Orion System VCC-X Controller - Manual (Page 56)

Zone
Zone
SEQUENCE OF OPERATIONS
VCC-X Controller Technical Guide 56
HVAC Modes of Operation
There are 8 possible HVAC Modes of Operation. They are as follows:
• Cooling Mode
• Heating Mode
•
Vent Mode
• Dehumidifi cation Mode
• Purge Mode
• Heat Pump
• Warm-Up Mode / Cool-Down Mode
• Off Mode
Cooling Mode
Occupied Cooling is enabled when the temperature at the Mode
Enable Sensor rises one deadband above the Cooling Setpoint.
Cooling is disabled when the Mode Enable temperature falls one
deadband below the Cooling Setpoint. The setpoint and deadband
are user-adjustable.
Unoccupied Cooling operation is enabled when the Space
Temperature rises above the Cooling Mode Enable Setpoint plus
the Unoccupied Cooling Offset.
Mechanical cooling is disabled if the Outdoor Air Temperature
(OAT) falls 1° below the Cooling Lockout Setpoint and will
remain disabled until the OAT rises 1° above the Cooling Lockout
Setpoint. If the OAT disables mechanical cooling while it is currently
operating, mechanical cooling will stage off as minimum run times
and stage down delays are satisfi ed.
If the economizer is enabled, it will function as the fi rst stage of
cooling (see Economizer section).
Staged Cooling without the Refrigeration
System Module for VFD Compressors (RSMV)
Available cooling options are staged DX and On/Off Chilled Water.
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), cooling will
begin to stage on. Each stage must meet its Minimum Off Time (adj.)
before it is allowed to energize, and successive stages are subject to
a Cooling Stage Up Delay (adj).
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 off.
Each stage must meet its Minimum Run Time (adj.) before it is
allowed to stage off and successive stages are subject to a Cooling
Stage Down Delay (adj.).
Cooling with the Refrigeration System Module
for VFD Compressors (RSMV)
In the Cooling Mode, as the Supply Air Temperature (SAT) rises
above the Active SAT Cooling Setpoint (see Supply Air Temperature
Setpoint Reset section for explanation), the compressors will stage
on and modulate to maintain the Active SAT Cooling Setpoint. One
set of tandem compressors (a VFD compressor and a fi xed stage
compressor) are controlled per Refrigerant System Module-VFD
Compressor (RSMV). Multiple RSMVs are needed for multiple
sets of tandem compressors
In units with one set of tandem compressors, if the VFD compressor
modulates to 100% and the SAT is still above the SAT Cooling
Setpoint for the Cooling Stage Up Delay, then the fi xed compressor
will stage on. The VFD compressor will then be allowed to modulate
as necessary to maintain the SAT Cooling Setpoint. Minimum off
times must also be met before compressors can stage on.
In units with multiple tandem compressors, if the 1st VFD
compressor modulates to 100% and the SAT is still above the SAT
Cooling Setpoint for the Cooling Stage Up Delay, then the 2nd VFD
compressors will enable and the two VFD Compressors will then
modulate together to maintain the Cooling SAT Setpoint. Fixed
compressors will then stage on sequentially based on the same logic
while the VFD compressors are allowed to modulate as needed to
maintain the Cooling SAT Setpoint.
To stage down compressors, if the VFD compressor(s) have
modulated down to 30% for the Stage Down Delay period and the
SAT has fallen below the SAT Cooling Setpoint minus the Stage
Control Window, then the last compressor to have staged on (VFD
or Fixed) will stage off – assuming its Minimum Run Time has been
met. Any remaining VFD compressors are then allowed to modulate
as needed. If the last remaining VFD compressor reaches 0% for the
Stage Down Delay, it will stage off.
Chilled Water Cooling Signal Control
If Modulating Chilled Water is being used, 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 differential 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.
Cooling Mode