Daikin WMC Instruction Manual download pdf (Page 20)

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IOM 1210-1 • MAGNITUDE

MODEL WMC CHILLERS 20 www.DaikinApplied.com

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Operator Responsibilities

It is important that the operator become familiar with the

equipment and the system before attempting operation. During

the initial startup of the chiller, the McQuay International

technician will be available to answer any questions and

instruct the proper operating procedures. It is recommended

that the operator maintain an operating log for each individual

chiller unit. In addition, a separate maintenance log should be

kept of the periodic maintenance and servicing activities.

Operator Schools

Training courses for Magnitude

Centrifugal Maintenance and

Operation are held through the year at the Daikin Learning

Institute in Staunton, Virginia. The school duration is three and

one-half days and includes instruction on basic refrigeration,

MicroTech

II controllers, enhancing chiller efciency and

reliability, MicroTech

II troubleshooting, system components,

and other related subjects. For more information, visit us

at www.DaikinApplied.com and click on Training or call the

Training Department. Refer to the back cover of this document

for contact information.

Sequence of Unit Operation

The following is a general chiller sequence of operation for

Magnitude

Model WMC chillers. Certain conditions and chiller

alarms may alter this sequence, but the chiller’s objective is to

achieve the target temperature of the leaving water.

1. Chiller enabled

With the chiller enabled via its onboard interlocks

and selected external control source, it will start the

evaporator pump and check for ow and chiller load.

2. Water ow and load proven

Once evaporator ow has been conrmed and the

chiller load proven, compressor wear balancing logic will

determine which compressor to start as the Lead.

3. Lead compressor start

As the Lead compressor approaches its maximum

capacity it will assess the need for the Lag compressor.

If the Lag compressor is needed, the Lead compressor

will signal the Lag compressor to start, and may adjust its

capacity to assist the Lag compressor start.

4. Lag compressor start

Once started, the Lag compressor will quickly ramp up to

balance the chiller load between the two compressors.

5. Dual compressor loading

As building load increases, the compressors will load

up maximizing the Inlet Guide Vane (IGV) position and

impeller speed. Maximum capacity at a given operating

condition can be found either when the compressors

have reached their maximum speed limit (Mechanical

limitation) or when the compressors have reached the

chiller’s Rated Load Amperage (Electrical limitation).

6. Dual compressor unloading

As load decreases, the compressors will unload to

sustain the water temperature set point by reducing

speed until the minimum speed limit has been reached.

If further unloading is required, the IGV assemblies will

close as required to satisfy the load.

7. Staging down to one compressor running

With the chiller running two compressors on condition

and the building load reducing to the point that one

compressor can carry the load, compressor wear

balancing logic will again determine which compressor to

shutdown.

8. Chiller shutdown

The remaining compressor will adjust capacity to

manage the chiller load until the load increases to the

point where another compressor is needed, or the load

reduces below the minimum capacity of one compressor

and the leaving water temperature goes below set point

and reaches the stop delta temperature. Anytime the

chiller is disabled, it will perform an orderly unload and

shutdown both compressors.

Unit Enabling/Disabling

There are multiple switches that will enable and disable the

chiller and its compressors:

1. Unit Switch - The top switch on the switch bracket that is

mounted inside the control box.

2. Compressor 1 Switch - Located underneath the Unit

Switch on the switch bracket.

3. Compressor 2 Switch - Located underneath the

Compressor 1 Switch on the switch bracket.

4. External Switch - Located on the outer, left side of the

control box.

5. Remote Switch - Optional. Replaces a jumper between

Field Terminals 54 and 70 (see "Figure 12: Wiring Index"

on page 12).

The switches listed above work in conjunction with the “Control

Source” that is selected in the OITS via the MODES Setpoint

Screen using Setpoint button #3. (See Figure 44 and Table 10

on page 38.) The three options for “Control Source” are:

1. Switches - This is the default mode. This mode will

ignore BAS commands.

2. Local - When this mode is set, a STOP button and an

AUTO button will appear at the top of the OITS screens,

as shown in Figure 16 on page 22. This mode will

ignore all functionality of a connected Remote

Switch. It will also ignore BAS commands.

3. BAS - This mode adds BAS capability to the Switches

functionality.

Enabling and disabling the unit and its compressors using the

switches in conjunction with the selected “Control Source” are

discussed next.

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Daikin WMC Instruction Manual Page 20

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