion pressure.
Equalized run time — The controller will equalize run
time on each circuit through the lead / lag feature. If a cir-
cuit becomes disabled, the control will automatically set the
active circuit to lead, keeping the chiller online at a reduced
capacity.
Sensors — Thermistors are used to control temperature
sensing inputs to the microprocessor. No additional ther-
mistor sensors are required for leaving chilled water tem-
perature, optional return water reset, or outdoor air reset.
The following sensors can be used on 30XW units:
• Evaporator leaving fluid temperature (T1)
sor power usage and saving energy. Three reset options
are offered. With any chilled water reset application, hu-
midity control should be considered since higher coil tem-
peratures will reduce latent capacity. For details on apply-
ing a reset option, refer to the Controls, Start-Up, Opera-
tion, Service and Troubleshooting guide.
Return fluid temperature reset — This feature
increases LWT set point as return (entering) fluid tempera-
ture decreases (indicating load decrease). This option may
be used where return fluid temperature provides accurate
load indication. No additional hardware is required.
Outdoor-air temperature reset — This feature
increases LWT set point as outdoor ambient temperatures
decreases (indicating load decrease). This reset should only
be applied where outdoor ambient temperature is an indi-
cation of load. A field-installed thermistor is required.
Space temperature reset — This feature increases the
LWT as space temperature decreases (indicating load
decrease). This reset should only be applied where space
temperature is an indication of load. A field-supplied ther-
mistor is required.
Minimum load control — The main base board (MBB)
responds to the supply chilled water temperature to match
cooling load requirements and controls the minimum load
control valve. The minimum load control valve allows hot
gas to pass directly into the evaporator circuit permitting
the unit to operate at lower loads with less compressor
cycling. Minimum load control should be given consider-
ation when operation is anticipated below the minimum
unloading step.
Pull down control — If pulldown control has been
selected (adjustable setting), no additional capacity is added
as long as the difference between fluid temperature and the
set point is greater than 4 F (2.2 C) and rate of change in
leaving water temperature is greater than the 90 seconds
since the last capacity change, compressors will continue
to run unless a safety device trips. This prevents rapid
cycling and also helps return oil during short operating
periods.
Maximum operating pressure control — If the enter-
ing fluid temperature is 95 F (35 C) and the saturated suc-
tion temperature is 50 F (10 C) or higher, the maximum
operating pressure (MOP) feature limits the suction to keep
the chiller online. The control automatically starts the
chiller in the unloaded state to eliminate the potential of
compressor overload due to high head pressure or low suc-
tion pressure.
Equalized run time — The controller will equalize run
time on each circuit through the lead / lag feature. If a cir-
cuit becomes disabled, the control will automatically set the
active circuit to lead, keeping the chiller online at a reduced
capacity.
Sensors — Thermistors are used to control temperature
sensing inputs to the microprocessor. No additional ther-
mistor sensors are required for leaving chilled water tem-
perature, optional return water reset, or outdoor air reset.
The following sensors can be used on 30XW units:
• Evaporator leaving fluid temperature (T1)
Controls