McQuay WMC 400DBS Installation Manual

Operating & Ma intenance Manual

OMM 1008-3

Magnitude™ Magnetic Bearing Chillers

Model WMC 145SBS – 400DBS Model WMM 075SBS – 400DBS

Control Software Version: WMCU3UU10K

Group: Chiller Part Number: 331374711 Effective: April 26, 2012

Supersedes: February 2012

Rev

Table of Contents

Introduction ............................................. 3

Features of the Control Panel ................. 4

Definitions ................................................ 5

General Description................................. 8

Control Panel ........................................... 9

Use with On-Site Generators ................ 10

Multi-Chiller Setup ............................... 10

Operating the Control System .............. 14

Interface Panel On/Off ...................................... 14

Start/Stop Unit .................................................. 14

Change Setpoint s .............................................. 14

Alarms .............................................................. 14

Component Failure ........................................... 15

Component Description ........................ 15

Operator Interface Touch Screen ...................... 15

Controller Description ...................................... 15

Navigating......................................................... 16

Controller ............................................... 18

Controller Setpoints .......................................... 18

Unit Related Faults, Problems, Warnings ......... 21

Controller Functions ......................................... 22

Compressor Related Faults, Problems, Warnings23

Control Functi ons ............................................. 24

Compressor On-Board

Controllers .............................................. 28

Field Wiring Diagram ........................... 29

Operator Interface Touch

Screen ..................................................... 30

Navigation......................................................... 30

Screen Descriptions .......................................... 32

VIEW Screens .................................................. 32

SET Screens ...................................................... 37

See Field Wiring Diagram ................................ 44

See Field Wiring Diagram ................................ 46

SERVICE Screen .............................................. 50

HISTORY Screens ............................................ 51

Download Data ................................................. 52

ACTIVE ALARM Screen ................................. 53

Controller Menu Screens ...................... 55

Menu Matrix ..................................................... 56

BAS Interface ........................................ 72

Sequence of Operation ......................... 72

Annual Shutdown ................................. 74

Seasonal Startup ................................................ 74

Maintenance .......................................... 75

Pressure/Temperature Chart .............................. 75

Routine Maintenance ........................................ 75

Repair of System ............................................... 76

Maintenance Schedule .......................... 79

Service Programs .................................. 80

Operator Schools ................................... 80

Limited Warranty ................................. 80

Manufactured in an ISO Cer tified Facility

©2012 McQ uay International. Illustrat ions and data cover the McQuay Internat ional product at the tim e of publication and we reserve the right to make changes in design and construction at anyt i me without notice.

™® The following are trademarks or registered t rademarks of their respect ive companies: BACnet from ASHRAE; L

ONWORKS, and the LONMARK logo are managed, granted and used by LONMARK International under a license granted by Echel on

Corporation; Modbus from Schnei der E l ectric; MicroTech II, and Open Choices from McQuay Internati onal .

2 OMM 1008-3

LONMARK, LonTalk,

WARNING

CAUTION

DANGER

WARNING

CAUTION

Introduction

This manual provides, operating, troubleshooting and maintenance information for Daikin McQuay WMC Magnitude™ centrifugal chillers with the MicroTech ΙΙ® controller. It includes versions software versions F, G, H and J.

Please refer to the current version of installation manual IM 1029 for information relating to installing the unit.

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 knowledgeable in the operation of the equipment being controlled..

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, may cause interference to radio communications. Operation of this equipment in a residential area is likely to cause harmful interference, in which case the owner will be required to correct the interference at the owner’s own expense.

McQuay International disclaims any liability resulting from any interference or for the correction thereof.

Chiller Location

The chillers are intended only for installation in an indoor or weather protected area consistent with the NEMA 1 rating on the chiller, controls, and electrical panels. Equipment room temperature for operating and standby conditions is 40°F to 104°F (4.4°C to 40°C).

HAZARD IDENTIFICATION INFORMATION

Dangers indicate a hazardous situation which will result in death or serious injury if not

avoided.

Warnings indicate potentially hazardous situations, which can result in property damage,

severe personal injury, or death if not avoided.

Cautions indicate potentially hazardous situations, which can result in personal injury or

equipment damage if not avoided.

OMM 1008-3 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 15-inch Super VGA touch-screen operator

interface

• 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 sub-cooling 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 manufacture).

• Soft loading feature reduces electrical consumption and peak demand charges during system loop pull-

down.

• 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

BAS manufacturers.

• 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 open protocols for most

4 OMM 1008-3

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 f or the durat ion 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 dur ati on of t he 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 c ontrol the flow of r efrigerant to the evaporat or, controlled by the circuit microprocessor.

OMM 1008-3 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 (Inhi bit) 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.

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 selecti ng the percent load to start ramping up and by selecting the time to ramp up to full load (up to 60 minutes).

6 OMM 1008-3

Setpoint

Suction Superheat

Suction superheat is calculated for each circuit using the following equation: Suction Superheat = Suction Temperature – Evapo rator Saturated T em perature

Stageup/Stagedown Delta-T

Staging is the act of starting or stopping a compressor or fan when another is still operat ing. 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 1008-3 7

Compressor #2

Power Panel

Unit Control Panel

Panel (OITS)

Electronic Expansion Valve

Condenser Behind Panel

General Description

Major Components

Figure 1, Major Component Location

Evaporator Relief

Valve, Behind Panel

Compressor #1

Operator Interface

Relief Valves

(Front End Box)

Control Panel

General Description

The centrifugal MicroTech ΙΙ control system consists of a microprocessor-based controller 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.

• Controller, controls unit functions and communicates with other auxiliaries. It is the secondary location

for setpoint input if, and only if, the OITS is inoperative.

• 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.

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.

8 OMM 1008-3

Emergency

Outside Panel

Controller

OITS PC

Universal

Field Wiring Knockouts

On/Off

Comp #2 I/O

Comp #1 I/O

Control Panel

Figure 2, Control Panel

EXV Board

Switches UNIT COMP #1 COMP #2

Communication

Module

Shutdown Switch,

The controller, the OITS microprocessor, the unit and compressor on/off switches and other minor components are mounted in the control panel. The 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 controller's function is acquiring and processing data relating to the chiller operation and issuing instructions to various components to maintain controlled operation. The controller also sends information to the OITS for graphic display. The controller has a 4x20 LCD display and keys for accessing data and changing setpoints. If the OITS should become inoperable, 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.

Terminal Board TB UTB1 for Field Wiring Connections

OMM 1008-3 9

WARNING

Use wi t h On-Site Generators

Magnitude chillers have their total tonnage divided between two compressors (all but single compressor Model WMC 145S) that start sequentially and they are operated with variable frequency drives. These features make Magnitude 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 is typically

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 f or reconnecting power from the generator back to the utility grid is show below. These procedures are not peculiar to Daikin McQuay units only, but should be observed for any chiller manufacturer.

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 Field Wiring Diagr am

Figure 8 on page 29. A start signal can be given anytime after the stop signal since the three-minute start-tostart 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.

Multi-Chiller Setup

Component Description & Communication Setup

The communication wiring and setup required for dual compressor operation is performed 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 co ntrol hardware. RS485 communication wiring between chillers should be field wired before start-up and installed as a NEC Class 1 wiring system.

10 OMM 1008-3

IMPORTANT NOTE

Chillers connected via pLAN connections MUST share the same software revision. WMC B-vintage models may not be LAN interconnected to any other models, including WMC A-vintage models, WSC, WDC, WCC or WME chillers.

OMM 1008-3 11

(1)

Setting

Controller

Interface (2)

Dec. 1 2 5 6 7 8

Dec. 9 10

Table 1, pLAN Address for Units Using pLAN for multi-unit interconnection.

Chiller

Comp 1

Comp 2

Unit

Reserved

Operator

Reserved

NOTES for pLAN multi-chiller communication setup:

1. Up to four Magnitude WMC units can be interconnected. (See Important Note on page 10).

2. The 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 letters for the OITS address for the chiller that it is on. T hen clo se the scr e e n. N ote that A is the default setting from the factory.

3. For the pCo3 controller, the pLAN address can be confirmed as follows:

A) Disconnect pLAN (connectors J10 and J11) from all pCo3

controllers.

B) Cycle power to the controller and then hold down both the

Left Arrow (alarm) and the Up Arrow keys simultaneously as the controller completes its Self-Test routine. The controller will then show you the present pLAN address of t he controller. Verify that the pLAN address matches the desired address from the above table. If the address needs to be changed, follow the instructions displayed on the pCo3 controller’s LCD display. Press enter when done.

C) Only after all controllers pLAN addresses have been set andconfirmed can the pLAN network connectors be

re-connected.

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 Compressors ON – 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.

Communication Setup

1. With no communication connections between chillers, disconnect control power and set the pLan

address as shown in Table 1.

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 J6 connections on each unit’s isolation boards.

The boards are not furnished, separate RS485 isolators must be field supplied.

5. Verify correct nodes on each OITS Service Screen. See Figure 26 on page 50.

12 OMM 1008-3

Low Condenser Water Temperature Operation

When the ambient wet bulb temperature is lower than design, the entering condenser water temperature can be allowed to fall to improve chiller performance. This is especially true of an advanced design such as the Daikin McQuay Magnitude chiller that features variable compressor speed.

It is an engineering fact that as the compressor discharge pressure is reduced, the amount of power to pump a given amount of gas also is reduced. The reduction can result in significant energy savings.

However, as with most centrifugal chiller applications, a tower bypass valve must be installed and must be controlled by the chiller MicroTech II controller. Figure 3 illustrates two temperature actuated tower bypass arrangements. The “Cold Weather” scheme provides better startup under cold ambient air temperature conditions. The check valve may be required to prevent entraining air at the pump inlet.

Figure 3, Bypass, Mild Weather Operation

Bypass, Cold Weather Operation

OMM 1008-3 13

Operating the Control System

Interface Panel On/Off

The Operator Interface Panel is turned on and off with a switch located at the lower front of the panel. Screen control buttons are located to either side of it and elicit on-screen prompts when pressed.

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 botton.

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 Pane l (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 start ed 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 r emote switch that must be wired into the control panel (see Field Wirin g Diag ram Figure 8 on page 8).

3. BAS

BAS input is field-wired into a module that is factory-installed on the 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 38. Setpoints can also be changed in the controll er, but this is not recommended except in an emergency when the OITS is unavailable.

Alarms

A red ALARM light in the lower middle of any OITS 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. 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.

14 OMM 1008-3

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 wi thout the O perator Interface Panel

The Operator Interface Touch Screen communicates with the controller, displaying data and transmitting touch screen inputs to the controll ers. 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 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 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 downloaded 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 programmed into the system. The screen is reactivated by touching it anywhere.

Controller Description

Hardware Structure

The controller is 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 t he event of power fail ure without requiring a back-up battery.

The controller c onnects to othe r control boa rds, the on-board compressor microprocessors and the OITS via a local communications network. The controller can also have an optional module to provide communication for a BAS using standard open protocols.

OMM 1008-3 15

MENU Key

ARROW Keys (4)

Key-to-Screen Pathway

Keypad

A 4-line by 20-character/line liquid crystal display and 6-button keypad is mounted on the controller. Its layout is shown below.

Figure 4, Controller Keypad

Red Alarm Light Behind

ENTER Key with

Green Run Light

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.

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

b) Depending on the top-level selected, a second level of screens will appear. For example, selecting

16 OMM 1008-3

ALARM, VIEW, and SET as shown in Figure 4. One of these choices can then be selected by pressing the key connected to it via the pathway shown in the figure.

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.

ALARM LOG

(data)

< ALARM

< VIEW

< SET

VIEW < COMPRESSOR

< UNIT

< EVAPORATOR

< CONDENSER

VIEW COMP (n)

(screen n data)

ENTER Key

show:

After pressing the “COMPRESSOR” menu button, the selected

Where “n” is the number of the last viewed COMPRESSOR

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 5, Typical Menu Display and Keypad Layout

MENU Key

ARROW Keys

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:

After pr essing the MENU but ton, the top-level menu screen will show:

After pressing the “V IEW” menu button, a menu screen will

data screen will show;

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.

OMM 1008-3 17

Description

Signal Source

Range

Reset of Leaving Wat er T emperature

4-20 mA Current

0-(10 to 80°F)

Entering Evaporator Water Temperature

Entering Condenser Wat er Temperature

Leaving Condenser Water Temperature

NTC Thermistor (10k@25°C)

-58 to 212°F

Demand Limit

4-20 mA Current

0-100 %RLA

Condenser Water Flow

4 to 20 mA Current

0 to 10,000 gpm

Refrigerant Leak Sensor

4 to 20 mA Current

0 to 100 ppm

Leaving Evaporator Water Temperature

NTC Thermistor (10k@25°C)

-58 to 212°F

Description

Signal

Remote Start/St op

0 VAC (Stop)

24 VAC (Start)

Not Used

Evaporator Water Flow Switch

0 VAC (No Flow)

24 VAC (Flow)

Condenser Water Flow Switch

0 VAC (No Flow)

24 VAC (Flow)

Description

Load

Output OFF

Output ON

Evaporator Water Pump #1

Pump Contactor

Pump OFF

Pump ON

Condenser Water Pump #1

Pump Contactor

Pump OFF

Pump ON

Condenser Water Pump #2

Pump Contactor

Pump OFF

Pump ON

Tower Fan #1

Fan Contactor

Fan OFF

Fan ON

Tower Fan #2

Fan Contactor

Fan OFF

Fan ON

Alarm

Alarm Indicator

Alarm OFF

Alarm ON

Tower Fan #4

Fan Contactor

Fan OFF

Fan ON

Circuit Breaker

OFF

Description

Output Signal

Range

Cooling Tower VFD Speed

0 to 10 VDC

0 to 100%

EXV signal to IB Valve Control Bd.

0 to 10 VDC

0 to 100%

Y3 Electronic Expansion Val ve

0 to 10 VDC

0 to 100% Open

Controller

Table 2, Controller, Analog Inputs

2 3

5 Liquid Line Refrigerant Temperature NTC Thermistor (10k@25°C) -58 to 212°F

7 Evaporator Water Flow 4 to 20 mA Current 0 to 10,000 gpm

NTC Thermistor (10k@25°C) -58 to 212°F NTC Thermistor (10k@25°C) -58 to 212°F

Table 3, Controller, Digital Inputs

1 Unit OFF Switch 0 VAC (Stop) 24 VAC (Auto)

6 Manual Off 0 VAC (Off) 24 VAC (Auto)

Table 4, Controller, Digital Outputs

2 Evaporator Water Pump #2 Pump Contact or Pump OFF Pump O N

7 Spare

9 Tower Fan #3 Fan Contactor Fan OFF Fan ON

11 Compressor Off Emer. Solenoid

Table 5, Controller, Analog Outputs

1 Cooling Tower Bypass Valve Position 0 to 10 VDC 0 to 100% Open

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 Range column.

The “Type” column defines whether the setpoint is part of a coordinated set of duplicate setpoints i n different controllers. There are three 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. S = Slave setpoint - Setpoint is a copy of the master setpoint (in the controller).

18 OMM 1008-3

Description

Default

Range

Type

KEYPAD, BAS,

NONE, BACnet, LonWorks,

Leaving Water

3.0°F

0.0 to 10.0 °F

Pump #1

Pump #1 Only, Pump #2 Only, Auto

Pump #1

Pump #1 Only, Pump #2 Only, Auto

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 = T echnician (not available through the 4x20 display/keypad). The following table groups setpoints that relate to the entire unit operation and are stored in the controller.

All settings are made through the OITS.

Table 6, Controller Setpoints

Unit Unit Enable OFF OFF, ON M O

Control Source KEYPAD Display Units

Language ENGLISH ENGLISH, (TBD) N O BAS Protocol NONE

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 Normal, Effici ency, Pump, Standby N M Sequence # 1 1,2, … (# of Compressors ) N M 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

°F/psi °F/psi, °C/kPa

0.5 °F/min 0.1 to 5.0 °F/min

0.1 °F/min 0.0 to 5.0 °F/min

DIGITAL INPUT

MODBUS, N2

N O N O

N M

D M D M

Cool LWT Startup Delta T Shutdown Delta T LWT Reset Type NONE NONE, RE T URN, 4-20mA N M Max Reset Delta T Start Reset Delta T

Timers

Evap Recirculate 30 sec 15 sec to 5 min N M Start-Start 40 min 15 to 60 min N M Stop-Start 3 min 3 to 20 min N M Source No Start

Pumps

Evap Pump Cond Pump

Cooling Tower

Tower Control None None, Temperature, Lift N M Tower Stages 2 1 to 4 N M

Continued on next page

OMM 1008-3 19

44. 0°F 36.0 to 60.0 °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

70 °F 50 to 100 °F

Only Only

Lead, #1 Primary, #2 Prim ary Lead, #1 Primary, #2 Prim ary

M O M O M O

N M N M

D T

N M N M

Description

Default

Range

Type

70 °F

40 to 120 °F

80 °F

40 to 120 °F

None, Valve Setpoint, Valve S t age,

(To Tower)

90 °F

0 to 100 °F

34.0 °F

-9.0 to 45.0 °F

High Discharge TemperatureShutdown

High Discharge TemperatureLoad

25 °F

5 to 45 °F

Stage Up Time 2 min 1 to 60 min N M Stage Down Time 5 min 1 to 60 min N M Stage Differential (Temp) Stage Differential (Lift ) 6.0 psi 1.0 to 20.0 psi N M 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 Stage #2 On (Lift) 45 psi 10 to 130 psi N M Stage #3 On (Lift) 55 psi 10 to 130 psi N M Stage #4 On (Lift) 65 psi 10 to 130 psi N M

Cooling Tower Valve / VFD

Valve/VFD Control None Valve Setpoint (Temp)

Valve Setpoint (Lift) 30 psi 10 to 130 psi N M Valve Deadband (Temp) Valve Deadband (Lift) 4.0 psi 1.0 to 20.0 psi N M Stage Down @ 20% 0 to 100% N M Stage Up @ 80% 0 to 100% N M Valve Control Range (Min) 10% 0 to 100% N M Valve Control Range(Max) 90% 0 to 100% N M

Valve Type Minimum Start P osition 0% 0 to 100% N M

Minimum Posit i on @ Maximum Start Posit i on 100% 0 to 100% N M Maximum Position @ Error Gain 25 10 to 99 N M Slope Gain 25 10 to 99 N M 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

3.0 °F 1.0 to 10.0 °F

75 °F 40 t o 120 °F

85 °F 40 t o 120 °F

VFD Stage, Valve SP/VFD Stage

65 °F 40 t o 120 °F

2.0 °F 1.0 to 10.0 °F

NC, NO N M

60 °F 0 to 100 °F

34.0 °F -9.0 to 45.0 °F

190 °F 120 to 240 °F

N M

N M N M N M N M

N M N M

N M

D T D T

N T

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

These setpoints are normally viewed or changed on the OITS.

20 OMM 1008-3

170 °F 120 to 240 °F

50 °F 25 to 90 °F

N T

N T N T

Description

Occurs When:

Action Taken

Reset

SP) AND has not faulted]

No flow indicated for (5 sec) with Condenser Pump #1 ON

SP) AND has not faulted]

No flow indicated for (5 sec) with Condenser Pump #2 ON

Manual.

Water)

Entering Evaporator Temperature

Entering Condenser Temperature Sensor Fault

Leaving Condenser Temperature Sensor Fault

Liquid Line Refrigerant Temperature Sensor Fault

Unit Related 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, Controller Limit Alarms

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 P ump #1 ON

AND [the other pump is availabl e (per the Evap Pump

No flow indicated for (5 sec) with Evaporator Pump #2 ON

AND [the other pump is availabl e (per the Evap Pump

AND [the other pump is availabl e (per t he 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

Reset mode is

set to No Reset

(Reset mode goes back to

Entering

Warnings

The following “alarms” only generate a warning message to the operator. Chiller operation is not affected.

Table 8, Controller Warnings

Description Occurs When: Action Taken Reset

Sensor Fault

Sensor is open or shorted Annunciation Automatic Sensor is open or shorted Annunciation Automatic

OMM 1008-3 21

Sensor is open or shorted Annunciation Automatic Sensor is open or shorted Annunciation Automatic

20 ma

(54.0°F)

Cool LWT Set-Point

(44.0°F)

4 ma

LWT Reset (Cool mode)

(temperatures are examples only)

0 ma

Max Reset Delta T

(10.0°F)

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 t he 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 Type 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 t han 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.

22 OMM 1008-3

Temp > Surge High Suct SH-Start SP during first 5 m i nutes

of Compressor ON

Temp > Surge High Suct SH-Run SP after first 5 minut es of

Compressor ON

%RLA > Motor Current Threshold SP with Com pres sor OFF

for 30 sec

Starter Fault Digital I nput = Faul t AND Compressor State =

START, INTLOK , RUN, or UNLOAD

Leaving Evaporator Water Temperature Sensor Fault

Fault

Low Evaporator Pressure – Inhibit Loading

Pressure < Low Evap Pressure–Inhibit

setpoint

Evap Press rises above

(SP + 3psi)

– Unload

setpoint

(SP + 3psi)

Protect

setpoint

pump

SP + 2°F)

Protect

Setpoint

pump

SP + 2°F)

Suction superheat < 15°F

Superheat > 18°F

Compressor Related Faults, Problems, Warnings

Faults (Equipment Protection Shutdowns)

Equipment protection faults cause rapid compressor shutdown. The compressor is stopped i mmediately (if the compressor was running).

The following table identifies each alarm, gives the condition that causes the alarm to occur, and states t he action taken because of the alarm. All equipment protection alarms require a manual reset.

These faults are accessed by first selecting Comp 1 or Comp 2 on the controller screen

Table 9, Compressor 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 Thres hol d with Compressor ON for 30 sec Rapid S top High Discharge Temperature Temp > High Discharge Temperat ure SP Rapid S top Mechanical High Pressure (Note 1) Digital Input = High Pressure Rapid Stop High Motor Temperature Digital Input = High Temperature Rapid S t op

Surge High Suct SH-Starting

Rapid Stop Surge High Suct SH-Running No Compressor Stop Starter Fault

Sensor shorted or open Rapi d S top

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

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

Sensor shorted or open Rapi d S top

Rapid Stop

Annunciation

Rapid Stop

NOTES:

Since there is no mechanical high pressure switch on these units, the alarm is actually triggered by a closed compressor discharge valve. The OITS will display the fault as Mech-Press-Switch and the controller display will show Compressor n Check Valve.

Compressor Events (Limit Alarms)

The following alarms do not cause compressor shut down but limit operati on of the chil ler as des cribed in t he Action Taken column.

Table 10, Compressor Events

Description Occurs When: Action Taken Automatic Reset

Inhibit loading

Low Evaporator Pressure Evaporator Freeze

Pressure < Low Evap Pressure–Unload

Evap Sat Refr Temp < Evaporator Freeze

Unload

Start evaporator

Evap Press rises above

Temp > (Evaporator Freeze

Condenser Freeze

High Discharge Temperature

Cond Sat Refr Temp < Condenser Freeze

Temperature > High Discharge

Temperature-Load SP AND

OMM 1008-3 23

Start condenser

Load

Temp > (Condenser Freeze

Temp < (High Dsch Temp

Load SP – 3°F) OR

%RLA

100

150

%RLA Factor

0.35

0.75

1.00

1.50

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.

Control Functions

Each compressor determines if it has reached 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 Absolut e Capacity setpoint from the equation:

Absolute Capacity = (%RLA Factor) * (Absolute Capacity setpoint) where the %RLA Factor is interpolated from the following table.

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.

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, A vailable/Unavailable, Starting, Running, etc.)

24 OMM 1008-3

OFF

InterLock

RUN

UNLOAD

VaneCloseDelay

InterLok Timer Ex pired

OR Unload Timer Expired OR Safety Alarm

& STOP Timer Expired

Power ON

Configuration Rules

1. Each standby compressor must have a sequence number greater than or equal to all non-standby

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.

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 condi tion statements in the TEST boxes. TASK boxes indicate actions that must be performed.

Figure 6, Compressor State

TEST: Motor Current < Motor Current Threshold SP

TEST: Manu al OFF DI = OFF OR Vanes Closed OR Unit State = OFF

TEST: Manu al OFF DI = OFF OR

Unit State = (OFF OR SHUTDOWN) OR Safety Alarm

TEST: Unit State=AUTO & Evap State=RUN & Next On = Yes & 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

START

TASK: Start STOP Timer

Start Stop-Start Timer & Update Run Hours

TEST: Unit State = SHUTDOWN OR [Next Off = Yes & Stage Down Now = Yes]

TASK: Start Unload Timer

TASK: Start Interlok Timer (10sec)

TEST: Manu al OFF DI = OFF OR Unit State = OFF

TEST: Unit State = AUTO & Next Off = No

TEST: Unit State= AUTO & Evap State=R UN & Cond State = RUN & Vanes Closed &

TASK: Increment # of starts

OMM 1008-3 25

Compressor Capacity Control

Leaving Water Control Mode

Compressor capacity is determined by the status of the leaving chilled water temperature (LWT), which i s a direct indicator of whether the c hiller 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 descr ibed i n the foll owing subparagraphs override normal capacity control when t he 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.

Low Evaporator Pressure

If the evaporator pressure drops below the Low Evaporator Pressure – Inhibit setpoint, the unit will inhibit capacity increase. If the evaporator pressure drops below the Low Evaporator Pressure - Unload setpoint, the unit will begin capacity decrease.

High Discharge Temperature - Load

If the discharge temperature rises above the High Discharge Temperature - Load setpoint and the motor current is < 50% RLA, the unit will begin capacity increase.

Soft Load

Soft Loading is a confi gurable func tion used at compressor startup t o limit the maximum current draw on the compressor in a ramp-up type manner. It is only active on the first compressor to start. The setpoints that control this function are:

•

Soft Load – (ON/OFF)

•

Begin Am p Limit – (%RLA)

•

Maximum Amps – (%RLA)

•

Soft Load Ramp – (seconds)

•

The active soft load limit value (in % RLA) increases linearly from the Begin Amp Limit setpoint to the Maximum Amps setpoint over the amount of time specified by the Soft Load Ramp setpoint. If the amp draw rises above the currently active soft load limit value, the unit will inhibit capacity increases. If the amp draw rises to 5% or more above this value, the unit will begin capacity decrease.

Maximum LWT Rate

The maximum rate at which the leaving water temperature can drop (chiller mode = COOL) is limited at all times by the Maximum Rate setpoint. If the rate exceeds this setpoint, capacity increases is inhibited.

Demand Limit

The maximum amp draw of the compressor can be limited by a 4 to 20 mA signal on the Demand Limit analog input. This function is only enabled if the Demand Limit setpoint is set to ON. The amp limit decreases linearly from the Maximum Amp Limit setpoint (at 4 mA) to the Minimum Amp Limit setpoint (at 20mA). If the amp draw rises above the limit value, the unit will inhibit capacity increases. If the amp draw rises to 5% or more above this value, the unit will begin capacity decrease.

Network Limit

The maximum amp draw of the compressor can be limited by a value sent through a BAS network connection and stored in the Network Limit variable. If the amp draw rises above the limit value, the unit will inhibit capacity increases. If the amp draw rises to 5% or more above this value, the unit will begin capacity decrease.

26 OMM 1008-3

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