McQuay AGS 120C Installation Manual
Operation Manual
OM AGSC-11
Air-Cooled Screw Compressor Chiller
AGS 120C through AGS 210C
Software Version AGSD30101G/H
60 Hertz, R-134a
Group: Chiller
Part Number: 331373501
Date: May 2008
Supersedes: OM AGSC-10
Table of Contents
©2007 McQuay International
ISO Certified facility
CONTROLLER FEATURES......................... 4
GENERAL DESCRIPTION........................... 5
Power Panel Layout...................................... 6
Control Panel Layout.................................... 7
COMPONENT DESCRIPTION .................... 8
Definitions .................................................... 8
Unit and Circuit Controller Description ..... 11
SEQUENCE OF OPERATION.................... 12
CONTROL OPERATION ............................17
UNIT CONTROLLER ..................................17
Inputs/Outputs ............................................17
Setpoints .....................................................18
UNIT CONTROLLER FUNCTIONS..........20
Parameter Definitions .................................20
Unit Enable ................................................. 20
Unit Mode Selection................................... 21
Unit States................................................... 23
Ice Mode Start Delay.................................. 24
Evaporator Pump Control........................... 24
Leaving Water Temperature (LWT) Reset.. 25
Unit Capacity Overrides .............................27
Building Automation System Interface.......28
Quiet Night Operation ................................ 28
CIRCUIT CONTROLLER........................... 29
Inputs/Outputs ............................................29
Setpoints .....................................................30
CIRCUIT CONTROLLER FUNCTIONS ..32
Refrigerant Calculations .............................32
Circuit Operating Mode.............................. 33
Compressor Control.................................... 33
Pumpdown .................................................. 37
Slide Positioning......................................... 37
Unit controllers are LONM
ARK
certified with an optional LONW
ORKS
communications module
Expansion Valve (EXV) Control.................39
Oil Heater Control.......................................41
Economizer Control....................................42
Starter Communications..............................43
Condenser Fan Control ...............................45
ALARMS AND EVENTS..............................48
Unit Stop Alarms.........................................48
Unit Events..................................................49
Circuit Stop Alarms.....................................49
Circuit Events..............................................53
Alarm Logging............................................54
Event Logging.............................................55
USING THE CONTROLLER ......................56
Security .......................................................58
Entering Passwords.....................................58
Editing Setpoints.........................................58
Clearing Alarms ..........................................59
Unit Controller Menus ................................59
Circuit Controller Menus ............................68
SEE "ALARMS AND EVENTS ...................69
Unit Stop Alarms.........................................69
Unit Events..................................................70
Circuit Stop Alarms.....................................70
Circuit Events..............................................74
Alarm Logging............................................75
Event Logging.............................................76
Editing Review............................................82
START-UP AND SHUTDOWN ...................84
Temporary Shutdown..................................84
Extended (Seasonal) Shutdown ..................85
BAS INTERFACE .........................................87
FIELD WIRING DIAGRAM........................91
reserve the right to make changes in design and construction at anytime without notice. ™® The following are trademarks or
registered trademarks of their respective companies: BACnet from ASHRAE; LONM
logo are managed, granted and used by LONM
from Copeland Corporation; ElectroFin from AST ElectroFin Inc.; Modbus from Schneider Electric; FanTrol, MicroTech II, Open
Choices, and SpeedTrol from McQuay International.
2 OM AGSC-11
. Illustrations and data cover the McQuay International product at the time of publication and we
ARK
ARK
International under a license granted by Echelon Corporation; Compliant Scroll
, LonTalk, LONW
ORKS
, and the LONM
ARK
This manual provides setup, operating, and troubleshooting information for the McQuay
MicroTech ΙΙ controller for Model AGS-C vintage, air-cooled, rotary screw compressor
chillers. Please refer to the current version of the installation and maintenance manual IMM
AGSC (available on www.mcquay.com) for information relating to the unit itself.
Among other revisions and upgrades, this software version modifies EXV valve and
economizer operation, modifies start logic and some alarms and events, changes some set
points, and adds to the BAS interface logic.
Software Version: This manual covers units with Software Version AGSD30101G and H.
Version G contains the above changes and Version H only corrects an EXV bug and does
not change this manual. The unit’s software version number can be viewed by pressing the
MENU and ENTER keys (the two right keys) simultaneously. Then, pressing the MENU
key will return to the Menu screen.
BOOT Version: 3.0F
BIOS Version: 3.62
!
DANGER
Electric shock hazard. Can cause personal injury or equipment damage. This equipment
must be properly grounded. Connections to, and service of, the MicroTech II control panel
must be performed only by personnel who are knowledgeable in the operation of the
equipment being controlled.
!
WARNING
Static sensitive components. A static discharge while handling electronic circuit boards can
cause damage to the components. Discharge any static electrical charge by touching the
bare metal inside the control panel before performing any service work. Never unplug any
cables, circuit board terminal blocks, or power plugs while power is applied to the panel.
NOTICE
This equipment generates, uses and can radiate radio frequency energy and, if not installed and used
in accordance with this instruction manual, can cause interference to radio communications. Operation
of this equipment in a residential area can cause harmful interference, in which case the user will be
required to correct the interference at the user’s own expense.
McQuay International Corporation disclaims any liability resulting from any interference or for the
correction thereof.
Temperature and Humidity Limitations
The MicroTech ΙΙ controller is designed to operate within an ambient temperature range of
-20°F to +149°F (-29°C to +65.1°C) with a maximum relative humidity of 95% (noncondensing).
Language
This version of the software is set up for English language and inch-pounds units of measure
only.
OM AGSC-11 3
Controller Features
• Readout of the following temperature and pressure readings:
• Entering and leaving chilled water temperature
• Saturated evaporator refrigerant temperature and pressure
• Saturated condenser temperature and pressure
• Outside air temperature
• Suction line, liquid line, and discharge line temperatures − calculated superheat for
discharge and suction lines
• Automatic control of primary and standby chilled water pumps. The control will start one
of the pumps (based on lowest run-hours) when the unit is enabled to run (not necessarily
running on a call for cooling) and when the water temperature reaches a point of freeze
possibility.
• Three levels of security protection against unauthorized changing of setpoints and other
control parameters.
• Warning and fault diagnostics to inform operators of warning and fault conditions in plain
language. All events and alarms are time- and date-stamped for identification of when the
fault condition occurred. In addition, the operating conditions that existed just prior to an
alarm shutdown can be recalled to aid in isolating the cause of the problem.
• Twenty-five previous alarms and related operating conditions are available.
• Remote input signals for chilled water reset, demand limiting, and unit enable.
• Test mode allows the service technician to manually control the controllers’ outputs and
can be useful for system checkout.
• Building Automation System (BAS) communication capability via LONW
Modbus, or BACnet open standard protocols for all BAS manufacturers-simplified
with McQuay’s Open Choices feature.
• Service Test mode for troubleshooting controller hardware.
• Pressure transducers for direct reading of system pressures. Preemptive control of low
evaporator pressure conditions and high discharge temperature and pressure to take
corrective action prior to a fault trip.
• Distributed control-one unit controller and two independent circuit controllers improves
unit reliability.
• Quiet Night operation limits unit capacity and fan operation to reduce unit sound levels
during low-load, night-time operation.
ORKS
,
4 OM AGSC-11
General Description
General Description
The AGS-C MicroTech ΙΙ distributed control system consists of multiple microprocessorbased controllers that provide monitoring and control functions required for the controlled,
efficient operation of the chiller. The system consists of the following components:
• Unit Controller, one per chiller − controls functions and settings that apply to the unit
and communicates with the other controllers. It is located in the control panel and is
labeled “UNIT CONTROL”.
• Circuit Controllers for each compressor/circuit that control compressor functions and
settings specific to the circuit. The controllers are also located in the control panel and
are labeled “CIRCUIT CONROL”.
In addition to providing all normal operating controls, the MicroTech II control system
monitors equipment protection devices on the unit and will take corrective action if the
chiller is operating outside of its normal design envelope. If an alarm condition develops,
the controller will shut down the compressor, or entire unit, and activate an alarm output.
Important operating conditions at the time an alarm condition occurs are retained in the
controller’s memory to aid in troubleshooting and fault analysis.
The system is protected by a password scheme that allows access only by authorized
personnel. The operator must enter the operator password into the controller's keypad before
any setpoints can be altered.
Control Architecture
Figure 1, Major Control Components
BAS Interface-
Modbus,
BACnet,
Lonworks
Chiller
RS485/
LON
Unit Controller
4x20 LCD
Solid
State
Starter
RS485 RS485
Circuit Controller
4x20 LCD
Solid
State
Starter
Circuit Controller
4x20 LCD
Carel pLAN
pLAN Addressing
The pLAN (proprietary local area network) addressing is based on a common scheme used
on all pLAN networked MicroTech II controllers. Only three addresses are needed, and are
designated as shown in the table below.
Controller Address
Dip Sw 1
Position
Unit 5 Up Down Up
Circuit 1 1 Up Down Down
Circuit 2 2 Down Up Down
The Dip switches are located on the upper front of the controller above the screen.
Dip Sw 2
Position
Dip Sw 3 Position
OM AGSC-11 5
Power Panel Layout
Control Transformer
Fuses
Breakers
The power panel is located on the front of the unit, to the right of the control panel.
Figure 2, Power Panel Components (Single Point Power)
Line
Reactors
for
Optional
VFD
Fan
Circuit
Cir#2 Fan
VFD
(Optional)
Cir#2 Circuit Breaker,
Single Point Power
Primary Control Power
Fuses
Cir#1 Circuit Breaker,
Single Point Power
Unit Circuit
Breaker
(Optional)
Grounding
Lug
Cir#1 Fan
VFD
Fan Contactors
Cir#2 Starter
Incoming
Power
Connection
Cir#1 Starter
6 OM AGSC-11
Control Panel Layout
The control panel is located on the front of the unit, to the left of the power panel.
Distributed control architecture enhances unit reliability. Each compressor circuit has its own
microprocessor controller so that if one circuit controller is inoperative, the other circuit controller
will still be able to run its compressor and circuit components.
Figure 3, Control Panel Components
T2 T13 T14 T15 T23 T24 T25
T2 24V Unit Controller Transformer
T13, T23 24V Circuit Controller Transformers
T14, T24 24V Compressor Load/Unload Trns.
T15, T25 24V EXV Driver Transformer
Transformers
Unit Controller
Cir#1 Controller
Cir#2 Controller
OM AGSC-11 7
Component Description
Definitions
Active Setpoint
The active setpoint is the setting in effect at any given moment. This variation occurs on
setpoints that can be altered during normal operation. Resetting the chilled water leaving
temperature setpoint by one of several methods, such as return water temperature, is an
example.
Active Capacity Limit
The active setpoint is the setting in effect at any given moment. Any one of several external
inputs can limit a compressor’s capacity below its maximum value.
Condenser Saturated Temperature Target
The saturated condenser temperature target is calculated by first using the following
equation:
Sat condenser temp target raw = 0.833(evaporator sat temp) + 68.34
The “raw” value is the initial calculated value. This value is then limited to a range defined
by the Condenser Saturated Temperature Target minimum and maximum setpoints. These
setpoints simply cut off the value to a working range, and this range can be limited to a
single value if the two setpoints are set to the same value.
CPU Error
These are problems caused by a malfunction of the central processing unit.
Dead Band
The dead band is a range of values surrounding a setpoint such that a change in the variable
occurring within the dead band range causes no action from the controller. For example, if a
temperature setpoint is 44°F and it has a dead band of ± 2 degrees F, nothing will happen
until the measured temperature is less than 42°F or more than 46°F.
DIN
Digital input, usually followed by a number designating the number of the input.
Discharge Superheat
Discharge superheat shall be calculated for each circuit using the following equation:
Discharge Superheat = Discharge Temperature – Condenser Saturated Temperature
Error
In the context of this manual, “Error” is the difference between the actual value of a variable
and the target setting or setpoint.
Evaporator Approach
The evaporator approach is calculated for each circuit. The equation is as follows:
Evaporator Approach = LWT – Evaporator Saturated Temperature
Evap Recirc Timer
A timing function, with a 30-second default, that holds off any reading of chilled water for
the duration of the timing setting. This delay allows the chilled water sensors (especially
water temperatures) to take a more accurate reading of the chilled water system conditions.
8 OM AGSC-11
EXV
Electronic expansion valve, used to control the flow of refrigerant to the evaporator,
controlled by the circuit microprocessor.
High Saturated Condenser – Hold Value
High Cond Hold Value = Max Saturated Condenser Value – 5°F
This function prevents the compressor from loading whenever the pressure approaches
within 5 degrees of the maximum discharge pressure. The purpose is to keep the compressor
online during periods of possibly temporary elevated pressures.
High Saturated Condenser – Unload Value
High Cond Unload Value = Max Saturated Condenser Value – 3°F
This function unloads the compressor whenever the pressure approaches within 3 degrees of
the maximum discharge pressure. The purpose is to keep the compressor online during
periods of possibly temporary elevated pressures.
High Superheat Error
The degrees of temperature difference between 40°F and the actual discharge temperature.
Light Load Stg Dn Point
The percent load point at which one of two operating compressors will shut off, transferring
the unit load to the remaining compressor.
Load Limit
An external signal from the keypad, the BAS or a 4-20 ma signal that limits the compressor
loading to a designated percent of full load. Frequently used to limit unit power input.
Load Balance
Load balance is a technique that equally distributes the total unit load among the running
compressors on a unit or group of units.
Low Ambient Lockout
Prevents the unit from operating (or starting) at ambient temperatures below the setpoint.
Lockout cancels when ambient temperature rises 5-degfrees above the setpoint
Low Pressure Hold Setpoint
The psi evaporator pressure setting at which the controller will not allow further compressor
loading.
Low/High Superheat Error
The difference between actual evaporator superheat and the superheat target.
LWT
Leaving water temperature. The “water” is any fluid used in the chiller circuit.
LWT Error
Error in the controller context is the difference between the value of a variable and the
setpoint. For example, if the LWT setpoint is 44°F and the actual temperature of the water at
a given moment is 46°F, the LWT error is +2 degrees.
LWT Slope
The LWT slope is an indication of the trend of the water temperature. It is calculated by
taking readings of the temperature every few seconds and subtracting them from the previous
value, over a rolling one minute interval.
ms
Milli-second
OM AGSC-11 9
Maximum Saturated Condenser Temperature
The maximum saturated condenser temperature allowed is calculated based on the
compressor operational envelope.
OAT
Outside ambient air temperature
Offset
Offset is the difference between the actual value of a variable (such as temperature or
pressure) and the reading shown on the microprocessor as a result of the sensor signal. See
page 31.
pLAN
Peco Local Area Network is the proprietary name of the network connecting the control
elements.
Refrigerant Saturated Temperature
Refrigerant saturated temperature is calculated from the pressure sensor readings for each
circuit. The pressure is fitted to an R-134a temperature/pressure curve to determine the
saturated temperature.
Soft Load
Soft Loading is a configurable function used to ramp up the unit capacity over a given time
period, usually used to influence building electrical demand by gradually loading the unit.
SP
Setpoint
SSS
Solid state starter as used on McQuay screw compressors.
Suction Superheat
Suction superheat is calculated for each circuit using the following equation:
Suction Superheat = Suction Temperature – Evaporator Saturated Temperature
Stage Up/Down Accumulator
The accumulator can be thought of as a bank storing occurrences that indicate the need for
an additional fan.
Stageup/Stagedown Delta-T
Staging is the act of starting or stopping a compressor or fan when another is still operating.
Startup and Stop is the act of starting the first compressor or fan and stopping the last
compressor or fan. The Delta-T is the “dead band” on either side of the setpoint in which no
action is taken.
Stage Up Delay
The time delay from the start of the first compressor to the start of the second.
Startup Delta-T
Number of degrees above the LWT setpoint required to start the first compressor.
Stop Delta-T
Number of degrees below the LWT setpoint required for the last compressor to stop.
VDC
Volts, Direct current, sometimes noted as vdc.
VFD
Variable Frequency Drive, a device used to vary an electric motor’s speed.
10 OM AGSC-11
Unit and Circuit Controller Description
ALARM
Hardware Structure
The controllers are fitted with a 16-bit microprocessor for running the control program.
There are controller terminals for connection to the controlled devices (for example: solenoid
valves, expansion valves, chilled water pumps). The program and settings are saved
permanently in FLASH memory, preventing data loss in the event of power failure without
requiring a back-up battery. The controllers also have optional remote communication
access capability for a BAS interface using standard protocols.
Each chiller has one unit controller and a circuit controller for each of two compressor
circuits. The controllers are connected and communicate via a pLAN (local area network).
The circuit controllers communicate with, and control the operation of, the compressor's
solid state starter and the circuit’s electronic expansion valve (EXV).
Keypad
A 4-line by 20-character liquid crystal display and 6-button keypad are mounted on the unit
and compressor controllers.
Figure 4, Keypad
Red Alarm Light Behind Arrow
MENU Key
Key-to-Screen Pathway
Air Conditioning
<
VIEW
<
<
SET
ARROW Keys (4)
ENTER Key
The four arrow keys (UP, DOWN, LEFT, RIGHT) have three modes of use.
1. Scroll between data screens in the direction indicated by the arrows (default mode).
2. Select a specific data screen in the menu matrix using dynamic labels on the right side of
the display such as ALARM, VIEW, etc. (pressing the MENU key enters this mode).
For ease of use, a visual pathway connects the appropriate button to its respective label
on the screen.
3. Change field values in setpoint programming mode as follows:
LEFT key = Default (D) RIGHT key = Cancel (C)
UP key = Increase (+) DOWN key = Decrease (-)
These four programming functions are indicated by a one-character abbreviation ( ) on the
right side of the display. This programming mode is entered by pressing the ENTER key.
OM AGSC-11 11
Sequence of Operation
Unit power up
The chiller may be disabled via the unit switch, the remote switch, the keypad
Unit in Off state
Is unit enabled?
Yes
Evaporator pump output on
Is flow present?
enable setting, or the BAS network. In addition, the chiller will be disabled if both
circuits are disabled, either because of an alarm or the circuit pumpdown switch on
each circuit, or if there is a unit alarm. If the chiller is disabled, the unit status
display will reflect this and also show why it is disabled.
No
If the unit switch is off, the unit status will be
disabled due to network command, the unit status will be
the remote switch is open, the unit status will be
alarm is active, the unit status will be
are enabled, the unit status will be
If the chiller is enabled, then the unit will be in the Auto state and the evaporator
water pump output will be activated.
No
The chiller will then wait for the flow switch to close, during which time the unit
status will be
Auto:Wait for flow
Off:Unit Switch
Off:Remote Switch
Off:Unit Alarm
Off:All Cir Disabled
.
. If the chiller is
Off:BAS Disable
. When
. When a unit
. In cases where no circuits
.
Yes
Wait for chilled water loop to
recirculate.
Keep pump output on while
unit is enabled.
Is there enough load to
start chiller?
Yes
Start first circuit.
After establishing flow, the chiller will wait some time to allow the chilled water loop
to recirculate for an accurate reading of the leaving water temperature. The unit
status during this time is
Auto:Evap Recirc
.
The chiller is now ready to start if enough load is present. If the LWT is not high
enough to start, the unit status will be
No
If the LWT is high enough to start, the unit status will be
Auto:Wait for load
.
Auto
. A compressor can
start at this time.
The first circuit to start is generally the one with the least number of starts, or circuit
one if there is a tie. This circuit will go through its start sequence at this point.
A number of fans may be started with the compressor based on the OAT. Fan
stages will be added/removed as needed to control condenser pressure. The EXV
will begin controlling at this point as well. The compressor cannot start loading until
it has at least 22o discharge superheat for more than 30 seconds.
12 OM AGSC-11
Load/unload as needed to
satisfy load.
Is more capacity
needed to satisfy load?
Yes
Has the stage up time
delay expired?
Yes
Start second circuit.
Load/unload as needed to
satisfy load.
No
The first circuit will load and unload as needed in an attempt to satisfy the load. It
will eventually get to a point where it is considered to be at full load. A circuit is at
full load when it reaches 75% slide target, it reaches the max slide target setting, or
it encounters a problem and is running in an inhibited state.
No
If a single circuit is not enough to satisfy the load, the second circuit will need to be
started.
A minimum time must pass between the start of the first circuit and the second
circuit.
The second circuit will go through its start sequence at this point.
A number of fans may be started with the compressor based on the OAT. Fan
stages will be added/removed as needed to control condenser pressure. The EXV
will begin controlling at this point as well. The compressor cannot start loading until
it has at least 22o discharge superheat for more than 30 seconds.
Both circuits will now load/unload as needed to satisfy the load. In addition, they will
load balance so that both circuits are providing nearly equal capacity.
No
Can one circuit handle
the load?
Yes
Shut down one circuit.
Load/unload as needed to
satisfy load.
Is load satisfied?
Yes
Shut down last circuit.
As the load drops off, the circuits will unload accordingly. If the LWT gets low
enough, or both circuits unload enough, one circuit can shut off.
The first circuit to shut off is generally the one with the most run hours. The circuit
will do a pumpdown by closing the EXV and continuing to run the compressor until it
reaches the pumpdown pressure or exceeds the pumpdown time limit. Then, the
compressor and all fans will be turned off.
The single running circuit will load/unload as needed to satisfy the load.
No
With one circuit running, the load may drop off to the point where even minimum
unit capacity is too much. The load has been satisfied when the LWT drops below
the shutdown point. At this time the only running circuit can shut down.
The last circuit running now shuts down. The circuit will do a pumpdown by closing
the EXV and continuing to run the compressor until it reaches the pumpdown
pressure or exceeds the pumpdown time limit. Then, the compressor and all fans
will be turned off.
The unit should be ready to start again when the LWT gets high enough. The unit
status at this time will be
Auto:Wait for load
.
OM AGSC-11 13
The preceding flow diagram illustrates the sequence of operation.
The following sequence of operation expands and clarifies the flow diagram. The sequence
may vary slightly depending on the software revision or various options that may be installed
on the chiller.
Off Conditions
Power is supplied to the power section of the electric panel. The standard power connection
is two separate sources, one to each circuit. Optionally, the power may be supplied to a
single power connection, either a power block or optional disconnect switch.
With power supplied to the unit, 115 VAC power is applied through the control fuse F1 to the
compressor heaters, HTR1 and HTR2, evaporator heater, and the primary of the 24V control
circuit transformer.
!
CAUTION
Compressor heaters must be on for at least 12 hours prior to start-up to avoid compressor
damage..
The 24V transformer provides power to the MicroTech II controller and related components.
With 24V power applied, the controller will check the position of the front panel system
switch. If the switch is in the "stop" position, the chiller will remain off, and the display will
indicate the operating mode to be OFF: Unit Switch. The controller will then check the
pumpdown switches. If any of the switches are in the "stop" position, that circuit’s operating
mode will be displayed as OFF: Pump Down Switch. If the switches for both circuits are
in the "Stop" position, the unit status will display OFF: All Circuits Disabled. If the remote
start/stop switch is open the chiller will be OFF: Remote Switch. The chiller may also be
commanded off via communications from a separate communicating panel such a BAS
protocol interface. The display will show OFF: BAS Disable if this operating mode is in
effect.
If an alarm condition exists which prevents normal operation of both refrigerant circuits, the
chiller will be disabled and the display will indicate OFF: Unit Alarm. If the control mode
on the keypad is set to "Manual Unit Off," the chiller will be disabled and the unit status will
display OFF: Keypad Disable.
Alarm
The red alarm light in back of the left arrow key on the controller will be illuminated when
one or more of the cooling circuits has an active alarm condition which results in the circuit
being locked out or a unit alarm is active and manual reset is required. If only a circuit alarm
is active, the remaining circuits will operate as required. Events (low-level occurrences) will
not cause the key to light.
Start-up
If none of the above "off" conditions are true, the MicroTech II controller will initiate a start
sequence and energize the chilled water pump output relay. The chiller will remain in the
WaitForFlow mode until the field-installed flow switch indicates the presence of chilled
water flow. Once flow is established, the controller will sample the chilled water
temperature and compare it against the Leaving Chilled Water Setpoint, the Control Band,
and the Start-up Delta-Temperature, which have been programmed into the controller’s
memory.
If the leaving chilled water temperature is above the Active Chilled Water Setpoint plus the
adjustable Start-up Delta-T, the controller will select the refrigerant circuit with the lowest
number of starts as the lead circuit and initiate a start request. The circuit controller will
14 OM AGSC-11
open the EXV and start the compressor. A green light under the Enter key on the circuit
controller will illuminate to indicate that the compressor is running.
If additional cooling capacity is required, the controller will activate additional cooling. As
the system load increases, the controller will start the lag refrigerant circuit when the lead
circuit reaches 75%, or some other capacity limit is reached, and the interstage timers are
satisfied. The compressors and capacity control solenoids will automatically be controlled as
required to meet the cooling needs of the system. The electronic expansion valves are
operated by the MicroTech II controller to maintain precise refrigerant control to the
evaporator at all conditions.
Standard FanTrol Condenser Fan Control
When the compressor starts, a number of fans may be started, depending on the OAT and the
Forced Fan setpoints. The MicroTech II controller will activate the remaining condenser
fans as needed to maintain proper condenser pressure. The MicroTech II controller
continuously monitors the condenser pressure and will adjust the number of operating
condenser fans as required. The number of condenser fans operating will vary with outdoor
temperature and system load. The condenser fans are matched to the operating compressors
so that when a compressor is off, all fans for that circuit will also be off.
Pumpdown
As the system chilled water load requirements diminish, the compressors will unload. As the
system load continues to drop, the electronic expansion valve will be stepped closed, the
solenoid valve will close, and the refrigerant circuits will go through a pumpdown sequence.
As the evaporator pressure falls below the pumpdown pressure setpoint while pumping
down, the compressor and condenser fans will stop. The unit has a one-time pumpdown
control logic; therefore, if the evaporator pressure rises while the compressor is in the off
state, the controller will not initiate another pumpdown sequence. The circuit controller will
keep the compressor off until the next call for cooling occurs.
The chilled water pump output relay will generally remain energized until the unit is in the
Off State due to the remote stop switch, unit Off switch, BAS command, or keypad setting
calling for the unit to be disabled.
Liquid Line Solenoid Valve (LLSV)
The LLSV cycles with the compressor starter. Its purpose is to provide a positive seal in the
liquid line in the event of a power failure. A power failure may prevent the expansion valve
from closing completely by removing power before the valve steps all the way closed.
OM AGSC-11 15
Figure 5, AGS-C Piping Schematic
WATER IN
DX EVAPORATOR
FIELD CONNECTION
SUCTION
SUCTION
CHARGING
330591001-R3
FACTORY PIPING
DISCHARGE
CHECK AND
SCHRADER
(HEADER)
AIR
FLOW
CHARGING
VALV E
AIR
LIQUID
SHUT-OFF
VALVE
LIQUID
TUBING
FLOW
FIELD CONNECTION
LIQUID LINE
VALVE
CONDENSOR
DISCHARGE
AIR
FLOW
ASSEMBLY
TUBING
SCHRADER
VALVE
RELIEF
VALVE
SHUT-OFF
VALVE
FRAME 3200
COMPRESSOR
SHUT-OFF
VALVE
SUCTION LINE
RELIEF
VALVE
VALVE
TUBING
SCHRADER
VALVE
FILTER
DRIER
SCHRADER
VALVE
SOLENOID
VALVE
SIGHT
GLASS
EXPANSION
VALVE
WATER OUT
FIELD PIPING
NOTE: The above figure illustrates the piping for the remote evaporator option. For the standard packaged
version, the field piping shown as dotted would be installed in the factory.
16 OM AGSC-11
Control Operation
This section on MicroTech II control is divided into three subsections:
• Unit Controller, explains the functions of the unit controller, see page 17.
• Circuit Controller, explains the functions of the circuit controller, see page 29
• Using the Controller, explains how to navigate through the menus and how to make
entries, see page 48.
Unit Controller
Inputs/Outputs
Analog Inputs
The following parameters are analog inputs to this controller. They are used internally as
needed and are sent via the pLAN to other control devices.
Table 1, Unit Analog Inputs
# Description Signal Source Range
1 Outdoor Ambient Temperature Thermister (10k@25°C) -58 to 212°F
2 Demand Limit 4-20 mA Current, External 0 to 100% limit
3 Chilled Water Reset 4-20 mA Current, External 0 to max reset
4 Leaving Evaporator Water Temperature Thermister (10k@25°C) -58 to 212°F
5 Entering Evaporator Water Temperature Thermister (10k@25°C) -58 to 212°F
Analog Outputs
Table 2, Unit Analog Outputs
# Description Output Signal Range
1 Open -- --
2 Open -- --
3 Open -- --
4 Open -- --
Digital Inputs
Table 3, Unit Digital Inputs
# Description Signal Signal
1 Unit Switch 0 VAC (Stop) 24 VAC (On)
2 Remote Switch 0 VAC (Stop) 24 VAC (Start)
3 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
4 Mode Switch 0 VAC (Cool) 24 VAC (Ice)
5 Open -- --
6 Open -- --
7 Open -- --
8 Open -- --
OM AGSC-11 17
Digital Outputs
Table 4, Unit Digital Outputs
# Description Output OFF Output ON
1 Evaporator Water Pump 1 Pump OFF Pump ON
2 Evaporator Water Pump 2 Pump OFF Pump ON
3 Open
4 Open
5 Open
6 Open
7 Open
8 Alarm No alarm Stop alarm
Setpoints
The following parameters are remembered during power off, are factory set to the Default
value, and can be adjusted to any value in the Range column.
The Type column defines whether the setpoint is part of a coordinated set of duplicate
setpoints in different controllers. There are two possibilities as given below:
N = Normal setpoint - Not copied from, or copied to, any other controller
M = Master setpoint - Setpoint is copied to all controllers in the “Sent To” column
The PW (password) column indicates the required password level.
Codes are as follows:
O = Operator, Password is 100 M = Manager
Toggle: Setpoints that have two choices, such as ON and OFF are toggled between the two
settings using the Up or Down keys on the controller.
NOTE: in some software versions the terms “inhibit” and “hold” are used interchangeably.
Table 5, Unit Setpoints
Description Default Range Type PW
UNIT
Unit Enable OFF OFF, ON N O
Unit Mode Cool Cool, Ice, Test M O
Control source Switches Switches, Keypad, Network N O
Available Modes Cool
Cool LWT
Ice LWT
Startup Delta T
Stop Delta T
Stage Up Delta T
Stage Down Delta T
Max Pulldown
Evap Recirc Timer 30 0 to 300 seconds N M
Evap Pump Select #1 Only #1 Only, #2 Only, Auto N M
LWT Reset Type NONE NONE, RETURN, 4-20mA, OAT N M
Max Reset
Start Reset Delta T
Soft Load Off Off, On N M
Begin Capacity Limit 40% 20-100% N M
Soft Load Ramp 20 min 1-60 minutes N M
Demand Limit Off Off, On N M
Low Ambient Lockout
Ice Time Delay 12 1-23 hours N M
Clear Ice Timer No No,Yes N M
Remote Evaporator No No, Yes M M
Quiet Night Disabled Disabled, Enabled N M
Quiet Night Start Time 21:00 18:00 - 23:59 N M
Cool, Cool w/Glycol, Cool/Ice w/Glycol, ICE
44°F 25(40) to 60°F
25°F 20 to 38°F
10°F 0 to 10°F
1.5°F 0 to 3°F
2°F 0 to 3°F
1°F 0 to 3°F
5 °F/min 0.5-5.0°F /min
0°F 0 to 20°F
10 °F 0 to 20°F
55°F 0(35) to 70°F
N M
N O
N O
M O
M O
M O
M O
M M
N M
N M
N M
Continued on next page.
18 OM AGSC-11
Recirculate Timeout
3 min 1 to 10 min
N M
35 to 70
°F
150 to 200
°F
Unit Setpoints, Continued
Description Default Range Type PW
Quiet Night End Tme 6:00 5:00 – 9:59 N M
Quiet Night Cond Offset
BAS Protocol Modbus BACnet, LONW
Ident number 1 0-200 N M
Baud Rate 19200 1200,2400,4800,9600,19200 N M
COMPRESSORS
Sequence # Cir 1 1 1-2 M M
Sequence # Cir 2 1 1-2 M M
Start-start timer 20 min 15-60 minutes M M
Stop-start timer 5 min 3-20 minutes M M
Pumpdown Pressure 25 psi 10 to 40 psi M M
Pumpdown Time Limit 120 sec 0 to 180 sec M M
Light Load Stg Dn Point 25% 20 to 50% M M
Stage Up Delay 5 min 0 to 60 min M M
Disc Temp Sensor Type PT 1000 NTC, PT 1000 (see note) M M
ALARMS
Low Evap PressureLow Evap PressureLow Oil Level Delay 120 sec 10-180 sec M M
High Oil Press Diff Delay 15 sec 0-90 sec M M
High Discharge
High Lift Pressure Delay 5 sec 0 to 30 sec M M
Evaporator Water
Evaporator Flow Proof 15 sec 5 to 15 sec N M
Startup Timer 60 sec 20 to 180 sec M M
10.0°F 0.0 to 25.0°F
ORKS
, Modbus N M
28 psi 0(26) to 45 psi M M
30 psi 0(28) to 45 psi M M
200°F
36°F 15(36) to 42°F
150 to 200 F M M
N N
N M
SENSORS
Evap LWT sensor offset 0 -5.0 to 5.0 deg N M
Evap EWT sensor offset 0 -5.0 to 5.0 deg N M
OAT sensor offset 0 -5.0 to 5.0 deg N M
NOTE: AGS-C vintage can have either PT1000 or NTC sensors. If an NTC sensor is used with a control setting of
PT1000, the unit will not run because the discharge temperature displayed will be above the allowable operating
temperature and a fault will occur. However, if a PT1000 sensor is used with a control setting of NTC, an unsafe
operating condition exists since the sensor will show the temperature as decreasing, while it is increasing .
Auto-Adjusted Ranges
Some settings have different ranges that are automatically adjusted, based on other settings.
Table 6, Auto Adjusted Ranges
Cool LWT Evaporator Water Freeze
Mode Range Mode Range
Unit Mode = Cool
Unit Mode = Cool w/Glycol
40 to 60°F
25 to 60°F
Low Evaporator Pressure Inhibit Low Evaporator Pressure Unload
Mode Range Mode Range
Unit Mode = Cool 28 to 45 Psig Unit Mode = Cool 26 to 45 Psig
Unit Mode = Cool w/Glycol,
Ice w/ Glycol
0 to 45 Psig
Low Ambient Lockout
Fan VFD Enable Range
= No for All Circuits
= Yes for Any Circuit
-10 to 70°F
It is critical that the chiller system has sufficient anti-freeze to support the settings entered
for freeze-up protection. The glycol freeze or burst temperature must be at least 10
degrees F below the freeze-up setpoint.
Unit Mode = Cool
Unit Mode = Cool w/Glycol,
Ice w/ Glycol
Unit Mode = Cool w/Glycol,
Ice w/ Glycol
High Discharge Temperature
Discharge Temp Type Range
NTC
PT 1000
36 to 42°F
10 to 42°F
0 to 45 Psig
150 to 230°F
OM AGSC-11 19
Unit Controller Functions
Parameter Definitions
LWT Slope
LWT slope is calculated so that the slope represents the change in LWT over a time frame of
one minute and is used to help determine the slide valve target.
Every 12 seconds, the current LWT is subtracted from the value 12 seconds back. This value
is added to a buffer containing values calculated at the last five 12-second intervals. The
final result is a slope value that represents the action of the LWT for the past 60 seconds.
Unit Capacity
Unit capacity is estimated based on the slide target of each running circuit. The capacity of a
running circuit is estimated with this equation:
Circuit capacity = 0.8(slide target) + 20
A circuit that is off is assumed to be at 0% capacity. The unit capacity is then calculated by
this equation:
Unit capacity = (Circuit 1 capacity + Circuit 2 capacity)/2
Unit Enable
Enabling and disabling the chiller is controlled by the Unit Enable Setpoint, with options of
OFF and ON. Enabling allows the unit to start if there is a call for cooling and also starts the
evaporator pump.
This setpoint (in other words, enabling the unit to run) can be altered by the Unit OFF input
(unit On/Off switch), a field installed remote stop switch, a keypad entry, or a BAS request.
The Control Source Setpoint determines which sources can change the Unit Enable Setpoint
with options of SWITCHES, KEYPAD or NETWORK.
Changing the Unit Enable Setpoint can be accomplished according to the following table.
NOTE: An “x” indicates that the value is ignored.
Table 7, Enable Sources
Unit On/Off
Switch
OFF x x x x OFF
On/OFF SWITCHES OFF x x OFF
ON SWITCHES ON x x ON
ON KEYPAD x OFF x OFF
ON KEYPAD x ON x ON
ON NETWORK x x OFF OFF
ON NETWORK OFF x x OFF
ON NETWORK ON x ON ON
NOTE: An “x” indicates that the value is ignored.
Control
Source
Setpoint
Remote
Stop
Switch
Key-pad
Entry
BAS
Request
Unit
Enable
Example:
1. If the Control Source is set to Switches, the field-installed remote Stop Switch controls
enabling. If the unit-mounted On/Off switch is either On or Off, the unit will be disabled
if the remote switch is Off. If the unit-mounted On/Off switch is On, the unit will be
enabled if the remote switch is On.
2. With the unit-mounted switch On, if the Control Source is Network, and the BAS signal
is Off, the unit is not enabled. If a Remote Switch is Off, the unit is not enabled. If a
Remote Switch is ON and the BAS input is On, the unit will be enabled.
20 OM AGSC-11
Chiller Control Source Options:
Set Unit Setpoints Screen #1 (shown below) has three fields: “Enable”, “Mode” and
“Source.”
Unit Setpoints
SET UNIT SPs (1)
Enable=On
Mode= COOL
Source = KEYPAD
1. The Enable field can only be used with Source = Keypad. To enable and disable the
chiller through the keypad, any other control inputs including unit and pumpdown
switches and BAS controls are ignored. The Enable field toggles between On and Off.
2. The Mode field is an informational display, showing the active control mode of the
chiller. It is used as an input only when the source is set to keypad. Only then can this
field be changed manually.
3. The Source field has three options, “SWITCHES”(default), “KEYPAD”, and “BAS
NETWORK”.
a. Switches source is used when there is no BAS interface used. This allows the unit
switches to function as pumpdown and shutdown switches for the circuit. This
option is used with applications using the remote start/stop input and not using a
BAS interface.
b. Keypad source is used to override BAS or remote start/stop commands. This would
be used for servicing only.
c. BAS Network source would be used for those applications using “MODBUS”,
“BACnet”, or “LON” communications through a building automation system. BAS
Protocol is set at Set Unit Setpoints item #14.
All methods of disabling the chiller, except for the unit switch, will cause a normal
pumpdown shutdown of any running circuits. Any time the unit switch is used to disable the
chiller, all running circuits will shut down immediately, without pumping down.
Shutdown by the unit switch without going through the pumpdown cycle is undesirable and
should only be used for an emergency shutdown or for manually and locally disabling the
unit after both circuits have gone through a normal shutdown.
Unit Mode Selection
The overall operating mode of the chiller is set by the Unit Mode setpoint with options of
COOL, ICE and TEST. This setpoint can be altered by the keypad, BAS, and Mode input.
Changes to the Unit Mode Setpoint are controlled by two additional setpoints.
• Available Modes setpoint: usually set during initial setup and determines the operational
modes available at any time with options of:
• COOL, cooling only operation, with setpoints available for normal chilled water
temperatures
• COOL w/Glycol, cooling only operation, allows lower setpoints than COOL
• COOL/ICE w/Glycol, allows both cooling and ice mode operation, switchable by a
field installed remote ICE mode switch, by the network (BAS) or locally through the
keypad.
• ICE w/Glycol, ice mode only, i.e., full load operation until LWT setpoint is reached
• TEST
OM AGSC-11 21
• Control Source Setpoint: The setting determines the source that can change the Unit
Mode Setpoint with options of KEYPAD, NETWORK, or SWITCHES.
When the Control source is set to KEYPAD, the Unit Mode stays at its previous setting until
changed by the operator. When the Control source is set to BAS, the most recent BAS mode
request goes into effect, even if it changed while the Control source was set to KEYPAD or
DIGITAL INPUTS.
Changing the Unit Mode Setpoint can be accomplished according to the following table.
NOTE: An “x” indicates that the value is ignored.
Table 8, Unit Mode Setpoint Sources
Control Source
Setpoint
x x x x COOL COOL
x x x x COOL w/Glycol COOL w/Glycol
SWITCHES OFF x x COOL/ICE w/Glycol COOL w/Glycol
SWITCHES ON x x COOL/ICE w/Glycol ICE w/Glycol
KEYPAD x COOL w/Glycol x COOL/ICE w/Glycol COOL w/Glycol
KEYPAD x ICE w/Glycol x COOL/ICE w/Glycol ICE w/Glycol
NETWORK x x COOL COOL/ICE w/Glycol COOL w/Glycol
NETWORK x x ICE COOL/ICE w/Glycol ICE w/Glycol
x x x x ICE w/Glycol ICE w/Glycol
x x x x TEST TEST
Remote
ICE Mode
Switch
Keypad Entry BAS Request
Available Modes
Setpoint
Resultant Unit
Mode
The Remote ICE Mode Switch (usually a time clock) is a field installed option and is used to
switch from ice mode operation at night to cooling mode operation during the day. This
requires that the Control Source be set to SWITCHES, which in this case refers to the
Remote ICE Mode Switch.
There are really only three operational modes for the unit, although they can be used in
combination:
1. COOL, the unit unloading and compressor staging is controlled by the Active LWT
Setpoint. COOL w/ Glycol is a special case of this mode, providing for lower setpoint
ranges.
2. ICE, the unit runs with all compressors fully loaded until the LWT (set for making ice) is
reached, and the unit shuts off. The Ice Delay Timer can be set to prevent restarting until
the next ice making cycle.
3. TEST, manually energize outputs for service testing.
Unit Test Mode
The unit test mode allows manual testing of controller outputs. Entering this mode requires
the following conditions.
• Unit OFF input = OFF (i.e. entire chiller is shut down).
• Technician password active.
• Available Circuit Mode setpoint = TEST
A test menu can then be selected to allow activation of the outputs. It is possible to switch
each digital output ON or OFF and set the analog outputs to any value.
22 OM AGSC-11
Unit States
The unit will always be in one of three states. Transitions between these states occur as
shown below.
Unit States
Power ON
T3
PUMPDOWN
OFF
T1
T4
T2
AUTO
Transitions:
T1 – Transition from Off to Auto requires all of the following:
• Unit enabled based on settings and switches.
• If unit mode is ice, the ice timer has expired
• No unit alarms exist.
• At least one circuit is enabled and available to start.
T2 – Transition from Auto to Pumpdown requires any of the following:
• Control source is keypad and the unit enable keypad setting is Off.
• Control source is BAS and either the remote switch is Off or the BAS command is Off
• Control source is switches and the remote switch is Off
T3 – Transition from Pumpdown to Off requires any of the following:
• All circuits have finished pumpdown and are Off.
• A unit alarm is active.
• Unit switch is Off.
T4 – Transition from Auto to Off requires any of the following:
• Unit switch is Off.
• A unit alarm is active.
• All circuits are unavailable to start (cannot start even after any cycle timers have
expired).
• The unit mode is ice, all circuits are Off, and the ice mode delay is active.
OM AGSC-11 23
Ice Mode Start Delay
An adjustable start-to-start Ice Time Delay limits the frequency with which the chiller may
start in Ice mode. The timer starts when the first compressor starts while the unit is in ICE
mode. While this timer is active, the chiller cannot restart in ICE mode. The time delay is
user adjustable from 1 to 23 hours.
The ice delay timer may be manually cleared to force a restart in ice mode. The Clear Ice
Timer setpoint is specifically for clearing the ICE mode delay. In addition, cycling the
power to the controller will clear the ice delay timer.
Evaporator Pump Control
Operation of the evaporator pump is controlled by the state-transition diagram shown below.
Figure 6, Evaporator Pump States
Evaporator Pump
States
Power ON
T3
RUN
OFF
T1
T4
T2
START
T5
Transitions:
T1 – Transition from Off to Start requires any of the following:
• Unit state = Auto AND If Low OAT Lockout is active then LWT <= 40 °F
• LWT < Freeze setpoint - 1
T2 – Transition from Start to Run:
• Flow OK for time > evaporator recirculate time
T3 – Transition from Run to Off requires any of the following:
• Unit state = Off AND LWT > Freeze setpoint
• Low OAT Lockout is in effect AND No compressors running AND LWT > 70°F
T4 – Transition from Start to Off requires all of the following:
• Unit state = Off AND LWT > Freeze set point
• LWT > Freeze setpoint + 1
T5 – Transition from Run to Start
• Evaporator flow input low AND Evaporator state = Run for time greater than Flow Proof
set point
Pump selection
The pump output used will be determined by the Evap Pump Control set point. This setting
allows the following configurations:
24 OM AGSC-11
#1 only – Pump 1 will always be used
#2 only – Pump 2 will always be used
Auto – The primary pump is the one with the least run hours, the other is used as a backup
#1 Primary – Pump 1 is used normally, with pump 2 as a backup
#2 Primary – Pump 2 is used normally, with pump 1 as a backup
Primary/Standby Pump Staging
The pump designated as primary will start first. If the evaporator state is Start for a time
greater than the recirculate timeout set point and there is no flow, then the primary pump will
shut off and the standby pump will start. When the evaporator is in the Run state, if flow is
lost for more than half of the flow proof set point, the primary pump will shut off and the
standby pump will start. Once the standby pump is started, the flow loss alarm logic will
apply if flow cannot be established in the evaporator start state, or if flow is lost in the
evaporator run state.
Auto Control
If auto pump control is selected, the primary/standby logic above is still used. When the
evaporator is not in the run state, the run hours of the pumps will be compared. The pump
with the least hours will be designated as the primary at this time.
Leaving Water Temperature (LWT) Reset
It is often desirable to raise (reset) the LWT setpoint to reduce unit energy consumption.
The Active Leaving Water variable (setpoint value) is normally set to the current Leaving
Water Temperature (LWT) setpoint, unless the unit is in COOL mode and any of the reset
methods shown below are selected and in effect. Reset is not available when in the ICE
mode.
The type of reset in effect is determined by the LWT Reset Type setpoint. The Active
Leaving Water variable is sent from the unit controller to all circuits for capacity control after
the applicable reset is applied.
Reset Type – NONE
The Active Leaving Water variable is set equal to the current LWT setpoint.
Reset Type – RETURN
The Active Leaving Water variable is adjusted by the return water temperature.
Figure 7, Return Water Reset
Return Reset
LWT set Point+Max Reset
(54)
Active
LWT
(oF)
Max Reset
(10)
LWT Set Point
(44)
0
Start Reset Delta T
Evap Delta T (oF)
OM AGSC-11 25
The active setpoint is reset using the following parameters:
1. Cool LWT setpoint
2. Max Reset setpoint
3. Start Reset Delta T setpoint
4. Evap Delta T
Reset is accomplished within the controller by changing the Active Leaving Water variable
from the Cool LWT setpoint to the Cool LWT set-point + Max Reset setpoint as the
Evaporator EWT – LWT (Evap Delta T) varies from the Start Reset Delta T set-point to 0.
Referring to Figure 7 as an example, the LWT is 44°F and a 10-degree maximum reset value
was selected. In other words, the Active LWT setpoint would range from the normal 44°F
setting up to 54°F depending on the Evap Delta-T. The amount of reset would be at the
maximum value (10 degrees) when the Evap Delta-T is zero and at the minimum value when
the Evap Delta-T is at the Start Reset Delta T value and is proportional in between. The Start
Reset Delta T function is available so that the start of reset can be adjusted. For example, on
a system with a 10-degree Delta-T, it may be desirable to not start the resetting until the
evaporator Delta-T goes down to eight degrees (80% load), or some other value.
Reset Type – 4-20 mA
The Active Leaving Water variable is adjusted by the 4 to 20 mA reset analog input.
Parameters used:
1. Cool LWT setpoint
2. Max Reset setpoint
3. LWT Reset signal
Reset is 0 if the reset signal is less than or equal to 4 mA. Reset is equal to the Max Reset
Delta T setpoint if the reset signal equals or exceeds 20 mA. The amount of reset will vary
linearly between these extremes if the reset signal is between 4 mA and 20 mA. An example
of the operation of 4-20 reset in Cool mode is shown below.
Figure 8, 4-20 mA Remote Reset Signal
4-20 mA Reset - Cool Mode
(54)
Active
LWT
(oF)
Max Reset
(10)
Cool LWT Set
Point (44)
0
4
Reset Signal (mA)
20
Reset Type – OAT
The Active Leaving Water variable is reset based on the outdoor ambient temperature (OAT).
Parameters used:
1. Cool LWT setpoint
2. Max Reset setpoint
3. OAT
26 OM AGSC-11
Reset is 0 if the outdoor ambient temperature is greater than 75°F. From 75°F down to 60°F
the reset varies linearly from no reset to the max reset at 60°F. At ambient temperatures less
than 60°F, reset is equal to the Max Reset setpoint.
Figure 9, Outside Air Reset
OAT Reset
Cool LWT+Max Reset
(54)
Active
LWT
(oF)
Max Reset
(10)
Cool LWT Set-Point
(44)
60
OAT (oF)
75
Unit Capacity Overrides
Unit capacity limits can be used to limit total unit capacity in COOL mode only. Multiple
limits may be active at any time, and the lowest limit is always used in the compressor
capacity control.
The estimated unit capacity and the active capacity limit are sent to all circuits for use in
compressor capacity control.
Soft Load
Soft Loading is a configurable function used to ramp up the unit capacity over a given time,
usually to influence building electrical demand by gradually loading the unit. The setpoints
that control this function are:
• Soft Load – (ON/OFF)
• Begin Capacity Limit – (Unit % load at start)
• Soft Load Ramp – (1 to 60 minutes))
The Soft Load Unit Limit increases linearly from the Begin Capacity Limit set-point to
100%, over the amount of time specified by the Soft Load Ramp set-point. If the option is
turned off, the soft load limit is set to 100%.
Demand Limit
The maximum unit capacity can be limited by a 4 to 20 mA signal wired to the Demand
Limit terminals, 70 and 71 on TB1. This function is only enabled if the Demand Limit
setpoint is set to ON.
As the signal varies from 4 mA up to 20 mA, the maximum unit capacity changes linearly
from 100% to 0%. Although the demand limit can call for 0% capacity, this signal will never
cause a running compressor to shut down. Rather, all running compressors will be held at
minimum load, and this may occur at a demand limit value that is actually less than 20mA.
OM AGSC-11 27
Network (BAS) Limit
The maximum unit capacity can be limited by a network signal. This function is only
enabled if the unit control source is set to NETWORK. The signal will be received through
the BAS interface on the unit controller.
As the signal varies from 0% up to 100%, the maximum unit capacity changes linearly from
0% to 100%. Although the network limit can call for 0% capacity, this signal will never
cause a running compressor to shut down. Rather, all running compressors will be held at
minimum load, and this may occur at a network limit value that is actually less than more
than 0%.
Building Automation System Interface
Connection to Chiller
Connection to the chiller for all BAS protocols will be at the unit controller. An interface
card (communication module) will have been installed in the unit controller at the factory, if
so ordered, or the module can be field installed after unit installation. The specific module
will depend on the protocol being used. Setting is made in Set Unit Setpoints, menu 14.
Additional information can be found in the following manuals:
LONW
ORKS –
BACnet – ED 15062 Modbus – ED 15063
IM 735 BACnet – IM 736 Modbus – IM 743
Quiet Night Operation
Logic has been added to limit unit capacity and fans running during nighttime hours.
• Settings were added to enable or disable this logic, set the start and end times, and set the
condenser target offset.
• Quiet Night operation is in effect if it is enabled via the set point, the unit is running in
cool mode, and the unit time is between the start and end time settings.
• When Quiet Night is in effect, the maximum LWT reset will be applied. This is to limit
the capacity of the compressors. In addition, the circuits will offset their condenser
targets up. Depending on conditions, this can result in less fans running and/or the VFD
running at a lower speed.
• The unit status will indicate when Quiet Night is in effect (assuming no overriding status
is active).
•
The Quiet Night reset will be overridden by any other reset source (4-20mA, return
water, OAT).
28 OM AGSC-11
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