McQuay AGS 225D, Operating Manual

Page: 33 / 82

OM AGSD-1 33
Unit Capacity Overrides
Unit capacity limits can be used to limit total unit capacity in COOL mode only. Multiple
limits may be active at any time, and the lowest limit is always used in the compressor
capacity control.
The estimated unit capacity and the active capacity limit are sent to all circuits for use in
compressor capacity control.
Soft Load
Soft Loading is a configurable function used to ramp up the unit capacity over a given time.
The setpoints that control this function are:
•
Soft Load – (ON/OFF)
•
Begin Capacity Limit – (Unit %)
•
Soft Load Ramp – (seconds)
The Soft Load Unit Limit increases linearly from the Begin Capacity Limit setpoint to
100% over the amount of time specified by the Soft Load Ramp setpoint. If the option is
turned off, the soft load limit is set to 100%.
Demand Limit
The maximum unit capacity can be limited by a 4-to-20 mA signal on the Demand Limit
analog input at the unit controller. This function is only enabled if the Demand Limit
setpoint is set to ON.
As the signal varies from 4 mA up to 20 mA, the maximum unit capacity changes linearly
from 100% to 0%. Although the demand limit can call for 0% capacity, this signal will
never cause a running compressor to shut down. Rather, all running compressors will be
held at minimum load, and this may occur at a demand limit value that is actually less than
20mA.
Network Limit
The maximum unit capacity can be limited by a network signal. This function is only
enabled if the unit control source is set to network. The signal will be received through the
BAS interface on the unit controller.
As the signal varies from 0% up to 100%, the maximum unit capacity changes linearly from
0% to 100%. Although the network limit can call for 0% capacity, this signal will never
cause a running compressor to shut down. Rather, all running compressors will be held at
minimum load, and this may occur at a network limit value that is actually less than more
than 0%.