44 CNT-SVX17G-EN
Sequence of Operations
Heating Operation
Under space temperature control, during the heating mode (communicated heat/cool
mode is heat), the controller attempts to maintain the space temperature at the active
heating setpoint. Based on the controller occupancy mode, the active space heating
setpoint is either the occupied heating setpoint, the occupied standby heating setpoint,
or the unoccupied heat setpoint. Reference Table 30 for information on controller
ope
ration during occupied heating and cooling. All ventilation requirements are in force
during occupied heating and cooling.
The outputs are controlled based on the unit conf
iguration and the required heating
capacity. At 0% required heating capacity, the air valve is at its minimum flow setpoint.
As the required heating capacity increases, the air valve opens above its minimum
position. At 100% required heating capacity, the air valve opens to its maximum position.
All units have a modulating air valve
. The modulating air valve is used to control how
much air is flowing through the diffusers and into the space. By modulating the volume
of air flowing, the unit heating capacity is modulated.
Units may also have local or remote reheat. This reheat may be hydronic or electric.
Re
heat is used to maintain the space temperature at the heating setpoint. For more
information on reheat, refer to “Reheat Control” on page 45).
Table 30.Controller operation during occu
pied heating and cooling
PAT
(a)
Space Temperature
Primary airflow control active minimum
airflow setpoints
Fan control Reheat control
Cold
< Active Heat Stpt At the highest min position:
• Local heat min airflow
• Min airflow
• Effective ventilation setpoint
Series On
Parallel On
Reheat On
HSP < ZT < HSP + 2 At the highest min position:
• Min airflow
• Effective ventilation setpoint
Series On
Parallel On
Reheat Off
> Active Cool Stpt Modulate from cool max to highest min:
• Min airflow
• Effective ventilation setpoint
Series On
Pa
rallel Off
Reheat Off
Warm
< Active Heat Stpt Modulate from heat max to highest min:
• Local heat min airflow
• Heating min airflow
• Effective ventilation setpoint
Series On
Parallel Off
Reheat Not
P
resent
< Active Heat Stpt Modulate from heat max to highest min:
• Local heat min airflow
• Heating min airflow
• Effective ventilation setpoint
Series On
Parallel On (w/
reheat)
Reheat On
HSP < ZT < HSP + 2 At the highest min position:
• Heating min airflow
• Effective ventilation setpoint
Series On
Pa
rallel Off
Reheat Off
> Active Cool Stpt At the highest min position:
• Heating min airflow
• Effective ventilation setpoint
Series On
Pa
rallel Off
Reheat Off
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