RT-SVX063E-EN
75
space Cool Setpoint before the controller can
change to Cool.
3. The controller switches to Heat (from cool) after the
error integrator exceeds 900°F seconds or Space
Temperature <= (Heat Setpoint – 1°F).
Space Temperature Control
Units
Single Zone VAV and Constant Volume Space
Temperature units use the Space Temperature Control
sequence of operation in Occupied Heat and Occupied
Cool modes of operation; however, the Discharge Air
Control method is used for all other modes. The table
below summarizes each mode of operation and the
control method applied. See Operating Modes section
for more details
Table 31.
Mode of operation and applied control method
Heat Cool Mode
Control Method
Discharge Air Temperature
Setpoint
Space/Discharge Setpoints
Cool
Space Temperature Control
Calculated
(cascade)
Space Temperature Setpoint
Active
Discharge Air Temperature
Setpoint Active
Heat
Space Temperature Control
Calculated
(cascade)
Space Temperature Setpoint
Active
Discharge Air Temperature
Setpoint Active
Morning Warm Up
Discharge Air Control
Fixed
Morning Warmup Setpoint
Discharge Air Heating Setpoint
Active
Pre Cool
Discharge Air Control
Fixed
Pre Cool Setpoint
Discharge Air Cooling Setpoint
Active
Night Purge
Discharge Air Control
Fixed
Unoccupied Cool
Discharge Air Control
Fixed
Unoccupied Cooling Setpoint
Discharge Air Cooling Setpoint
Active
Unoccupied Heat
Discharge Air Control
Fixed
Unoccupied Heating Setpoint
Discharge Air Heating Setpoint
Active
Single Zone VAV
Single Zone VAV equipment is configured with a
variable speed supply fan that modulates with Space
Temperature Control to minimize fan energy while
maintaining space comfort. When there is no demand
for heating or cooling the supply fan operates at the
minimum speed setting while providing ventilation
according to occupancy setpoints. Alternately, the
supply fan can be setup to cycle off when there is no
demand for heating or cooling.
Single Zone VAV – Cooling
C
Co
oo
oll —
— When there is a space cooling demand, DX
cooling will initialize and increase to satisfy space
temperature. The supply fan will continue to operate at
a low, fixed speed at low cooling capacities until the
cooling capacity requires additional airflow to keep
compressor operation optimal. The supply fan speed
will increase as the demand for cooling capacity
increases. The minimum supply fan speed is calculated
by DX cooling capacity. As the space requires
additional cooling capacity, Space Temperature
Control will calculate a lower discharge air temperature
setpoint increasing DX cooling which in turn increases
the supply fan speed (to prevent coil frost). Cooling
capacity and supply fan speed both can increase to
100%.
If the unit discharge air temperature reduces to the
Discharge Air Temperature Minimum Cool Limit
setting or DX cooling reaches 100% capacity, cooling
capacity increases will hold while the supply fan speed
will continue to increase to 100% or modulate to
manage space comfort cooling.
C
Co
oo
oll E
Ecco
on
no
om
miizze
err —
— If the unit is configured for a
modulating outdoor air damper and conditions are
suitable for economizer cooling, the supply fan will
operate at minimum speed while the economizer
damper modulates between the Outdoor Air Damper
Minimum Position (or Flow) Setpoint and 100% to
satisfy the discharge air temperature setpoint. If the
economizer damper reaches 100% open and additional
cooling capacity is required, the supply fan will then
modulate between minimum speed and 100% to
provide additional cooling to the space.
S
Se
eq
qu
ue
en
ncce
e o
off O
Op
pe
erra
attiio
on
n
