McQuay AGS 225D, Руководство по эксплуатации

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26 OM AGSD-1
Controller Functions
Parameter Definitions
LWT Slope
LWT slope is calculated so that the slope represents the change in LWT over a time frame of
one minute and is used to help determine the slide valve target.
Every 12 seconds, the current LWT is subtracted from the value 12 seconds back. This
value is added to a buffer containing values calculated at the last five 12-second intervals.
The final result is a slope value that represents the action of the LWT for the past 60
seconds.
Pulldown Rate
The slope value calculated above will be a negative value as the water temperature is
dropping. For use in some control functions, the negative slope is converted to a positive
value by multiplying by –1.
Circuit Capacity
The capacity of each circuit is estimated based on slide position. A circuit that is not
running is always considered to be at 0% capacity. A running circuit can have a capacity
value ranging from 20% to 100%.
The slide position and capacity value for running compressors are related as shown by the
following formula:
Circuit capacity = 0.8(Slide position) + 20
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 calculated using the following formula:
Unit capacity = (Circuit 1 ca Circuit 2 capacity)/2 or for a three circuit unit (Circuit
1 ca Circuit 2 ca Circuit 3 capacity)/3
Unit Enable
Enabling and disabling the chiller is controlled by the Unit Enable Setpoint, with options of
OFF and ON. Enabling allows the unit to start if there is a call for cooling and also starts
the evaporator pump.
This setpoint (in other words, enabling the unit to run) can be altered by the Unit Switch
input (unit On/Off switch), a field installed remote stop switch, a keypad entry, or a BAS
request. The Control Source Setpoint determines which sources can change the Unit Enable
Setpoint with options of SWITCHES, KEYPAD or NETWORK.
Changing the Unit Enable Setpoint can be accomplished according to Table 3
NOTE: An “x” indicates that the value is ignored.
All methods of disabling the chiller, except for the Override Stop switch, will cause a
normal shutdown of any running circuits with pumpdown. Any time the Override Stop
switch is used to disable the chiller, all running circuits will shut down immediately, without
pumping down.