McQuay WMC 300D Installation Manual
Operating and Maintenance Manual
OMM WMC-3 OITS
Group: Chiller
Part Number: 331374701
Effective: April 2006
Supersedes: OM WMC-2
WMC Magnetic Bearing Compressor Chillers
Model WMC 035T, 300D
50/60 Hertz
OITS Software Version: 2.02.01
Control Software Version: WMCUU02C
Table of Contents
Introduction.............................................3
Features of the Control Panel.................4
Definitions ................................................5
General Description ................................8
Control Panel.........................................10
Use with On-Site Generators................11
Sequence of Operation..........................12
Multi-Chiller Setup ...............................13
Operating the Control System..............15
Interface Panel On/Off......................................15
Start/Stop Unit..................................................
Change Setpoints..............................................
Alarms ..............................................................
Component Failure...........................................
15
15
15
16
Component Description........................16
Operator Interface Touch Screen......................16
Unit/Compressor Controller Description..........
Navigating ........................................................
16
17
Unit Controller.......................................19
Unit Controller Setpoints..................................19
Faults, Problems, Warnings ..............................
Unit Controller Functions.................................
21
22
Compressor Controller .........................23
Compressor Controller Setpoints......................24
Compressor Faults, Problems, Warnings..........
Compressor Controller Functions.....................
25
26
Compressor On-Board
Controllers..............................................
30
Interface Touch Screen..........................32
Navigation ........................................................32
Screen Descriptions ..........................................
VIEW Screens ..................................................
SET Screens......................................................
SERVICE Screen..............................................
HISTORY Screens............................................
Download Data.................................................
ACTIVE ALARM Screen.................................
34
34
39
52
53
54
55
Unit Controller Menu Screens .............57
Menu Matrix.....................................................58
Compressor Controller Menu
Screens....................................................
Menu Matrix.....................................................75
75
BAS Interface.........................................77
Operation...............................................
Operator Responsibilities..................................78
Compressor Operation......................................
Operating Limits:..............................................
Pressure Drop Curves.......................................
MicroTech II™ Control ....................................
Capacity Control System..................................
Surge and Stall..................................................
Condenser W ater Temperature..........................
Normal Unit Startup/Shutdown........................
Annual Unit Startup/Shutdown.........................
78
78
78
80
81
82
82
82
84
85
Maintenance...........................................85
Pressure/Temperature Chart ..............................86
Routine Maintenance........................................
Repair of System...............................................
87
88
Maintenance Schedule..........................90
Service Programs...................................91
Operator Schools...................................91
Warranty Statement..............................
91
Manufactured in an ISO Certified Facility
©
Illustrations and information cover McQuay International products at the time of publication and we reserve the right to make changes in design and
®™ The following are trademarks or registered trademarks of their respective companies: BACnet from ASHRAE; Modbus from Gould, Inc; L
2 OMM WMC-3 OITS
LONWORKS from Echelon Corporation; and MicroTech II from McQuay International.
and
2005 McQuay International
construction at anytime without notice.
Controllers are LONMARK certified with an
optional LONWORKS communication module.
ONMARK
Introduction
This manual provides setup, operating, and troubleshooting information for McQuay WMC
centrifugal chillers with the MicroTech ΙΙ™ controller. Please refer to the current version of IMM
WMC for information relating to the unit itself.
Electric shock hazard. Improper handling of this equipment 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 that are
Static sensitive components. A static discharge while handling electronic circuit boards
WARNING
knowledgeable in the operation of the equipment being controlled.
CAUTION
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,
may cause interference to radio communications. Operation of this equipment in a
residential area is likely to cause harmful interference in which case the user
will be required to correct the interference at the owner’s own expense.
McQuay disclaims any liability resulting from any interference or for the correction thereof.
Temperature and humidity considerations
The unit controllers are designed to operate within an ambient temperature range of 20°F to
+130°F (-7°C to +54°C) with a maximum relative humidity of 95% (non-condensing).
OMM WMC-3 OITS 3
Features of the Control Panel
• Control of leaving chilled water within a ±0.2°F (±0.1°C) tolerance.
• Display of the following temperatures and pressures on a 12-inch Super VGA touch-screen
operator interface (depending on date of manufacture):
• Entering and leaving chilled water temperature
• Enter and leaving condenser water temperature
• Saturated evaporator refrigerant temperature and pressure
• Saturated condenser temperature and pressure
• Outside air temperature (optional)
• Suction line, liquid line and discharge line temperatures, calculated superheat for discharge
and suction lines, and calculated subcooling for liquid line
• Automatic control of primary and standby evaporator and condenser pumps.
• Control of up to 4 stages of cooling tower fans plus modulating bypass valve and/or tower fan
VFD. Although fan staging is available, continuous, modulated control of tower capacity is
preferred and recommended.
• History trend feature that will constantly log chiller functions and setpoints. The controller will
store and display all accumulated data for recall in a graphic format on the screen. Data can be
downloaded for archival purposes.
• Three levels of security protection against unauthorized changing of setpoints and other control
parameters.
• Plain language warning and fault diagnostics to inform operators of most warning or fault
conditions. Warnings, problems and faults are time and date stamped for identification of when
the fault condition occurred. In addition, the operating conditions that existed just prior to
shutdown can be recalled to aid in resolving the cause of the problem.
• Twenty-five previous faults and related operating conditions are available from the display. Data
can be exported for archival purposes via a 3.5-inch floppy drive or other device (depending on
date of manuafacture).
• Soft loading feature reduces electrical consumption and peak demand charges during system
loop pulldown.
• Remote input signals for chilled water reset, demand limiting and unit enable.
• Manual control mode allows the service technician to command the unit to different operating
states. Useful for system checkout.
• BAS communication capability via L
most BAS manufacturers.
• Service Test mode for troubleshooting controller outputs.
• Pressure transducers for direct reading of system pressures.
• Preemptive control of low evaporator and high discharge pressure conditions to take corrective
action prior to a fault trip.
ONTALK®, Modbus® or BACnet® standard protocols for
4 OMM WMC-3 OITS
Definitions
Active Setpoint
The active setpoint is the parameter setting in effect at any given moment. This variation can occur
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 capacity 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.
Active-Amp-Limit
Active amp limit is the actual amp limit imposed by an outside signal such as the load limit
function.
Condenser Recirc (Recirculation) Timer
A timing function, with a 30-second default, that holds off any reading of condenser water for the
duration of the timing setting. This delay allows the sensors to take a more accurate reading of the
condenser water temperature.
Dead Band
The dead band is a set of values associated with a setpoint such that a change in the variable
occurring within the dead band causes no action from the controller. For example, if a temperature
setpoint is 44°F and it has a dead band of ± 2.0 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 is calculated 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 Hold-loading
This is a setpoint that establishes the minimum evaporator pressure to which the chiller is allowed
to go. It signals that the unit is at full load so the no further loading will occur that would lower the
pressure even further.
Evap Recirc (Evaporation Recirculation) 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 to take a more accurate
reading of the chilled water temperature.
EXV
Electronic expansion valve, used to control the flow of refrigerant to the evaporator, controlled by
the circuit microprocessor.
OMM WMC-3 OITS 5
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. Used to limit unit power input.
Load Balance
Load balance is a technique that equally distributes the total unit load between two or more running
compressors.
Low Pressure Hold (Inhibit) Setpoint
The psi evaporator pressure setting at which the controller will not allow further compressor
loading. “Hold” and “Inhibit” are used interchangeably.
Low Pressure Unload Setpoint
The psi evaporator pressure setting at which the controller will unload the compressor in an effort
to maintain the minimum setting.
LWT
Evaporator 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 chilled 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
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.
OITS
Operator Interface Touch Screen, one screen per unit provides operating data visually and
accommodates setpoint entry.
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. The pressure is
fitted to an R-134a temperature/pressure curve to determine the saturated temperature.
Soft Load
Soft Load is a control sub-routine that allows the chiller to load up gradually. It requires setpoint
inputs of selecting it by Yes or No inputs, by selecting the percent load to start ramping up, and by
selecting the time to ramp up to full load (up to 60 minutes).
6 OMM WMC-3 OITS
SP
Setpoint
Suction Superheat
Suction superheat is calculated for each circuit using the following equation:
Suction Superheat = Suction Temperature – Evaporator Saturated Temperature
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 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 located on the compressor, used to vary the compressor speed.
OMM WMC-3 OITS 7
f
General Description
Major Components
Figure 1, Major Component Location
Unit Control Panel
Evaporator Relie
Valve
Operator
Interface Panel
Compressor #1
with On-Board
Compressor #2
with On-Board
Controls
Condenser
Relief Valves
Optional Unit Disconnect Switch
& Single Point Power Connection
Circuit #1
Power Panel
Electronic Expansion Valve
Circuit #2
Power Panel
General Description
The centrifugal MicroTech ΙΙ control system consists of microprocessor-based controllers in the
control panel, as well as on-board the compressors, providing monitoring and control functions
required for the controlled, efficient operation of the chiller. The system consists of the following
components:
• Operator Interface Touch Screen (OITS), one per unit-provides unit information and is the
primary setpoint input instrument. It has no control function.
• Unit Controller, one per chiller-controls unit functions and communicates with all other
controllers. It is the secondary location for setpoint input if the OITS is inoperative. It is
located in the control panel that is adjacent to the OITS Panel.
• Compressor Controller for each compressor-controls compressor functions. They are located
in the control panel.
• On-board compressor controller mounted on each compressor that monitors compressor
operation and controls bearing operation.
The operator can monitor all operating conditions by using the unit-mounted OITS. 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 conditions. If a fault condition develops, the controller will shut a compressor, or
the entire unit, down 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.
8 OMM WMC-3 OITS
The system is password protected and only allows access by authorized personnel. The operator
must enter the password into the touch screen (or one of the controller's keypad) before any
setpoints can be altered.
NOTE: It is important to understand that the OITS is the operator interface device under normal
conditions. If, and only if, it is unavailable, should the unit controller be used to change setpoints
or operate the chiller.
Figure 2, Major Control Components
Comm. Module
Universal
pLAN
OPERATOR
INTERFACE
TOUCH-SCREEN
UNIT
CONTROLLER
#1 COMPRESSOR
CONTROLLER
#2 COMPRESSOR
CONTROLLER
BAS
Onboard
Control
Onboard
Control
Color Graphics
Touch-Screen Interface
View Data, Input Setpoints
Stores History
UNIT
Analog Inputs
Analog Outputs
Digital Inputs
Digital Outputs
COMPRESSOR
Analog Inputs
Analog Outputs
Digital Inputs
Digital Outputs
OMM WMC-3 OITS 9
Control Panel
The unit and compressor
controllers along with unit and
compressor on/off switches are
mounted in the unit control panel,
which is mounted adjacent to the
OITS panel. See
switches are designated “I” for on
and “0” for off. The compressor
on/off switch should only be used
when an immediate stop is
required since the normal shut
down sequence is bypassed.
The switch panel also has a Circuit
Breaker that interrupts power to
the cooling tower fans, valves and
evaporator and condenser pumps,
if any of these are tied into the
MicroTech II controller for control
of their operation. If these
components operate independently
from the chiller control, the
breaker has no effect.
The unit controller's primary
function is processing data relating
to the entire chiller
as compared to data relating to the
compressor operation. The unit
controller processes information
and sends data to the compressor
controllers and devices and relays information to the OITS for graphic display. It has a 4x20 LCD
display and keys for accessing data and changing setpoints. The controller LCD can display most
of the same information as the OITS and can operate the chiller independently if the OITS is not
available.
Figure 1. The
unit operation
Figure 3, Control Panel Interior
Switch Panel and
Switches, See Below.
Unit Controller
SW5, Emergency
Shutdown Switch,
Outside Panel
USB Port Located on
PC Located in this Area
Compressor #1
Controller
Compressor #2
Controller
Figure 4, Switch Locations
Compressor #1 Switch
Compressor #2 Switch
SWT 5, Emergency
Shutdown Switch
Outside Panel
Unit Switch
Circuit breaker
10 OMM WMC-3 OITS
Use with On-Site Generators
WMC chillers have their total tonnage divided between two compressors that start sequentially and they are
operated with variable frequency drives. These features make WMC chillers especially appropriate for use
in applications where they may be required to run with on-site electrical generators. This is particularly
true when the generators are used for temporary power when the utility power is lost.
Starting/Stopping Procedure: The stopping of the chiller in the event of a power failure should be
uneventful. The chiller will sense a loss of voltage and the compressors will stop, coasting down using
power generated from their dynamic braking to maintain the bearing magnetic field. The stop signal will
initiate a three-minute stop-to-start timer, effectively preventing compressor restart for three minutes. The
timer is adjustable from three to fifteen minutes, but the recommended, and default value, is three minutes.
This interval allows the generator sufficient time to get up to speed and stabilize. The chiller will restart
automatically when the start-to-start timer expires.
Transfer Back to Grid Power: Proper transfer from stand-by generator power back to grid power is
essential to avoid compressor damage.
Stop the chiller before transferring supply power from the generator back to the utility
power grid. Transferring power while the chiller is running can cause severe
compressor damage.
The necessary procedure for reconnecting power from the generator back to the utility grid is show below.
These procedures are not peculiar to McQuay units only, but should be observed for any chiller
manufacturer.
CAUTION
1. Set the generator to always run five minutes longer than the unit start-to-start timer, which could be set
from 15 to 60 minutes. The actual setting can be viewed on the operator interface panel on the
Setpoint/Timer screen.
2. Configure the transfer switch, provided with the generator, to automatically shut down the chiller
before transfer is made. The automatic shut-off function can be accomplished through a BAS interface
or with the “remote on/off” wiring connection shown in
after the stop signal since the three-minute start-to-start timer will be in effect.
Chiller Control Power: For proper operation on standby power, the chiller control power must remain as
factory-wired from a unit-mounted transformer. Do not supply chiller control power from an external
power source because the chiller may not sense a loss of power and do a normal shutdown sequence.
Figure 9. A start signal can be given anytime
OMM WMC-3 OITS 11
Sequence of Operation
Start-up of WMC Compressors:
“Next On” status
If none of the “OFF” conditions are true, then all the MicroTech II compressor controls in a
network of up to 2 units (four compressors) will pole the status of each to determine the one having
“Next On” status, which is usually the compressor with the least starts. This takes about one
minute.
Evap (Evaporator) Pump Start
Once this is determined, the unit controller of the chiller with the ‘Next On’ compressor (when
there are two chillers) will start the evaporator pump and determine if there is load based on the
water temperature. This is determined if the leaving evaporator water is above the ‘LWT Setpoint’
plus ‘Startup Delta T’. If there is no load, based on the temperature, the unit is in the state of
‘Awaiting Load’.
Interlock On
If there is load, the unit waits for the Evaporator Recirculation Timer period (default value of 30
seconds) and starts the Interlock Timer for 10 sec.
Cond (Condenser) Pump Start
After Interlock is confirmed, the controller starts the Condenser Pump and checks for condenser
flow before starting the first compressor.
Compressor Start
Starting the compressor is accomplished by setting the Demand to 25% of the MAX KW setpoint.
When the actual RPM of the compressor exceeds 350 RPM, the demand setting is allowed to be
governed by the normal control logic.
Compressor Run
The compressor that is running will signal all other compressors when it reaches full load.
Full load status is determined when
1. Percent RLA exceeds 100% or the Active-Amp-Limit from an external-limiting source.
2. Evap Saturation pressure drops below the Evap Hold-Loading pressure setpoint.
3. Actual compressor RPM exceeds 97% of Max RPM limit from compressor.
any one of the following tests is true:
Lag Compressor Staging
The ‘Next On’ compressor, will initiate the following staging sequence when it receives a Full
Load indication from the Lead compressor, or all other running compressors in the case of a four
compressor (two units) setup.
12 OMM WMC-3 OITS
The lag compressor will start (Demand set to 25% of Max KW setpoint). When the actual RPM
exceeds 350 RPM, the lead compressor will unload to 25% of the MAX KW setpoint. The lead
compressor will maintain this demand setting for a time period set by the Step-Down timer (found
in Set COMP1 SPs (8) ). When the Step–Down timer expires, both compressors should be nearly
matched in capacity and can began amp balancing to share the load equally.
Note: If the “Next On” compressor is on another chiller, the controller will start that chiller’s
evaporator and condenser pumps, if they are separate from the lead unit’s pumps. Only
compressors on the same unit will unload the lead compressor before starting the lag compressor.
Unloading compressors:
The setpoint of ‘Nominal Capacity’ is used for defining the point to unload a compressor on a
single or two-chiller system. With each compressor having its ‘Nominal Capacity’ defined, then
the network, which is load balanced, continues to unload at 0.2 tenths or more below setpoint.
Each compressor keeps computing the spare capacity of the network. When the designated ‘Next
Off’ sees enough spare capacity, it will turn off. Then similarly, in about 40 seconds, a new
compressor will be designated as the ‘Next Off’ and the spare capacity will continue to be
calculated between the remaining compressors. Compressors continue to unload and stage off until
there is only one compressor running. It will shut off when the water temperature reaches the LWT
Setpoint minus the Shutdown Delta T.
Multi-Chiller Setup
Component Description
pLAN Setup
The pLAN communication wiring and setup required for dual compressor operation is
setup in the factory and should be reviewed when the chiller is initially started after
installation or if there is any change made in the chiller control hardware.
pLan RS485 communication wiring between chillers should be field wired before start-up
and installed as a NEC Class 1 wiring system.
Table 1, Address DIP Switch Settings for Controllers Using pLAN).
Chiller Comp 1 Comp 2
A
B
NOTES:
1 2 5 6 7 8
100000 010000 101000 011000 111000 000100
9 10 13 14 15 16
100100 010100 101100 011100 111100 000010
Unit
Controller
Reserved
1. Two WMC units can be interconnected.
2. The interface setting is not a DIP switch setting. The ‘Operator Interface Touch Screen’ (OITS)
address is selected by selecting the ‘service’ set screen. Then, with the Technician level
password active, select the ‘pLAN Comm’ button. Buttons A(7), B(15), C(23), D(31) will
appear in the middle of the screen, then select the letter for the OITS address for the chiller that
it is on. Then close the screen. Note that A is the default setting from the factory.
3. There are six Binary DIP Switches: Up is ‘On’, indicated by ‘1’. Down is ‘Off’, indicated by
‘0’. They are slide and not rocker switches. They are located on the upper-left corner of the
face of the controller.
Operator
Interface
Reserved
OMM WMC-3 OITS 13
Operator Interface Touch Screen (OITS) Settings
Settings for any type of linked multiple compressor operation must be made to the MicroTech II
controller. Settings on a dual compressor unit are made in the factory prior to shipment, but must
be verified in the field before startup. Settings for multiple chiller installations are set in the field
on the Operator Interface Touch Screen as follows:
Maximum Co mpr esso rs O N
– SETPOINTS - MODES screen, Selection #10 = 2 for a WMC, 4 for
2 WMCs.
Sequence and Staging
– SETPOINTS - MODES screen, Selection #11 & #13; #12 & #14.
Sequence sets the sequence in which compressors will start. Setting all to “1” evokes the automatic
lead/lag feature and is the preferred setting.
Nominal Capacity
– SETPOINTS - MOTOR screen, Selection #10. The setting is the compressor
design tons. Compressors on dual units are always of equal capacity.
pLAN Setup
1. With no pLAN connections between chillers, disconnect control power and set the DIP
switches as shown in
2. With all manual switches off, turn on control power to each chiller and set each OITS address
(see Note 2 above).
3. Verify correct nodes on each OITS Service Screen.
4. Connect chillers together (pLAN, RS485, between pLAN connections on each unit’s UCM or
J10 and J11 terminals on the unit controller. The UCM board part number is 330276202 and
can be ordered with this units or separately after shipment.
5. Verify correct nodes on each OITS Service Screen. See
Table 1.
Figure 27 on page 52.
14 OMM WMC-3 OITS
Operating the Control System
Interface Panel On/Off
The Operator Interface Panel is turned on and off with a push-push switch located at the upper-left
corner of the panel. ON is the outermost switch position and a white band will be visible on the
switch stem. Off is innermost and no white is visible.
The screen is equipped with a screen saver that blackens the screen. Touching the screen anywhere
reactivates the screen. If the screen is black, touch it first to be sure it is on before using the
ON/OFF switch.
Start/Stop Unit
There are four ways to start or stop the chiller. Three are shown below and selected in SETPOINT\
MODE\SP3; the fourth way is through panel-mounted switches:
1. Operator Interface Panel (LOCAL)
Home Screen 1 has AUTO and STOP buttons that are only active when the unit is in "LOCAL
CONTROL". This prevents the unit from being accidentally started or stopped when it is normally
under control from a remote switch or BAS. When these buttons are pressed, the unit will cycle
through its normal starting or stopping sequence.
2. Remote SWITCH
Selecting SWITCH in SP3 will put the unit under the control of a remote switch that must be wired
into the control panel (see
Figure 9 on page 31).
3. BAS
BAS input is field-wired into a module that is factory-installed on the unit controller.
Control Panel Switches
The unit control panel, located adjacent to the Interface Panel, has switches inside the panel for
stopping the entire unit or individual compressors. When the UNIT switch is placed in the OFF
position the chiller will shut down through the normal shutdown sequence, whether one or two
compressors are on.
The COMPRESSOR switches will immediately shut down the compressor without going through
the shutdown sequence when placed in the OFF position. It is equivalent to an emergency stop
switch.
Change Setpoints
Setpoints are easily changed on the Operator Interface Touch Screen (OITS). A complete
description of the procedure begins on page
controller, but this is not recommended except in an emergency, when the OITS is unavailable.
40. Setpoints can also be changed in the unit
Alarms
A red ALARM light in the lower middle of any screen is illuminated if there is an alarm. If the
optional remote alarm is wired in, it too will be energized.
There are three types of alarms:
• Fault, equipment protection alarms that shut a unit or compressor off.
• Problem, limit alarms that limit compressor loading in response to an out-of-normal condition.
If the condition that caused a limit alarm is corrected, the alarm light will be cleared
automatically.
• Warning, notification only, no action taken by controller.
OMM WMC-3 OITS 15
Any type will light the ALARM light. Procedures for dealing with alarms are shown below:
1. Press the alarm light button. This will go directly to the ACTIVE ALARMS screen.
2. The alarm description (with date stamp) will be shown.
3. Press the ACKNOWLEDGE button to recognize the alarm.
4. Correct the condition causing the alarm.
5. Press the CLEAR button to clear the alarm from the controller. If the fault condition is not
fixed, the alarm will continue to be on and the unit will not be able to be restarted.
Component Failure
Chiller Operation without the Operator Interface Panel
The Interface Panel communicates with the unit and compressor controllers, displaying data and
transmitting touch screen inputs to the controllers. It does no actual controlling and the chiller can
operate without it. Should the Touch Screen become inoperable, no commands are necessary for
continuing unit operation. All normal inputs and outputs will remain functional. The unit
controller can be used to view operational data, to clear alarms and to change setpoints, if
necessary.
Component Description
Operator Interface Touch Screen
The operator interface touch screen (OITS) is the
primary device for entering commands and entries
into the control system. (Settings can also be made
directly into the unit controller.) The OITS can also
display controller data and information on a series of
graphic screens. A single OITS is used per unit.
Selected information from the OITS panel can be
down-loaded via a USB port located in the unit
control panel.
The OITS panel is mounted on a moveable arm to
allow placement in a convenient position for the
operator.
There is a screen-saver programed into the system. The screen is reactivated by touching it
anywhere.
Unit/Compressor Controller Description
Hardware Structure
The controllers are fitted with a microprocessor for running the control program. There are
terminals for connection to the controlled devices (for example: solenoid valves, tower fans,
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.
Each controller connects to other controllers, the on-board compressor microprocessors and the
OITS via a local communications network (pLAN). The unit controller also has remote
communication capability for BAS interface.
16 OMM WMC-3 OITS
A
t
Keypad
A 4 line by 20 character/line liquid crystal display and 6-button keypad is mounted on the unit and
compressor controllers. Its layout is shown below.
Figure 5, Controller Keypad
Key-to-Screen Pathway
Air Conditioning
LARM
<
VIEW
<
SET
<
MENU Key
ARROW Keys (4)
ENTER Key with
Green Run Ligh
Behind
The four arrow keys (UP, DOWN, LEFT, RIGHT) have three modes of use:
• Scroll between data screens in the direction indicated by the arrows (default mode).
• Select a specific data screen in the menu matrix using dynamic labels on the right side of the
display such as ALARM, VIEW, etc (this mode is entered by pressing the MENU key). For
ease of use, a pathway connects the appropriate button to its respective label on the screen.
• Change field values in setpoint programming mode according to the following table:
LEFT key = Default RIGHT key = Cancel
UP key = Increase (+) DOWN key = Decrease (-)
These four programming functions are indicated by one-character abbreviation on the right side of
the display. This programming mode is entered by pressing the ENTER key.
Getting Started
There are two basic procedures to learn in order to utilize the MicroTech II controller:
1. Navigating through the menu matrix to reach a desired menu screen and knowing where a
particular screen is located.
2. Knowing what is contained in a menu screen and how to read that information or how to
change a setpoint contained in the menu screen.
Navigating
The menus are arranged in a matrix of screens across a top horizontal row. Some of these top-level
screens have sub-screens located under them. The location of each controller’s screens can be
found in the following table:
Controller Screen Matrix Screen Details
Unit Page 58 Page 60
Compressor Page 75 Not Applicable
There are two ways to navigate through the menu matrix to reach a desired menu screen.
1) One is to scroll through the matrix from one screen to another using the four ARROW keys.
2) Another way is to use shortcuts to work through the matrix hierarchy. From any menu screen,
a) Pressing the MENU key will take you to the top level of the hierarchy. The display will
show ALARM, VIEW, and SET as shown in
Figure 5. One of these choices can then be
selected by pressing the key connected to it via the pathway shown in the figure.
OMM WMC-3 OITS 17
b) Depending on the top-level selected, a second level of screens will appear. For example,
selecting ALARM will go the next level of menus under ALARM (ALARM LOG or
ACTIVE ALARM). Selecting VIEW will go the next level of menus (VIEW
COMPRESSOR STATUS, VIEW UNIT STATUS, VIEW EVAPORATOR, or VIEW
CONDENSER). Selecting SET will go to a series of menus for looking at and changing
setpoints.
c) After selecting this second level, the desired screen can be acquired using the arrow keys.
A typical final screen is shown below.
Pressing the MENU key from any menu screen will automatically return you to the MENU mode.
Figure 6, Typical Menu Display and Keypad Layout
MENU Key
Air Conditioning
VIEW UNIT STATUS
Unit = COOL
Compr. #1/#2=OFF/OFF
Evap Pump = RUN
ARROW Keys
ENTER Key
Menu Screens
A hierarchical menu structure is used to access the various screens. Each menu screen can have
one to four lines of information. Optionally, the last menu selection can access one of a set of
screens that can be navigated with the UP/DOWN arrow keys (see the scrolled menu structure
below). Menu selection is initiated by pressing the MENU key, which changes the display from a
data screen to a menu screen. Menu selections are then made using the arrow keys according to
labels on the right side of the display (the arrows are ignored). When the last menu item is
selected, the display changes to the selected data screen. An example follows showing the
selection of the “VIEW COMPRESSOR (n) screen. Suppose the initial screen is:
ALARM LOG
(data)
(data)
After pressing the MENU button, the top-level menu screen will
show:
(data)
< ALARM
< VIEW
< SET
After pressing the “VIEW” menu button, a menu screen will
show:
<
VIEW < COMPRESSOR
< UNIT
< EVAPORATOR
After pressing the “COMPRESSOR” menu button, the selected
data screen will show
< CONDENSER
VIEW COMP (n)
(screen n data)
(screen n data)
(screen n data)
.
18 OMM WMC-3 OITS
Where “n” is the number of the last viewed COMPRESSOR
screen. The arrow keys will automatically return to the
“scroll” mode at this time. Different compressor screens can
then be selected with the UP/DOWN arrow keys
Unit Controller
Table 2, Unit Controller, Analog Inputs
# Description Signal Source Range
1 Reset of Leaving Water Temperature 4-20 mA Current 0-(10 to 80°F)
Entering Evaporator Water
2
Temperature
Entering Condenser Water
3
Temperature
4 Leaving Condenser Water Temperature NTC Thermistor (10k@25°C) -58 to 212°F
5 Liquid Line Refrigerant Temperature NTC Thermistor (10k@25°C) -58 to 212°F
6 Demand Limit 4-20 mA Current 0-100 %RLA
7 Evaporator Water Flow 4 to 20 mA Current 0 to 10,000 gpm
8 Condenser Water Flow 4 to 20 mA Current 0 to 10,000 gpm
9 Refrigerant Leak Sensor 4 to 20 mA Current 0 to 100 ppm
10 Spare
Table 3, Unit Controller, Digital Inputs
# Description Signal Signal
1 Unit OFF Switch 0 VAC (Stop) 24 VAC (Auto)
2 Remote Start/Stop 0 VAC (Stop) 24 VAC (Start)
3 Not Used
4 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
5 Condenser Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
NTC Thermistor (10k@25°C) -58 to 212°F
NTC Thermistor (10k@25°C) -58 to 212°F
Table 4, Unit Controller, Digital Outputs
# Description Load Output OFF Output ON
1 Evaporator Water Pump #1 Pump Contactor Pump OFF Pump ON
2 Evaporator Water Pump #2 Pump Contactor Pump OFF Pump ON
3 Condenser Water Pump #1 Pump Contactor Pump OFF Pump ON
4 Condenser Water Pump #2 Pump Contactor Pump OFF Pump ON
5 Tower Fan #1 Fan Contactor Fan OFF Fan ON
6 Tower Fan #2 Fan Contactor Fan OFF Fan ON
7 Spare
8 Alarm Alarm Indicator Alarm OFF Alarm ON
9 Tower Fan #3 Fan Contactor Fan OFF Fan ON
10 Tower Fan #4 Fan Contactor Fan OFF Fan ON
Table 5, Unit Controller, Analog Outputs
# Description Output Signal Range
1 Cooling Tower Bypass Valve Position 0 to 10 VDC 0 to 100% Open
2 Cooling Tower VFD Speed 0 to 10 VDC 0 to 100%
3 EXV signal to IB Valve Control Bd. 0 to 10 VDC 0 to 100%
4 Y3 Electronic Expansion Valve 0 to 10 VDC 0 to 100% Open
Unit Controller 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
The “Type: column defines whether the setpoint is part of a coordinated set of duplicate setpoints
in different controllers. There are three possibilities as given below:
Range column.
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
S = Slave setpoint - Setpoint is a copy of the master setpoint (in the unit controller)
OMM WMC-3 OITS 19
At power-up the slave node checks if the master node is operational and if so, it sets its copy of the
setpoint equal to the master’s. Otherwise, the setpoint remains unchanged. During normal
operation, any time the master setpoint changes, the slave is updated as well.
The PW (password) column indicates the password that must be active in order to change the
setpoint. Codes are as follows:
O = Operator, M = Manager, T = Technician (not available through the 4x20 display/keypad)
The following table groups setpoints that relate to the entire unit operation and are stored, for the
most part, in the unit controller. All settings are made through the OITS, indiscriminately as to
whether they are “unit” or “compressor”.
Table 6, Unit Controller Setpoints
Description Default Range Type PW
Unit
Unit Enable OFF OFF, ON M O Pg. 50
Control Source KEYPAD
Display Units
Language ENGLISH ENGLISH, (TBD) N O -BAS Protocol NONE
Leaving Water
Cool LWT
Startup Delta T
Shutdown Delta T
LWT Reset Type NONE NONE, RETURN, 4-20mA N M Pg. 22
Max Reset Delta T
Start Reset Delta T
Timers
Evap Recirculate 30 sec 15 sec to 5 min N M Pg. 5
Pumps
Evap Pump
Cond Pump
Cooling Tower
Tower Control None None, Temperature, Lift N M Pg. 46
Tower Stages 2 1 to 4 N M Pg. 46
Stage Up Time 2 min 1 to 60 min N M Pg. 46
Stage Down Time 5 min 1 to 60 min N M Pg. 46
Stage Differential (Temp)
Stage Differential (Lift) 6.0 psi 1.0 to 20.0 psi N M Pg. 46
Stage #1 On (Temp)
Stage #2 On (Temp)
Stage #3 On (Temp)
Stage #4 On (Temp)
Stage #1 On (Lift) 35 psi 10 to 130 psi N M Pg. 46
Stage #2 On (Lift) 45 psi 10 to 130 psi N M Pg. 46
Stage #3 On (Lift) 55 psi 10 to 130 psi N M Pg. 46
Stage #4 On (Lift) 65 psi 10 to 130 psi N M Pg. 46
Cooling Tower Valve / VFD
Valve/VFD Control None
Valve Setpoint (Temp)
Valve Setpoint (Lift) 30 psi 10 to 130 psi N M Pg. 46
Valve Deadband (Temp)
Valve Deadband (Lift) 4.0 psi 1.0 to 20.0 psi N M Pg. 46
°F/psi °F/psi, °C/kPa
None, Local, Remote, BACnet, LON,
44. 0°F 40.0 to 80.0 °F
3.0°F 0.0 to 10.0 °F
3.0°F 0.0 to 3.0 °F
0.0°F 0.0 to 20.0 °F
10. 0°F 0.0 to 20.0 °F
Pump #1
Only
Pump #1
Only
3.0 °F 1.0 to 10.0 °F
70 °F 40 to 120 °F
75 °F 40 to 120 °F
80 °F 40 to 120 °F
85 °F 40 to 120 °F
65 °F 40 to 120 °F
2.0 °F 1.0 to 10.0 °F
Pump #1 Only, Pump #2 Only, Auto
Pump #1 Only, Pump #2 Only, Auto
None, Valve Setpoint, Valve Stage,
VFD Stage, Valve SP/VFD Stage
KEYPAD, BAS,
DIGITAL INPUT
MODBUS, CSC
Lead, #1 Primary, #2 Primary
Lead, #1 Primary, #2 Primary
N O Pg. 50
N O --
N M Pg. 50, Pg 77
M O Pg. 11, Pg. 51
M O Pg. 11, Pg. 51
M O Pg. 11, Pg. 51
N M Pg. 22
N M Pg. 22
N M Pg. 65
N M Pg. 65
N M Pg. 46
N M Pg. 46
N M Pg. 46
N M Pg. 46
N M Pg. 46
N M Pg. 46
N M Pg. 46
N M Pg. 46
Continued on next page
Manual
Reference
20 OMM WMC-3 OITS
Description Default Range Type PW
Stage Down @ 20% 0 to 100% N M Pg. 46
Stage Up @ 80% 0 to 100% N M Pg. 46
Valve Control Range (Min) 10% 0 to 100% N M Pg. 46
Valve Control Range(Max) 90% 0 to 100% N M Pg. 46
Valve Type
Minimum Start Position 0% 0 to 100% N M Pg. 46
Minimum Position @
Maximum Start Position 100% 0 to 100% N M Pg. 46
Maximum Position @
Error Gain 25 10 to 99 N M Pg. 46
Slope Gain 25 10 to 99 N M Pg. 46
NC
(To Tower)
60 °F 0 to 100 °F
90 °F 0 to 100 °F
NC, NO N M Pg. 46
N M Pg. 46
N M Pg. 46
Manual
Referance
These setpoints are normally viewed or changed on the OITS.
Faults, Problems, Warnings
Faults (Equipment Protection Shutdowns)
There are no Unit protection shutdown alarms; all such alarms are handled through the compressor
controllers.
Problems (Limit Alarms)
The following alarms limit operation of the chiller in some way as described in the Action Taken
column.
Table 7, Unit Controller Limit Alarms
Description Occurs When: Action Taken Reset
Evaporator Pump #1
Fault
Evaporator Pump #2
Fault
Condenser Pump #1
Fault
Condenser Pump #2
Fault
Entering Evaporator
Water Temperature
Sensor Fault
No flow indicated for (5 sec) with Evaporator Pump #1 ON
AND [the other pump is available (per the Evap Pump SP)
AND has not faulted]
No flow indicated for (5 sec) with Evaporator Pump #2 ON
AND [the other pump is available (per the Evap Pump SP)
AND has not faulted]
No flow indicated for (5 sec) with Condenser Pump #1 ON
AND [the other pump is available (per the Evap Pump SP)
AND has not faulted]
No flow indicated for (5 sec) with Condenser Pump #2 ON
AND [the other pump is available (per the Evap Pump SP)
AND has not faulted]
Sensor fault AND leaving water reset is based on entering
water
Start pump #2 Manual
Start pump #1 Manual
Start pump #2 Manual
Start pump #1 Manual
Manual.
Reset mode is
set to No Reset
(Reset mode
goes back to
Entering
Water)
Warnings
The following “alarms” only generate a warning message to the operator. Chiller operation is not
affected.
Table 8, Unit Controller Warnings
Description Occurs When: Action Taken Reset
Entering Evaporator Temperature Sensor Fault Sensor is open or shorted Annunciation Automatic
Entering Condenser Temperature Sensor Fault Sensor is open or shorted Annunciation Automatic
Leaving Condenser Temperature Sensor Fault Sensor is open or shorted Annunciation Automatic
Liquid Line Refrigerant Temperature Sensor Fault Sensor is open or shorted Annunciation Automatic
OMM WMC-3 OITS 21
Unit Controller Functions
Leaving Water Temperature (LWT) Reset
The Active Leaving Water variable shall be set to the current Leaving Water Temperature (LWT)
setpoint unless modified by one of the reset methods below. (The current LWT setpoint is Cool
LWT as determined by the chiller mode.) The type of reset in effect is determined by the LWT
Reset T ype setpoint.
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.
When the chiller mode = COOL, the Active Leaving Water variable is reset using the following
parameters:
1. Cool LWT setpoint
2. Max Reset Delta T setpoint
3. Start Reset Delta T setpoint
Reset is accomplished by changing the Active Leaving Water variable from the (Cool LWT
setpoint) to the (Cool LWT setpoint + Max Reset Delta T setpoint) when the evaporator (return –
leaving) water temperature delta varies from the (Start Reset Delta T setpoint) to 0.
The Active Leaving Water variable is set equal to the Cool LWT setpoint if the reset signal is less
than or equal to 4 mA. It is set equal to (Cool LWT setpoint + Max Reset Delta T setpoint) if the
reset signal equals or exceeds 20 mA. The Active Leaving Water variable will vary linearly
between these extremes if the reset signal is between 4 mA and 20 mA. An example of this action
is shown below.
LWT Reset (Cool mode)
(temperatures are examples only)
(54.0°F)
Max Reset Delta T
(10.0°F)
Cool LWT Set-Point
(44.0°F)
0 ma
4 ma
20 ma
22 OMM WMC-3 OITS
Compressor Controller
The compressor controller's primary function is controlling and protecting the compressor. No
setpoints are input to it. There is one compressor controller for each compressor on the unit. The
compressor controller receives, processes, and sends data to the unit controller, the compressor onboard microprocessors and to external devices. With some operator intervention the compressor
controller can operate the compressor if the operator interface touch screen is unavailable. Inputs
and outputs are as follows:
Table 9, Compressor Controller, Analog Inputs
# Description Signal Source Range
Leaving Evaporator Water
1
Temperature
2 Spare
3 Motor Current 0 to 5 VDC 0 to 125% RLA
Table 10, Compressor Controller, Digital Inputs
# Description Signal Signal
1 Manual Off 0 VAC (Off) 24 VAC (Auto)
2 Spare
3 Spare
4 Spare
5 Spare
6 Spare
7 Evaporator Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
8 Condenser Water Flow Switch 0 VAC (No Flow) 24 VAC (Flow)
9 Spare
NTC Thermistor
(10k@25°C)
-58 to 212°F
Table 11, Compressor Controller, Analog Outputs
# Description Output Signal Range
1 Spare
Table 12, Compressor Controller, Digital Outputs
# Description Load Output OFF Output ON
1 Compressor Off Emer. Solenoid Circuit Breaker ON
2 Spare
3 Spare
4 Spare
5 Spare
6 Spare
7 Spare
8 Inter Lock Solenoid Comp Disabled OFF Comp. Enabled ON
9 Spare
Circuit Breaker
OFF
OMM WMC-3 OITS 23
Compressor Controller Setpoints
The following parameters in Table 13 are remembered during power off, are factory set to the
Default value, and can be adjusted to any value in the Range column.
Type: column defines whether the setpoint is part of a coordinated set of duplicate setpoints
The “
in different controllers. The possibilities are given below:
• N = Normal setpoint - Not copied from, or copied to, any other controller.
• D = Duplicate setpoint. Setpoint is duplicated (same value) in all compressor controllers on the
same chiller.
• G = Group setpoint. Setpoint is duplicated (same value) in all compressor controllers on all
chillers in a group.
• M = Master setpoint - Setpoint is copied to all controllers in the “Sent To” column.
• S = Slave setpoint - Setpoint is a copy of the master setpoint (in the Unit controller).
At power-up the slave controller checks if the master is operational and if so, it sets its copy of the
setpoint equal to the master’s. Otherwise, the setpoint remains unchanged. During normal
operation, any time the master setpoint changes, the slave is updated as well.
PW (password) column indicates the password that must be active in order to change the
The
setpoint. Codes are as follows:
O = Operator, M = Manager, T = Technician (not available through the 4x20 display/keypad)
The following table groups setpoints that relate to compressor operation and are stored, for the
most part, in the compressor controllers. All settings are made through the OITS, indiscriminately
as to whether they are “unit” or “compressor”.
Table 13, Compressor Controller Setpoints
Description Default Range Type PW
Motor Amps
Demand Limit OFF OFF, ON N O
Minimum Amps 40% 20 to 80% N T
Maximum Amps 100% 40 to 100% N T
Soft Load OFF OFF, ON D M
Begin Amp Limit 40% 20 to 100% N M
Soft Load Ramp 5 min 1 to 60 min D M
Maximum Rate
Minimum Rate
Staging
Mode Normal
Sequence # 1
Maximum Compressors ON 16 1-16 G M
Stage Delta T 1.0 0.5-5.0 G M
Full Load 120 sec 30 to 300 sec N T
Absolute Capacity 100 Tons 0 to 9999 Tons D T
Timers
Start-Start 40 min 15 to 60 min N M
Stop-Start 3 min 3 to 20 min N M
Source No Start
0.5 °F/min 0.1 to 5.0 °F/min
0.1 °F/min 0.0 to 5.0 °F/min
Normal, Efficiency,
Pump, Standby
1,2, … (# of
Compressors)
70 °F 50 to 100 °F
D M
D M
N M
N M
D T
Continued next page.
Manual
Reference
24 OMM WMC-3 OITS
Description Default Range Type PW
Alarms
Evaporator Freeze
Condenser Freeze
Low Evap Pressure 26 psi 10 to 45 psi D T
Low Evap Pressure-Inhibit 38 psi 20 to 45 psi D T
Low Evap Pressure-Unload 31 psi 20 to 45 psi D T
High Discharge Temperature-Shutdown
High Discharge Temperature-Load
High Condenser Pressure 140 psi 120 to 240 psi D T
Motor Current Threshold 10% 1 to 20% N T
Surge High Suction SH - Start
Surge High Suction SH - Run
Service
Vane Mode AUTO AUTO, MANUAL N T
Unload Timer 10 sec 10 to 240 sec N T
STOP Timer 1 sec 1 to 240 sec N T
34.0 °F -9.0 to 45.0 °F
34.0 °F -9.0 to 45.0 °F
190 °F 120 to 240 °F
170 °F 120 to 240 °F
50 °F 25 to 90 °F
25 °F 5 to 45 °F
D T
D T
N T
N T
N T
N T
Manual
Reference
These setpoints are normally viewed or changed on the OITS, but can be changed on the unit
controller if the OITS is not available.
Compressor Faults, Problems, Warnings
Faults (Equipment Protection Shutdowns)
Equipment protection faults cause rapid compressor shutdown. The compressor is stopped
immediately (if the compressor was running).
The following table identifies each alarm, gives the condition that causes the alarm to occur, and
states the action taken because of the alarm. All equipment protection alarms require a manual
reset.
Table 14, Compressor Controller Faults (Equipment Protection Shutdowns)
Description Occurs When: Action Taken
Low Evaporator Pressure Evaporator Press < Low Evap Pressure SP Rapid Stop
High Condenser Pressure Cond Press > High Condenser Pressure SP Rapid Stop
Low Motor Current I < Motor Current Threshold with Compressor ON for 30 sec Rapid Stop
High Discharge Temperature Temp > High Discharge Temperature SP Rapid Stop
Mechanical High Pressure Digital Input = High Pressure Rapid Stop
High Motor Temperature Digital Input = High Temperature Rapid Stop
Surge High Suct SH-Starting
Surge High Suct SH-Running
No Compressor Stop
Starter Fault
Leaving Evaporator Water
Temperature Sensor Fault
Evaporator Pressure Sensor Fault Sensor shorted or open Rapid Stop
Condenser Pressure Sensor Fault Sensor shorted or open Rapid Stop
Suction Temperature Sensor Fault Sensor shorted or open Rapid Stop
Discharge Temperature Sensor
Fault
Evaporator Water Flow Loss Evaporator Flow DI = No Flow for > 10 sec Rapid Stop
Condenser Water Flow Loss Condenser Flow DI = No Flow for > 10 sec Rapid Stop
Temp > Surge High Suct SH-Start SP during first 5 minutes
of Compressor ON
Temp > Surge High Suct SH-Run SP after first 5 minutes of
Compressor ON
%RLA > Motor Current Threshold SP with Compressor OFF
for 30 sec
Starter Fault Digital Input = Fault AND Compressor State =
START, INTLOK, RUN, or UNLOAD
Sensor shorted or open Rapid Stop
Sensor shorted or open Rapid Stop
Rapid Stop
Rapid Stop
Annunciation
Rapid Stop
OMM WMC-3 OITS 25
Compressor Controller Events (Limit Alarms)
The following alarms do not cause compressor shutdown but limit operation of the chiller in some
way, as described in the Action Taken column.
Table 15, Compressor Controller Events
Description Occurs When: Action Taken Automatic Reset
Low Evaporator Pressure
– Inhibit Loading
Low Evaporator Pressure
– Unload
Evaporator Freeze
Protect
Condenser Freeze
Protect
High Discharge
Temperature
Pressure < Low Evap Pressure–Inhibit
setpoint
Pressure < Low Evap Pressure–Unload
setpoint
Evap Sat Refr Temp < Evaporator Freeze
setpoint
Cond Sat Refr Temp < Condenser Freeze
Setpoint
Temperature > High Discharge
Temperature-Load SP AND
Suction superheat < 15°F
Inhibit loading
Unload
Start evaporator
pump
Start condenser
pump
Load
Evap Press rises above
(SP + 3psi)
Evap Press rises above
(SP + 3psi)
Temp > (Evaporator Freeze
SP + 2°F)
Temp > (Condenser Freeze
SP + 2°F)
Temp < (High Dsch Temp
Load SP – 3°F) OR
Superheat > 18°F
Warnings
Warnings advise that a non-catastrophic problem exists, such as failed temperature sensor that
provides a signal for information, not control purposes. There are no Warnings associated with the
compressor controllers.
Compressor Controller Functions
Each compressor determines if it is at its maximum capacity (or maximum allowed capacity) and if
so, set its Full Load flag. The flag is based on a number of conditions.
Absolute Capacity
Each compressor estimates its absolute capacity from the present value of %RLA and the Absolute
Capacity setpoint from the equation:
Absolute Capacity = (%RLA Factor) * (Absolute Capacity setpoint)
where the %RLA Factor is interpolated from the following table.
%RLA 0 50 75 100 150
%RLA Factor 0 0.35 0.75 1.00 1.50
Multiple Compressor Staging
This section defines which compressor is the next one to start or stop. The next section defines
when the start, or stop, is to occur.
Functions
1. Can start/stop compressors according to an operator defined sequence.
2. Can start compressors based on the number of starts (run hours if starts are equal) and stop on
run hours
3. The above two modes can be combined so that there are two or more groups where all
compressors in the first group are started (based on number of starts/hours) before any in the
second group, etc. Conversely, all compressors in a group are stopped (based on run hours)
before any in the preceding group, etc.
4. An “efficiency priority” mode can be selected for two or more chillers where one compressor is
started on each chiller in the group before a second is started on any of them.
26 OMM WMC-3 OITS
5. A “pump priority” mode can be selected for one or more chillers where all compressors on a
given chiller are started before going to the next chiller in the group.
6. One or more compressor can be defined as “standby” where it is never used unless one of the
normal compressors is unavailable.
Required Parameters
1. Sequence number setpoint (SQ#_SP) for all compressors. Possible settings = (1-4).
2. Compressor Staging Mode setpoint (CSM_SP) for all compressors. Possible settings are:
NORMAL,
EFFICIENCY PRIORITY,
PUMP PRIORITY,
STANDBY
3. Maximum Number of compressors ON setpoint (MAX_ON_SP). Possible settings = (1-4).
This setpoint is the same for all compressors.
4. Number of starts for all compressors.
5. Number of run hours for all compressors.
6. Status of all compressors (On-line, Available/Unavailable, Starting, Running, etc.).
Configuration Rules
1. Each standby compressor must have a sequence number greater than or equal to all nonstandby compressors for which it is in standby.
2. All compressors in an “efficiency priority” or “pump priority” group must be set to the same
sequence number.
OMM WMC-3 OITS 27
m
p
Compressor State Control (Comp State)
Operation of the compressor is controlled by the state-transition diagram shown below. A state
variable (Comp State) shall be used to maintain the current state (OFF, START, INTLOK, RUN,
UNLOAD, or STOP). Transitions from one state to another are controlled by the condition
statements in the
Figure 7,Compressor State
TEST: Motor Current < Motor Current Threshold SP
& STOP Timer Ex
TEST boxes. TASK boxes indicate actions that must be performed.
TEST:
& Evap State=RUN & Next On = Yes &
ired
Power ON
OFF
Unit State=AUTO
Stage Up Now = YES & (Unit Mode NOT= HEAT OR
EvLWT Temperature > Source No Start SP) &
Start-Start Timer Expired & Stop-Start Timer Expired &
No Safety Alarms
TASK: Restart Start-Start Timer
VaneCloseDelay
TEST: Manual OFF DI = OFF OR
Vanes Closed
TASK: Start STOP Timer
Start Stop-Start Timer & Update Run Hours
OR Unit State = OFF
OR Unload Timer Expired OR Safety Alar
UNLOAD
TEST: Unit State = SHUTDOWN OR
[Next Off = Yes
& Stage Down Now = Yes
TASK: Start Unload Timer
Compressor Capacity Control
TEST: Manual OFF DI = OFF OR
Unit State = (OFF
TEST: Manual OFF DI = OFF
OR Unit State = OFF
TEST: Unit State = AUTO
& Next Off = No
OR SHUTDOWN)
OR Safety Alarm
TEST: Unit State= AUTO & Evap State=RUN &
RUN
START
TASK: Start Interlok Timer (10sec)
InterLock
Cond State = RUN & Vanes Closed &
InterLok Timer Expired
TASK: Increment # of starts
Leaving Water Control Mode
Compressor capacity is determined by the status of the leaving chilled water temperature (LWT),
which is a direct indicator of whether the chiller is producing enough cooling to satisfy the cooling
load. The LWT is compared to the active chilled water setpoint and compressor loading or
unloading ensues, considering any capacity overrides that may be in effect.
Capacity Overrides
The conditions described in the following subparagraphs override normal capacity control when
the chiller is in the COOL mode. These overrides are not in effect for loading and unloading when
the Vane Mode is set to MANUAL. Of the following limits, the one creating the lowest amp limit
is in effect. The resulting present limit value for compressor current is stored in the Active Demand
Limit variable.
28 OMM WMC-3 OITS
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