| System Control Options The following control options provide a complete range of control alternatives for
almost any application. If none of the following
are selected, then the unit can be enabled via an external signal to the External
Interlock Auto/Stop terminals in the unit control
panel. (Refer to page 14 under Unit Control Features for a description of this feature.)
Programmable Night Heat Morning Warmup Control
This option provides comprehensive cooling and heating controls using the microprocessor logic of the unit control
module along with a unit mounted programmable timer.
With this control option the unit is capable of operating in four modes:
- Unoccupied Night Heat Mode
- Morning Warm-up Mode
- Occupied Heating Mode
- Occupied Cooling Mode
In all modes, the inlet guide vanes (if provided) are driven to the fully closed
position when the fan is turned off. When the fan is
turned on the inlet guide vanes modulate in response to supply air static pressure.
Two separate zone temperature sensors ship with the VAV units for field
installation. One sensor is provided to sense the night
heat temperature level. The other sensor is for morning warm-up/occupied heat
temperature control. Both setpoints are adjustable from
40 to 90 degrees F at the unit control module. Sensors are to be field installed
in the conditioned space or mechanical equipment room
as required.
On non-VAV units the standard zone cooling temperature sensor is used to sense temperature. Separate set points are
provided for night heat, day heat/morning warm-up and
zone cooling. The morning warm-up setpoint is the same as the day heat set point. The night heat setpoint setting
must be less than the day heat/morning warm-up set
point setting. If not, the unit control module will control both day and night
modes of heat based on the day heat/morning warm-up
setpoint.
The operation of each mode is described below:
UNOCCUPIED NIGHT HEAT MODE — This mode is initiated by the programmable
timer. The unit control module will respond as follows:
- An unoccupied output (a set of normally open and normally closed contacts) is
energized.
- A ventilation output (a set of normally open and normally closed contacts) is
de-energized. This can be used to close fresh air
damper.
- The supply air fan and heat relay contact closure output (a set of normally open
and normally closed contacts) are cycled on and off in
response to a demand for heat based on the zone temperature setting.
- The airside economizer fresh air damper (if provided) is fully closed.
- The heat/cool mode output (a set of normally open and normally closed contacts)
is energized. This can be used to put the VAV boxes in
heating mode.
- Water flow through the waterside economizer (if provided) is shut off.
- The economizer and mechanical cooling functions are disabled.
- The cooling tower/condenser water pump output (a set of normally open and
normally closed contacts) is de-energized.
MORNING WARM-UP MODE – This mode is initiated by the programmable timer.
The fan and heat output is energized until the morning warm-up temperature setpoint
is reached. All other conditions remain the same as in
the unoccupied night heat mode.
When the morning warm-up temperature
setpoint is reached, the unit will switch over to the
occupied heating mode.
If no heat is required in the morning warm-up mode, the unit will go directly
into the occupied heating mode.
OCCUPIED HEATING MODE — This mode provides a transition between morning
warm-up and the occupied cool mode. In this mode, the
unit will function as follows:
- The supply air fan is on continuously.
- The heat relay output is de-energized.
- The unoccupied output is de-energized.
- The ventilation output is energized.
- The airside economizer fresh air damper (if provided) is open to minimum
position.
- The heat/cool mode output remains energized.
- Water flow through the waterside economizer (if provided) remains shut Off.
- The economizer and mechanical cooling functions remain disabled.
- The cooling tower/condenser water pump interlock output remains de-energized.
If the conditioned zone temperature drops 2 degrees F below the morning
warm-up setpoint setting, the heat relay cycles to
maintain zone temperature.
If the conditioned zone temperature rises 2 degrees F above the morning warm-up setpoint setting, the unit will switch
over to the occupied cooling mode. At this point, the
heating cycle will be locked out until the next night setback/morning warm-up
cycle is initiated.
With the factory installed electric heat option, the controls are all prewired
to the heat relay output. With a steam or hot water
coil, the heating controls must be field wired to the heat relay output. |
