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SEQUENCE OF OPERATION
Constant Volume (CV) Units —
control module will activate the initialization software. The
initialization software will determine the unit configuration and
also initialize any controls loops and input/output devices. All
alarms and configurations are saved in memory and maintained
during power outages. All alarms will be maintained in
memory and must be cleared through the scrolling marquee
display.
The unit can be configured with two different control types:
thermostat control or space temperature sensor control.
THERMOSTAT CONTROL — If the unit is equipped with a
thermostat with Y1, Y2, W1, W2 and G connections, then the
control will perform the following sequence.
When terminal G is energized, the indoor fan will turn on.
The fan must be running for heating or cooling to occur. If Y1
is closed (first stage of cooling is energized), then the unit
control will first check the ability to use the economizer. If the
economizer can be used, then the unit control will modulate the
damper open to maintain the low-load economizer leaving air
temperature set point.
If Y2 closes (second stage of cooling is energized), then the
unit control will lower the leaving air temperature set point to
the configured set point. If the economizer cannot satisfy the
load, then the compressors will be sequenced on to maintain
either the low or high load temperature set points. If the
economizer cannot be used or the enable control disables the
economizer, then the control will sequence the compressors
based on the Y1 and Y2 signals.
If two-stage control has been selected, then the unit control
will map the compressors to the Y1 and Y2 inputs (first and
second stage cooling) as defined in the loading sequence. If
Adaptive mode has been selected, then the control will add and
remove compressor stages to maintain the high and low
demand set points. If Y1 is closed (first stage of cooling
energized), at least one compressor stage will be turned on.
If W1 closes (first stage of heating is energized), then the
unit will be in the Heating mode. The economizer will be
closed to the minimum position. If the unit is equipped with
gas or electric heat, then the first stage of heat will be
energized. If W2 closes, then the unit control will turn on the
second stage of heat. If the unit is equipped with a staged gas
heat control option, then the W1 and W2 signal will be used to
control the gas heat to the configurable low and high heat load
leaving air temperature set points. If the unit is equipped with
gas heat, then the integrated gas control (IGC) board will con-
trol the operation of the gas heat. See the Gas Heat Unit Opera-
tion section for the IGC board sequence of operation.
SPACE TEMPERATURE SENSOR CONTROL — If space
temperature operation has been selected using a T55, T56, or
T58 sensor, then a wire jumper must be added between R, W1,
and W2. If a remote occupancy control method has been
selected, then the remote occupancy input must first be closed
for the unit to go into heating, vent, or cooling modes. If the
internal timeclock is used, the unit control module determines
the occupancy state based on the system time schedules.
If Temperature Compensated Start is active, the unit will
be controlled as in the occupied mode. The Temperature
Compensated Start function will start the unit before the
scheduled occupied time (as determined by prior operation) to
bring the space to the set point temperature when occupied
time starts. As an example, if the unoccupied set point is 60 F,
the occupied set point is 72 F, and the occupied time period
starts at 8:00 AM, the Temperature Compensated Start function
will bring on the unit at 7:45 AM (as determined from previous
operation) so the room temperature will be at 72 F when the
occupied time starts.
On power up, the
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If the unit has been configured for a pre-occupancy purge,
then the control will start the unit in Vent mode prior to the
occupancy time to vent the space. If an IAQ (indoor air quality)
sensor is being used and the low IAQ set point is satisfied, then
the occupancy Purge mode will be terminated.
The set points for heat and cooling are configurable through
the scrolling marquee display.
NOTE: If a T56 sensor is being used, then the slide bar on the
sensor can offset the set point by has much as 5 degrees.
If the space temperature rises above the cooling set point,
then the unit will go into Cooling mode. If the economizer can
be used, the control will first try to control to the Leaving
Air Temperature set point. The set point will depend on the
space temperature. If the temperature is above the Low
Demand set point, then the Low Economizer Load Discharge
Air Temperature set point will be used. If the temperature is
above the High Load Space Temperature set point, then the
High Load Leaving Air Temperature set point will be used. If
the economizer cannot satisfy the load the compressors will
be sequenced on to maintain either the low or high load
temperature set points. If the economizer cannot be used or the
unit control disables the economizer, then the unit control will
sequence the compressors based on the low and high load
space temperature variables. If two-stage control has been
selected then the control will map the compressors to the low
and high loads as defined in the loading sequence. If Adaptive
mode has been selected then the control will add and remove
compressors stages to maintain the low and high demand
leaving air set points.
If the load goes below the heating space temperature set
points, the Heating mode will initiate. The economizer will be
closed to the minimum position and (if the unit is equipped
with gas or electric heat) the first stage of heat will be
energized. If the space temperature goes below the High Load
Space Temperature set point then the control will turn on the
second stage of heat. If the unit is equipped with a staged gas
heat control option then the low load and high load demand
signal will control the Leaving Air Temperature set point and
will turn on heating stages to maintain the Leaving Air
Temperature set points.
If the unit is configured for unoccupied free cooling,
mechanical cooling, or heating and the room temperature goes
above or below the unoccupied configuration set points, then
the unit control will turn on free cooling, mechanical cooling,
or heat as needed to return room temperature within the
unoccupied set points. When in this mode, the economizer
dampers will be maintained fully closed or to the minimum
unoccupied ventilation set point.
Variable Air Volume Control —
control module will activate the initialization software. The
initialization software will determine the unit configuration and
also initialize any control loops and input/output devices. All
alarms and configurations are saved in memory and maintained
during power outages. All alarms will be maintained in
memory and must be cleared through the scrolling marquee
display.
The unit will first determine the mode of operation. If the
unit has been configured for space temperature demand then
the control will determine, based on the configurable set points,
if the unit should be in the Heating mode, Vent mode or Cool-
ing mode. If the unit is configured for return air temperature
control, then the unit control will start the fan and monitor the
return air temperature against the configurable set point to
determine if the unit should be in Cooling, Vent or Heating
mode.
On power up, the
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