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VCCX2 Controller Technical Guide
Cooling stages will continue to run until the SAT falls below the
Active Supply Air Temperature Setpoint minus the Cooling Stage
Control Window at which point the cooling will begin to stage
o. Each stage must meet its Minimum Run Time (adj.) before
it is allowed to stage o and successive stages are subject to a
Cooling Stage Down Delay (adj.).
Modulating Chilled Water Cooling Control
In the Cooling Mode, as the Supply Air Temperature (SAT)
rises above the Active Supply Air Cooling Setpoint (see Supply
Air Temperature Setpoint Reset section for explanation). The
Modulating Cooling Proportional Window is used to determine
the signal to the Chilled Water Valve and is user-adjustable. The
Modulating Cooling signal is calculated based on the dierential
between the Supply Air Temperature and the Active Supply
Air Temperature Setpoint based on the Modulating Cooling
Proportional Window.
The Maximum Signal Adjustment per Time Period is 10% and is
not user-adjustable. The Minimum Signal Adjustment per Time
Period is based on the Modulating Cooling Proportional Window.
The larger the Modulating Cooling Proportional Window, the
smaller the signal adjustment will be per Time Period. The
Time Period is the delay between another increase or decrease
in the Chilled Water Cooling Signal and is user-adjustable. For
example, if the Modulating Cooling Proportional Window is
5°F, the signal would adjust 2% per °F each Time Period above
or below the Active Supply Air Temperature Setpoint. When the
Supply Air Temperature is above or below the Active Supply Air
Temperature Setpoint by 5°F or more, the signal would adjust
10% each Time Period.
SEQUENCE OF OPERATIONS
HVAC Modes of Operation
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