Daikin McQuay AGZ-D, Operating And Maintenance Manual, Page: 21 / 82

OMM 1087 AGZ 025D through 190D 21
Unit Capacity
For applying unit capacity limits, an estimate of
total unit capacity is needed. Unit capacity will be
based on the estimated circuit capacities.
The unit capacity is the number of compressors
running (on circuits that are not pumping down)
divided by the number of compressors on the unit.
Control Band
The Control Band defines the band in which unit
capacity will not be increased or decreased.
The Control Band is calculated as follows:

Four compressor units: Control Band =
Nominal Evap Delta T Set Point * 0.3

Six compressor units: Control Band =
Nominal Evap Delta T Set Point * 0.2
Staging Temperatures
If the unit is configured for use without glycol:
When the LWT target is more than half the
Control Band above 3.9°C (39.0°F)

Stage Up Temperature = LWT
(Control Band/2)

Stage Down Temperature = LWT target –
(Control Band/2)
If the LWT target is less than half the Control
Band above 3.9°C (39.0°F)

Stage Down Temperature = LWT target –
(LWT target - 3.9°C)

Stage Up temperature = LWT
Control Band – (LWT target – 3.9°C)
If the unit is configured for use with glycol, the
compressor staging temperatures are calculated as
shown below:

Stage Up Temperature = LWT
(Control Band/2)

Stage Down Temperature = LWT target –
(Control Band/2)
The Start up and Shutdown temperatures are
referenced from the Control Band:

Start Up Temperature = Stage Up Temperature
+ Start Up Delta set point

Shutdown Temperature = Stage Down
Temperature – Shutdown Delta set point
Unit Enable
Enabling and disabling the chiller is accomplished
using setpoints and inputs to the chiller. The unit
switch, remote switch input, and Unit Enable Set
Point all are required to be ‘on’ for the unit to be
enabled when the control source is set to ‘local’.
The same is true if the control source is set to
‘network’, with the additional requirement that the
building automation system (BAS) Enable set
point must be ‘on’. The BAS should enable the
chiller only when there is a demand for cooling.
Unit is enabled according to the following table
:
Unit
Switch
Control Source
Set Point
Remote
Switch Input
Unit Enable
Set Point
BAS Enable
Set Point
Unit Enable
Off Off
Off Off
Off Off
On Local On On On
Network Off Off
On Network On On On On